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Introduction For years, the experts of cardiovascular diseases (CVDs) have focussed on the detrimental roles of the renin-angiotensin system (RAS) and have neglected the protective and beneficial functions of the [...], The renin-angiotensin system (RAS) generates, maintains, and makes worse hypertension and cardiovascular diseases (CVDs) through its biologically active component angiotensin II (Ang II), that causes vasoconstriction, sodium retention, and structural alterations of the heart and the arteries. A few endogenous vasodilators, kinins, natriuretic peptides, and possibly angiotensin (1-7), exert opposite actions and may provide useful therapeutic agents. As endothelial autacoids, the kinins are potent vasodilators, active natriuretics, and protectors of the endothelium. Indeed, the kallikrein-kinin system (KKS) is considered the dominant mechanism for counteracting the detrimental effects of the hyperactive RAS. The 2 systems, RAS and KKS, are controlled by the angiotensin-converting enzyme (ACE) that generates Ang II and inactivates the kinins. Inhibitors of ACE can reduce the impact of Ang II and potentiate the kinins, thus contributing to restore the cardiovascular homeostasis. In the last 20 years, ACE-inhibitors (ACE-Is) have become the drugs of first choice for the treatments of the major CVDs. ACE-Is not only reduce blood pressure, as sartans also do, but by protecting and potentiating the kinins, they can reduce morbidity and mortality and improve the quality of life for patients with CVDs. This paper provides a brief review of the literature on this topic. Key words: cardiovascular diseases, kinins, angiotensins, natriuretic peptides, angiotensin-converting enzyme inhibitors. Le systeme renine-angiotensine (SRA) engendre, maintient et aggrave l'hypertension et les maladies cardiovasculaires (MCV) par l'angiotensine II (Ang II), sa composante biologiquement active, qui cause une vasoconstriction, une retention sodique et des modifications structurelles du creur et des arteres. Quelques substances vasodilatatrices, les kinines, les peptides natriuretiques et peut-etre l'angiotensine (1-7), exercent des actions opposees et pourraient permettre d'obtenir des agents therapeutiques utiles. En tant qu'autacoides endotheliaux, les kinines sont des vasodilatateurs puissants, actifs sur le plan de la natriurese et protecteurs de l'endothelium. De fait, on considere que le systeme kallicreine-kinines (SKK) correspond au mecanisme qui domine l'antagonisme du SRA hyperactif dans ses effets deleteres. Le SRA et le SKK sont tous deux sous l'emprise de l'enzyme de conversion de l'angiotensine (ECA), qui entraine la production d'Ang II et l'inactivation des kinines. Les inhibiteurs de l'ECA (IECA) peuvent attenuer les effets de l'Ang II et potentialiser ceux des kinines, ce qui contribue a retablir l'homeostasie cardiovasculaire. Au cours des 20 dernieres annees, les IECA sont devenus les medicaments de premier choix dans le traitement des MCV majeures. En plus d'entrainer, tout comme les sartans, une diminution de la tension arterielle en protegeant et en potentialisant les effets des kinines, les IECA peuvent entrainer une reduction des taux de morbidite et de mortalite, ainsi qu'ameliorer la qualite de vie des patients atteints de MCV. Cet article offre une breve synthese de la litterature portant sur le sujet. [Traduit par la Redaction] Mots-cles: maladies cardiovasculaires, kinines, angiotensines, peptides natriuretiques, inhibiteurs de l'enzyme de conversion de l'angiotensine.

Introduction Branching morphogenesis of the ureteric bud (UB) is a fundamental developmental process that controls organogenesis of the metanephros. Notably, derangements in UB morphogenesis cause a spectrum of congenital anomalies [...], Branching morphogenesis of the ureteric bud (UB) is a key developmental process that controls organogenesis of the entire metanephros. Notably, aberrant UB branching may result in a spectrum of congenital anomalies of the kidney and urinary tract (CAKUT). Genetic, biochemical and physiological studies have demonstrated that the renin-angiotensin system (RAS), a key regulator of the blood pressure and fluid/electrolyte homeostasis, also plays a critical role in kidney development. All the components of the RAS are expressed in the metanephros. Moreover, mutations in the genes encoding components of the RAS in mice or humans cause diverse types of CAKUT which include renal papillary hypoplasia, hydronephrosis, duplicated collecting system, renal tubular dysgenesis, renal vascular abnormalities, abnormal glomerulogenesis and urinary concentrating defect. Despite widely accepted role of the RAS in metanephric kidney and renal collecting system (ureter, pelvis, calyces and collecting ducts) development, the mechanisms by which an intact RAS exerts its morphogenetic actions are incompletely defined. Emerging evidence indicates that defects in UB branching morphogenesis may be causally linked to the pathogenesis of renal collecting system anomalies observed under conditions of aberrant RAS signaling. This review describes the role of the RAS in UB branching morphogenesis and highlights emerging insights into the cellular and molecular mechanisms whereby RAS regulates this critical morphogenetic process. Keywords Kidney development * Ureteric bud * Renin-angiotensin * GDNF * Ret * EGF receptor

This study evaluated endothelium-dependent vascular relaxation in response to acetylcholine (ACh) in isolated middle cerebral arteries (MCA) from Dahl salt-sensitive (Dahl SS) rats and three different congenic strains that contain a portion of Brown Norway (BN) chromosome 13 introgressed onto the Dahl SS genetic background through marker-assisted breeding. Two of the congenic strains carry a 3.5-Mbp portion and a 2.6-Mbp portion of chromosome 13 that lie on opposite sides of the renin locus, while the third contains a 2.0-Mbp overlapping region that includes the BN renin allele. While maintained on a normal salt (0.4% NaCl) diet, MCAs from Dahl SS rats and the congenic strains retaining the Dahl SS renin allele failed to dilate in response to ACh, whereas MCAs from the congenic strain carrying the BN renin allele exhibited normal vascular relaxation. In congenic rats receiving the BN renin allele, vasodilator responses to ACh were eliminated by nitric oxide synthase inhibition with [N.sup.G]-nitro-L-arginine methyl ester, angiotensin-converting enzyme inhibition with captopril, and [AT.sub.1] receptor blockade with losartan. [N.sup.G]-nitro-L-arginine methyl ester-sensitive vasodilation in response to ACh was restored in MCAs of Dahl SS rats that received either a 3-day infusion of a subpressor dose of angiotensin II (3 ng x [kg.sup.-1] x [min.sup.-1] iv), or chronic treatment with the superoxide dismutase mimetic tempol (15 mg x [kg.sup.-1] x [day.sup.-1]). These findings indicate that the presence of the Dahl SS renin allele plays a crucial role in endothelial dysfunction present in the cerebral circulation of the Dahl SS rat, even in the absence of elevated dietary salt intake, and that introgression of the BN renin allele rescues endothelium-dependent vasodilator responses by restoring normal activation of the renin-angiotensin system. renin-angiotensin system; vascular dysfunction; physiological genomics; vasodilation; angiotensin II; oxidant stress doi: 10.1152/ajpheart.00700.2010.

Epithelial-to-mesenchymal transformation (EMT) of tubular cells into a myofibroblastic phenotype is an important mediator of renal scarring in chronic nephropatby. This study examines the role of the renin-angiotensin system (RAS) in this process. NRK-52E cells were exposed to angiotensin (ANG) II and ANG 1-7 in the presence or absence of inhibitors and agonists of RAS signaling. EMT was assessed at 3 days by expression of [alpha]-smooth muscle actin ([alpha]-SMA) and E-cadherin and the induction of a myofibroblastic phenotype. Expression of fibrogenic growth factors and matrix proteins was assessed by RT-PCR and immunofluorescence microscopy. To confirm findings in vivo, rats were also infused with ANG 1-7 (24 [micro]g x [kg.sup.-1] x [h.sup.-1]) or saline via an osmotic minipump for 10 days, and renal fibrogenesis was then assessed. Treatment of NRK-52E cells with ANG II induced characteristic changes of EMT. Selective blockade of the [AT.sub.1] receptor or the [AT.sub.2] receptor failed to inhibit ANG II-induced EMT. However, blockade of the ANG 1-7 receptor, Mas-1, was able to prevent ANG II-dependent EMT. To confirm these findings, both ANG 1-7 and the selective Mas receptor agonist, AVE-0991, were able to induce NRK-52E cells in a dose-dependent manner. Exposing cells to recombinant ACE2 was also able to induce EMT. In addition, an infusion of ANG 1-7 induced the tubular expression of [alpha]-SMA and the expression of matrix proteins in the kidney. ANG II is a potent stimulus for EMT, but not through conventional pathways. This study points to the possible limitations of conventional RAS blockade, which not only fails to antagonize this pathway, but also may enhance it via augmenting the synthesis of ANG 1-7. renin-angiotensin system; epithelial-to-mesenchymal transition; fibrosis; proximal tubule doi: 10.1152/ajprenal.00538.2009.

Following sinoaortic denervation, which eliminates arterial baroreceptor input into the brain, there are slowly developing adaptations that abolish initial sympathetic activation and hypertension. In comparison, electrical stimulation of the carotid sinus for 1 wk produces sustained reductions in sympathetic activity and arterial pressure. However, whether compensations occur subsequently to diminish these responses is unclear. Therefore, we determined whether there are important central and/or peripheral adaptations that diminish the sympathoinhibitory and blood pressure-lowering effects of more sustained carotid sinus stimulation. To this end, we measured whole body plasma norepinephrine spillover and [[alpha].sub.1]-adrenergic vascular reactivity in six dogs over a 3-wk period of baroreflex activation. During the first week of baroreflex activation, there was an ~45% decrease in plasma norepinephrine spillover, along with reductions in mean arterial pressure and heart rate of ~20 mmHg and 15 beats/min, respectively; additionally, plasma renin activity did not increase. Most importantly, these responses during week 1 were largely sustained throughout the 3 wk of baroreflex activation. Acute pressor responses to [alpha]-adrenergic stimulation during ganglionic blockade were similar throughout the study, indicating no compensatory increases in adrenergic vascular reactivity. These findings indicate that the sympathoinhibition and lowering of blood pressure and heart rate induced by chronic activation of the carotid baroreflex are not diminished by adaptations in the brain and peripheral circulation. Furthermore, by providing evidence that baroreflexes have long-term effects on sympathetic activity and arterial pressure, they present a perspective that is opposite from studies of sinoaortic denervation. blood pressure: sympathetic nervous system; renin-angiotensin system doi: 10.1152/ajpheart.00372.2010.

Myocardial fibrosis increases arrhythmia vulnerability of the diseased heart. The renin-angiotensin-aldosterone system (RAAS) governs myocardial collagen synthesis. We hypothesized that reducing cardiac fibrosis by chronic RAAS inhibition would result in reduced arrhythmia vulnerability of the senescent mouse heart. Wild-type mice (52 wk old) were treated for 36 wk: 1) untreated control (C); 2) eplerenone (E); 3) losartan (L); and 4) cotreatment with eplerenone and losartan (EL). Ventricular epicardial activation mapping was performed on Langendorff-perfused hearts. Arrhythmia inducibility was tested by one to three premature stimuli and burst pacing. Longitudinal and transverse conduction velocity and dispersion of conduction were determined during pacing at a basic cycle length of 150 ms. Sirius red staining (collagen) was performed. As a result, in the RV of mice in the E, L, and EL groups, transverse conduction velocity was significantly increased and anisotropic ratio was significantly decreased compared with those values of mice in the C group. Anisotropic reentrant arrhythmias were induced in 52% of untreated mice and significantly reduced to 22%, 26%, and 16% in the E, L, and EL groups, respectively. Interstitial fibrosis was significantly decreased in both the RV and LV of all treated groups. Scattered patches of replacement fibrosis were found in 90% of untreated hearts, which were significantly reduced in the E, L, and EL groups. A strong correlation between the abundance of patchy fibrosis and arrhythmia inducibility was found. In conclusion, chronic RAAS inhibition limited aging-related interstitial fibrosis. The lower arrhythmogeneity of treated mice was directly correlated to the reduced amount of patchy fibrosis. renin-angiotensin-aldosterone system inhibition doi: 10.1152/ajpheart.01137.2009.

The kidney is one of the major organs involved in whole-body homeostasis while chronic renal impairment usually leads to fat redistribution and hyperlipidemia. The aim of this study was to elucidate the role of tissue renal renin-angiotensin system (RAS) components, lipogenic peroxisome proliferator-activated receptor-[gamma] (PPAR[gamma]), and cytokine TNF-[alpha] in the development of ectopic adipogenesis and lipid deposition. Adult male Sprague-Dawley rats were randomized into three groups: untreated uninephrectomized (UNX) rats, UNX rats treated with an angiotensin-converting enzyme inhibitor (ACEI), lisinopril, and sham-operated rats. All animals were euthanized at 10 mo postoperation. The untreated UNX rats showed increased protein expression of renin, angiotensinogen, PPAR[gamma] and the angiotensin II type 2 receptor (AT2R) but reduced protein expression of ATIR and TNF-[alpha] in their remnant kidneys. Immunofluorescence staining revealed increased reactivity of angiotensinogen and angiotensin I/II in renal tubular cells and adipocytes of the untreated UNX rats. ACEI treatment largely prevented these disorders in association with restored normolipidemia and normalized renal adipogenesis and lipid deposition. These findings support the notion that tissue RAS, PPAR[gamma] and TNF-[alpha] collectively play an important role in the renal adipogenesis and lipid metabolism. unilateral nephrectomy; rat; peroxisome proliferator-activated receptor-% lipid; kidney doi: 10.1152/ajprenal.00445.2009

ANG II, the main circulating effector hormone of the renin-angiotensin system, is produced by enzymatic cleavage of angiotensinogen. The present study aimed to examine whether targeted deletion of the angiotensinogen gene (Agt) altered brain ANG II receptor density or responsiveness to ANG II. In vitro autoradiography was used to examine the distribution and density of angiotensin type 1 (ATe) and type 2 receptors. In most brain regions, the distribution and density of angiotensin receptors were similar in brains of Agt knockout mice ([Agt.sup.-/-]) and wild-type mice. In [Agt.sup.-/-] mice, a small increase in A[T.sub.1] receptor binding was observed in the rostral ventrolateral medulla (RVLM), a region that plays a critical role in blood pressure regulation. To examine whether [Agt.sup.-/-] mice showed altered responses to ANG II, blood pressure responses to intravenous injection (0.01-0.1 [micro]g/kg) or RVLM microinjection (50 pmol in 50 nl) of ANG II were recorded in anesthetized [Agt.sup.-/-] and wild-type mice. Intravenous injections of phenylephrine (4 [micro]g/kg and 2 [micro]g/kg) were also made in both groups. The magnitude of the pressor response to intravenous injections of ANG II or phenylephrine was not different between [Agt.sup.-/-] and wild-type mice. Microinjection of ANG II into the RVLM induced a pressor response, which was significantly smaller in [Agt.sup.-/-] compared with wild-type mice (+10 [+ or -] 1 vs. +23 [+ or -] 4 mmHg, respectively, P = 0.004). Microinjection of glutamate into the RVLM (100 pmol in 10 nl) produced a robust pressor response, which was not different between [Agt.sup.-/-]and wild-type mice. A diminished response to ANG II microinjection in the RVLM of [Agt.sup.-/-] mice, despite an increased density of A[T.sub.1] receptors suggests that signal transduction pathways may be altered in RVLM neurons of [Agt.sup.-/-] mice, resulting in attenuated cellular excitation. blood pressure; brain microinjection; angiotensin II; brain renin-angiotensin system doi: 10.1152/ajpregu.00462.2009

Am J Physiol Renal Physiol 298: F187-F195, 2010. First published November 4, 2009; doi:10.1152/ajprenal.00088.2009.--An increase in blood pressure (BP) due to angiotensin II (ANG II) infusion or other means is associated with adaptive pressure natriuresis due to reduced sodium reabsorption primarily in proximal tubule (PT) and thick ascending limb (TAL). We tested the hypothesis that male and female mice would show differential response to ANG II infusion with regard to the regulation of the protein abundance of sodium transporters in the PT and TAL and that these responses would be modulated by aging. Young (~3 mo) and old (~21 mo) male and female mice were infused with ANG II at 800 ng x kg body [wt.sup.-1] x [min.sup.-1] by osmotic minipump for 7 days or received a sham operation. ANG II increased mean arterial pressure (MAP), measured by radiotelemetry, significantly more in male mice of both ages (increased ~30-40 mmHg), compared with females (increased ~ 15-25 mmHg). On day 1, MAP was also significantly increased in old mice, relative to young (P = 0.01). ANG II infusion was associated with a significant decline in plasma testosterone (to renin-angiotensin-aldosterone system; testosterone; hypertension; gender differences; sodium phosphate cotransporter; sodium hydrogen exchanger; Na-K-2Cl cotransporter

Am J Physiol Renal Physiol 298: F150-F157, 2010. First published October 21, 2009; doi:10.1152/ajprenal.00477.2009.--Angiotensin-converting enzyme (ACE) inhibition (ACEi) ameliorates the development of hypertension and the intrarenal ANG II augmentation in ANG II-infused mice. To determine if these effects are associated with changes in the mouse intrarenal renin-angiotensin system, the expression of angiotensinogen (AGT), renin, ACE, angiotensin type 1 receptor ([AT.sub.1]R) mRNA (by quanitative RT-PCR) and protein [by Western blot (WB) and/or immunohistochemistry (IHC)] were analyzed. C57BL/6J male mice (9-12 wk old) were distributed as controls (n = 10), ANG II infused (ANG II = 8,400 ng x [kg.sup.-1] x [min.sup.-1] for 12 days), ACEi only (ACEi = 10, lisinopril, 100 mg/1), and ANG II infused + ACEi (ANG II + ACEi = 11). When compared with controls (1.00), AGT protein (by WB) was increased by ANG II (1.29 [+ or -] 0.13, P < 0.05), and this was not prevented by ACEi (ACEi + ANG II, 1.31 [+ or -] 0.14, P < 0.05). ACE protein (by WB) was increased by ANG II (1.21 [+ or -] 0.08, P < 0.05), and it was reduced by ACEi alone (0.88 [+ or -] 0.07, P < 0.05) or in combination with ANG II (0.80 [+ or -] 0.07, P < 0.05). [AT.sub.1]R protein (by WB) was increased by ANG II (1.27 [+ or -] 0.06, P < 0.05) and ACEi (1.17 [+ or -] 0.06, P < 0.05) but not ANG II + ACEi [1.15 [+ or -] 0.06, not significant (NS)]. Tubular renin protein (semiquantified by IHC) was increased by ANG II (1.49 [+ or -] 0.23, P < 0.05) and ACEi (1.57 [+ or -] 0.15, P < 0.05), but not ANG II + ACEi (1.10 [+ or -] 0.15, NS). No significant changes were observed in AGT, ACE, or [AT.sub.1]R mRNA. In summary, reduced responses of intrarenal tubular renin, ACE, and the [AT.sub.1]R protein to the stimulatory effects of chronic ANG II infusions, in the presence of ACEi, are associated with the effects of this treatment to ameliorate augmentations in blood pressure and intrarenal ANG II content during ANG II-induced hypertension. angiotensin-converting enzyme; angiotensinogen; renin; lisinopril

During nephrogenesis, renin expression shifts from the vessel walls of interlobular arteries to the terminal portions of afferent arterioles in a wavelike pattern. Since the mechanisms responsible for the developmental deactivation of renin expression are as yet unknown, we hypothesized that the developing renin-angiotensin system (RAS) may downregulate itself via negative feedback to prevent overactivity of renin. To test for a possible role of angiotensin II in the developmental deactivation of renin expression, we studied the development of intrarenal renin expression in mice lacking ANG II [AT.sub.1a], [AT.sub.1b], or [AT.sub.2] receptors and in animals with abolished circulating ANG II due to deletion of the gene for angiotensin I-converting enzyme (ACE). The development of intrarenal renin expression was normal in mice lacking ANG II [AT.sub.1b] or [AT.sub.2] receptors. In animals lacking both ANG II [AT.sub.1a] and [AT.sub.1b] receptors, ACE, or ANG II [AT.sub.1a] receptors, renin expression was normal early and renin disappeared from mature vessels until development of cortical interlobular and afferent arterioles began. The development of cortical vessels in these genotypes was accompanied by a markedly increased number of renin-expressing cells, many of which were ectopically located and attached in a grapelike fashion to the outer vessel perimeter. Although the number of renin-expressing cells declined during final maturation of the kidneys, the atypical distribution pattern of renin cells was maintained. These findings suggest that ANG II does not play a central role in the typical developmental shift in renin expression from the arcuate vessels to the afferent arterioles. During postnatal maturation of mouse kidneys, interruption of the RAS causes severe hyperplasia of renin cells via a mechanism that centrally involves [AT.sub.1a] receptors. However, the distribution pattern of renin cells in adult kidneys with an interrupted RAS does not mimic any normal developmental stage since renin expression is frequently found in cells outside the arteriolar vessel walls in RAS mutants. development; angiotensin II doi: 10.1152/ajprenal.00378.2009.

The intrarenal renin-angiotensin system (RAS) plays a key role in the development of diabetic nephropathy. Recently, we showed that combination therapy with an [AT.sub.1] receptor blocker (ARB) and an activated vitamin D analog produced excellent synergistic effects against diabetic nephropathy, as a result of blockade of the ARB-induced compensatory renin increase. Given the diversity of vitamin D analogs, here we used a pro-drug vitamin D analog, doxercalciferol (1[alpha]-hydroxyvitamin [D.sub.2]), to further test the efficacy of the combination strategy in long-term treatment. Streptozotocin-induced diabetic DBA/2J mice were treated with vehicle, losartan, doxercalciferol (0.4 and 0.6 [micro]g/kg), or losartan and doxercalciferol combinations for 20 wk. Vehicle-treated diabetic mice developed progressive albuminuria and glomerulosclerosis. Losartan alone moderately ameliorated kidney injury, with renin being drastically upregulated. A similar therapeutic effect was seen with doxercalciferol alone, which markedly suppressed renin and angiotensinogen expression. The losartan and doxercalciferol combination most effectively prevented albuminuria, restored glomerular filtration barrier structure, and dramatically reduced glomerulosclerosis in a dose-dependent manner. These effects were accompanied by blockade of intrarenal renin upregulation and ANG II accumulation. These data demonstrate an excellent therapeutic potential for doxercalciferol in diabetic renal disease and confirm the concept that blockade of the compensatory renin increase enhances the efficacy of RAS inhibition and produces synergistic therapeutic effects in combination therapy. renin-angiotensin system; compensatory renin increase; albuminuria; glomerulosclerosis

Streptozotocin-induced (Type 1) diabetes mellitus (T1DM) in rats promotes jejunal glucose transport, but the trigger for this response remains unclear. Our recent work using euglycemic rats has implicated the enterocyte renin-angiotensin system (RAS) in control of sodium-dependent glucose transporter (SGLT1)-mediated glucose uptake across the jejunal brush border membrane (BBM). The aim of the present study was to examine whether expression of enterocyte RAS components is influenced by T1DM. The effects of mucosal addition of angiotensin II (AII) on [[sup.14]C]-D-glucose uptake by everted diabetic jejunum was also determined. Two-week diabetes caused a fivefold increase in blood glucose level and reduced mRNA and protein expression of AII type 1 ([AT.sub.1] and [AT.sub.2] receptors and angiotensin-converting enzyme in isolated jejunal enterocytes. Angiotensinogen expression was, however, stimulated by diabetes while renin was not detected in either control or diabetic enterocytes. Diabetes stimulated glucose uptake into everted jejunum by 58% and increased the BBM expression of SGLT1 and facilitated glucose transporter 2 (GLUT2) proteins, determined by Western blotting by 25% and 135%, respectively. Immunohistochemistry confirmed an enhanced BBM expression of GLUT2 in diabetes and also showed that this was due to translocation of the transporter from the basolateral membrane to BBM. All (5 [micro]M) or L-162313 (1 [micro]M), a nonpeptide All analog, decreased glucose uptake by 18% and 24%, respectively, in diabetic jejunum. This inhibitory action was fully accountable by an action on SGLTl-mediated transport and was abolished by the [AT.sub.1] receptor antagonist losartan (1 [micro]M). The decreased inhibitory action of All on in vitro jejunal glucose uptake in diabetes compared with that noted previously in jejunum from normal animals is likely to be due to reduced RAS expression in diabetic enterocytes, together with a disproportionate increase in GLUT2, compared with SGLT1 expression at the BBM. enterocytes; angiotensin II; sodium-dependent glucose transporter; facilitated glucose transporter; intestine

The importance of dietary salt in the development of hypertension has long been a source of controversy. Recent studies suggest a combination of high-salt and ANG II infusion may increase sympathetic drive; however, the effect of a change in dietary salt alone is unclear. Using telemetry, we recorded renal sympathetic nerve activity (RSNA), arterial pressure (MAP), and heart rate (HR) in seven New Zealand white rabbits before and during a 6-day period of increased salt intake (normal NaCl 0.5 g x [kg.sup.-1] x [day.sup.-1], high NaCl 2.5 g x [kg.sup.-1] x [day.sup.-1]) and a second group of seven rabbits with normal salt intake throughout. The responses to stressful stimuli encountered in the laboratory were recorded and compared with rest in control and high-salt groups. Resting MAP, HR, and RSNA were not significantly altered with high salt intake [88 [+ or -] 5 vs. 91 [+ or -] 6 mmHg; 251 [+ or -] 8 vs. 244 [+ or -] 9 beats per minute (bpm); 9.7 [+ or -] and 1.2 vs. 10.8 [+ or -] 1.7 normalized units (nu)] despite significant reductions in plasma renin activity ( 1.88 [+ or -] 0.18 vs. 1.27 [+ or -] 0.15 nmol ANG I x [1.sup.-1] x [h.sup.-1]; P < 0.05) and ANG II (7.5 [+ or -] 1.2 vs. 4.3 [+ or -] 0.8 pmol/1). Increasing levels of stressful stimuli (resting in home cage, containment in box, handling, and nasopharyngeal activation) in animals on a normal salt diet caused graded increases in MAP (89 [+ or -] 2 mmHg, 95 [+ or -] 2 mmHg, 107 [+ or -] 4 mmHg, and 122 [+ or -] 5 mmHg, respectively) and RSNA (9.7 [+ or -] 0.9 nu; 11.8 [+ or -] 2.7 nu; 31.4 [+ or -] 3.7 nu; 100 nu) but not HR (245 [+ or -] 8 bpm; 234 [+ or -] 8 bpm; 262 [+ or -] 9 bpm; 36 [+ or -] 5 bpm). High dietary salt did not significantly alter the responses to stress. We conclude that a 6-day period of high salt intake does not alter the level of RSNA, with non-neural mechanisms primarily responsible for the observed renin-angiotensin system suppression. blood pressure; dietary salt; renin-angiotensin system

The (pro)renin receptor [(P)RR] plays a pivotal role in the renin-angiotensin system. Experimental models emphasize the role of (P)RR in organ damage associated with hypertension and diabetes. However, a mutation of the (P)RR gene, resulting in frame deletion of exon 4 [[DELTA]4-(P)RR] is associated with X-linked mental retardation (XLMR) and epilepsy pointing to a novel role of (P)RR in brain development and cognitive function. We have studied (P)RR expression in mouse brain, as well as the effect of transfection of [DELTA]4-(P)RR on neuronal differentiation of rat neuroendocrine PC-12 cells induced by nerve growth factor (NGF). In situ hybridization showed a wide distribution of (P)RR, including in key regions involved in the regulation of blood pressure and body fluid homeostasis. In mouse neurons, the receptor is on the plasma membrane and in synaptic vesicles, and stimulation by renin provokes ERK 1/2 phosphorylation. In PC-12 cells, (P)RR localized mainly in the Golgi and in endoplasmic reticulum and redistributed to neurite projections during NGF-induced differentiation. In contrast, [DELTA]4-(P)RR remained cytosolic and inhibited NGF-induced neuronal differentiation and ERK1/2 activation. Cotransfection of PC-12 cells with (P)RR and [DELTA]4-(P)RR cDNA resulted in altered localization of (P)RR and inhibited (P)RR redistribution to neurite projections upon NGF stimulation. Furthermore, (P)RR dimerized with itself and with [DELTA]4-(P)RR, suggesting that the XLMR and epilepsy phenotype resulted from a dominant-negative effect of [DELTA]4-(P)RR, which coexists with normal transcript in affected males. In conclusion, our results show that (P)RR is expressed in mouse brain and suggest that the XLMR and epilepsy phenotype might result from a dominant-negative effect of the [DELTA]4-(P)RR protein. brain (P)RR expression; functional (P)RR; X-linked mental retardation

Autoregulation of renal blood flow comprises three mechanisms: the myogenic response (MR), the tubuloglomerular feedback (TGF), and a third mechanism (3M). The nature of 3M is unknown; it may be related to hypotensive resetting of autoregulation that probably relies on pressure-dependent stimulation of the renin-angiotensin system (RAS). Thus we used a normotensive angiotensin II clamp in anesthetized rats and studied autoregulation 1) by slow ramp-shaped reductions in renal perfusion pressure (RPP) followed by ramp-shaped RPP restorations and 2) by means of the step response technique: after 30 s of either total or partial suprarenal aortic occlusion, a step increase in RPP was made and the response of renal vascular conductance analyzed to assess the mechanisms' strength and initial direction (vasodilation or constriction). The angiotensin clamp abolished the resetting of autoregulation during ramp-shaped RPP changes. Under control conditions, the initial TGF response was dilatory after total occlusions but constrictive after partial occlusions. The initial 3M response presented a mirror image to the TGF: it was constrictive after total but dilatory after partial occlusions. The angiotensin clamp suppressed the TGF and turned the initial 3M response following total occlusions into dilation. We conclude that 1) pressure-dependent RAS stimulation is a major cause behind hypotensive resetting of autoregulation, 2) TGF sensitivity strongly depends on pressure-dependent changes in RAS activity, 3) the 3M is modulated, but not mediated, by the RAS, and 4) the 3M acts as a counterbalance to the TGF and might possibly be related to the recently described connecting tubule glomerular feedback. renal hemodynamics; time domain; oscillations; hindquarter

The renin-angiotensin system plays a pivotal role in regulating blood pressure and is involved in the pathogenesis of kidney disorders and other diseases. Here, we report that the growth factor midkine is what we believe to be a novel regulator of the renin-angiotensin system. The hypertension induced in mice by 5/6 nephrectomy was accompanied by renal damage and elevated plasma angiotensin II levels and was ameliorated by an angiotensin-converting enzyme (ACE) inhibitor and an angiotensin receptor blocker. Notably, ACE activity in the lung, midkine expression in the lung, and midkine levels in the plasma were all increased after 5/6 nephrectomy. Exposure to midkine protein enhanced ACE expression in primary cultured human lung microvascular endothelial cells. Furthermore, hypertension was not induced and renal damage was less severe in midkine-deficient mice. Supplemental administration of midkine protein to midkine-deficient mice restored ACE expression in the lung and hypertension after 5/6 nephrectomy. Oxidative stress might be involved in midkine expression, since expression of NADH/NADPH oxidase-1, -2, and -4 was induced in the lung after 5/6 nephrectomy. Indeed, the antioxidative reagent tempol reduced midkine expression and plasma angiotensin II levels and consequently ameliorated hypertension. These results suggest that midkine regulates the renin-angiotensin system and mediates the kidney-lung interaction after 5/6 nephrectomy., Introduction The renin-angiotensin system (RAS) is a hormonal cascade that functions in the homeostatic control of arterial pressure, tissue perfusion, and extracellular volume. Dysregulation of the RAS results in the [...]

In angiotensin II (ANG II)-induced hypertension, intrarenal ANG II levels are increased by [AT.sub.1] receptor-mediated ANG II internalization and endogenous ANG II generation. The objective of the present study was to determine the relative contribution of de novo formation of endogenous ANG II. Male Sprague-Dawley rats were divided into three groups: sham operated (n = 6), [Val.sup.5]-ANG II infused (n = 16), and [Ile.sup.5]-ANG II infused (n = 6). [Val.sup.5]-ANG II and [Ile.sup.5]-ANG II were infused at 80 ng/min via subcutaneous osmotic minipump for 13 days, followed by harvesting of blood and kidney samples. In six [Val.sup.5]-ANG II-infused rats, urine was collected on the day before infusion and on day 12 of infusion. Extracted samples were subjected to HPLC to separate [Val.sup.5]-ANG II from [Ile.sup.5]-ANG II followed by RIA. Systolic blood pressure increased significantly from 121 [+ or -] 2 to 206 [+ or -] 4 mmHg in the [Val.sup.5]-ANG II-infused rats and from 124 [+ or -] 3 to 215 [+ or -] 5 mmHg in the [Ile.sup.5]-ANG II-infused rats. In the [Val.sup.5]-ANG II-infused rats, the plasma [Ile.sup.5]-ANG II levels increased 196.2 [+ or -] 70.1% compared with sham plasma [Ile.sup.5]-ANG II concentration. [Val.sup.5]-ANG II levels were 150.0 [+ or -] 28.2 fmol/ml which accounted for 53.5 [+ or -] 10.1% of the total ANG II in plasma. The kidney [Ile.sup.5]-ANG II levels in the [Val.sup.5]-ANG II-infused rats increased 69.9 [+ or -] 30.7% compared with sham kidney [Ile.sup.5]-ANG II concentrations. Intrarenal accumulation of [Val.sup.5]-ANG II accounted for 52.5 [+ or -] 5.3% of the total kidney ANG II during [Val.sup.5]-ANG II infusion while endogenous [Ile.sup.5]-ANG II accounted for 47.5 [+ or -] 8.6%. The urinary [Ile.sup.5]-ANG II excretion rate on day 12 increased 93.2 [+ or -] 32.1% compared with preinfusion level indicating increased formation of endogenous ANG II. Thus, the increases in intrarenal ANG II levels during chronic ANG II infusions involve substantial stimulation of endogenous ANG II formation which contributes to overall augmentation of intrarenal ANG II. angiotensin II-induced hypertension; renin-angiotensin system; high-performance liquid chromatography

Intracerebroventricular (ICV) infusion of NaCl mimics the effects of a high-salt diet in salt-sensitive hypertension, raising the sodium concentration in the cerebrospinal fluid (CSF [Na]) and subsequently increasing the concentration of an endogenous ouabain-like substance (OLS) in the brain. The OLS, in turn, inhibits the brain [Na.sup.+]-[K.sup.+]-ATPase, causing increases in the activity of the brain renin-angiotensin system (RAS) and blood pressure. The [Na.sup.+]-[K.sup.+]-ATPase [alpha] (catalytic)-isoform(s) that mediates the pressor response to increased CSF [Na] is unknown, but it is likely that one or more isoforms that bind ouabain with high affinity are involved (e.g., the [Na.sup.+]-[K.sup.+]-ATPase [[alpha].sub.2]- and/or [[alpha].sub.3]-subunits). We hypothesize that OLS-induced inhibition of the [[alpha].sub.2]-subunit mediates this response. Therefore, a chronic reduction in [[alpha].sub.2] expression via a heterozygous gene knockout ([[alpha].sub.2] +/-) should enhance the pressor response to increased CSF [Na]. Intracerebroventricular (ICV) infusion of artificial CSF containing 0.225 M NaCl increased mean arterial pressure (MAP) in both wild-type (+/+) and [[alpha].sub.2] +/- mice, hut to a greater extent in [[alpha].sub.2] +/-. Likewise, the pressor response to ICV ouabain was enhanced in [[alpha].sub.2] +/- mice, demonstrating enhanced sensitivity to brain [Na.sup.+]-[K.sup.+]-ATPase inhibition per se. The pressor response to ICV ANG I but not ANG II was also enhanced in [[alpha].sub.2] +/- vs. [[alpha].sub.2]+/+ mice, suggesting an enhanced brain RAS activity that may be mediated by increased brain angiotensin converting enzyme (ACE). The latter hypothesis is supported by enhanced ACE ligand binding in the organum vasculosum laminae terminalis. These studies demonstrate that chronic downregulation of [Na.sup.+]-[K.sup.+]-ATPase [[alpha].sub.2]-isoform expression by heterozygous knockout increases the pressor response to increased CSF [Na] and activates the brain RAS. Since these changes mimic those produced by the endogenous brain OLS, the brain [[alpha].sub.2]-isoform may be a target for the brain OLS during increases in CSF [Na], such as in salt-dependent hypertension. [[alpha].sub.2]-isoform; gene knockout; sodium chloride; brain ouabain-like substance; brain renin-angiotensin system; intracerebroventricular infusion

The kallikrein kinin system (KKS) is involved in arterial and renal functions. It may have an antihypertensive effect in both essential and secondary forms of hypertension. The role of the KKS in the development of two-kidneys, one-clip (2K1C) hypertension, a high-renin model, was investigated in mice rendered deficient in tissue kallikrein (TK) and kinins by TK gene inactivation (TK-/-) and in their wild-type littermates (TK+/+). Four weeks after clipping the renal artery, blood flow was reduced in the clipped kidney (2K1C-TK+/+: -90%, 2K1C-TK-/-: -93% vs. sham-operated mice), and the kidney mass had also decreased (2K1C-TK+/+: -65%, 2K1C-TK-/-: -66%), whereas in the unclipped kidney, blood flow (2K1C-TK+/+: +19%, 2K1C-TK-/-: +17%) and kidney mass (2K1C-TK+/+: +32%, 2K1C-TK-/-: +30%) had both increased. The plasma renin concentration (2K1C-TK+/+: +78%, 2K1C-TK-/-: +65%) and renal renin content of the clipped kidney (2K1C-TK+/+: +58%, 2K1C-TK-/-: +65%) had increased significantly. There was no difference for these parameters between 2K1C-TK+/+ and 2K1C-TK-/- mice. Blood pressure monitored by telemetry and by plethysmography, rose immediately after clipping in both genotypes, and reached similar levels (2K1C-TK+/+: +24%, 2K1C-TK-/-: +21%). 2K1C-TK+/+ and 2K1C-TK-/- mice developed similar concentric left ventricular hypertrophy (+24% and +17%, respectively) with normal cardiac function. These findings suggest that in the context of chronic unilateral reduction in renal blood flow, TK and kinins do not influence the trophicity of kidneys, the synthesis and secretion of renin, blood pressure increase, and cardiac remodeling due to renin angiotensin system activation. kallikrein kinin system; renin-angiotensin system; mice

Blood pressure (BP) is more salt sensitive in men than in premenopausal women. In Dahl salt-sensitive rats (DS), high-salt (HS) diet increases BP more in males than females. In contrast to the systemic renin-angiotensin system, which is suppressed in response to HS in male DS, intrarenal angiotensinogen expression is increased, and intrarenal levels of ANG II are not suppressed. In this study, the hypothesis was tested that there is a sexual dimorphism in HS-induced upregulation of intrarenal angiotensinogen mediated by testosterone that also causes increases in BP and renal injury. On a low-salt (LS) diet, male DS had higher levels of intrarenal angiotensinogen mRNA than females. HS diet for 4 wk increased renal cortical angiotensinogen mRNA and protein only in male DS, which was prevented by castration. Ovariectomy of female DS had no effect on intrarenal angiotensinogen expression on either diet. Radiotelemetric BP was similar between males and castrated rats on LS diet. HS diet for 4 wk caused a progressive increase in BP, protein and albumin excretion, and glomerular sclerosis in male DS rats, which were attenuated by castration. Testosterone replacement in castrated DS rats increased BP, renal injury, and upregulation of renal angiotensinogen associated with HS diet. Testosterone contributes to the development of hypertension and renal injury in male DS rats on HS diet possibly through upregulation of the intrarenal renin-angiotensin system. androgens; hypertension; renal injury; glomerular sclerosis; angiotensinogen

The neuropeptide hormone arginine-vasopressin (AVP) is well known to exert its antidiuretic effect via the vasopressin V2 receptor (V2R), whereas the role of the vasopressin Vla receptor (V1aR) in the kidney remains to be clarified. Previously, we reported decreased plasma volume and blood pressure in V1a receptor-deficient ([V1aR.sup.-/-]) mice (Koshimizu T, Nasa Y, Tanoue A, Oikawa R, Kawahara Y, Kiyono Y, Adachi T, Tanaka T, Kuwaki T, Mod T. Proc Natl Acad Sci USA 103: 7807-7812, 2006). In this study, we investigated the role of V 1 aR in urine concentration, renal function, and the renin-angiotensin system (RAS) using [V1aR.sup.-/-] mice. Urine volume of [V1aR.sup.-/-] mice was greater than that of wild-type mice, particularly when water was loaded, while the glomerular filtration rate (GFR), urinary NaCl excretion, AVP-dependent cAMP generation, V2R, and aquaporin 2 (AQP2) expression in the kidney were lower, indicating that the diminished GFR and V2R-AQP2 system led to impaired urinary concentration in [V1aR.sup.-/-] mice. Since the GFR and V2R-AQP2 system are regulated by RAS, we analyzed renin and angiotensin II in [V1aR.sup.-/-] mice and found that the plasma renin and angiotensin II were decreased. The expression of renin in granule cells was decreased in [V1aR.sup.-/-] mice, which led to a decreased level of plasma renin. In addition, the expression of renin stimulators such as neuronal nitric oxide synthase and cyclooxygenase-2 in macula densa (MD) cells, where V1aR was specifically expressed, was decreased in [V1aR.sup.-/-] mice. These data indicate that AVP regulates body fluid homeostasis and GFR via the V1aR in MD cells by activating RAS and subsequently the V2R-AQP2 system. renin-angiotensin system

Sex differences in blood pressure are evident in experimental models and human subjects, yet the mechanisms underlying this disparity remain equivocal. The current study sought to define the extent of male-female differences in the circulating and tissue renin-angiotensin aldosterone systems (RAASs) of congenic mRen(2).Lewis and control Lewis rats. Male congenics exhibited higher systolic blood pressure than females [200 [+ or -] 4 vs. 146 [+ or -] 7 mmHg, P < 0.01] or Lewis males and females [113 [+ or -] 2 vs. 112 [+ or -] 2 mmHg, P > 0.05]. Plasma ANG II levels were twofold higher in male congenics [47 [+ or -] 3 vs. 19 [+ or -] 3 pM, P < 0.01] and fivefold higher than in male or female Lewis rats [6 [+ or -] 1 vs. 6 [+ or -] 1 pM]. ANG I levels were also highest in the males; however, plasma ANG-(1-7) was higher in female congenics. Male congenics exhibited greater circulating renin and angiotensin-converting enzyme (ACE) activities, as well as angiotensinogen, than female littermates. Renal cortical and medullary ANG II levels were also higher in the male congenics versus all the other groups; ANG I was lower in the males. Cortical ACE2 activity was higher in male congenics, yet neprilysin activity and protein were greater in the females, which may contribute to reduced renal levels of ANG II. These data reveal that sex differences in both the circulating and renal RAAS are apparent primarily in the hypertensive group. The enhanced activity of the RAAS in male congenics may contribute to the higher pressure and tissue injury evident in the strain. angiotensin II; angiotensin-converting enzyme; angiotensin-(1-7), estrogen; neprilysin; cardiac hypertrophy; proteinuria; renin-angiotensin aldosterone system

Angiotensin II (Ang II) stimulation of the Ang type 1 receptor (A[T.sub.I]R) facilitates myocardial remodeling through NADPH oxidase-mediated generation of oxidative stress. Components of the renin-angiotensin system constitute an autocrine/paracrine unit in the myocardium, including renin, which is the rate-limiting step in the generation of Ang II. This investigation sought to determine whether cardiac oxidative stress and cellular remodeling could be attenuated by in vivo renin inhibition and/or A[T.sub.1]R blockade in a rodent model of chronically elevated tissue Ang II levels, the transgenic (mRen2)27 rat (Ren2). The Ren2 overexpresses the mouse renin transgene with resultant hypertension, insulin resistance, and cardiovascular damage. Young (6- to 7-wk-old) heterozygous (+/-) male Ren2 and age-matched Sprague-Dawley rats were treated with the renin inhibitor aliskiren, which has high preferential affinity for human and mouse renin, an A[T.sub.1]R blocker, irbesartan, or placebo for 3 wk. Myocardial NADPH oxidase activity and immunostaining for NADPH oxidase subunits and 3-nitrotyrosine were evaluated and remodeling changes assessed by light and transmission electron microscopy. Blood pressure, myocardial NADPH oxidase activity and subunit immunostaining, 3-nitrotyrosine, perivascular fibrosis, mitochondrial content, and markers of activity were significantly increased in Ren2 compared with SD littermates. Both renin inhibition and blockade of the A[T.sub.1]R significantly attenuated cardiac functional and structural alterations, although irbesartan treatment resulted in greater reductions of both blood pressure and markers of oxidative stress. Collectively, these data suggest that both reduce changes driven, in part, by Ang II-mediated increases in NADPH oxidase and, in part, increases in blood pressure. cardiac remodeling; reduced nicotinamide adenine dinucleotide phosphate oxidase; oxidative stress

Renin-angiotensin-aldosterone system (RAAS) activation mediates increases in reactive oxygen species (ROS) and impaired insulin signaling. The transgenic Ren2 rat manifests increased tissue renin-angiotensin system activity, elevated serum aldosterone, hypertension, and insulin resistance. To explore the role of aldosterone in the pathogenesis of insulin resistance, we investigated the impact of in vivo treatment with a mineralocorticoid receptor (MR) antagonist on insulin sensitivity in Ren2 and aged-matched Sprague-Dawley (SD) control rats. Both groups (age 6-8 wk) were implanted with subcutaneous time-release pellets containing spironolactone (0.24 mg/day) or placebo over 21 days. Systolic blood pressure (SBP) and intraperitoneal glucose tolerance test were determined. Soleus muscle insulin receptor substrate-1 (IRS-1), tyrosine phosphorylated IRS-1, protein kinase B (Akt) phosphorylation, GLUT4 levels, and insulin-stimulated 2-deoxyglucose uptake were evaluated in relation to NADPH subunit expression/oxidase activity and ROS production (chemiluminescence and 4-hydroxy-2-nonenal immunostaining). Along with increased soleus muscle NADPH oxidase activity and ROS, there was systemic insulin resistance and reduced muscle IRS-1 tyrosine phosphorylation, Akt phosphorylation/activation, and GLUT4 expression in the Ren2 group (each P < 0.05). Despite not decreasing blood pressure, low-dose spironolactone treatment improved soleus muscle insulin signaling parameters and systemic insulin sensitivity in concert with reductions in NADPH oxidase subunit expression/activity and ROS production (each P < 0.05). Our findings suggest that aldosterone contributes to insulin resistance in the transgenic Ren2, in part, by increasing NADPH oxidase activity in skeletal muscle tissue. Ren2 rat; mineralocorticoid receptor blockade

Macula densa (MD) cells express the [Na.sup.+]/[H.sup.+] exchanger (NHE) isoform NHE2 at the apical membrane, which may play an important role in tubular salt sensing through the regulation of cell volume and intracellular pH. These studies aimed to determine whether NHE2 participates in the MD control of renin synthesis. Renal renin content and activity and elements of the MD signaling pathway were analyzed using wild-type (NHE[2.sup.+/+]) and NHE2 knockout (NHE[2.sup.-/-]) mice. Immunofluorescence studies indicated that NHE[2.sup.-/-] mice lack NHE3 at the MD apical membrane, so the other apical NHE isoform has not compensated for the lack of NHE2. Importantly, the number of reninexpressing cells in the afferent arteriole in NHE[2.sup.-/-] mice was increased ~2.5-fold using renin immunohistochemistry. Western blotting confirmed ~20% higher renal cortical renin content in NHE[2.sup.-/-] mice compared with wild type. No-salt diet for 1 wk significantly increased renin content and activity in NHE[2.sup.+/+] mice, but the response was blunted in NHE[2.sup.-/-] mice. Renal tissue renin activity and plasma renin concentration were elevated three-and two-fold, respectively, in NHE[2.sup.-/-] mice compared with wild type. NHE[2.sup.-/-] mice also exhibited a significantly increased renal cortical cyclooxygenase-2 (COX-2) and microsomal prostaglandin E synthase (mPGES) expression, indicating MD-specific mechanisms responsible for the increased renin content. Significant and chronic activation of ERK1/2 was observed in MD cells of NHE[2.sup.-/-] kidneys. Removal of salt or addition of NHE inhibitors to cultured mouse MD-derived (MMDD1) cells caused a time-dependent activation of ERK1/2. In conclusion, the NHE2 isoform appears to be important in the MD feedback control of renin secretion, and the signaling pathway likely involves MD cell shrinkage and activation of ERK1/2, COX-2, and mPGES, all well-established elements of the MD-PGE2-renin release pathway. macula densa; cell volume; renin release; mitogen-activated protein kinases; cyclooxygenase-2

The tetradecythioacetic acid (TTA) is a modified fatty acid known to exhibit pleiotropic effects. First, we compared the effect of TTA on the blood pressure in spontaneously hypertensive rats (SHR) with two-kidney, one-clip (2K1C)-hypertensive rats. Second, we examined mechanisms involved in the blood pressure reduction. TTA had minor effect on systolic blood pressure (SBP) in young SHR up to 8 wk of age. In 2K1C we confirmed the blood pressure-lowering effect of TTA (SBP: 173[+ or -] 4 before vs. 138 [+ or -] 3 mmHg after TTA, P < 0.001). No effect on SBP was seen in Wistar-Kyoto rat (WKY) controls. Plasma renin activity (PRA) was low in SHR and WKY controls and TTA did not change it. PRA decreased from 22.9 [+ or -] 1.3 to 16.2 [+ or -] 2.2 ng.[ml.sup.-1].[h.sup.-1] (p = 0.02) in 2K1C. Plasma ANG II concentration declined from 101 [+ or -] 3 to 81 [+ or -]5 fmol/l after TTA treatment (P = 0.005). In the clipped kidney, tissue ANG I concentration decreased from 933 [+ or -] 68 to 518 [+ or -] 60 fmol/g tissue (P = 0.001), and ANG II decreased from 527 [+ or -] 38 to 149 [+ or -] 21 fmol/g tissue (P < 0.001) after TTA treatment. In the nonclipped kidney, TTA did not change ANG I and moderately reduced ANG II levels. The renal blood flow response to injection of ANG II into the nonclipped kidney was blunted compared with controls and normalized with TTA treatment (10 [+ or -] 2 before vs. 20 [+ or -] 2%, P < 0.001). The results indicate that TTA downregulates the renin-angiotensin system in high renin animals but has no effect in low renin models. Angiotensin I; angiotensin II

Transgenic rats with inducible ANG II-dependent malignant hypertension [TGR(Cyp1a1-Ren2)] were generated by inserting the mouse Ren2 renin gene into the genome of the rat. The present study was performed to assess renal morphological changes occurring during the development of ANG II-dependent malignant hypertension in these rats. Male Cyplal-Ren2 rats (n = 10) were fed normal rat food containing indole-3-carbinol (I3C; 0.3%) for 10 days to induce malignant hypertension. Rats induced with I3C had higher mean arterial pressures (173 [+ or -] 9 vs. 112 [+ or -] 11 mmHg, P < 0.01) than noninduced normotensive rats (n = 9). Glomerular damage was evaluated by determination of the glomerulosclerosis index (GSI) in tissue sections stained with periodic acid-Schiff. Kidneys of hypertensive rats had a higher GSI than normotensive rats (21.3 [+ or -] 5.6 vs. 3.5 [+ or -] 1.31 units). Quantitative analysis of macrophage ED-1-positive cells and proliferating cell nuclear antigen using immunohistochemistry demonstrated increased macrophage numbers in the renal interstitium (106.4 [+ or -] 11.4 vs. 58.7 [+ or -] 5.0 cells/[mm.sup.2]) and increased proliferating cell number in cortical tubules (37.8 [+ or -] 5.7 vs. 24.2 [+ or -] 2.1 cells/mm2), renal cortical vessels (2.2 [+ or -] 0.5 vs. 0.13 [+ or -] 0.07 cells/vessel), and the cortical interstitium (33.6 [+ or -] 5.7 vs. 4.2 [+ or -] 1.4 cells/[mm.sup.2]) of hypertensive rat kidneys. These findings demonstrate that the renal pathological changes that occur during the development of malignant hypertension in Cyplal-Ren2 rats are characterized by inflammation and cellular proliferation in cortical vessels and tubulointerstitium. kidney; glomerulosclerosis; renal injury; immunohistochemistry; renin-angiotensin system; renal pathology; peptide hormones doi:10.1152/ajprenal.00469.2006

Components of the renin-angiotensin system (RAS) are expressed in a number of areas in the brain involved in cardiovascular control. However, it has been difficult to link RAS actions in [...]

The renin-angiotensin system plays a key role in the initiation and maintenance of elevated blood pressure associated with altered intrauterine milieu. The current studies were undertaken to verify whether vascular response to ANG II is increased in adult offspring of low-protein fed dams (LP) compared with control (CTRL) and if so, to examine underlying mechanism(s). ANG II-induced contraction of carotid rings was increased in LP ([E.sub.max] the maximum asymptote of the curve, relative to maximal response to KC1 80 mM: 230 [+ or -] 3% LP vs. 201 [+ or -] 2% CTRL, P < 0.05). In both groups, contraction to ANG II was mediated solely by [AT.sub.1]R. Responses to thromboxane A2 analog U-46619 and to KCl 80 mM under step increases in tension were similar between groups. Endothelium depletion enhanced contraction to ANG II in both groups, more so in LP. Blockade of endothelin formation had no effect on response to ANG II, and ANG-(1-7) did not elicit vasomotor response in either group. Superoxide dismutase (SOD) analog Tempol normalized LP without modifying CTRL response to ANG II. Basal levels of superoxide (aortic segments, lucigenin-enhanced chemiluminescence and fluorescent dye hydroethidine) were higher in LP. ANG II further increased superoxide production in LP only, and this was inhibited by coincubation with diphenylene iodonium or apocynin (inhibitor of NADPH oxidase complex). [AT.sub.1]R expression in carotid arteries was increased in LP, whereas SOD expression was unchanged. In conclusion, vasoconstriction to ANG II is exaggerated in this model of developmental programming of hypertension, secondary to enhanced vascular production of superoxide anion by NADPH oxidase with concomitant increase of [AT.sub.1]R expression. oxidative stress; angiotensin; isolated vessels

The activities of both sarcolemmal (SL) [Na.sup.+]-[K.sup.+]-ATPase and [Na.sup.+]/[Ca.sup.2+] exchanger, which maintain the intracellular cation homeostasis, have been shown to be depressed in heart failure due to myocardial infarction (MI). Because the renin-angiotensin system (RAS) is activated in heart failure, this study tested the hypothesis that attenuation of cardiac SL changes in congestive heart failure (CHF) by angiotensin-converting enzyme (ACE) inhibitors is associated with prevention of alterations in gene expression for SL [Na.sup.+]-[K.sup.+]-ATPase and [Na.sup.+]/[Ca.sup.2+] exchanger. CHF in rats due to MI was induced by occluding the coronary artery, and 3 wk later the animals were treated with an ACE inhibitor, imidapril (1 mg * [kg.sup.-1] * [day.sup.-1]), for 4 wk. Heart dysfunction and cardiac hypertrophy in the infarcted animals were associated with depressed SL [Na.sup.+]-[K.sup.+]-ATPase and [Na.sup.+]/[Ca.sup.+2] exchange activities. Protein content and mRNA levels for [Na.sup.+]/ [Ca.sup.2+] exchanger as well as [Na.sup.+]-[K.sup.+]-ATPase [[alpha].sub.1],[[alpha].sub.2]-, [[beta].sub.2-] and [[beta].sub.1]-isoforms were depressed, whereas those for [[alpha].sub.3]-isoform were increased in the failing heart. These changes in SL activities, protein content, and gene expression were attenuated by treating the infarcted animals with imidapril. The beneficial effects of imidapril treatment on heart function and cardiac hypertrophy as well as SL [Na.sup.+]-[K.sup.+]-ATPase and [Na.sup.1]/ [Ca.sup.2+] exchange activities in the infarcted animals were simulated by enalapril, an ACE inhibitor, and Iosaltan, an angiotensin receptor antagonist. These results suggest that blockade of RAS in CHF improves SL [Na.sup.+] -[K.sup.1]-ATPase and [Na.sup.+] /[Ca.sup.2+] exchange activities in the failing heart by preventing changes in gene expression for SL proteins. cardiac sarcolemma; [Na.sup.+]-[K.sup.+]-ATpase isoforms; cardiac gene expression; congestive heart failure; angiotensin-converting enzyme inhibitors

Preeclampsia is a hypertensive disorder unique to pregnancy with consistent involvement of the kidney. The renin-angiotensin system (RAS) has been implicated in the pathogenesis of preeclampsia. In the gravid state, in addition to the RAS in the kidney, there is a tissue-based RAS in the uteroplacental unit. Increased renin expression observed both in human preeclampsia and in a transgenic mouse model with a human preeclampsia-like syndrome supports the concept that activation of the uteroplacental RAS, with angiotensin II entering the systemic circulation, may mediate the pathogenesis of preeclampsia. A novel disease paradigm of the two-kidney one-clip (2K-1C) Goldblatt model is presented for preeclampsia, wherein the gravid uterus is the clipped 'kidney' and the two maternal kidneys represent the unclipped kidney. Validation of the 2K-1C Goldblatt model analogy requires evidence of elevated angiotensin II in the peripheral circulation before vascular maladaptation in preeclampsia. Convincing evidence of the elevation of angiotensin II in preeclampsia does not exist despite the fact that much of vascular pathogenesis appears to be due to angiotensin type I ([AT.sub.1]) receptor activation. Vascular maladaptation with increased vasomotor tone, endothelial dysfunction, and increased sensitivity to angiotensin II and norepinephrine in manifest preeclampsia may be explained on the basis of angiotensin II-mediated mechanisms. Recently, novel angiotensin II-related biomolecular mechanisms have been described in preeclampsia. These include [AT.sub.1] and bradykinin [B.sub.2] receptor heterodimerization and the production of an autoantibody against [AT.sub.1]. Various organ systems with a predilection for involvement in preeclampsia are each a site of a tissue-based RAS. How angiotensin II-mediated mechanisms may explain the primary clinical-pathological features of preeclampsia is described. Future investigations are proposed to more precisely define the role of activation of the uteroplacental RAS in the mechanisms underlying preeclampsia.

The roles of nitric oxide (NO) and plasma renin activity (PRA) in the depressor response to chronic administration of Tempol in spontaneously hypertensive rats (SHR) are not clear. The present study was done to determine the effect of 2 wk of Tempol treatment on blood pressure [mean arterial pressure (MAP)], oxidative stress, and PRA in the presence or absence of chronic NO synthase inhibition. SHR were divided into four groups: control, Tempol (1 mmol/1) alone, nitro-L-arginine methyl ester (L-NAME, 4.5 mg x [kg.sup.-1] x [day.sup.-1]) alone, and Tempol + L-NAME for 2 wk. With Tempol, MAP decreased by 22%: 191 [+ or -] 3 and 162 [+ or -] 21 mmHg for control and Tempol, respectively (P < 0.05). L-NAME increased MAP by 16% (222 [+ or -] 2 mmHg, P < 0.01), and L-NAME + Tempol abolished the depressor response to Tempol (215 [+ or -] 3 mmHg, P < 0.01). PRA was not affected by Tempol but was increased slightly with L-NAME alone and 4.4-fold with L-NAME + Tempol. Urinary nitrate/nitrite increased with Tempol and decreased with L-NAME and L-NAME + Tempol. Tempol significantly reduced oxidative stress in the presence and absence of L-NAME. In conclusion, in SHR, Tempol administration for 2 wk reduces oxidative stress in the presence or absence of NO, but in the absence of NO, Tempol is unable to reduce MAP. Therefore, NO, but not changes in PRA, plays a major role in the blood pressure-lowering effects of Tempol. These data suggest that, in hypertensive individuals with endothelial damage and chronic NO deficiency, antioxidants may be able to reduce oxidative stress but not blood pressure. nitric oxide; superoxide; antioxidant; renin-angiotensin system

This study was designed to test the hypothesis that blockade of the renin-angiotensin system improves cardiac function in congestive heart failure by preventing changes in gene expression of sarcoplasmic reticulum (SR) proteins. We employed rats with myocardial infarction (MI) to examine effects of an angiotensin-converting enzyme inhibitor, imidapril, on SR [Ca.sup.2+] transport, protein content, and gene expression. Imidapril (1 mg x [kg.sup.-1] x [day.sup.-1]) was given for 4 wk starting 3 wk after coronary artery occlusion. Infarcted rats exhibited a fourfold increase in left ventricular end-diastolic pressure, whereas rates of pressure development and decay were decreased by 60 and 55%, respectively. SR [Ca.sup.2+] uptake and [Ca.sup.2+] pump ATPase, as well as [Ca.sup.2+] release and ryanodine receptor binding activities, were depressed in the failing hearts; protein content and mRNA levels for [Ca.sup.2+] pump ATPase, phospholamban, and ryanodine receptor were also decreased by ~55-65%. Imidapril treatment of infarcted animals improved cardiac performance and attenuated alterations in SR [Ca.sup.2+] pump and [Ca.sup.2+] release activities. Changes in protein content and mRNA levels for SR [Ca.sup.2+] pump ATPase, phospholamban, and ryanodine receptor were also prevented by imidapril treatment. Beneficial effects of imidapril on cardiac function and SR [Ca.sup.2+] transport were not only seen at different intervals of MI but were also simulated by another angiotensin-converting enzyme inhibitor, enalapril, and an ANG II receptor antagonist, losartan. These results suggest that blockade of the renin-angiotensin system may increase the abundance of mRNA for SR proteins and, thus, may prevent the depression in SR [Ca.sup.2+] transport and improve cardiac function in congestive heart failure due to MI. myocardial infarction; cardiac gene expression; renin-angiotensin system

The brain renin-angiotensin system (RAS) has long been considered pivotal in cardiovascular regulation and important in the pathogenesis of hypertension and heart failure. However, despite more than 30 years of study, the brain RAS continues to defy explanation. Our lack of understanding of how the brain RAS is organized at the cellular and regional levels has made it difficult to resolve long-sought questions of how ANG II is produced in the brain and the precise mechanisms by which it exerts its actions. A major reason for this is the difficulty in experimentally dissecting the brain RAS at the regional, cellular, and whole organism levels. Recently, we and others developed a series of molecular tools for selective manipulation of the murine brain RAS, in parallel with technologies for integrative analysis of cardiovascular and volume homeostasis in the conscious mouse. This review, based in part on a lecture given in conjunction with the American Physiological Society Young Investigator Award in Regulatory and Integrative Physiology (Water and Electrolyte Homeostasis Section), outlines the physiological genomics strategy that we have taken in an effort to unravel some of the complexities of this system. It also summarizes the principles, progress, and prospects for a better understanding of the brain RAS in health and disease. transgenic mice; gene transfer; blood pressure; heart rate; dipsogenesis; reactive oxygen species; Cre-lox system; hypertension; heart failure

The renin-angiotensin system (RAS) plays a central role in body physiology, controlling blood pressure and blood electrolyte composition. ACE.1 (null) mice are null for all expression of angiotensin-converting enzyme (ACE). These mice have low blood pressure, the inability to concentrate urine, and a maldevelopment of the kidney. In contrast, ACE.2 (tissue null) mice produce one-third normal plasma ACE but no tissue ACE. They also have low blood pressure and cannot concentrate urine, but they have normal indices of renal function. These mice, while very informative, show that the null approach to creating knockout mice has intrinsic limitations given the many different physiological systems that no longer operate in an animal without a functioning RAS. To investigate the fine control of body physiology by the RAS, we developed a novel promoter swapping approach to generate a more selective tissue knockout of ACE expression. We used this to create ACE.3 (liver ACE) mice that selectively express ACE in the liver but lack all ACE within the vasculature. Evaluation of these mice shows that endothelial expression of ACE is not required for blood pressure control or normal renal function. Targeted homologous recombination has the power to create new strains of mice expressing the RAS in selected subsets of tissues. Not only will these new genetic models be useful for studying blood pressure regulation but also they show great promise for the investigation of the function of the RAS in complicated disease models. angiotensin-converting enzyme; blood pressure; angiotensin II; liver; renin-angiotensin system

Activation of the renin-angiotensin system in the brain is considered important in the arousal and expression of sodium appetite. To clarify the effects of directly activating this hormonal cascade, taste neurons in the nucleus of the solitary tract of rats were tested with a battery of sapid stimuli after intracerebroventricular injection of renin or its vehicle. The rats were chronically prepared but lightly anesthetized during the recording procedure. Eighty-five taste neurons were tested: 46 after renin injections and 39 after vehicle. Neural activity was counted for 5.0-s periods without stimulation (spontaneous) and during stimulation with water and sapid chemicals. The averaged responses to each of the standard stimuli (0.1 M NaCl, 0.3 M sucrose, 0.01 M citric acid, and 0.01 M quinine hydrochloride) did not differ significantly between the two conditions. When the rats were tested with a concentration range of NaCl however, after renin the average responses to the hypertonic 0.3 and 1.0 M stimuli were reduced to 74 and 70%, respectively, compared with those after vehicle injections. A similar tendency was evident for the subsample of neurons that responded best to NaCl, but the effect was smaller. These data are consistent with, but not as dramatic as, those reported after dietary-induced sodium appetite. sodium appetite; single-unit activity; need-free sodium intake; renin-angiotensin system; neuropeptide

The intracardiac ANG II-forming pathway is activated in the senescent myocardium, raising the possibility of enhanced ANG II effects on cardiac fibroblasts. This study established an in vitro model of cultured cardiac fibroblasts from aged rats to examine if the response of these cells to ANG II is modified in the aged heart. Levels of mRNA encoding renin, angiotensinogen, and the A[T.sub.1] receptor subtype in cardiac fibroblasts from young adult and senescent rats were quantified by RT-PCR, net collagen production by a hydroxyproline-based assay, and transforming growth factor (TGF)-[beta] levels using a commercial kit. In cardiac fibroblasts from young adult rats, ANG II significantly enhanced A[T.sub.1] mRNA levels, net collagen production, and TGF-[beta] production. In fibroblasts from the aged myocardium, ANG II downregulated A[T.sub.1] mRNA expression, had a less pronounced effect on net collagen production, and had no effect on TGF-[beta] production. Such age-related modification of the response of cardiac fibroblasts to ANG II may counteract the effects of augmented intracardiac ANG II production in the senescent heart, limiting fibrogenesis. renin-angiotensin system; transforming growth factor-[beta]; angiotensin type 1 receptor; collagen; cardiac fibrosis

Primary cultures of rat type II alveolar epithelial cells (AECs) or human AEC-derived A549 cells, when exposed to bleomycin (Bleo), exhibited concentration-dependent apoptosis detected by altered nuclear morphology, fragmentation of DNA, activation of caspase-3, and net cell loss over time. In both cell culture models, exposure to Bleo caused time-dependent increases in angiotensinogen (ANGEN) mRNA. Antisense oligonucleotides against ANGEN inRNA inhibited Bleo-induced apoptosis of rat AEC or A549 cells by 83 and 84%, respectively (P < 0.01 and P < 0.05), and prevented Bleo-induced net cell loss. Apoptosis of rat AECs or A549 cells in response to Bleo was inhibited 91% by the ANG-converting enzyme inhibitor captopril or 82%, respectively, by neutralizing antibodies specific for ANG II (both P < 0.01). Antagonists of ANG receptor AT1 (losartan, L-158809, or saralasin), but not an AT2-selective blocker (PD-123319), inhibited Bleo-induced apoptosis of either rat AECs (79%, P < 0.01) or A549 cells (83%, P < 0.01) and also reduced the activity of caspase-3 by 52% (P < 0.05). These data indicate that Bleo, like FasL or TNF-[alpha], induces trans-activation of ANG synthesis de novo that is required for AEC apoptosis. They also support the theory that ANG system antagonists have potential for the blockade of AEC apoptosis in situ. renin-angiotensin system; type II pneumocyte; lung fibrosis; programmad cell death; angiotensinogen

Renal interstitial inflammation is an important factor in the pathogenesis of chronic cyclosporin A (CsA) nephropathy. We studied the expression of the chemoattractant osteopontin (OPN) and the relationship between OPN expression and tubulointerstitial injury in a rat model of chronic CsA nephropathy. Chronic CsA nephropathy was induced in Sprague-Dawley rats by administering CsA (15 mg/kg sc) for 5 wk and then withdrawing it for 5 or 10 wk. Renal function, histopathology (arteriolopathy, ED-1-positive cells, and tubulointerstitial fibrosis), renin-angiotensin system (RAS) activity, and OPN expression were observed during the follow-up period. Renal function deteriorated in CsA-treated rats, with the development of typical histopathology and activation of RAS. After CsA withdrawal, these parameters were significantly reversed (all P < 0.05). The upregulation of OPN mRNA and protein expression seen in CsA-treated rat kidneys was decreased 5 wk after CsA withdrawal and was further decreased after 10 wk. Of note, OPN mRNA expression correlated with the number of infiltrating macrophage (r = 0.651, P < 0.01) and tubulointerstitial fibrosis (r = 0.729, P < 0.01). These findings suggest that OPN expression and macrophage infiltration decrease after long-term CsA withdrawal in rats with established chronic CsA nephropathy, and this is closely associated with recovery from renal injury. cyclosporin withdrawal; osteopontin; macrophage; tubuloin-terstitial fibrosis; renin-angiotensin system

We investigated the effect of cyclooxygenase (COX) activity on the regulation of the renin-angiotensin-aldosterone system by salt intake. Therefore, Sprague-Dawley rats were subjected to different salt diets [0.02, 0.6, and 8% NaCl (wt/wt)] and treated with the selective COX-2 inhibitor rofecoxib (10 mg * kg body [wt.sup.-1] * [day.sup.-1]) or with ketorolac at a dose selective for COX-1 inhibition (2 mg * kg body [wt.sup.-1] * [day.sup.-1) for 3, 7, 14, and 21 days. Rofecoxib and ketorolac caused a similar reduction of renocortical PG[E.sub.2] formation with a low-salt diet. Rofecoxib did not change plasma renin activity or renocortical renin mRNA abundance with any of the diets but clearly lowered plasma aldosterone concentration. In contrast, ketorolac delayed the increase in plasma renin activity and of renin mRNA in response to low salt intake but did not change plasma aldosterone concentration. Prolonged treatment with rofecoxib but not with ketorolac caused an upregulation of COX-2 expression while COX-1 mRNA abundance remained unchanged. These findings suggest that COX-l-derived, but not COX-2-derived, prostanoids are of relevance for the regulation of the renin system by salt intake. cyclooxygenase; kidney

The renin-angiotensin-aldosterone system excites hypothalamic paraventricular nucleus neurons in heart failure. Am J Physiol Heart Circ Physiol 283: H423-H433, 2002; 10.1152/ajpheart.00685.2001.--The paraventricular nucleus (PVN) of the hypothalamus has critical homeostatic functions, including the regulation of fluid balance and sympathetic drive. It has been suggested that altered activity of this nucleus contributes to the progression of congestive heart failure (HF). We hypothesized that forebrain influences of the renin-angiotensin-aldosterone system augment the activity of PVN neurons in HF. The rate of PVN neurons (n = 68) from rats with ischemia-induced HF was higher than that of PVN neurons (n = 42) from shamoperated controls (8.7 [+ or -] vs. 2.7 [+ or -] 0.3 spikes/s, P < 0.001, HF vs. SHAM). Forebrain-directed intracarotid artery injections of the angiotensin type 1 receptor antagonist losartan, the angiotensin-converting enzyme inhibitor captopril, and the mineralocorticoid receptor antagonist spironolactone all significantly (P < 0.05) reduced PVN neuronal activity in HF rats. These findings demonstrate that the renin-angiotensinaldosterone system drives PVN neuronal activity in HF, likely resulting in increased sympathetic drive and volume accumulation. This mechanism of neurohumoral excitation in HF is accessible to manipulation by blood-borne therapeutic agents. angiotensin type 1 receptors; angiotensin-converting enzyme; mineralocorticoid receptors; spironolactone; baroreceptors

Intrauterine growth restriction in rats is associated with hypertension and renal dysfunction in adulthood. Am J Physiol Endocrinol Metab 283: E 124-E131, 2002; 10.1152/ajpendo.00004.2001.--Epidemiological studies have produced evidence that unfavorable intrauterine environments during fetal life may lead to adverse outcomes in adulthood. We have previously shown that a low-sodium diet, given to pregnant rats over the last week of gestation, results in intrauterine growth restriction (IUGR). We hypothesize that pups born with IUGR are more susceptible to the development of hypertension in adulthood. IUGR fetuses and rats aged 1 wk were characterized for organ growth and renal morphogenesis. The adults (12 wk) were evaluated for weight, systolic blood pressure, activity of the renin-angiotensin-aldosterone system (AA), and renal function; hearts and kidneys underwent a histological examination. Brain and cardiac ventricle-to-body ratios were increased in IUGR fetuses compared with age-matched controls, whereas the kidney-to-body ratio was unchanged. Systolic blood pressure was elevated in both IUGR male and female adults. Plasma aldosterone levels were not correlated with increased plasma renin activity. Moreover, urinary sodium was decreased, whereas plasma urea was elevated in both males and females, and creatinine levels were augmented only in females, suggesting a glomerular filtration impairment in IUGR. In our model of IUGR induced by a low-sodium diet given to pregnant rats, high blood pressure, alteration of the RAAS, and renal dysfunction are observed in adult life. Differences observed between male and female adults suggest the importance of gender in outcomes in adulthood after IUGR. fetal programming; renin-angiotensin-aldosterone system

The proximal tubule synthesizes and secretes angiotensin II into the lumen, where it regulates transport. Renal denervation abolishes the effect of angiotensin II on proximal tubule transport. Using in vivo microperfusion, we examined whether renal nerve stimulation modulates the effect of angiotensin II on transport. The effect of angiotensin II was assessed by measuring the decrease in volume reabsorption with the addition of [10.sup.-4] M luminal enalaprilat. Luminal enalaprilat did not alter volume reabsorption (2.80 [+ or -] 0.18 vs. 2.34 [+ or -] 0.14 nl * [mm.sup.-1] * [min.sup.1]). However, with renal nerve stimulation, enalaprilat decreased volume reabsorption (3.45 [+ or -] 0.22 vs. 1.67 [+ or -] 0.20 nl * [mm.sup.-1] * [min.sup.-1], P < 0.0005). The absolute and percent decrements in volume reabsorption with luminal enalaprilat were higher with renal nerve stimulation than with native innervation (1.78 [+ or -] 0.19 vs. 0.46 [+ or -] 0.23 nl * [mm.sup.-1] * [min.sup.-1], P < 0.02, and 51.8 [+ or -] 5.0 vs. 14.6 [+ or -] 7.4%, P < 0.05, respectively). Renal nerve stimulation did not alter the glomerular filtration rate or renal blood flow. Renal nerve stimulation augments the stimulatory effect of intraluminal angiotensin II. The sympathetic renal nerves modulate the proximal tubule renin-angiotensin system and thereby regulate proximal tubule transport. renin-angiotensin system; enalaprilat; in vivo microperfusion

The hypothesis that increases in plasma sodium induce natriuresis independently of changes in body fluid volume was tested in six slightly dehydrated seated subjects on controlled sodium intake (150 mmol/day). NaCl (3.85 mmol/kg) was infused intravenously over 90 min as isotonic (Iso) or as hypertonic saline (Hyper, 855 mmol/l). After Hyper, plasma sodium increased by 3% (142.0 [+ or -] 0.6 to 146.2 [+ or -] 0.5 mmol/l). During Iso a small decrease occurred (142.3 [+ or -] 0.6 to 140.3 [+ or -] 0.7 mmol/l). Iso increased estimates of plasma volume significantly more than Hyper. However, renal sodium excretion increased significantly more with Hyper (291 [+ or -] 25 vs. 199 [+ or -] 24 [micro]mol/min). This excess was not mediated by arterial pressure, which actually decreased slightly. Creatinine clearance did not change measurably. Plasma renin activity, ANG II, and aldosterone decreased very similarly in Iso and Hyper. Plasma atrial natriuretic peptide remained unchanged, whereas plasma vasopressin increased with Hyper (1.4 [+ or -] 0.4 to 3.1 [+ or -] 0.5 pg/ml) and decreased (1.3 [+ or -] 0.4 to 0.6 [+ or -] 0.1 pg/ml) after Iso. In conclusion, the natriuretic response to Hyper was 50% larger than to Iso, indicating that renal sodium excretion may be determined partly by plasma sodium concentration. The mechanism is uncertain but appears independent of changes in blood pressure, glomerular filtration rate, the renin system, and atrial natriuretic peptide. hypertonic sodium loading; osmoreceptors; renin-angiotensin-aldosterone system