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The novel peptide, angiotensin (ANG)-(1-12), elicits a systemic pressor response and vasoconstriction. These effects are blocked by ANG converting enzyme (ACE) inhibitors or AT1 receptor antagonists, suggesting a role as an ANG II precursor. However, ANG-(1-12) can serve as a substrate for either ANG II or ANG-(1-7) formation, depending on the local tissue enzymes. Although levels of ANG-(1-12) are higher than ANG I or ANG II in brain, the role and processing of this peptide for autonomic control of heart rate (HR) has yet to be considered. Thus we examined the effects of nucleus tractus solitarii (NTS) microinjection of ANG-(1-12) on baroreflex sensitivity for control of HR, resting arterial pressure (AP) and HR, and indexes of sympathovagal balance in urethane/chloralose anesthetized Sprague-Dawley rats. NTS injection of ANG-(1-12) (144 fmol/120 nl) significantly impaired the evoked baroreflex sensitivity to increases in AP [n = 7; 1.06 [+ or -] 0.06 baseline vs. 0.44 [+ or -] 0.07 ms/mmHg after ANG-(1-12)], reduced the vagal component of spontaneous baroreflex sensitivity and HR variability, and elicited a transient depressor response (P < 0.05). NTS pretrcatment with an AT1 receptor antagonist or ACE inhibitor prevented ANG-(1-12)-mediated autonomic and depressor responses. ANG-(1-12) immunostaining was observed in cells within the NTS of SpragueDawley rats, providing a potential intracellular source for the peptide. However, acute NTS injection of an ANG-(1-12) antibody did not alter resting baroreflex sensitivity, AP, or HR in these animals. Collectively, these findings suggest that exogenous ANG-(1-12) is processed to ANG II for cardiovascular actions at AT1 receptors within the NTS. The lack of acute endogenous ANG-(1-12) tone for cardiovascular regulation in Sprague-Dawley rats contrasts with chronic immunoneutralization in hypertensive rats, suggesting that ANG-(1-12) may be activated only under hypertensive conditions. baroreflex; autonomic doi: 10.1152/ajpheart.00345.2010.

To accelerate lung development and protect neonates from other early developmental problems, synthetic steroids are administered maternally in the third trimester, exposing fetuses that are candidates for premature delivery to them. However, steroid exposure at this point of gestation may lead to elevated blood pressure [mean arterial pressure (MAP)] during adolescence. We hypothesize that fetal exposure to steroids activates the renin-angiotensin system, inducing an elevation in blood pressure and attenuation of baroreflex sensitivity (BRS) that is angiotensin II dependent in early adulthood. To test this hypothesis, fetal sheep were exposed to betamethasone (Beta) or vehicle (control) administered to ewes at day 80 of gestation and delivered at full term. At 1.8 yr of age, male offspring were instrumented for conscious recording of MAP, heart rate, and measurement of BRS [as low-frequency-[alpha], high-frequency-co, sequence (seq) UP, seq DOWN, and seq TOTAL]. Beta-exposed sheep (n = 6) had higher MAP than control sheep (n = 5) (93 [+ or -] 2 vs. 84 [+ or -] 2 mmHg, P < 0.01). Acute blockade of angiotensin type 1 receptors with candesartan (0.3 mg/kg iv) normalized MAP in Beta-exposed sheep (85 [+ or -] 4 mmHg), with no effect in control sheep (82 [+ or -] 3 mmHg). Before angiotensin type 1 blockade, BRS maximum gain was significantly lower in Beta-exposed vs. control sheep (11 [+ or -] 3 vs. 26 [+ or -] 3 ms/mmHg, P < 0.0.01). However, 45 min after candesartan injection, BRS was increased in Beta-exposed (21 [+ or -] 5 ms/mmHg) and control (35 [+ or -] 4 ms/mmHg) sheep. Heart rate variability (HRV) and blood pressure variability (BPV) revealed lower HRV (SD of beat-to-beat interval and root mean square of successive beat-to-beat differences in R-R interval duration) and higher BPV (SD of MAP, systolic arterial pressure in low-frequency range) in Beta-exposed sheep. Candesartan partially restored HRV in Beta-exposed sheep and fully corrected BPV. Thus, in utero exposure to synthetic glucocorticoids causes long-lasting programming of the cardiovascular system via renin-angiotensin system-dependent mechanisms. spectral analysis; fetal programming; heart rate variability; blood pressure variability; renin-angiotensin system; hypertension doi: 10.1152/ajpheart.00100.2010.

The effects of chronic mild hypoxemia on the binding of angiotensin receptors in selected brain stem nuclei and reflex responses were studied in fetal sheep. Fetal and maternal catheters were placed at 120 days' gestation, and animals received intratracheal maternal administration of nitrogen (n = 16) or compressed air in controls (n = 19). Nitrogen infusion was adjusted to reduce fetal brachial artery P[O.sub.2] by 25% during 5 days. Spontaneous baroreflex sensitivity and spectral analysis of the pulse interval were analyzed during the 5 days hypoxemia period using 90 min of daily recording. Brains of control and hypoxemic animals were collected, and brain stem angiotensin receptor binding was studied by in vitro autoradiography at 130 days of gestation. After 5 days of hypoxemia, some animals in each group were submitted to one complete umbilical cord occlusion during 5 min. [[sup.125]I]sarthran binding showed that chronic mild hypoxemia significantly increases angiotensin type 1 receptor, angiotensin type 2 receptor, and ANG-(1-7) angiotensin receptor binding sites in the nucleus tractus solitarius and dorsal motor nucleus of the vagus (P < 0.05). Hypoxemia induced lower baroreflex sensitivity and a higher low frequency-to-high frequency ratio in the fetus, consistent with a shift from vagal to sympathetic autonomic cardiac regulation. Cord occlusion to elicit a chemoreflex response induced a greater bradycardic response in hypoxemic fetuses (slope of the initial fall in heart rate; 11.3 [+ or -] 1.9 vs. 6.4 [+ or -] 1.2 beats x [min.sup.-1] x [s.sup.-1], P < 0.05). In summary, chronic mild hypoxemia increased binding of angiotensin receptors in brain stem nuclei, decreased spontaneous barorefex gain, and increased chemoreflex responses to asphyxia in the fetus. These results suggest hypoxemia-induced alterations in brain stem mechanisms for cardiovascular control. fetus; hypoxemia; baroreflex

Angiotensin-(1-12) [ANG(1-12)] is a newly identified peptide detected in a variety of rat tissues, including the brain. To determine whether brain ANG-(1-12) participates in blood pressure regulation, we treated male adult (mRen2)27 hypertensive rats (24-28 wk of age) with Anti-ANG-(1-12) IgG or Preimmune IgG via an intracerebroventricular cannula for 14 days. Immunoneutralization of brain ANG-(1-12) lowered systolic blood pressure (-43 [+ or -] 8 mmHg on day 3 and -26 [+ or -] 7 mmHg on day 10 from baseline, P < 0.05). Water intake was lower on intracereroventricular day 6 in the Anti-ANG-(1-12) IgG group, accompanied by higher plasma osmolality on day 13, but there were no differences in urine volume, food intake, or body weight during the 2-wk treatment. In Preimmune IgG-treated animals, there were no significant changes in these variables over the 2-wk period. The antihypertensive effects produced by endogenous neutralization of brain ANG-(1-12) suggest that ANG-(1-12) is functionally active in brain pathways regulating blood pressure. hypertension; transgenic rats; renin-angiotensin system; brain; sympathetic nerve; antibody

Expression of nuclear angiotensin II type 1 ([AT.sub.1]) receptors in rat kidney provides further support for the concept of an intracellular renin-angiotensin system. Thus we examined the cellular distribution of renal ANG II receptors in sheep to determine the existence and functional roles of intracellular ANG receptors in higher order species. Receptor binding was performed using the nonselective ANG II antagonist [sup.125]I-[[Sar.sup.1],[Thr.sup.8]]-ANG II ([sup.125]I-sarthran) with the [AT.sub.1] antagonist losartan (LOS) or the [AT.sub.2] antagonist PD123319 (PD) in isolated nuclei (NUC) and plasma membrane (PM) fractions obtained by differential centrifugation or density gradient separation. In both fetal and adult sheep kidney, PD competed for the majority of cortical NUC ([greater than or equal to] 70%) and PM ([greater than or equal to]80%) sites while LOS competition predominated in medullary NUC ([greater than or equal to]75%) and PM ([greater than or equal to]70%). Immunodetection with an [AT.sub.2] antibody revealed a single ~42-kDa band in both NUC and PM extracts, suggesting a mature molecular form of the NUC receptor. Autoradiography for receptor subtypes localized [AT.sub.2] in the tubulointerstitium, [AT.sub.1] in the medulla and vasa recta, and both [AT.sub.1] and [AT.sub.2] in glomeruli. Loading of NUC with the fluorescent nitric oxide (NO) detector DAF showed increased NO production with ANG II (1 nM), which was abolished by PD and N-nitro-L-arginine methyl ester, but not LOS. Our studies demonstrate ANG II receptor subtypes are differentially expressed in ovine kidney, while nuclear [AT.sub.2] receptors are functionally linked to NO production. These findings provide further evidence of a functional intracellular renin-angiotensin system within the kidney, which may represent a therapeutic target for the regulation of blood pressure. nucleus; kidney; intracellular renin angiotensin system

The perivascular sensory nerve (PvN) [Ca.sup.2+]-sensing receptor (CAR) is implicated in [Ca.sup.2+]induced relaxation of isolated, phenylephrine (PE)-contracted mesenteric arteries, which involves the vascular endogenous cannabinoid system. We determined the effect of inhibition of diacylglycerol (DAG) lipase (DAGL), phospholipase [A.sub.2] (PL[A.sub.2]), and cytochrome P-450 (CYP) on [Ca.sup.2+]-induced relaxation of PE-contracted rat ruesenteric arteries. Our findings indicate that [Ca.sup.2+]-induced vasorelaxation is not dependent on the endothelium. The DAGL inhibitor RHC 802675 (1 [micro]M) and the CYP and PL[A.sub.2] inhibitors quinacrine (5 [micro] M) (E[C.sub.50]: RHC 802675 2.8 [+ or -] 0.4 mM vs. control 1.4 [+ or -] 0.3 mM; quinacrine 4.8 [+ or -] 0.4 mM vs. control 2.0 [+ or -] 0.3 mM; n = 5) and arachidonyltrifluoromethyl ketone (AACOC[F.sub.3], 1 [micro] M) reduced [Ca.sup.2+]induced relaxation of mesenteric arteries. Synthetic 2-arachidonoylglycerol (2-AG) and glycerated epoxyeicosatfienoic acids (GEETs) induced concentration-dependent relaxation of isolated arteries. 2-AG relaxations were blocked by iberiotoxin (IBTX) (E[C.sub.50]: control 0.96 [+ or -] 0.14 nM, IBTX 1.3 [+ or -] 0.5 [micro] M) and miconazole (48 [+ or -] 3%), and 11,12-GEET responses were blocked by IBTX (E[C.sub.50]: control 55 [+ or -] 9 nM, IBTX 690 [+ or -] 96 nM) and SR-141716A. The data suggest that activation of the CaR in the PvN network by [Ca.sup.2+] leads to synthesis and/or release of metabolites of the CYP epoxygenase pathway and metabolism of DAG to 2-AG and subsequently to GEETs. The findings indicate a role for 2-AG and its metabolites in [Ca.sup.2+]-induced relaxation of resistance arteries; therefore this receptor may be a potential target for the development of new vasodilator compounds for antihypertensive therapy. [Ca.sup.2+]-sensing receptor; arachidonic acid; vasorelaxation

Fischer-344 (F344) rats exhibit proteinuria and insulin resistance in the absence of hypertension as they age. We determined the effects of long-term (1 yr) treatment with the angiotensin (ANG) II type 1 (A[T.sub.1]) receptor blocker L-158,809 on plasma and urinary ANG peptide levels, systolic blood pressure (SBP), and indexes of glucose metabolism in 15-mo-old male F344 rats. Young rats at 3 mo of age (n = 8) were compared with two separate groups of older rats: one control group (n = 7) and one group treated with L-158,809 (n = 6) orally (20 mg/1) for 1 yr. SBP was not different between control and treated rats but was higher in young rats. Serum leptin, insulin, and glucose levels were comparable between treated and young rats, whereas controls had higher glucose and leptin with a similar trend for insulin. Plasma ANG I and ANG II were higher in treated than untreated young or older rats, as evidence of effective A[T.sub.1] receptor blockade. Urinary ANG II and ANG-(1-7) were higher in controls compared with young animals, and treated rats failed to show age-related increases. Protein excretion was markedly lower in treated and young rats compared with control rats (young: 8 [+ or -] 2 mg/day vs. control: 129 [+ or -] 51 mg/day vs. treated: 9 [+ or -] 3 mg/day, P < 0.05). Long-term A[T.sub.1] receptor blockade improves metabolic parameters and provides renoprotection. Differential regulation of systemic and intrarenal (urinary) ANG systems occurs during blockade, and suppression of the intrarenal system may contribute to reduced proteinuria. Thus, insulin resistance, renal injury, and activation of the intrarenal ANG system during early aging in normotensive animals can be averted by renin-ANG system blockade. angiotensin type 1 receptor blockade; glucose metabolosim; aging

The rat dorsal root ganglion (DRG) [Ca.sup.2+]-sensing receptor (CAR) was stably expressed in-frame as an enhanced green fluorescent protein (EGFP) fusion protein in human embryonic kidney (HEK)293 cells, and is functionally linked to changes in intracellular [Ca.sup.2+] concentration ([[[Ca.sup.2+]].sub.i]). RT-PCR analysis indicated the presence of the message for the DRG CaR cDNA. Western blot analysis of membrane proteins showed a doublet of 168-175 and 185 kDa, consistent with immature and mature forms of the CaR.EGFP fusion protein, respectively. Increasing extracellular [[Ca.sup.2+]] ([[[Ca.sup.2+]].sub.e]) from 0.5 to 1 mM resulted in increases in [[[Ca.sup.2+]].sub.i] levels, which were blocked by 30 [micro]M 2-aminoethyldiphenyl borate. [[[Ca.sup.2+]].sub.e]-response studies indicate a [Ca.sup.2+] sensitivity with an E[C.sub.50] of 1.75 [+ or -] 0.10 mM. NPS R-467 and [Gd.sup.3+] activated the CaR. When [[[Ca.sup.2+]].sub.e] was successively raised from 0.25 to 4 mM, peak [[[Ca.sup.2+]].sub.i], attained with 0.5 mM, was reduced by ~50%. Similar reductions were observed with repeated applications of 10 mM [Ca.sup.2+], 1 and 10 [micro]M NPS R-467, or 50 and 100 [micro]M [Gd.sup.3+], indicating desensitization of the response. Furthermore, [Ca.sup.2+] mobilization increased phosphorylated protein kinase C (PKC)[alpha] levels in the cells. However, the PKC activator, phorbol myristate acetate did not inhibit CaR-mediated [Ca.sup.2+] signaling. Rather, a spectrum of PKC inhibitors partially reduced peak responses to [Ca.sup.2+.sub.e]. Treatment of cells with 100 nM PMA for 24 h, to downregulate PKC, reduced [[Ca.sup.2+].sub.i] transients by 49.9 [+ or -] 5.2% (at 1 mM [Ca.sup.2+]) and 40.5 [+ or -] 6.5% (at 2 mM [Ca.sup.2+]), compared with controls. The findings suggest involvement of PKC in the pathway for [Ca.sup.2+] mobilization following CaR activation. desensitization; protein kinase C doi:10.1152/ajpcell.00404.2006

Endogenous angiotensin (ANG) II and ANG-(1-7) act at the nucleus tractus solitarius (NTS) to differentially modulate neural control of the circulation. The role of these peptides endogenous to NTS on cardiovascular reflex function was investigated in transgenic rats with low brain angiotensinogen (Aogen) due to glial overexpression of an antisense to Aogen (ASrAOGEN) and in Sprague-Dawley (SD) rats. Arterial baroreceptor reflex sensitivity (BRS) for control of heart rate (HR) in response to increases in mean arterial pressure (MAP) was tested before and after bilateral microinjection of the angiotensin type 1 (A[T.sub.1]) receptor blocker candesartan or the ANG-(1-7) receptor blocker (D-[Ala.sup.7])-ANG-(1-7) into the NTS of urethane-chloralose-anesthetized ASrAOGEN and SD rats. Baseline MAP was higher in ASrAOGEN than in SD rats under anesthesia (P < 0.01). Injection of candesartan or (D-[Ala.sup.7])-ANG-(1-7) decreased MAP (P < 0.01) and HR (P < 0.05) in ASrAOGEN, but not SD, rats. The BRS at baseline was similar in ASrAOGEN and SD rats. Candesartan increased BRS by 41% in SD rats (P < 0.01) but was without effect in ASrAOGEN rats. In contrast, the reduction in BRS after (D-[Ala.sup.7])-ANG-(1-7) administration was comparable in SD (31%) and ASrAOGEN rats (34%). These findings indicate that the absence of glia-derived Aogen is associated with 1) an increase in MAP under anesthesia mediated via A[T.sub1] and ANG-(1-7) receptors within the NTS, 2) the absence of an endogenous ANG II contribution to tonic inhibition of BRS, and 3) a continued contribution of endogenous ANG-(1-7) to tonic enhancement of BRS. baroreceptors; solitary tract nucleus; brain renin-angiotensin system; transgenic rats

Despite the evidence that angiotensin-converting enzyme (ACE)2 is a component of the reninangiotensin system (RAS), the influence of ACE2 on angiotensin metabolism within the kidney is not well known, particularly in experimental models other than rats or mice. Therefore, we investigated the metabolism of the angiotensins in isolated proximal tubules, urine, and serum from sheep. Radiolabeled [[sup.125]I]ANG I was hydrolyzed primarily to ANG II and ANG-(1-7) by ACE and neprilysin, respectively, in sheep proximal tubules. The ACE2 product ANG-(1-9) from ANG I was not detected in the absence or presence of ACE and neprilysin inhibition. In contrast, the proximal tubules contained robust ACE2 activity that converted ANG II to ANG-(1-7). Immunoblots utilizing an [NH.sub.2] terminal-directed ACE2 antibody revealed a single 120-kDa band in proximal tubule membranes. ANG-(1-7) was not a stable product in the tubule preparation and was rapidly hydrolyzed to ANG-(1-5) and ANG-(1-4) by ACE and neprilysin, respectively. Comparison of activities in the proximal tubules with nonsaturating concentrations of substrate revealed equivalent activities for ACE (ANG I to ANG II: 248 [+ or -] 17 fmol*[mg.sup.-1]*[min.sup.-1]) and ACE2 [ANG II to ANG-(1-7): 253 [+ or -] 11 fmol*[mg.sup.-1]*[min.sup.-1]], but lower neprilysin activity [ANG II to ANG-(1-4): 119 [+ or -] 24 fmol*[mg.sup.-1]*[min.sup.-1]; p < 0.05 vs. ACE or ACE2]. Urinary metabolism of ANG I and ANG II was similar to the proximal tubules; soluble ACE2 activity was also detectable in sheep serum. In conclusion, sheep tissues contain abundant ACE2 activity that converts ANG II to ANG-(1-7) but does not participate in the processing of ANG I into ANG-(1-9). ANG-(1-7); ANG-(1-5); neprilysin; ACE; ANG-(1-9)

The aim of this study was to test the hypothesis that treatment with angiotensin-(1-7) [ANG-(1-7)] or ANG-(1-7) nonpeptide analog AVE-0991 can produce protection against diabetes-induced cardiovascular dysfunction. We examined the influence of chronic treatment (4 wk) with ANG-(1-7) (576 [micro]g*[kg.sup.-1]*[day.sup.-1] ip) or AVE-0991 (576 [micro]g*[kg.sup.-1]*[day.sup.-1] ip) on proteinuria, vascular responsiveness of isolated carotid and renal artery ring segments and mesenteric bed to vasoactive agonists, and cardiac recovery from ischemia-reperfusion in streptozotocin-treated rats (diabetes). Animals were killed 4 wk after induction of diabetes and/or treatment with ANG-(1-7) or AVE-0991. There was a significant increase in urine protein (231 [+ or -] 2 mg/24 h) in diabetic animals compared with controls (88 [+ or -] 6 mg/24 h). Treatment of diabetic animals with ANG-(1-7) or AVE-0991 resulted in a significant reduction in urine protein compared with vehicle-treated diabetic animals (183 [+ or -] 16 and 149 [+ or -] 15 mg/24 h, respectively). Treatment with ANG-(1-7) or AVE-0991 also prevented the diabetes-induced abnormal vascular responsiveness to norepinephrine, endothelin-1, angiotensin II, carbachol, and histamine in the perfused mesenteric bed and isolated carotid and renal arteries. In isolated perfused hearts, recovery of left ventricular function from 40 min of global ischemia was significantly better in ANG-(1-7)- or AVE-0991-treated animals. These results suggest that activation of ANG-(1-7)-mediated signal transduction could be an important therapeutic strategy to reduce cardiovascular events in diabetic patients. diabetes; AVE-0991; vascular dysfunction; carotid artery

We established a new congenic model of hypertension, the mRen(2).Lewis rat and assessed the intracellular expression of angiotensin peptides and receptors in the kidney. The congenic strain was established from the backcross of the (mRen2)27 transgenic rat that expresses the mouse renin 2 gene onto the Lewis strain. The 20-wk-old male congenic rats were markedly hypertensive compared with the Lewis controls (systolic blood pressure: 195 [+ or -] 2 vs. 107 [+ or -] 2 mmHg, P < 0.01). Although plasma ANG II levels were not different between strains, circulating levels of ANG-(1-7) were 270% higher and ANG I concentrations were 40% lower in the mRen2.Lewis rats. In contrast, both cortical (CORT) and medullary (MED) ANG II concentrations were 60% higher in the mRen2.Lewis rats, whereas tissue ANG I was 66 and 84% lower in CORT and MED. For both strains, MED ANG II, ANG I, and ANG-(1-7) were significantly higher than CORT levels. Intracellular ANG II binding distinguished nuclear (NUC) and plasma membrane (PM) receptor using the ANG II radioligand [sup.125]I-sarthran. Isolated CORT nuclei exhibited a high density (B.sub.max] >200 fmol/mg protein) and affinity for the sarthran ligand ([K.sub.D]95%) were the A[T.sub.1] receptor subtype. CORT ANG II receptor [B.sub.max] and [K.sub.D] values in nuclei were 75 and 50% lower, respectively, for the mRen2.Lewis vs. the Lewis rats. In the MED, the PM receptor density (Lewis: 50 [+ or -] 4 vs. mRen2.Lewis: 21 [+ or -] 5 fmol/mg protein) and affinity (Lewis: 0.31 [+ or -] 0.1 vs. 0.69 [+ or -] 0.1 nM) were lower in the mRen2.Lewis rats. In summary, the hypertensive mRen2.Lewis rats exhibit higher ANG II in both CORT and MED regions of the kidney. Evaluation of intracellular ANG II receptors revealed lower CORT NUC and MED PM A[T.sub.1] sites in the mRen2.Lewis. The downregulation of A[T.sub.1] sites in the mRen2.Lewis rats may reflect a compensatory response to dampen the elevated levels of intrarenal ANG II. ANG II type 1 receptor; hypertension; intrarenal angiotensin; renal cortex; renal medulla; ANG II

This study evaluated the contribution of angiotensin peptides acting at various receptor subtypes to the arterial pressure and heart rate of adult 9-wk-old male conscious salt-depleted spontaneously hypertensive rats (SHR). Plasma ANG II and ANG I in salt-depleted SHR were elevated sevenfold compared with peptide levels measured in sodium-replete SHR, whereas plasma ANG-(1-7) was twofold greater in salt-depleted SHR compared with salt-replete SHR. Losartan (32.5 [micro]mol/kg), PD-123319 (0.12 [micro]mol.[kg.sup.-1] [min.sup.-1]), [D-[Ala.sup.7]]ANG-(1-7) (10 and 100 [micro]mol/min), and a polyclonal ANG II antibody (0.08 mg/min) were infused intravenously alone or in combination. Combined blockade of A[T.sub.2] and A[T.sub.(1-7)] receptors significantly increased the blood pressure of losartan-treated SHR (+ 15 [+ or -] 1 mmHg; P < 0.01); this change did not differ from the blood pressure elevation produced by the sole blockade of A[T.sub.(1-7)] receptors (15 [+ or -] 4 mmHg). On the other hand, sole blockade of A[T.sub.2] receptors in losartan-treated SHR increased mean arterial pressure by 8 [+ or -] 1 mmHg (P < 0.05 vs. 5% dextrose in water as vehicle), and this increase was less than the pressor response produced by blockade of A[T.sub.(1-7)] receptors alone or combined blockade of A[T.sub.(1-7)] and A[T.sub.2] receptors. The ANG II antibody increased blood pressure to the greatest extent in salt-depleted SHR pretreated with only losartan (+ 11 [+ or -] 2 mmHg) and to the least extent in salt-depleted SHR previously treated with the combination of losartan, PD-123319, and [D-[Ala.sup.7]]ANG-(1-7) (+7 [+ or -] 1 mmHg; P < 0.01). Losartan significantly increased heart rate, whereas other combinations of receptor antagonists or the ANG II antibody did not alter heart rate. Our results demonstrate that ANG II and ANG-(1-7) act through non-A[T.sub.1] receptors to oppose the vasoconstrictor actions of ANG II in salt-depleted SHR. Combined blockade of A[T.sub.2] and A[T.sub.(1-7)] receptors and ANG II neutralization by the ANG II antibody reversed as much as 67% of the blood pressure-lowering effect of losartan. angiotensin II; angiotensin-(1-7); angiotensin receptor antagonists; hypertension; losartan; PD-123319; salt depletion; spontaneously hypertensive rats

Researchers have investigated whether a specific substance P antagonist can block the actions of angiotensin II (ANG II) exogenously administered into the nucleus of the solitary tract (NTS) of halothane-anesthetized male Sprague-Dawley rats. It was found that the substance P antagonist blocks the acute depressor and bradycardic responses of ANG II almost entirely. This indicates that postsynaptic cells may be a key source of the substance P mediating the acute cardiovascular responses to ANG II.

Angiotensin 1-7 (ANG I-7) is an active depressor heptapeptide in intact animals and may have an important role in the vasodepressor system, inhibiting hemodynamic actions of angiotensin II (ANG II). Experiments on hypertensive rats were conducted to examine the effects of the ANG 1-7 on the maintenance of elevated blood pressures. After infusion with ANG 1-7 for two weeks, researchers observed a reduction in vasopressin, and a lowering then rise in arterial blood pressure.

Allred, Alicia J., Debra I. Diz, Carlos M. Ferwario, and Mark C. Chappell. Pathways for angiotensin-(1--7) metabolism in pulmonary and renal tissues. Am J Physiol Renal Physiol 279: F841-F850, 2000.--Two of the primary sites of actions for angiotensin (ANG)-(1-7) are the vasculature and the kidney. Because little information exists concerning the metabolism of ANG-(1-7) in these tissues, we investigated the hydrolysis of the peptide in rat lung and renal brush-border membrane (BBM) preparations. Radiolabeled ANG-(1-7) was hydrolyzed primarily to ANG-(1-5) by pulmonary membranes. The ANG-converting enzyme (ACE) inhibitor lisinopril abolished the generation of ANG-(1-5), as well as that of smaller metabolites. Kinetic studies of the hydrolysis of ANG-(1-7) to ANG-(1-5) by somatic (pulmonary) and germinal (testes) forms of rat ACE yielded similar values, suggesting that the COOH-domain is responsible for the hydrolysis of ANG-(1-7). Pulmonary metabolism of ANG-(1-5) yielded ANG-(3-5) and was independent of ACE but may involve peptidyl or dipeptidyl aminopeptidases. In renal cortex BBM, ANG-(1-7) was rapidly hydrolyzed to mono- and dipeptide fragments and ANG-(1-4). Aminopeptidase (AP) inhibition attenuated the hydrolysis of ANG-(1-7) and increased ANG-(1-4) formation. Combined treatment with AP and neprilysin (Nep) inhibitors abolished ANG-(1-4) formation and preserved ANG-(1-7). ACE inhibition had no effect on the rate of hydrolysis or the metabolites formed in the BBM. In conclusion, ACE was the major enzymatic activity responsible for the metabolism of ANG-(1-7) in the lung, which is consistent with the ability of ACE inhibitors to increase the half-life of circulating ANG-(1-7) and raise endogenous levels of the peptide. An alternate pathway of metabolism was revealed in the renal cortex, where increased AP and Nep activities, relative to ACE activity, promote conversion of ANG-(1-7) to ANG-(1-4) and smaller fragments. angiotensin-converting enzyme; neprilysin; lisinopril; SCH-39370; aminopeptidase; amastatin

Allred, Alicia J., Mark C. Chappell, Carlos M. Ferrario, and Debra I. Diz. Differential actions of renal ischemic injury on the intrarenal angiotensin system. Am J Physiol Renal Physiol 279: F636-F645, 2000.--The present study determined the effect of either occlusion of the left renal artery for 60 min (ischemia) or sham operation on angiotensin (ANG) receptors and tissue and urinary levels of ANG peptides between 24 and 72 h recovery in male Sprague-Dawley rats. At 24 h postischemia, urinary concentrations of ANG I and ANG-(1-7) rose by an average of 83 and 64%, respectively (P [is less than] 0.05) but had declined to control levels by 72 h. Tissue ANG II rose at 24 h in postischemic kidneys by an average of 63% compared with the contralateral nonischemic kidney (P [is less than] 0.05). Whereas the enzymatic activity of angiotensin-converting enzyme and neprilysin was reduced after ischemia, renal renin activity in ischemic kidneys rose by 74% compared with sham-operated kidneys. Receptor autoradiography using [sup.125]I-labeled [[Sar.sup.1],[Thr.sup.8]ANG II ([sup.125]I-Sarthran) (0.8 nM) revealed a decreased apparent density of ANG receptors ([is greater than] 80% [AT.sub.1]) in ischemic kidneys with a trend for a decrease in the contralateral nonischemic kidneys compared with the kidneys from sham-operated rats. Twenty-four hours after ischemia, ANG II receptors decreased by 68% in glomeruli (P [is less than] 0.05), 49% in the outer cortical tubulointerstitial area (P [is less than] 0.05), and 48% in the inner cortical-outer medullary area of the vasa recta (P [is less than] 0.05). Medullary binding decreased ~50% in both the ischemic kidney and the contralateral nonischemic kidney compared with sham. In all regions of the ischemic kidney, receptors recovered by 72 h to levels not different from sham control rats. The marked change in urinary ANG I and ANG-(1-7) at 24 h following occlusion indicates these peptides may be potential urinary markers for acute renal ischemia. The reduction of receptors in vascular and tubular regions of the ischemic kidney provides a mechanism for the loss of vasoconstrictor responses to ANG II following ischemia previously reported by others. angiotensin II; angiotensin-(1-7), angiotensin receptors; [AT.sub.1] receptor; [AT.sub.2] receptor; renal ischemia; urinary angiotensins