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Inhibition of nitric oxide synthesis (NOS) induces hypertension and heavy proteinuria. Renal structure and function have shown striking improvement after interventions targeting ANG II or endothelin (ET) receptors in rats recovering after long-term NOS inhibition. To search for mechanisms underlying losartan-assisted regression of renal disease in rodents, we measured NO release and contractility to ET in afferent arterioles (AAs) from Sprague-Dawley rats recovering for 2 wk after 4 wk of [N.sup.G]-nitro-L-arginine methyl ester treatment. Losartan administration during the recovery period decreased blood pressure (113 [+ or -] 4 vs. 146 [+ or -] 5 mmHg, P < 0.01), reduced protein/creatinine ratio more (proteinuria decrease: [DELTA]1,836 [+ or -] 214 vs. [DELTA]1,024 [+ or -] 180 mg/retool, P < 0.01), and normalized microvascular hypertrophy (AA media/lumen ratio: 1.74 [+ or -] 0.05 vs. 2.09 [+ or -] 0.08, P < 0.05) compared with no treatment. In diaminofluorescein-FM-loaded AAs from losartan-treated animals, NO release (% of baseline) was increased compared with untreated animals after stimulation with [10.sup.-7] M ACh (118 [+ or -] 4 vs. 90 [+ or -] 7%, t = 560 s, P < 0.001) and [10.sup.-9] MET (123 [+ or -] 4 vs. 101 [+ or -] 5%, t = 560 s, P < 0.001). There was also a blunted contractile response to [10.sup.-7] MET in AAs from losartan-treated animals compared with untreated animals ([DELTA]4.01 [+ or -] 2.9 vs. [DELTA]14.6 [+ or -] 1.7 [micro]m, P < 0.01), which disappeared after acute NOS inhibition ([DELTA]10.7 [+ or -] 3.7 vs. [DELTA]12.5 [+ or -] 2.9 [micro]m, not significant). Contractile dose responses to ET ([10.sup.-9], [10.sup.-8], [10.sup.-7] M) were enhanced by NOS inhibition and blunted by exogenous NO (10 2 mM S-nitroso-N-acetyl-penicillamine) in losartan-treated but not in untreated vessels. Reducing blood pressure similar to losartan with hydralazine did not improve AA hypertrophy, ET-induced contractility, ET-induced NO release, and NO sensitivity. In conclusion, blockade of the local action of ANG II improved endothelial function in AAs, a mechanism that is likely to contribute to the beneficial effects of [AT.sub.1a]R antagonism during the recovery of renal function after long-term NOS inhibition in rats. endothelin; nitric oxide; endothelial dysfunction; angiotensin II; vascular remodeling doi: 10.1152/ajprenal.00056.2009.

Ischemic focal ventricular tachycardia (VT) occurs in animals and humans. Angiotensin-converting enzyme inhibitors and receptor blockers reduce sudden death in patients with ischemic heart disease. In our dog model of coronary artery occlusion (CAO), we tested the hypothesis that angiotensin II (AGII) will selectively promote focal VT and that the specific [AT.sub.2] blocker PD-123319 (PD), or ATI blocker losartan, will affect this VT. Anesthetized dogs (n = 90) underwent CAO, followed by three-dimensional activation mapping of inducible VT. Dogs without VT in 1-3 h after CAO received AGII, and those with VT received either PD or losartan. Focal endocardium excised from ischemic sites was studied in vitro with standard microelectrode. Of 33 dogs with no inducible VT, AGII infusion resulted in sustained VT of only focal Purkinje origin in 13 (39%) compared with 0 of 20 dogs with saline. Of 26 dogs with inducible VT at baseline, given PD, reinduction was blocked in 8 of 10 (P < 0.05) focal VT, but only 1 of 15 with reentry. In contrast, of 11 dogs given losartan, reinduction of either mechanism was not blocked. In vitro triggered activity in Purkinje was blocked by PD in 13 of 19 (P < 0.05), but not by losartan in 8. Also, triggered activity was promoted by AGII, losartan, or the combination in 9 of 12 tissues. AGII promotes only focal, mainly Purkinje ischemic VT. PD, but not losartan, preferentially blocked focal VT, which is likely due to triggered activity due to delayed afterdepolarizations in Purkinje. triggered activity; canine model; lorsartan doi: 10.1152/ajpheart.00080.2009.

Angiotensin II promotes liver fibrogenesis by stimulating nonphagocytic NADPH oxidase (NOX)-induced oxidative stress. Angiotensin II type 1 (AT1) receptor blockers attenuate experimental liver fibrosis, yet their effects in human liver fibrosis are unknown. We investigated the effects of losartan on hepatic expression of fibrogenic, inflammatory, and NOX genes in patients with chronic hepatitis C (CHC). Fourteen patients with CHC and liver fibrosis received oral losartan (50 mg/ day) for 18 mo. Liver biopsies were performed at baseline and after treatment. The degree of inflammation and fibrosis was evaluated by histological analysis (METAVIR). Collagen content was measured by morphometric quantification of Sirius red staining. Overall collagen content and fibrosis stage remained stable in the whole series, yet the fibrosis stage decreased in seven patients. Inflammatory activity improved in seven patients. The effect of losartan on hepatic expression of 31 profibrogenic and inflammatory genes and components of the NOX complex was assessed by quantitative PCR. Losartan treatment was associated with a significant decrease in the expression of several profibrogenic and NOX genes including procollagen [alpha]1(I) and [alpha]1(IV), urokinase-type plasminogen activator, metalloproteinase type 2, NOX activator 1 (NOXA-1) and organizer 1 (NOXO-I), and Rac-1. Losartan was well tolerated in all patients and was effective in attenuating the activity of the systemic renin-angiotensin system. No effects on serum liver tests or viral load were observed. We conclude that prolonged administration of losartan, an oral AT1 receptor blocker, is associated with downregulation of NOX components and fibrogenic genes in patients with CHC. Controlled studies are warranted to assess the effect of AT1 receptor blockers in chronic liver injury. angiotensin; liver fibrosis; antifibrogenic doi: 10.1152/ajpgi.00162.2009

In rats, both central and systemic ANG II type 1 ([AT.sub.1]) receptor blockade attenuate sympathetic hyperactivity, but central blockade more effectively attenuates left ventricular (LV) dysfunction post-myocardial infarction (MI). In protocol 1, we examined whether functional effects on cardiac load may play a role and different cardiac effects disappear after withdrawal of the blockade. Wistar rats were infused for 4 wk post-MI intracerebroventricularly (1 mg x [kg.sup.-1] x [day.sup.-1]) or injected subcutaneously daily (100 mg x [kg.sup.-1] x [day.sup.-1]) with losartan. LV dimensions and function were assessed at 4 wk and at 6 wk post-MI, i.e., 2 wk after discontinuing treatments. At 4 and 6 wk post-MI, LV dimensions were increased and ejection fraction was decreased. Intracerebroventricular but not subcutaneous losartan significantly improved these parameters. At 6 wk, LV peak systolic pressure (LVPSP) and maximal or minimal first derivative of change in pressure over time (dP/[dt.sub.max/min]) were decreased and LV end-diastolic pressure (LVEDP) was increased. All four indexes were improved by previous intracerebroventricular losartan, whereas subcutaneous losartan improved LVEDP only. In protocol H, we evaluated effects of oral instead of subcutaneous administration of losartan for 4 wk post-MI. Losartan (~200 mg x [kg.sup.-1] x [day.sup.-1]) either via drinking water or by gavage similarly decreased [AT.sub.1] receptor binding densities in brain nuclei and improved LVEDP but further decreased LVPSP and dP/[dt.sub.max]. These results indicate that effects on cardiac load by peripheral [AT.sub.1] receptor blockade or the pharmacokinetic profile of subcutaneous versus oral dosing do not contribute to the different cardiac effects of central versus systemic [AT.sub.1] receptor blockade post-MI. losartan; cardiac remodeling; echocardiography; Millar catheter; brain; ANG II type 1

The mechanisms by which chronic infusion of an initially subpressor low dose of angiotensin II (ANG II) causes a progressive and sustained hypertension remain unclear. In conscious sheep (n = 6), intravenous infusion of ANG II (2 [micro]g/h) gradually increased mean arterial pressure (MAP) from 82 [+ or -] 3 to 96 [+ or -] 5 mmHg over 7 days (P < 0.001). This was accompanied by peripheral vasoconstriction; total peripheral conductance decreased from 44.6 [+ or -] 6.4 to 38.2 [+ or -] 6.7 ml x [min.sup.-1] x [mmHg.sup.-1] (P < 0.001). Cardiac output and heart rate were unchanged. In the regional circulation, mesenteric, renal, and iliac conductances decreased but blood flows were unchanged. There was no coronary vasoconstriction, and coronary blood flow increased. Ganglion blockade (125 mg/h hexamethonium for 4 h) reduced MAP by 13 [+ or -] 1 mmHg in the control period and by 7 [+ or -] 2 mmHg on day 8 of ANG II treatment. Inhibition of central A[T.sub.1] receptors by intracerebro-ventricular infusion of losartan (1 mg/h for 3 h) had no effect on MAP in the control period or after 7 days of ANG II infusion. Pressor responsiveness to incremental doses of intravenous ANG II (5, 10, 20 [micro]g/h, each for 15 min) was unchanged after 7 days of ANG II infusion. ANG II caused no sodium or water retention. In summary, hypertension due to infusion of a low dose of ANG II was accompanied by generalized peripheral vasoconstriction. Indirect evidence suggested that the hypertension was not neurogenic, but measurement of sympathetic nerve activity is required to confirm this conclusion. There was no evidence for a role for central angiotensinergic mechanisms, increased pressor responsiveness to ANG II, or sodium and fluid retention. ganglion blockade; losartan; regional blood flow; total peripheral resistance doi:10.1152/ajpregu.00803.2006

The cardiac 'sympathetic afferent' reflex (CSAR) has been reported to increase sympathetic outflow and depress baroreflex function via a central angiotensin II (ANG II) mechanism. In the present study, we examined the role of ANG II type 1 (ATe) receptors in the nucleus tractus solitarii (NTS) in mediating the interaction between the CSAR and the baroreflex in anesthetized rats. We examined the effects of bilateral microinjection of [AT.sub.1] receptor antagonist losartan (100 pmol) into the NTS on baroreflex control of renal sympathetic nerve activity (RSNA) before and after CSAR activation by epicardial application of capsaicin (0.4 [micro]g). Using single-unit extracellular recording, we further examined the effects of CSAR activation on the barosensitivity of barosensitive NTS neurons and the effects of intravenous losartan (2 mg/kg) on CSAR-induced changes in activity of NTS barosensitive neurons. Bilateral NTS microinjection of losartan significantly attenuated the increases in arterial pressure, heart rate, and RSNA evoked by capsaicin but also markedly (P < 0.01) reversed the CSAR-induced blunted baroreflex control of RSNA ([Gain.sub.max] from 1.65 [+ or -] 0.10 to 2.22 [+ or -] 0.11%/mmHg). In 17 of 24 (70.8%) NTS barosensitive neurons, CSAR activation significantly (P < 0.01) inhibited the baseline neuronal activity and attenuated the neuronal barosensitivity. In 11 NTS barosensitive neurons, intravenous losartan effectively (P < 0.01) normalized the decreased neuronal barosensitivity induced by CSAR activation. In conclusion, blockade of NTS [AT.sub.1] receptors improved the blunted baroreflex during CSAR activation, suggesting that the NTS plays an important role in processing the interaction between the baroreflex and the CSAR via an [AT.sub.1] receptor-dependent mechanism. cardiovascular reflexes; losartan; renal sympathetic nerve activity; microinjection; extracellular recording; barosensitivity

Both atrial (ANP) and brain (BNP) natriuretic peptide affect development of cardiac hypertrophy and fibrosis via binding to natriuretic peptide receptor (NPR)-A in the heart. A putative clearance receptor, NPR-C, is believed to regulate cardiac levels of ANP and BNP. The renin-angiotensin system also affects cardiac hypertrophy and fibrosis. In this study we examined the expression of genes for the NPRs in rats with pressure-overload cardiac hypertrophy. The ANG II type I receptor was blocked with losartan (10 mg * [kg.sup.-1] * [day.sup.-1]) to investigate a possible role of the renin-angiotensin system in regulation of natriuretic peptide and NPR gene expression. The ascending aorta was banded in 84 rats during Hypnorm/Dormicum-isoflurane anesthesia; after 4 wk the rats were randomized to treatment with losartan or placebo. The left ventricle of the heart was removed 1, 2, or 4 wk later. Aortic banding increased left ventricular expression of NPR-A and NPR-C mRNA by 110% (P < 0.001) and 520% (P < 0.01), respectively, after 8 wk; as expected, it also increased the expression of ANP and BNP mRNAs. Losartan induced a slight reduction of left ventricular weight but did not affect the expression of mRNAs for the natriuretic peptides or their receptors. Although increased gene expression does not necessarily convey a higher concentration of the protein, the data suggest that pressure overload is accompanied by upregulation of not only ANP and BNP but also their receptors NPR-A and NPR-C in the left ventricle. losartan: angiotensin II type 1 receptor: renin

Angiotensin receptor blockers (ARBs) reduce adverse left ventricular (LV) remodeling and improve LV function and survival when started postmyocardial infarction (MI). ARBs also reduce ventricular arrhythmias during ischemia-reperfusion injury when started pre-MI. No information exists regarding their efficacy and safety when started pre-MI and continued peri- and post-MI. We evaluated whether the ARB losartan improves the outcome when started pre-MI and continued peri- and post-MI. Male Wistar rats (n = 502) were treated for 7 days pre-MI with losartan at a high dose (30 mg x [kg.sup.-1] x [day.sup.-1]), progressively increasing dose (3 mg x [kg.sup.-1] x [day.sup.-1] increased to 10 mg x [kg.sup.-1] x [day.sup.-1] 10 days and 30 mg x [kg.sup.-1] x [day.sup.-1] 20 days post-MI), or no treatment. Ambulatory systolic blood pressure and Holter monitoring were performed for 24 h post-MI. Echocardiography was done 30 days post-MI, and LV remodeling, cardiac hemodynamics, and fetal gene expression were assessed 38 days post-MI. High-dose losartan reduced 24-h post-MI survival compared with the progressive dose and control (21.9% vs. 36.6% and 38.1%, P = 0.033 and P = 0.009, respectively). This was associated with greater hypotension in the high dose and no change in ventricular arrhythmias in all groups. In 24-h post-MI survivors, the progressive dose group had reduced mortality from 24 h to 38 days (8.5% vs. 28.6% for control vs. 38.9% for high dose, P = 0.032 and P = 0.01, respectively). Survivors of both losartan groups demonstrated improved LV remodeling, cardiac hemodynamics, preserved GLUT-4, and reduced cardiac fetal gene expression. Pretreatment with ARBs does not reduce 24-h post-MI ventricular arrhythmias or survival, and high doses increase mortality by causing excessive hypotension. In 24-h post-MI survivors, progressively increasing doses of losartan have multiple beneficial effects, including improved survival. angiotensin II receptor blockers; heart failure; infarction; remodeling; hypotension

Angiogenesis within an ischemic region of the brain may increase tissue viability and act to limit the extent of an infarct. The ANG II pathway can both stimulate and inhibit angiogenesis depending on the tissue and the activated receptors. Previous work showed that 2-wk losartan administration (ANG II type 1 receptor blockade) initiates a significant cerebral angiogenic response. We hypothesized that administration of losartan in the drinking water of rats for 2 wk before initiation of focal ischemia would decrease the extent of the resulting infarct. Adult male Sprague-Dawley rats were given losartan (50 mg/day) in drinking water for 2 wk before initiation of cerebral focal ischemia produced by cauterization of cortical surface vessels. Controls received normal drinking water. In control animals, three main vessels feeding the whisker barrel cortex were cauterized, resulting in cessation of blood flow. The same protocol was followed for losartan-treated animals but did not result in cessation of blood flow in the whisker barrel cortex. Another group of losartan-treated animals received between 8 and 14 cauterizations of surface vessels feeding the whisker barrel cortex, and cessation of blood flow was verified. Rats were killed 72 h after surgery. Morphological examination revealed angiogenesis, maintained vascular delivery, and significantly decreased infarct size in losartan-treated animals compared with controls. These results demonstrate that pretreatment with losartan reduces infarct size after cerebral focal ischemia and support the hypothesis that cerebral angiogenesis may be one of the mechanisms responsible. cerebrovascular regulation; rat model; losartan; stroke

DiBona, Gerald F., and Linda L. Sawin. Losartan corrects abnormal frequency response of renal vasculature in congestive heart failure. Am J Physiol Heart Circ Physiol 285: H1857-H1863, 2003. First published June 26, 2003; 10.1152/ajpheart.00364.2003.--In congestive heart failure, renal blood flow is decreased and renal vascular resistance is increased in a setting of increased activity of both the sympathetic nervous and renin-angiotensin systems. The renal vasoconstrictor response to renal nerve stimulation is enhanced. This is associated with an abnormality in the low-pass filter function of the renal vasculature wherein higher frequencies ([greater than or equal]0.01 Hz) within renal sympathetic nerve activity are not normally attenuated and are passed into the renal blood flow signal. This study tested the hypothesis that excess angiotensin II action mediates the abnormal frequency response characteristics of the renal vasculature in congestive heart failure. In anesthetized rats, the renal vasoconstrictor response to graded frequency renal nerve stimulation was significantly greater in congestive heart failure than in control rats. Losartan attenuated the renal vasoconstrictor response to a significantly greater degree in congestive heart failure than in control rats. In control rats, the frequency response of the renal vasculature was that of a first order (-20 dB/frequency decade) low-pass filter with a corner frequency (-3 dB, 30% attenuation) of 0.002 Hz and 97% attenuation (-30 dB) at [greater than or equal to]0.1 Hz. In congestive heart failure rats, attenuation did not exceed 45% (-5 dB) over the frequency range of 0.001-0.6 Hz. The frequency response of the renal vasculature was not affected by losartan treatment in control rats but was completely restored to normal by losartan treatment in congestive heart failure rats. The enhanced renal vasoconstrictor response to renal nerve stimulation and the associated abnormality in the frequency response characteristics of the renal vasculature seen in congestive heart failure are mediated by the action of angiotensin II on renal angiotensin II A[T.sub.1] receptors. renal sympathetic nerves; renal blood flow; angiotensin A[T.sup.1] receptors

Pressor responses to increases in cerebrospinal fluid (CSF) sodium in Wistar rats and to high salt intake in spontaneously hypertensive rats (SHR) involve both brain ouabainlike activity ('ouabain') and the brain renin-angiotensin system (RAS). Because some of the effects of 'ouabain' are mediated by the median preoptic nucleus (MnPO) and this nucleus contains all elements of the RAS, the present study assessed possible interactions of 'ouabain' and ANG II in this nucleus. In conscious Wistar rats, injection of ANG II into the MnPO significantly increased mean arterial pressure (MAP) and heart rate (HR). This response was not affected by pretreatment with a subpressor dose of ouabain. MAP and HR increases by ouabain in the MnPO were significantly attenuated by MnPO pretreatment with losartan. In Wistar rats, losartan in the MnPO also abolished pressor and HR responses to intracerebroventricular 0.3 M NaCl and attenuated MAP and HR responses to intracerebroventricular ouabain. Five weeks of a high-salt diet in SHRs resulted in exacerbation of hypertension and increased responses to air-jet stress and intracerebroventricular guanabenz. Losartan injected into the MnPO reversed the salt-sensitive component of the hypertension and normalized the depressor response to guanabenz but did not change responses to air-jet stress. We conclude that in the MnPO, ANG II via [AT.sub.1] receptors mediates cardiovascular responses to an acute increase in CSF sodium as well as the chronic pressor responses to high sodium intake in SHR. ouabain; sympathetic activity; guanabenz; losartan; renin-angiotensin system

Results from our laboratory have suggested a pathway involving angiotensin II type 1 ([AT.sub.1]) receptors and vascular endothelial growth factor (VEGF) in angiogenesis induced by electrical stimulation. The present study investigated if similar mechanisms underlie the angiogenesis induced by short-term exercise training. Seven days before training and throughout the training period, male Sprague-Dawley rats received either captopril or losartan in their drinking water. Rats underwent a 3-day treadmill training protocol. The tibialis anterior and gastrocnemius muscles were harvested under anesthesia and lightly fixed in formalin (vessel density) or frozen in liquid nitrogen (VEGF expression). In controls, treadmill training resulted in a significant increase in vessel density in all muscles studied. However, the angiogenesis induced by exercise was completely blocked by either losartan or captopril. Western blot analysis showed that VEGF expression was increased in the exercised control group, and both losartan and captopril blocked this increase. The role of VEGF was directly confirmed using a VEGF-neutralizing antibody. These results confirm the role of angiotensin II and VEGF in angiogenesis induced by exercise. growth factors; skeletal muscle; angiotensin-converting inhibitors; losartan

Weisinger, R. S., J. R. Blair-West, P. Burns, D. A. Denton, and B. Purcell. Cerebral Na concentration, Na appetite and thirst of sheep: influence of somatostatin and losartan. Am J Physiol Regulatory Integrative Comp Physiol 280: R686-R694, 2001.--Na and water intakes of Na-depleted sheep are influenced by changes in cerebral Na concentration. The effect of intracerebroventricular infusion of somatostatin or losartan, the ANG II type 1 receptor antagonist, on the Na appetite and thirst of Na-depleted sheep during infusions that decrease (intracerebroventricular hypertonic mannitol) or increase (intracerebroventricular or systemic hypertonic NaCl) cerebral Na concentration was investigated. Na intake was increased but water intake was unchanged during intracerebroventricular infusion of hypertonic mannitol. The increased Na appetite caused by intracerebroventricular infusion of hypertonic mannitol was decreased by concurrent intracerebroventricular infusion of either somatostatin or losartan, with somatostatin being most effective. Water intake was increased during intracerebroventricular infusion of hypertonic mannitol and somatostatin. Na intake was decreased and water intake was increased during systemic or intracerebroventricular infusion of hypertonic NaCl. Intracerebroventricular infusion of losartan blocked both (Na and water intake), whereas somatostatin did not influence either of these changes in intake. The results further consolidate a role for somatostatin and ANG II in the central mechanisms controlling Na appetite and thirst of sheep. angiotensin II; sodium intake; water intake

Levine, David Z., Michelle Iacovitti, Brian Luck, Maxwell T. Hincke, Kevin D. Burns, and James N. Fryer. Surviving rat distal tubule bicarbonate reabsorption: effects of chronic [AT.sub.1] blockade. Am. J. Physiol. Renal Physiol. 278: F476-F483, 2000.--To determine the in vivo effects of chronic ANG II type 1 ([AT.sub.1])-receptor blockade by losartan (Los) on enhanced unidirectional bicarbonate reabsorption ([MATHEMATICAL EXPRESSION NOT REPRODUCIBLE IN ASCII]) of surviving distal tubules, nephrectomized rats drank either water or a solution of Los, 7 days before microperfusion. [MATHEMATICAL EXPRESSION NOT REPRODUCIBLE IN ASCII] was suppressed by 50% after Los without further reduction by 5 nM concanamycin A (Conc), suggesting that Los suppresses all Conc-sensitive [H.sup.+]-ATPase pumping. Indeed, ultrastructural analysis of A-type intercalated cells revealed a 50% reduction of [H.sup.+]-ATPase immunogold labeling of the apical plasma membrane, whereas Western blotting showed that [H.sup.+]-ATPase protein levels were also reduced by one-half by Los treatment. To identify other transporters sustaining [MATHEMATICAL EXPRESSION NOT REPRODUCIBLE IN ASCII], we perfused three inhibitors simultaneously [5-(N,N,-dimethyl) amiloride hydrochloride, Conc, Schering 28080] with or without prior Los treatment: [MATHEMATICAL EXPRESSION NOT REPRODUCIBLE IN ASCII] was unchanged despite marked reduction of water reabsorption. We conclude enhanced distal tubule [MATHEMATICAL EXPRESSION NOT REPRODUCIBLE IN ASCII] of surviving nephrons is largely mediated by [AT.sub.1] receptor-dependent synthesis and insertion of apical [H.sup.+]-ATPase pumps in A-type intercalated cells. kidney failure; receptors; losartan; proton-transporting adenosine 5'-triphosphate synthase; concanamycin A