(1/1572) Addition of angiotensin II receptor blockade to maximal angiotensin-converting enzyme inhibition improves exercise capacity in patients with severe congestive heart failure.
BACKGROUND: Incomplete suppression of the renin-angiotensin system during long-term ACE inhibition may contribute to symptomatic deterioration in patients with severe congestive heart failure (CHF). Combined angiotensin II type I (AT1) receptor blockade and ACE inhibition more completely suppresses the activated renin-angiotensin system than either intervention alone in sodium-depleted normal individuals. Whether AT1 receptor blockade with losartan improves exercise capacity in patients with severe CHF already treated with ACE inhibitors is unknown. METHODS AND RESULTS: Thirty-three patients with severe CHF despite treatment with maximally recommended or tolerated doses of ACE inhibitors were randomized 1:1 to receive 50 mg/d losartan or placebo for 6 months in addition to standard therapy in a multicenter, double-blind trial. Peak aerobic capacity (V(O2)) during symptom-limited treadmill exercise and NYHA functional class were determined at baseline and after 3 and 6 months of double-blind therapy. Peak V(O2) at baseline and after 3 and 6 months were 13.5+/-0.6, 15.1+/-1.0, and 15.7+/-1.1 mL. kg-1. min-1, respectively, in patients receiving losartan and 14.1+/-0.6, 14.3+/-0.9, and 13.6+/-1.1 mL. kg-1. min-1, respectively, in patients receiving placebo (P<0.02 for treatment group-by-time interaction). Functional class improved by at least one NYHA class in 9 of 16 patients receiving losartan and 1 of 17 patients receiving placebo. CONCLUSIONS: Losartan enhances peak exercise capacity and alleviates symptoms in patients with CHF who are severely symptomatic despite treatment with maximally recommended or tolerated doses of ACE inhibitors. (+info)
(2/1572) Angiotensin converting enzyme inhibitors and angiotensin receptor (AT1) antagonists: either or both for primary renal disease?
At the present time we cannot assume that the proven benefits of ACEI on renal disease will be reproduced by using AT1-ra. With potentially differing modes of activity of these drugs, they cannot be seen as interchangeable and ACEI should remain the drug of choice in patients with progressive renal disease unless they are not tolerated. It is possible that AT1-ra may offer additional advantages in some patients or that synergy exists between the two agents, but this view will remain entirely speculative unless proper trials are conducted. Despite the results of the ELITE study , the uncertainty regarding the use AT1-ra in cardiovascular disease mirrors that of renal disease. This issue is obviously of relevance to the nephrologist in view of the spectrum of cardiac disease that accompanies chronic renal failure, such as left ventricular hypertrophy and cardiac failure, which provide multiple indications for manipulation of RAS. Despite their renoprotective effect, previous studies on ACEI [3,4] have not shown an overall reduction in mortality and this issue needs to be addressed in addition to renoprotection in studies comparing AT1-ra and ACEI. (+info)
(3/1572) Regulation of sympathetic nerve activity in heart failure: a role for nitric oxide and angiotensin II.
The mechanisms by which sympathetic function is augmented in chronic heart failure (CHF) are not well understood. A previous study from this laboratory (Circ Res. 1998;82:496-502) indicated that blockade of nitric oxide (NO) synthesis resulted in only an increase in renal sympathetic nerve activity (RSNA) when plasma angiotensin II (Ang II) levels were elevated. The present study was undertaken to determine if NO reduces RSNA in rabbits with CHF when Ang II receptors are blocked. Twenty-four New Zealand White rabbits were instrumented with cardiac dimension crystals, a left ventricular pacing lead, and a pacemaker. After pacing at 360 to 380 bpm for approximately 3 weeks, a renal sympathetic nerve electrode and arterial and venous catheters were implanted. Studies were carried out in the conscious state 3 to 7 days after electrode implantation. The effects of a 1-hour infusion of sodium nitroprusside (SNP; 3 microgram . kg-1. min-1) on RSNA and mean arterial pressure (MAP) were determined before and after Ang II blockade with losartan (5 mg/kg) in normal and CHF rabbits. Changes in MAP were readjusted to normal with phenylephrine. Before losartan, SNP evoked a decrease in MAP and an increase in RSNA in both groups that was baroreflex-mediated, because both MAP and RSNA returned to control when phenylephrine was administered. In the normal group, losartan plus SNP caused a reduction in MAP and an increase in RSNA that was 152.6+/-9.8% of control. Phenylephrine returned both MAP and RSNA back to the control levels. However, in the CHF group, losartan plus SNP evoked a smaller change in RSNA for equivalent changes in MAP (117.1+/-4.1% of control). On returning MAP to the control level with phenylephrine, RSNA was reduced to 65.2+/-2.9% of control (P<0. 0001). These data suggest that endogenous Ang II contributes to the sympathoexcitation in the CHF state and that blockade of Ang II receptors plus providing an exogenous source of NO reduces RSNA below the elevated baseline levels. We conclude that both a loss of NO and an increase in Ang II are necessary for sustained increases in sympathetic nerve activity in the CHF state. (+info)
(4/1572) Effects of AT1 receptor blockade after myocardial infarct on myocardial fibrosis, stiffness, and contractility.
Angiotensin II type 1 (AT1) receptor blockade attenuates myocardial fibrosis after myocardial infarction (MI). However, whether inhibition of fibrosis by AT1 receptor blockade influences myocardial stiffness and contractility is unknown. We measured left ventricular (LV) hemodynamics, papillary muscle function, and myocardial stiffness and fibrosis in rats randomized to losartan or placebo 1 day after MI and treated subsequently for 8 wk. Losartan decreased LV and right ventricular weights as well as mean aortic and LV systolic pressures in sham and MI rats. LV end-diastolic pressure increased after MI and was decreased with losartan. Maximal developed tension and peak rate of tension rise and decline were decreased in MI vs. sham rats. Interstitial fibrosis developed after MI and was prevented in losartan-treated MI rats. The development of abnormal myocardial stiffness after MI was prevented by losartan. After MI, AT1 receptor blockade prevents an abnormal increase in myocardial collagen content. This effect was associated with a normalization of passive myocardial stiffness. (+info)
(5/1572) Maintenance of blood pressure in normotensive dogs by endothelin.
The role of endothelin (ET)-1 in blood pressure homeostasis and the interaction with the renin-angiotensin system (RAS) was investigated in normotensive conscious dogs. ETA receptors were blocked by LU-135252 (1-30 mg/kg); trandolapril (2 mg/kg) or losartan (10 mg/kg) was used to inhibit the RAS. LU-135252 in oral doses of 3-30 mg/kg significantly reduced mean arterial pressure (MAP) by approximately 10 mmHg maximally, whereas trandolapril or losartan were without any effect. MAP reduction was more pronounced when LU-135252 was combined with either losartan (-15.5 +/- 3.2 mmHg; 2 h postadministration; P < 0.05) or trandolapril (-30.9 +/- 3.6 mmHg; P < 0.05). When endogenous nitric oxide (NO) generation was blocked but NO concomitantly infused, this synergistic effect on MAP was prevented. The data show that ET-1 contributes to the maintenance of blood pressure via ETA receptors. Furthermore, ET-1 and ANG II play a prominent role in the control of blood pressure by opposing the effects of NO. The pronounced blood pressure fall after combined blockade of ETA receptors and the RAS may be mediated by an enhanced release of NO. (+info)
(6/1572) Renal and hemodynamic effects of losartan in conscious dogs during controlled mechanical ventilation.
In 12 conscious dogs, we investigated whether the angiotensin II-receptor antagonist losartan increases renal sodium excretion and urine volume during controlled mechanical ventilation (CMV) with positive end-expiratory pressure. In four experimental protocols, the dogs were extracellular volume (ECV) expanded (electrolyte solution, 0.5 ml. kg-1. min-1 iv) or not and received losartan (100 micrograms. kg-1. min-1 iv) or not. They breathed spontaneously during the 1st and 4th hour and received CMV with positive end-expiratory pressure (mean airway pressure 20 cmH2O) during the 2nd and 3rd hours. In the expansion group, dogs with losartan excreted approximately 18% more sodium (69 +/- 7 vs. 38 +/- 5 micromol. min-1. kg-1) and 15% more urine during the 2 h of CMV because of a higher glomerular filtration rate (5.3 +/- 0.3 vs. 4.5 +/- 0.2 ml. min-1. kg-1) and the tubular effects of losartan. In the group without expansion, sodium excretion (2.0 +/- 0.6 vs. 2.6 +/- 1.0 micromol. min-1. kg-1) and glomerular filtration rate (3.8 +/- 0.3 vs. 3.8 +/- 0.4 ml. min-1. kg-1) did not change, and urine volume decreased similarly in both groups during CMV. Plasma vasopressin and aldosterone increased in both groups, and plasma renin activity increased from 4.9 +/- 0.7 to 7.8 +/- 1.3 ng ANG I. ml-1. h-1 during CMV in nonexpanded dogs without losartan. Mean arterial pressure decreased by 10 mmHg in nonexpanded dogs with losartan. In conclusion, losartan increases sodium excretion and urine volume during CMV if the ECV is expanded. If the ECV is not expanded, a decrease in mean arterial blood pressure and/or an increase in aldosterone and vasopressin during CMV attenuates the renal effects of losartan. (+info)
(7/1572) Inhibition of beta-myosin heavy chain gene expression in pressure overload rat heart by losartan and captopril.
AIM: To study the effects of losartan and captopril on beta-myosin heavy chain (MHC), and alpha-MHC gene expression. METHODS: Pressure overload was produced by abdominal aortic coarctation (AAC) in rats. alpha- and beta-MHC mRNA were measured by Northern blot. RESULTS: In left ventricular myocardium of sham-operated rats, the alpha-MHC mRNA predominated, while the beta-MHC mRNA was only detectable. In response AAC, there was a 70-fold increase in the beta-MHC mRNA (P < 0.01), while alpha-MHC mRNA reduced to 26% (P < 0.01). Losartan (3 mg.kg-1.d-1, i.g. for 11 d) to AAC rats caused inhibitions of beta-MHC by 96% and alpha-MHC by 86% gene expression without lowering blood pressure. A reduction in beta-MHC mRNA was also seen in captopril-treated rats (30 mg.kg-1.d-1, i.g. for 11 d), but the inhibitory effect of captopril on alpha-MHC mRNA was less than that of losartan (44% vs 86%, P < 0.05). CONCLUSIONS: The shift of MHC isoform induced by pressure overload is due to up-regulation of beta-MHC and down-regulation of alpha-MHC gene expression. Inhibition of beta-MHC gene expression by losartan is achieved primarily by direct blockade of angiotensin II type I receptors in the myocardium, independent on hemodynamics. (+info)
(8/1572) Angiotensin II-stimulated nitric oxide release from porcine pulmonary endothelium is mediated by angiotensin IV.
In this study, a nitric oxide (NO) sensor was used to examine the ability of angiotensin II (AngII), AngIV, and bradykinin (Bk) to stimulate NO release from porcine pulmonary artery (PPAE) and porcine aortic endothelial (PAE) cells and to explore the mechanism of the AngII-stimulated NO release. Physiologic concentrations of AngII, but not Bk, caused release of NO from PPAE cells. In contrast, Bk, but not AngII, stimulated NO release from PAE cells. AngIII-stimulated NO release from PPAE cells required extracellular L-arginine and was inhibited by L-nitro-arginine methyl ester. AT1 and AT2 receptor inhibition had no affect on AngII-mediated NO release or activation of NO synthase (NOS). AngIV, an AngII metabolite with binding sites that are pharmacologically distinct from the classic AngII receptors, stimulated considerably greater NO release and greater endothelial-type constitutive NOS activity than the same amount of AngII. The AngIV receptor antagonist, divalinal AngIV, blocked both AngII- and AngIV-mediated NO release as well as NOS activation. The results demonstrate that AngIV and the AngIV receptor are responsible, at least in part, for AngII-stimulated NO release and the associated endothelium-dependent vasorelaxation. Furthermore, these results suggest that differences exist in both AngII- and Bk-mediated NO release between PPAE and PAE cells, which may reflect important differences in response to these hormones between vascular beds. (+info)