Angiotensin converting enzyme inhibitors and angiotensin receptor (AT1) antagonists: either or both for primary renal disease?
(9/4593)
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 [22], 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)
Acute haemodynamic and proteinuric effects of prednisolone in patients with a nephrotic syndrome.
(10/4593)
BACKGROUND: Administration of prednisolone causes an abrupt rise in proteinuria in patients with a nephrotic syndrome. METHODS: To clarify the mechanisms responsible for this increase in proteinuria we have performed a placebo controlled study in 26 patients with a nephrotic syndrome. Systemic and renal haemodynamics and urinary protein excretion were measured after prednisolone and after placebo. RESULTS: After i.v. administration of 125-150 mg prednisolone total proteinuria increased from 6.66+/-4.42 to 9.37+/-6.07 mg/min (P<0.001). By analysing the excretion of proteins with different charge and weight (albumin, transferrin, IgG, IgG4 and beta2-microglobulin) it became apparent that the increase of proteinuria was the result of a change in size selectivity rather than a change in glomerular charge selectivity or tubular protein reabsorption. Glomerular filtration rate rose from 83+/-34 ml to 95+/-43 ml/min (P<0.001) after 5 h, whereas effective renal plasma flow and endogenous creatinine clearance remained unchanged. As a result filtration fraction was increased, compatible with an increased glomerular pressure, which probably contributes to the size selectivity changes. Since corticosteroids affect both the renin-angiotensin system and renal prostaglandins, we have evaluated the effects of prednisolone on proteinuria after pretreatment with 3 months of the angiotensin-converting enzyme inhibitor lisinopril or after 2 weeks of the prostaglandin synthesis inhibitor indomethacin. Neither drug had any effect on prednisolone-induced increases of proteinuria. CONCLUSIONS: Prednisolone increases proteinuria by changing the size selective barrier of the glomerular capillary. Neither the renin-angiotensin axis nor prostaglandins seem to be involved in these effects of prednisolone on proteinuria. (+info)
Antiproteinuric efficacy of verapamil in comparison to trandolapril in non-diabetic renal disease.
(11/4593)
BACKGROUND: Non-dihydropyridine calcium antagonists such as verapamil are equally effective in reducing proteinuria as ACE inhibitors in hypertensive patients with diabetic nephropathy. To date it is unknown whether verapamil elucidates such an antiproteinuric capacity in non-diabetic renal disease. METHODS: We performed a double-blind, placebo-controlled, random cross-over study which compared the antiproteinuric effect of 6 weeks treatment with verapamil SR (360 mg) to that of the ACE inhibitor trandolapril (4 mg), and their fixed combination vera/tran (180 mg verapamil SR and 2 mg trandolapril) in 11 non-diabetic patients with proteinuria of 6.6 (5.1-8.8) g/day, a creatinine clearance of 87 (74-106) ml/min, and a 24-h blood pressure of 136/85 (126/76-157/96) mmHg at baseline. RESULTS: Twenty-four-hour mean arterial pressure did not change during verapamil, whereas both trandolapril and vera/tran induced a significant reduction in MAP. Verapamil showed no significant effects on renal haemodynamics. Trandolapril and vera/tran did not significantly change GFR, but ERPF increased and FF decreased during both treatments (P<0.05). The antiproteinuric response of verapamil was significantly less compared to that of trandolapril and vera/tran (-12% (-17/-1) vs -51% (-56/-25) and -41% (-50/-19) respectively). The blood pressure and antiproteinuric response during verapamil tended to be greater in hypertensive patients than in normotensive patients, although this difference was not significant. Baseline blood pressure was related to the change in blood pressure during verapamil (r = -0.70; P < 0.02). CONCLUSIONS: The antiproteinuric and antihypertensive response of verapamil is less than that of the ACE inhibitor trandolapril in patients with non-diabetic renal disease. In contrast to the antiproteinuric response of trandolapril, the antiproteinuric reponse of verapamil seems to be completely dependent from effective blood pressure reduction. The fixed combination of verapamil and ACE inhibition at half doses has similar effects as ACE inhibition at full dose. (+info)
Maintenance of blood pressure in normotensive dogs by endothelin.
(12/4593)
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)
Contribution of endothelin to renal vascular tone and autoregulation in the conscious dog.
(13/4593)
Exogenous endothelin-1 (ET-1) is a strong vasoconstrictor in the canine kidney and causes a decrease in renal blood flow (RBF) by stimulating the ETA receptor subtype. The aim of the present study was to investigate the role of endogenously generated ET-1 in renal hemodynamics under physiological conditions. In six conscious foxhounds, the time course of the effects of the selective ETA receptor antagonist LU-135252 (10 mg/kg iv) on mean arterial blood pressure (MAP), heart rate (HR), RBF, and glomerular filtration rate (GFR), as well as its effects on renal autoregulation, were examined. LU-135252 increased RBF by 20% (from 270 +/- 21 to 323 +/- 41 ml/min, P < 0.05) and HR from 76 +/- 5 to 97 +/- 8 beats/min (P < 0. 05), but did not alter MAP, GFR, or autoregulation of RBF and GFR. Since a number of interactions between ET-1 and the renin-angiotensin system have been reported previously, experiments were repeated during angiotensin converting enzyme (ACE) inhibition by trandolaprilat (2 mg/kg iv). When ETA receptor blockade was combined with ACE inhibition, which by itself had no effects on renal hemodynamics, marked changes were observed: MAP decreased from 91 +/- 4 to 80 +/- 5 mmHg (P < 0.05), HR increased from 85 +/- 5 to 102 +/- 11 beats/min (P < 0.05), and RBF increased from 278 +/- 23 to 412 +/- 45 ml/min (P < 0.05). Despite a pronounced decrease in renal vascular resistance over the entire pressure range investigated (40-100 mmHg), the capacity of the kidneys to autoregulate RBF was not impaired. The GFR remained completely unaffected at all pressure levels. These results demonstrate that endogenously generated ET-1 contributes significantly to renal vascular tone but does not interfere with the mechanisms of renal autoregulation. If ETA receptors are blocked, then the vasoconstrictor effects of ET-1 in the kidney are compensated for to a large extent by an augmented influence of ANG II. Thus ET-1 and ANG II appear to constitute a major interrelated vasoconstrictor system in the control of RBF. (+info)
ACE inhibition and ANG II receptor blockade improve glomerular size-selectivity in IgA nephropathy.
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Protein trafficking across the glomerular capillary has a pathogenic role in subsequent renal damage. Despite evidence that angiotensin-converting enzyme (ACE) inhibitors improve glomerular size-selectivity, whether this effect is solely due to ANG II blocking or if other mediators also play a contributory role is not clear yet. We studied 20 proteinuric patients with IgA nephropathy, who received either enalapril (20 mg/day) or the ANG II receptor blocker irbesartan (100 mg/day) for 28 days in a randomized double-blind study. Measurements of blood pressure, renal hemodynamics, and fractional clearance of neutral dextran of graded sizes were performed before and after 28 days of treatment. Both enalapril and irbesartan significantly reduced blood pressure over baseline. This reduction reached the maximum effect 4-6 h after drug administration but did not last for the entire 24-h period. Despite transient antihypertensive effect, proteinuria was effectively reduced by both treatments to comparable extents. Neither enalapril nor irbesartan modified the sieving coefficients of small dextran molecules, but both effectively reduced transglomerular passage of large test macromolecules. Theoretical analysis of sieving coefficients showed that neither drug affected significantly the mean pore radius or the spread of the pore-size distribution, but both importantly and comparably reduced the importance of a nonselective shunt pathway. These data suggest that antagonism of ANG II is the key mechanism by which ACE inhibitors exert their beneficial effect on glomerular size-selective function and consequently on glomerular filtration and urinary output of plasma proteins. (+info)
Inhibition of beta-myosin heavy chain gene expression in pressure overload rat heart by losartan and captopril.
(15/4593)
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)
Electrophysiologic effect of enalapril on guinea pig papillary muscles in vitro.
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AIM: To study the direct effect of enalapril on cellular electrophysiology of myocardium. METHODS: Conventional microelectrodes technique was used to record the action potentials (AP) of guinea pig papillary muscles. RESULTS: Enalapril caused an increase of the AP amplitude (APA) and the resting potential (RP) in a concentration-dependent manner without any significant change of AP duration, Vmax and overshoot of AP. Superfusion of ouabain 0.5 mumol.L-1 reduced APA and RP, induced stable delayed after-depolarizations (DAD) at different basic cycle lengths (BCL) in a frequency-dependent manner. At BCL 200 ms, the amplitude of DAD was large enough to induce nonsustained triggered activity (TA). In additional presence of enalapril 10 mumol.L-1, the DAD amplitude at 500, 400, 300, and 200 ms were decreased from 5.3 +/- 2.3, 5.9 +/- 2.8, 7.4 +/- 2.1, and 8.9 +/- 1.3 to 2.6 +/- 0.7, 3.1 +/- 1.0, 3.7 +/- 1.5, and 5.3 +/- 1.1 (mV) respectively, all P < 0.01. The compensation intervals were increased in a similar frequency-dependent manner. The number of TA induced at BCL 200 ms was decreased from 3.6 +/- 0.7 to 0.8 +/- 0.2 (P < 0.05). CONCLUSION: Enalapril directly inhibits DAD and TA induced by ouabain through increasing RP and APA, which may contribute to its anti-arrhythmic effect. (+info)