Endothelium-mediated vasodilation during ACE inhibition

Endothelial Sp1/Sp3 are essential to the effect of captopril on blood pressure in male mice

Endothelial dysfunction represents a major cardiovascular risk factor for hypertension. Sp1 and Sp3 belong to the specificity protein and Krüppel-like transcription factor families. They are ubiquitously expressed and closely associated with cardiovascular development. We investigate the role of Sp1 and Sp3 in endothelial cells in vivo and evaluate whether captopril, an angiotensin-converting enzyme inhibitor (ACEI), targets Sp1/Sp3 to exert its effects. Inducible endothelial-specific Sp1/Sp3 knockout mice are generated to elucidate their role in endothelial cells. Tamoxifen-induced deletion of endothelial Sp1 and Sp3 in male mice decreases the serum nitrite/nitrate level, impairs endothelium-dependent vasodilation, and causes hypertension and cardiac remodeling. The beneficial actions of captopril are abolished by endothelial-specific deletion of Sp1/Sp3, indicating that they may be targets for ACEIs. Captopril increases Sp1/Sp3 protein levels by recruiting histone deacetylase 1, which elevates deacetylation and suppressed degradation of Sp1/Sp3. Sp1/Sp3 represents innovative therapeutic target for captopril to prevent cardiovascular diseases.

Activity of angiotensin-converting enzyme after treatment with L-arginine in renovascular hypertension

The renin-angiotensin system plays a role in the pathophysiology of renovascular hypertension. In addition, some studies have demonstrated a beneficial effect of L-arginine (L-Arg), the precursor of nitric oxide (NO), in this model of hypertension. This study was designed to investigate the effects of L-Arg on cardiovascular parameters and on the activity of the angiotensin-converting enzyme (ACE), after 14 days of renovascular hypertension. The experiments were performed on conscious male Wistar rats. Two-kidney, one-clip renovascular hypertension (2KIC) was initiated in rats by clipping the left renal artery during 14 days, while control rats were sham-operated. One group was submitted to a similar procedure and treated with L-Arg (10 mg/ml; average intake of 300mg/day) from the 7th to the 14th day after surgery, whereas the respective control group received water instead. At the end of the treatment period, the mean arterial pressure (MAP) was measured in conscious animals. The rats were sacrificed and the ACE activity was assayed in heart and kidneys, using Hip-His-Leu as substrate. In a separate group, the heart was removed, the left ventricle (LV) was weighed and the LV/body weight ratios (LV/BW) were determined. We observed significant differences in MAP between the L-Arg-treated and untreated groups (129 +/- 7 vs. 168 +/- 6 mmHg; P< 0.01). The cardiac hypertrophy described for this model of hypertension was attenuated in the 2K1C-L-Arg-treated group (14th day, wet LV/BW: 2K1C-L-Arg = 1.88 +/- 0.1; 2K1C = 2.20 +/- 0.1 mg/g; P < 0.05). L-Arg administration caused an important decrease in cardiac ACE activity (2K1C-L-Arg: 118 +/- 15; 2K1C: 266 +/- 34 micromol/min/mg; P < 0.01). L-Arg also decreased the ACE activity in the clipped kidney by 47% (P < 0.01), but not in the nonclipped kidney. These data suggest that increased NO formation and reduced angiotensin II formation are involved in the anthihypertensive effect of orally administered L-arginine.

DOSE-DEPENDENT EFFECT OF CAPTOPRIL ON AORTIC REACTIVITY OF STREPTOZOTOCIN-DIABETIC RATS

Diabetes mellitus is a primary risk factor for cardiovascular disorders. Strategies that interrupt the renin-angiotensin system have been known to reduce cardiovascular disease. The present study was performed to investigate the effect of sub-chronic administration of captopril on the aortic reactivity of streptozotocin-diabetic rats. Streptozotocin-diabetic rats received captopril (30 and 50 mg/kg per day) for 2 months. Contractile responses to phenylephrine (PE) and relaxation responses to acetylcholine (ACh) and isosorbide dinitrate (ISD) were obtained from aortic rings. Concentration-response curves from captopril-treated diabetic rats to PE were attenuated compared with vehicle (Saline)-treated diabetic rats, especially at a dose of 50 mg/kg captopril. In addition, endothelium-dependent relaxation responses induced by ACh were significantly higher in captopril-treated diabetic rats compared with diabetic rats. The endothelium-independent relaxation responses for ISD were found not to be significantly different among the groups. Therefore, sub-chronic treatment of diabetic rats with captopril in a dose-dependent manner could prevent the functional changes in vascular reactivity in diabetic rats.

Protective effect of enalapril on vascular reactivity of the rat aorta

Cardiovascular complications are the major cause of morbidity and mortality in patients with diabetes mellitus (DM). Strategies that interrupt the renin-angiotensin system have been shown to reduce the ensuing threatening risk factors. The present study was carried out to investigate the effect of subchronic administration of enalapril on the aortic reactivity of streptozotocin (STZ)-diabetic rats. For this purpose, STZ-diabetic rats received enalapril (10 and 20 mg/kg ip) daily for 2 months. Contractile responses to phenylephrine (PE) and relaxation responses to acetylcholine (Ach) and isosorbide dinitrate (ISD) were obtained from aortic rings. Concentration-response curves from enalapril-treated diabetic (ED) rats to PE were attenuated as compared to vehicle-treated diabetics (VD), especially at a dose of 20 mg/kg for enalapril. In addition, endothelium-dependent relaxation responses induced by Ach was significantly higher in ED rats as compared to diabetic ones. The endothelium-independent relaxation responses for ISD were also found not to be significantly different among the groups. Therefore, subchronic treatment of diabetic rats with enalapril in a dose-dependent manner could prevent the functional changes in vascular reactivity in diabetic rats.

Can angiotensin-converting enzyme inhibitors reverse atherosclerosis?

Angiotensin II, a potent vasoconstrictor, is mainly present in the vascular endothelium. Multiple studies have confirmed that angiotensin-converting enzyme (ACE) inhibitors, which block the formation of angiotensin II, lower blood pressure and also improve heart failure. These agents not only have beneficial hemodynamic effects but also bestow additional benefits on vascular function and prevent clinical cardiovascular events in patients at risk for coronary artery disease. These latter benefits may represent effects of ACE inhibitors on local endocrine pathways, inflammatory processes, and atherosclerosis taking place within the arterial wall. Current evidence suggests that, although ACE inhibitors may not substantially reverse atherosclerotic plaque already present, they may slow the progression of such atherosclerotic lesions. In addition, by modulating inflammatory pathways within and adjacent to the atherosclerotic lesion, they may stabilize an unstable plaque and therefore decrease the risk of plaque rupture and its complications.

Effects of angiotensin II receptor antagonist on endothelial vasomotor function and urinary albumin excretion in type 2 diabetic patients with microalbuminuria

BACKGROUND

Microalbuminuria is associated with dysfunction of the vascular endothelium in patients with diabetes mellitus. The objective of the present study was to determine whether treatment with losartan at a dose sufficient to lower urinary albumin excretion was accompanied by an improvement in endothelial function in type 2 diabetic patients with microalbuminuria.

METHODS

Endothelial function was measured in 80 type 2 diabetic patients with microalbuminuria and 68 non-diabetic controls using high-resolution vascular ultrasound. The diabetic patients were randomised to receive either losartan 50 mg daily or placebo in a 6-month double-blind study. Urinary albumin excretion and endothelial function were assessed at baseline, 3 and 6 months.

RESULTS

Both endothelium-dependent (p<0.01) and -independent vasodilation (p<0.01) were significantly impaired in diabetic patients with or without history of hypertension compared to the non-diabetic controls. At baseline, the losartan- and placebo-treated groups were comparable in their clinical characteristics. Blood pressure did not change significantly in either group throughout the study. Urinary mean albumin excretion rate (MAER) decreased in the losartan-treated group (p<0.01) whereas an increase was observed in the placebo group (p<0.05). At 6 months, the losartan-treated group had significantly lower MAER than the placebo-treated group [54.5 (58.3) vs 78.5 (100.5) microg/min, p<0.05; median (interquartile range)]. No significant differences were found in endothelium-dependent or -independent vasodilation.

CONCLUSIONS

Type 2 diabetic patients with microalbuminuria have impaired endothelium-dependent and -independent vasodilation. Treatment with low-dose losartan is sufficient to reduce microalbuminuria in these patients without alteration in endothelial function and systemic blood pressure.

Losartan, an angiotensin type 1 receptor antagonist, improves endothelial function in non-insulin-dependent diabetes

OBJECTIVES

The present study examined the effect on forearm endothelial function of an angiotensin II type 1 receptor antagonist, losartan, in subjects with non-insulin-dependent diabetes mellitus (NIDDM).

BACKGROUND

Angiotensin-converting enzyme (ACE) inhibition with enalapril improves acetylcholine (ACh)-dependent endothelial function in patients with NIDDM. This could be mediated through angiotensin II and the type 1 receptor or could be due to inhibition of kininase II and a bradykinin preserving effect. It is therefore relevant to determine whether a type 1 receptor antagonist improves endothelial function.

METHODS

The influence of losartan (50 mg daily for four weeks) on endothelium-dependent and independent vasodilator function was determined in 9 NIDDM subjects using a double-blinded placebo-controlled crossover protocol. Forearm blood flow was measured using strain-gauge plethysmography.

RESULTS

Losartan significantly decreased infused arm vascular resistance in response to three incremental doses of intrabrachial acetylcholine (p < 0.05, ANOVA). The forearm blood flow ratio (flow in infused to noninfused arm) was also increased (p < 0.01). Responses to sodium nitroprusside and monomethyl arginine were not significantly changed.

CONCLUSIONS

Losartan administration at 50 mg per day improved endothelium-dependent dilation of resistance vessels in patients with NIDDM. That is, blockade of the angiotensin II type 1 receptors improves endothelial function in NIDDM. At least some of the similarly beneficial effect of ACE inhibition is probably mediated also through the angiotensin II-type 1 receptor pathway. The use of a type 1 receptor antagonist seems a reasonable alternative to an ACE inhibitor to maintain endothelial function in NIDDM subjects.

Captopril increases the affinity of bradykinin receptor binding sites in bovine coronary arterial endothelial cells

In a radioligand binding study using bovine coronary artery endothelial cell membranes, captopril changed a single bradykinin (BK) binding site (Kd = 1.77 nM, Bmax = 60.2 fmol/mg protein) to high- (Kd = 0.68 pM, Bmax = 17.7 fmol/mg protein) and low- (Kd = 1.00 nM, Bmax = 72.5 fmol/mg protein) affinity binding sites. This effect was reversed by GppNHp. Captopril also enhanced BK-induced endothelium-dependent relaxation in saponin-treated coronary rings, and GppNHp partially suppressed this enhancement. These results suggest that captopril may affect BK receptors that couple to G-proteins.

Inhibition of arterial thrombogenesis by quinapril but not losartan

The cardioprotective effect of angiotensin converting enzyme (ACE) inhibitors and angiotensin type I (AT1) receptor blockers may relate to their antithrombotic effect. We determined the differential effects of the ACE inhibitor quinapril and the AT1 receptor blocker losartan on arterial thrombus formation in the rat. Sprague-Dawley rats were fed regular chow or chow mixed with low-dose quinapril (0. 6 mg/kg/day), high-dose quinapril (1.2 mg/kg/day), or losartan (10 mg/kg/day) for 15 days. Abdominal aorta was exposed and wrapped with Whatman paper impregnated with 29% FeCl(3) (ferric chloride). Time to occlusive thrombus formation and weight of the thrombus were recorded. Aortic superoxide anion generation, platelet aggregation, plasma angiotensin II levels, and morphology of the thrombus were also examined. Both losartan and quinapril caused similar reductions in arterial pressure. Losartan did not affect the time to thrombus formation, whereas quinapril (both low and high doses) delayed the time to thrombus formation (P<.01 vs control). Weight of the thrombus was similar in all groups of rats. Platelet aggregation was inhibited by approximately 50 in both quinapril- and losartan-treated rats. The high-dose quinapril-treated rats showed markedly reduced vascular superoxide anion generation compared with the control rats (P<.05). Plasma angiotensin II levels were unaffected by quinapril treatment but were elevated 7-fold in losartan-treated rats (P <.001 vs. control rats). The thrombi in the control rats consisted of platelet aggregates, fibrin, and red blood cells. The intravascular platelet aggregates were much smaller in the quinapril-treated rats (P<.05 vs. control), but were similar in control and losartan-treated rats. In conclusion, quinapril but not losartan prolongs time to arterial thrombus formation and results in smaller platelet aggregates in the thrombus. Both quinapril and losartan decrease platelet aggregation, but only quinapril decreases superoxide anion generation. This effect on superoxide anion generation as well as mechanisms other than AT1 receptor blockade may underlie the salutary effect of quinapril on arterial thrombogenesis.

Comparative effects of pretreatment with captopril and losartan on cardiovascular protection in a rat model of ischemia-reperfusion

OBJECTIVES

We sought to assess the comparative effects of pretreatment with captopril and losartan on myocardial infarct size and arrhythmias in a rat model of ischemia-reperfusion.

BACKGROUND

Angiotensin-converting enzyme (ACE) inhibitors and angiotensin II receptor blockers (ARBs) inhibit the renin-angiotensin system in different ways. However, the comparative effects of pretreatment with ACE inhibitors or ARBs on acute myocardial infarct size and arrhythmias are unknown.

METHODS

We randomly assigned 117 female Sprague-Dawley rats into three groups: group N was the normal control; group C was given 40 mg/kg body weight per day of captopril in drinking water; and group L was given 40 mg/kg per day of losartan in drinking water. After 10 weeks of pretreatment, 25 rats in each group were subjected to 17 min of left anterior descending coronary artery occlusion and 2 h of reperfusion with hemodynamic and electrocardiographic monitoring. Fourteen rats in each group had blood samples drawn and aortic rings removed to study vascular reactivity.

RESULTS

Mortality during ischemia and reperfusion was lower in combined groups L and C than in group N (4.2% vs. 19.2%, p = 0.042). Rats treated with losartan had significantly higher levels of angiotensin II in their plasma. Hemodynamic variables were not significantly different among the three groups. The thresholds of ventricular fibrillation (VF) before occlusion and after reperfusion were significantly higher in groups L and C than in group N (1.99 +/- 0.24 and 1.93 +/- 0.27 vs. 1.23 + 0.17 mA, p = 0.04; 2.13 +/- 0.25 and 1.78 +/- 0.22 vs. 0.95 +/- 0.11 mA, p = 0.001). The average episodes of ventricular tachycardia (VT) and VF per rat were significantly less in groups L and C than in group N (0.96 +/- 0.2 and 1.2 +/- 0.3 vs. 2.8 + 0.4 mA, p < 0.001). Myocardial infarct size was significantly smaller in groups L and C than in group N (34 +/- 3% and 35 +/- 3% vs. 44 +/- 3%, p = 0.031, 0.043). Endothelium-dependent vasorelaxation induced by a calcium ionophore (A23187) was increased in both groups but was only statistically significant in group C (p = 0.020).

CONCLUSIONS

Losartan and captopril have similar cardiovascular protective effects in a rat model of ischemia-reperfusion. They increased the threshold of VF, decreased mortality and decreased episodes of VT and VF, as well as decreased myocardial infarct size.

Enalapril and losartan augment endogenous nitric oxide release in Takayasu's arteritis--a case report

Prognosis in Takayasu's arteritis is limited owing to renovascular hypertension. The authors report a patient with Takayasu's arteritis who had been unilaterally nephrectomized and presented with malignant hypertension due to renal artery stenosis. Hypertension was refractory to conventional antihypertensive treatment, and stenosis was not accessible by interventional angioplasty. Initiation of enalapril and losartan therapy was successful in improving blood pressure without deterioration of renal function due to ischemic failure. Antihypertensive treatment resulted in dramatically stimulated endogenous nitric oxide (NO) synthesis, while elevated plasma endothelin-1 levels were unchanged. Renovascular hypertension in Takayasu's arteritis is associated with an imbalance of vasoconstrictor peptide endothelin-1 and vasodilator peptide NO. Successful treatment of hypertension by enalapril or losartan results in improved endogenous NO synthesis, which putatively counterbalances excessive vasoconstrictor actions and may retard the progression of renal failure.

Improvement in endothelial function by angiotensin-converting enzyme inhibition in non-insulin-dependent diabetes mellitus

OBJECTIVES

The aim of this study was to assess the effect of angiotensin-converting enzyme (ACE) inhibition with enalapril on forearm endothelial function in subjects with type II diabetes mellitus.

BACKGROUND

Endothelial function is depressed in the presence of conventional risk factors for atherosclerosis, and various therapies, such as lipid-lowering therapy in hypercholesterolemia, can improve endothelial-mediated vasodilation. ACE inhibition has improved such function in several conditions including type I diabetes, but there is no evidence for a beneficial effect in type II diabetes.

METHODS

The influence of enalapril (10 mg twice daily for 4 weeks) on endothelium-dependent and -independent vasodilator function was determined in 10 type II diabetic subjects using a double-blinded placebo-controlled crossover protocol. Forearm blood flow was measured using strain-gage plethysmography and graded intrabrachial infusion of acetylcholine (ACh), N(G)-monomethyl-L-arginine (LNMMA) and sodium nitroprusside (SNP).

RESULTS

Enalapril increased the response to the endothelium-dependent vasodilator, ACh (p < 0.02) and the vasoconstrictor response to the nitric oxide (NO) synthase inhibitor, LNMMA (p < 0.002). No difference was evident in the response to SNP.

CONCLUSIONS

In type II diabetic subjects without evidence of vascular disease, the ACE inhibitor enalapril improved stimulated and basal NO-dependent endothelial function. The study extends the spectrum of beneficial effects demonstrated to result from ACE inhibition in diabetes.

Regulation of aortic wall structure by the renin-angiotensin system in Wistar rats

The effects of long-term angiotensin-converting enzyme (ACE) inhibition, angiotensin II (AT1)-receptor blockade, calcium-entry blockade, or cyclosporin A treatment on rat aortic wall structure were investigated to determine the role of the renin-angiotensin system in the physiologic regulation of vascular structure in vivo. Groups of 15 Wistar rats were treated for 6 weeks either with the ACE inhibitors lisinopril or fosinopril or with the AT1-antagonists D 8731 or losartan (each 10 mg/kg/day) or with the calcium antagonist isradipine, 60 mg/kg/day, or cyclosporin A, 15 mg/kg/day, or a combination of cyclosporin with one of the vasodilators. Media thickness, vascular smooth-muscle cell density, and intima thickening were measured in histologic sections of the abdominal aorta. In addition, aortic contractility and heart weight were determined. Long-term ACE inhibition, AT1-receptor blockade, and calcium-entry blockade reduced aortic media thickness and increased media smooth-muscle cell density. Only ACE inhibition significantly reduced the extent of intima lesions. Media thickness correlated well with the maximal aortic contraction to phenylephrine and serotonin but not to angiotensin II. ACE inhibition and AT1-receptor blockade decreased heart weight, whereas calcium antagonism increased it. Cyclosporin treatment was without effect on any of these parameters. The data demonstrate a significant long-term influence of the renin-angiotensin system on aortic wall structure and function in Wistar rats.

Improvement in endothelial function by angiotensin converting enzyme inhibition in insulin-dependent diabetes mellitus

We postulated that nitric oxide (NO)-mediated endothelial function would be improved by acute and short-term treatment with an angiotensin converting enzyme (ACE) inhibitor in patients with type I diabetes mellitus, in whom endothelial function is depressed. Nine type I diabetic patients and eight healthy subjects underwent forearm blood flow measurement using strain gauge plethysmography during intraarterial infusion of incremental doses of endothelium-dependent (acetylcholine [ACh]) and endothelium-independent (sodium nitroprusside [SNP]) vasodilators. Pretreatment ACh responses were depressed in diabetic patients relative to the normal subjects (P < 0.05). No difference between the groups was evident in response to SNP. Acute ACE inhibition (with intrabrachial enalaprilat) enhanced ACh responses in the diabetic patients (P < 0.005), with a further improvement evident after 1 mo of oral therapy with enalapril (P < 0.001) when ACh responses were normalized. ACE inhibition did not affect SNP responses. We conclude that acute administration of the ACE inhibitor, enalaprilat, enhances NO-mediated endothelial function in type I diabetic patients, with further improvement evident after 4 wk of enalapril therapy.

ACE inhibitor potentiation of bradykinin-induced venoconstriction

1. Angiotensin-converting enzyme (ACE) inhibitors exert their cardiovascular effects not only by preventing the formation of angiotensin II (AII), but also by promoting the accumulation of bradykinin in or at the vessel wall. In addition, certain ACE inhibitors have been shown to augment the vasodilator response to bradykinin, presumably by an interaction at the level of the B2 receptor. We have investigated whether this is a specific effect of the ACE inhibitor class of compounds in isolated endothelium-denuded segments of the rabbit jugular vein where bradykinin elicits a constrictor response which is exclusively mediated by activation of the B2 receptor. 2. Moexiprilat and ramiprilat (< or = 3 nM) enhanced the constrictor response to bradykinin three to four fold. Captopril and enalaprilat were less active by approximately one and quinaprilat by two orders of magnitude. Moexiprilat and ramiprilat, on the other hand, had no effect on the constrictor response to AII or the dilator response to acetylcholine. 3. The bradykinin-potentiating effect of the ACE inhibitors was not mimicked by inhibitors of amino-, carboxy-, metallo- or serine peptidases or the synthetic ACE substrate, hippuryl-L-histidyl-L-leucine, at a concentration which almost abolished the residual ACE activity in the vessel wall. In contrast, angiotensin-(1-7) (10 microM), an angiotensin I metabolite, significantly enhanced the constrictor response to bradykinin. 4. Ramiprilat did not alter the binding of [3H]-bradykinin to a membrane fraction prepared from endothelium-denuded rabbit jugular veins or to cultured fibroblasts, and there was no ACE inhibitor-sensitive, bradykinin-induced cleavage of the B2 receptor in cultured endothelial cells. 5. These findings demonstrate that ACE inhibitors selectively potentiate the B2 receptor-mediated vascular effects of bradykinin. Their relative efficacy appears to be independent of their ACE-inhibiting properties and might be related to differences in molecule structure. Moreover, the potentiation of the biological activity of bradykinin by this class of compounds does not seem to be mediated by a shift in affinity of the B2 receptor or a prevention of its desensitization, but may involve an increase in the intrinsic activity of unoccupied B2 receptor molecules.