Captopril potentiates the effects of nitroglycerin in the coronary vascular bed

Beneficial effects of angiotensin-converting enzyme inhibitor and nitrate association on left ventricular remodeling in patients with large acute myocardial infarction: the Delapril Remodeling after Acute Myocardial Infarction (DRAMI) trial

BACKGROUND

In the large-scale trial, Gruppo Italiano per lo Studio della Sopravvivenza nell'Infarto Miocardico-3 (GISSI-3), patients receiving the combination of lisinopril and glyceryl trinitrate benefited most from experimental therapy. Therefore, a multicenter, randomized, double-blind study, Delapril Remodeling After Acute Myocardial Infarction (DRAMI), was designed to assess (1) the possible additive beneficial effect on left ventricular remodeling of nitrates when combined with an angiotensin-converting enzyme inhibitor (ACEI), and (2) the tolerability of a new ACEI, delapril, in respect to lisinopril in patients with large myocardial infarction (MI).

METHODS

A total of 177 patients were randomized to receive delapril plus isosorbide-5-mononitrate (IS5MN) placebo, delapril plus IS5MN, lisinopril plus IS5MN placebo, or lisinopril plus IS5MN starting within the first 36 hours after the onset of symptoms and continuing for 3 months.

RESULTS

More than 80% of the patients showed extensive ST-segment changes and 36.7% had signs or symptoms of heart failure during the first 36 hours. Over 3 months, IS5MN reduced, by 76%, the increase in LVEDV (17.4 +/- 5.0 mL placebo vs 4.2 +/- 4.4 mL IS5MN, P =.0439), reversed the increase in LVESV (7.5 +/- 3.9 mL placebo vs -5.5 +/- 2.9 mL IS5MN, P =.0052), and increased the recovery of LVEF (1.9% +/- 1.3% placebo vs 6.7% +/- 1.2% IS5MN, P =.0119). Overall, 3-month mortality was 10.2%; the most frequent clinical events were new episodes of severe heart failure (18.1%), persistent hypotension (10.7%), and post-MI angina (18.1%), with no differences between treatment groups.

CONCLUSIONS

Administration for 3 months of IS5MN combined with an ACEI, both started within 36 hours from the onset of symptoms, was safe and effective in reducing LV dilation and dysfunction after MI. The 2 ACEIs, delapril and lisinopril, appeared to be equally well tolerated.

Effect of angiotensin-converting enzyme inhibitors and nitroxy groups on human coronary resistance vessels in vitro

We investigated the interaction between nitroxy groups and angiotensin-converting enzyme (ACE) inhibitors to assess the role of sulfhydryl groups and adenosine triphosphate (ATP)-sensitive potassium channels in vasodilation of human coronary resistance vessels in vitro. Coronary resistance vessels were resected from the right atrial appendage of 27 patients undergoing open heart surgery. The vessel ends were inserted into a microglass pipette with the internal pressure maintained at 40 mm Hg. Nitroglycerin did not change the vasoresponse, whereas nicorandil induced a concentration-dependent vasodilation that was not affected by methylene blue, but was markedly inhibited by glibenclamide. The ACE inhibitors, captopril, with a sulfhydryl group (1 x 10(-6) M), and enalaprilat, without a sulfhydryl group (1 x 10(-6) M), were added to either nitroglycerin or nicorandil to assess the incremental response of the sulfhydryl group to vasodilation. The addition of captopril or L-cysteine (1 x 10(-6) M) enhanced the activity of both nitroglycerin and nicorandil, whereas addition of enalaprilat did not. The responses of nicorandil and nitroglycerin to captopril and were similar. Cromakalim was not enhanced by L-cysteine or captopril. The response of nitroglycerin was not enhanced by captopril or L-cysteine after addition of N(G)-monomethyl-L-ARGININE (L-NMMA). Both nitroglycerin and nicorandil exhibited an increase in vasodilation in the presence of an ACE inhibitor containing a sulfhydryl group. The mechanism of the vasodilatory action in the coronary resistance vessels may involve the opening of an ATP-sensitive potassium channel and subsequent guanylate cyclase activation. These interactions have important clinical implications.

The angiotensin II-receptor antagonist losartan does not prevent hemodynamic or vascular tolerance to nitroglycerin

Tolerance may involve increased production of angiotensin II. We tested the hypothesis that losartan would prevent the development of tolerance to continuous transdermal nitroglycerin (GTN). Twenty volunteers received losartan, 75 mg/day, or placebo in a randomized, double-blind, parallel fashion. After 1 week, continuous transdermal GTN, 0.6 mg/h, was given, in addition to losartan or placebo, to all volunteers for 1 week. Standing systolic blood pressure (SBP) and heart rate were measured, and forearm venous volume responses to sublingual GTN were evaluated. Measurements were made at baseline, after 1 week of losartan versus placebo, 3 h after initial therapy with transdermal GTN, and after 1 week of continuous transdermal GTN given in combination with losartan versus placebo. After sustained GTN therapy, SBP was unchanged from baseline in both groups, indicating that losartan did not prevent the development of tolerance. Tolerance also developed to the forearm venous volume responses and was not prevented by losartan. Therapy with an angiotensin II-receptor antagonist does not prevent the development of tolerance to continuous transdermal GTN.

Preventive effects of angiotensin-converting enzyme inhibitors on nitrate tolerance during continuous transdermal application of nitroglycerin in patients with chronic heart failure

This study was designed to investigate the effect of angiotensin-converting enzyme (ACE) inhibitors with and without a sulfhydryl group on intracellular production of cGMP, forearm blood flow, and neurohormonal factors during continuous transdermal application of nitroglycerin in patients with chronic heart failure. Platelet cGMP level and forearm blood flow were measured before and 5 min after sublingual administration of nitroglycerin (NTG) in 20 patients with chronic heart failure during the following 4 phases: (1) baseline phase; (2) NTG phase (1 week after NTG tape 10 mg/day); (3) CPT phase (1 week after both captopril 37.5 mg/day and NTG tape 10 mg/day); and (4) ENL phase (1 week after both enalapril 5 mg/day and NTG tape 10 mg/day). The platelet GMP level before sublingual NTG and forearm blood flow were significantly higher during the 3 phases with NTG tape than during the control phase. The percent increases in platelet cGMP level and forearm blood flow after sublingual NTG were significantly lower during the NTG phase than during the baseline phase. In contrast, concomitant application of ACE inhibitors maintained the percent increase in platelet cGMP level and forearm blood flow. These results indicate that concomitant therapy with ACE inhibitors may be helpful in preventing the attenuation of intracellular cGMP production in patients with chronic heart failure during continuous transdermal application of NTG.

No cross-tolerance between S-nitrosocaptopril and nitroglycerin in dog coronary arteries in vivo

S-Nitrosocaptopril (S-NO-Cap), a nitrate and an angiotensin-converting enzyme (ACE) inhibitor, may be produced after coadministration of nitroglycerin (NTG) and captopril (CAP). We synthesized S-NO-Cap and investigated its in vivo tolerance. In open-chest dogs, S-NO-Cap [300 microg; intracoronary (i.c.)] and NTG (50 microg, i.c.) increased coronary blood flow (CBF) similarly (8.0 vs. 9.0 ml/min; p = NS; n = 5). After a 2-h i.c. NTG infusion at high dose (1.32 micromol/min), NTG (50 microg, i.c.) had no significant effect on CBF, whereas S-NO-Cap (300 microg, i.c.) still produced an attenuated increase in CBF (4.9 ml/min; p < 0.05 vs. control). On the other hand, after a 2-h i.c. infusion of S-NO-Cap (1.32 micromol/min), the CBF response to S-NO-Cap (300 microg) showed no attenuation, whereas that to NTG (50 microg) was potentiated (8.8 vs. 12.6 ml/min; p < 0.05; n = 6). Under basal conditions, S-NO-Cap (30-300 microg, i.c.) increased CBF dose dependently, whereas CAP (30-300 microg, i.c.) had no effect on CBF, suggesting that S-NO-Cap dilates coronary vessels by a nitrate action but not by an ACE-inhibitory action. In nonsurgical dogs, 2-h intravenous (i.v.) infusion of S-NO-Cap (1.32 micromol/min) had a stable hypotensive effect, whereas that of NTG (1.32 micromol/min) gradually attenuated the effect. Plasma NO3-, an oxidative product of nitric oxide (NO), increased after both infusions, suggesting that S-NO-Cap may act partially as an NO donor, similarly to NTG. Plasma ACE activity was reduced after an S-NO-Cap infusion (5.84 vs. 4.10 IU/L; p < 0.01; n = 5), and plasma aldosterone was markedly increased after NTG infusion relative to that after S-NO-Cap infusion (243.0 vs. 38.6 pg/ml; p < 0.05). Plasma norepinephrine increased after both infusions (393.6 vs. 289.0 pg/ml; p = NS). As judged by the increase in CBF, whereas S-NO-Cap showed partial tolerance with NTG, no tolerance was found with S-NO-Cap itself. The in vivo coronary vascular response to S-NO-Cap may, therefore, be partially reduced by activation of the adrenergic or renin-angiotensin-aldosterone systems or both induced by NTG, because S-NO-Cap showed no cross-tolerance with NTG in our earlier in vitro study.

Effects of angiotensin-converting enzyme inhibitor alacepril in patients with stable effort angina during chronic isosorbide dinitrate treatment

Nitrate tolerance has been reported to be reversed by certain types of angiotensin-converting enzyme (ACE) inhibitors. We examined whether alacepril, a new long-acting oral ACE inhibitor, has beneficial effects against exercise-induced angina in patients with stable effort angina after substantial isosorbide dinitrate (ISDN) treatment. Thirteen men with stable effort angina were treated with oral ISDN (80 mg/d) for >3 weeks. After this period, efficacy of single oral administration of either alacepril (50 mg) or its placebo on exercise-induced angina and electrocardiographic changes was examined by treadmill exercise test in a double-blind crossover design. Alacepril significantly improved the exercise duration by 9.1% (p=0.03), the time to 1 mm ST-segment depression by 19% (p<0.01), and the maximal ST-segment depression by 33% (p=0.015) compared with placebo. Alacepril did not significantly alter the rate-pressure product, a marker of myocardial oxygen demand, during exercise test compared with placebo. Plasma renin activity was significantly increased (p<0.05) after administration of alacepril, indicating that alacepril significantly blocked ACE activity in our patients. In conclusion, a single oral administration of the ACE inhibitor alacepril (50mg) elicited beneficial effects against exercise-induced myocardial ischemia in patients with stable effort angina during chronic nitrate treatment. These effects may be mediated by increased coronary blood flow.

Nitric oxide and nitrovasodilators: similarities, differences, and interactions

The endothelium functions as a semipermeable membrane separating the blood from the body and allowing the transport of macromolecules from the blood to the interstitial space. The endothelium secretes a number of diffusible substances. These include endothelium-derived relaxing factor (EDRF), endothelium-derived hyperpolarizing factor (EDHF), and prostacyclin, in addition to vasoconstrictors including endothelin, angiotensin, and endothelium-derived contracting factor. EDRF is now known to be nitric oxide, or a closely related molecule, which affects signaling by stimulation of soluble guanylate cyclase, causing increased intracellular levels of cyclic guanosine monophosphate (cGMP), in turn leading to relaxation of vascular smooth muscle as well as a variety of additional effects that include altered function of platelets and cardiac myocytes. Nitric oxide can be made available to cellular elements in two ways: by endogenous synthesis via one or more of the three nitric oxide synthases now known to exist in mammalian species; or by exogenous administration of pharmacologic sources of nitric oxide, usually as organic nitrate vasodilators that can be metabolically converted to biologically activated nitric oxide. This process appears to require free sulfydryl groups. The metabolic machinery necessary to convert organic nitrates to a biologically active form exists mainly in the vasculature and not in the myocardium. Numerous studies have demonstrated that the presence of coronary artery disease is associated with interruption of the endogenous production of nitric oxide. Under these circumstances, exogenous nitrates still produce coronary vasodilation as well as relaxation of vascular smooth muscle in the periphery. Other articles in this supplement will focus on the vascular effects of nitric oxide and nitrovasodilators; this article will conclude with a brief discussion of the role of the nitric oxide pathway in the control of cardiac autonomic responsiveness and the potential role of cytokines and the nitric oxide pathway to impair the ability of the myocardium to respond to catecholamines or other stimuli with a normal increase in contractile function.

Coronary vasodilation induced by angiotensin-converting enzyme inhibition in vivo: differential contribution of nitric oxide and bradykinin in conductance and resistance arteries

BACKGROUND

We studied in coronary conductance and resistance arteries the coronary vasodilator effects of the angiotensin-converting enzyme inhibitor ramiprilat and the contribution of nitric oxide, bradykinin, and prostaglandins to this vasodilation.

METHODS AND RESEARCH

In seven anesthetized dogs, a Doppler guidewire was placed in the circumflex coronary artery to measure coronary flow velocity, and an ultrasound imaging catheter was introduced over the Doppler wire to measure coronary cross-sectional area. Drugs were infused directly into the left main coronary artery to minimize systemic effects. Ramiprilat increased both epicardial cross-sectional area and coronary blood flow velocity, resulting in an increase in absolute coronary blood flow. Pretreatment with N omega-nitro-L-arginine methyl ester (100 micromol/L intracoronary) to block nitric oxide synthase attenuated ramiprilat-induced increase in epicardial coronary cross-sectional area (P<.05) but not in coronary flow velocity or coronary blood flow. In contrast, pretreatment with the selective bradykinin antagonist HOE 140 (10 micromol/L) attenuated ramiprilat-induced increase in flow velocity (P<.025) and coronary blood flow (P<.05) but not epicardial coronary cross-sectional area. Pretreatment with indomethacin (5 mg/kg body wt IV) did not alter ramiprilat-induced increase in epicardial cross-sectional area, nor did it significantly influence coronary blood flow.

CONCLUSIONS

Other than decreasing angiotensin II production, acute ramiprilat-induced vasodilation in canine coronary conductance arteries is mediated in part by nitric oxide. Ramiprilat-induced vasodilation in resistance arteries is in part mediated by the action of bradykinin.

Influence of captopril on nitroglycerin-mediated vasodilation and development of nitrate tolerance in arterial and venous circulation

We investigated whether captopril is able to potentiate vasodilation and prevent tolerance to a 48-hour infusion of nitroglycerin (NTG). Twenty-six patients were randomly assigned to a 7-day regimen of captopril (50 mg/day) or placebo. The hemodynamic response to a 0.8 mg sublingual NTG dose was assessed by measuring mean arterial pressure (MAP), mean pulmonary artery pressure (PAP), pulmonary capillary wedge pressure (PCWP), right atrial pressure (RAP), and cardiac output (CO), and calculating systemic (SVR) and pulmonary vascular resistances (PVR). The parameters were obtained serially at baseline and 1 to 10 minutes after the sublingual NTG application (day 1). Then intravenous NTG was started and maintained for 48 hours (1.5 micrograms/kg/min), and the hemodynamic study was repeated (day 3). There was no difference between the captopril and the placebo groups at day 1 (baseline values and response to sublingual NTG). After the 48-hour infusion, there was a complete loss of the NTG effects in the placebo group (day 1 vs day 3: PAP, 20 +/- 5 mm Hg vs 21 +/- 8 mm Hg; MAP, 86 +/- 11 mm Hg vs 90 +/- 9 mm Hg; SVR, 1295 +/- 330 mm Hg vs 1380 +/- 465 dyne.sec.cm-5) whereas there was still evidence of a persistent vasodilation in the captopril group (day 1 vs day 3: PAP, 19 +/- 4 mm Hg vs 13 +/- 4 mm Hg; MAP, 84 +/- 9 mm Hg vs 74 +/- 10 mm Hg; SVR, 1265 +/- 280 mm Hg vs 1140 +/- 425 dyne.sec.cm-5). The response to sublingual NTG on day 3 was markedly attenuated in the placebo group only. We conclude that captopril does not increase the vasodilatory response to nitroglycerin but is able to prevent developing nitrate tolerance in arterial and venous circulation.

N-acetylcysteine in combination with nitroglycerin and streptokinase for the treatment of evolving acute myocardial infarction. Safety and biochemical effects

BACKGROUND

N-acetylcysteine (NAC) has been shown to potentiate the effects of nitroglycerin (NTG) and to have antioxidant activity. This is the first study to assess the safety and effect of NAC in the treatment of evolving acute myocardial infarction (AMI).

METHODS AND RESULTS

Patients with AMI received either 15 g NAC infused over 24 hours (n = 20) or no NAC (n = 7), combined with intravenous NTG and streptokinase. Peripheral venous plasma malondialdehyde (MDA), reduced (GSH) and oxidized (GSSG) glutathione concentrations, and rate of reperfusion (using continuous ST-segment analysis) were measured. Cardiac catheterization was performed between days 2 and 5. No significant adverse events occurred. Less oxidative stress occurred in patients treated with NAC than in patients not receiving NAC (GSH to GSSG ratio 44 +/- 25 versus 19 +/- 13 at 4 hours, P < .05). NAC concentration (mean 172 +/- 79 mumol/L at 4 hours) was correlated to GSH concentration (P = .006). MDA concentrations were lower (P = .001) over the first 8 hours of treatment with NAC. There was a trend toward more rapid reperfusion (median 58 minutes, 95% confidence interval [CI] 48 to 98 minutes versus median 95 minutes, 95% CI 59 to 106 minutes; P = .17) and better preservation of left ventricular function (cardiac index 3.4 +/- 0.8 versus 2.6 +/- 0.27 L.min.m2, P = .009) with NAC treatment.

CONCLUSIONS

NAC in combination with NTG and streptokinase appeared to be safe for the treatment of evolving AMI and was associated with significantly less oxidative stress, a trend toward more rapid reperfusion, and better preservation of left ventricular function.

Hyperactive tissue renin-angiotensin systems in cardiovascular dysfunction: experimental evidence and clinical hypotheses

In this review, hypotheses are discussed with regard to the role of local, tissue renin-angiotensin systems in the progression of cardiovascular dysfunction. After local renin-angiotensin systems had been described as functionally distinct systems, recent experimental studies have suggested an association between hyperactivity of these local renin-angiotensin systems, and cardiovascular dysfunction. Moreover, the existence of these local renin- angiotensin systems has been confirmed in humans, and early data indicate that the human cardiac renin-angiotensin system may be activated in heart disease. Furthermore, polymorphisms in genes coding for the renin-angiotensin system seem associated with hypertension and left ventricular hypertrophy. These observations may be clinically relevant as inhibition of local renin-angiotensin systems may be an important prerequisite to obtain an optimal clinical effect.

Nitric oxide and nitrovasodilators: similarities, differences and potential interactions

Many similarities exist between the exogenous nitrates and endothelium-derived relaxing factor, which is nitric oxide or a thiol derivative. Both act by way of guanylate cyclase, which increases intracellular concentrations of cyclic guanosine monophosphate, resulting in smooth muscle cell relaxation and antiplatelet effects. Thiols may be important in the biotransformation of exogenous nitrates and other intracellular processes involving nitric oxide. As such, important interactions might be expected between nitrates and endothelium-dependent processes that involve nitric oxide. This review explores the mechanisms of action, biologic effects and potential interactions between nitrates and endothelium-derived relaxing factor.

Potentiation of isosorbide dinitrate effects with N-acetylcysteine in patients with chronic heart failure

BACKGROUND

Supply of sulfhydryl groups with the administration of N-acetylcysteine (NAC) has been reported to reverse tolerance to nitroglycerin but not to isosorbide dinitrate (ISDN). Lack of interaction between NAC and ISDN was suggested as an explanation for these findings. The present study was therefore designed to further evaluate this hypothesis. For this purpose, we compared the hemodynamic and hormonal effects of ISDN when given alone and in combination with NAC.

METHODS AND RESULTS

We performed a randomized, cross-over design evaluation of the hemodynamic and hormonal effects of ISDN and ISDN + NAC in 14 patients with chronic congestive heart failure due to left ventricular systolic dysfunction. The findings of this study demonstrated a substantial NAC-mediated potentiation of ISDN effect on mean right atrial pressure (-11 +/- 21% versus -38 +/- 27%, -17 +/- 20% versus -34 +/- 27%, and -7 +/- 20% versus -25 +/- 26% at 2, 3, and 4 hours, respectively; all P < .05), mean pulmonary artery wedge pressure (-18 +/- 16% versus -33 +/- 14%, -15 +/- 25% versus -33 +/- 19%, -14 +/- 22% versus -25 +/- 22%, and -16 +/- 16% versus -26 +/- 16% at 2, 3, 4, and 5 hours, respectively; all P < .05), mean pulmonary artery pressure (-8 +/- 11% versus -20 +/- 15% at 3 hours, P < .05), and cardiac output (an increase of 2 +/- 16% versus 25 +/- 20% at 4 hours, P < .05). Although there were no significant changes in serum catecholamine levels and plasma renin concentration with both regimens, ISDN + NAC resulted in a greater fall in plasma levels of atrial natriuretic peptide (296 +/- 251 pg/mL after ISDN versus 202 +/- 118 pg/mL after ISDN + NAC, P < .05).

CONCLUSIONS

The results of this study provide strong evidence for the existence of an interaction between thiols and ISDN and further support the role of sulfhydryl groups in the activation and therapeutic action of organic nitrates. The discrepancy between the results of this study demonstrating NAC-induced potentiation of ISDN effects and a previous study showing failure to reverse ISDN tolerance with NAC may suggest that ISDN-NAC interaction requires normal intracellular levels of sulfhydryl groups and does not occur after intracellular sulfhydryl group depletion.