ACE inhibition attenuates sympathetic coronary vasoconstriction in patients with coronary artery disease

BACKGROUND

In humans, angiotensin converting enzyme (ACE) inhibition attenuates the vasoconstriction induced by sympathetic stimulation in a number of peripheral districts. Whether this is also the case in the coronary circulation is unknown, however.

METHODS AND RESULTS

In nine normotensive patients with angiographically assessed coronary atherosclerosis, we measured the changes in mean arterial pressure (intra-arterial catheter), heart rate, rate-pressure product (RPP), coronary sinus blood flow (CBF, thermodilution method), and coronary vascular resistance (CVR, ratio between mean arterial pressure and CBF) induced by the cold pressor test (CPT, 2 minutes) and diving (30 seconds), i.e., two stimuli eliciting a sympathetic coronary vasoconstriction. The measurements were performed in the control condition and 30 minutes after captopril 25 mg p.o. In the control condition, CPT caused an increase in mean arterial pressure and heart rate. Despite the increase in RPP (+20.7 +/- 3.2%, p less than 0.01), CBF did not change and CVR increased (+12.2 +/- 4.0%, p less than 0.05). diving caused an increase in mean arterial pressure and a reduction in heart rate. RPP increased (+14.3 +/- 3.5%, p less than 0.01), but despite this increase, there was a reduction in CBF and a marked increase in CVR (+37.3 +/- 7.4%, p less than 0.01). Captopril did not modify the blood pressure and heart rate responses to both stimuli except for a slight accentuation of the bradycardia to diving. Despite the unchanged or only slightly reduced RPP response, the increase in CVR was markedly and significantly attenuated (p less than 0.01).

CONCLUSIONS

ACE inhibition attenuates sympathetic coronary vasoconstriction in patients with coronary artery disease. This is probably due to removal of the facilitating influence of angiotensin II on sympathetic modulation of coronary vasomotor tone.

Neurohumoral changes and the inducibility of ventricular tachycardias: effect of early reperfusion on the ischemic porcine myocardium

The effects of early reperfusion were studied in closed-chest pigs subjected to either 45 min or 3 hr of regional ischemia. Myocardial enzyme release during early reperfusion and electrophysiological stability after two weeks were assessed. Coronary artery occlusion durations of 3 hr and early reperfusion after 45 min were compared. The creatine phosphokinase levels in the coronary effluent were lower after early reperfusion (p less than 0.001). Moreover, in the early reperfusion group, the coronary sinus catecholamine and purine levels rose to higher values than in the 3 hr group. The plasma levels of catecholamines and the plasma renin activity increased rapidly but transiently at reperfusion in the 45 min group. Both the rate-pressure product and the heart rate were elevated at the end of the reperfusion period (p less than 0.001) in the 45 min group. Survival for two weeks was 3 out of 6 animals in the 3 hr group and 5 out of 8 in the 45 min group. In all but one surviving animal, sustained ventricular tachycardias were inducible by programmed stimulation. Abnormally low QRS amplitudes and delayed potentials were found in the signal-averaged electrocardiogram in the early reperfusion group only. In conclusion, early reperfusion causes a reduction of myocardial tissue damage, but simultaneously, neurohumoral parameters showed a greater activation of the sympathetic nervous system and the renin-angiotensin system apparently causing a deleterious increase in oxygen consumption. Therefore, this injurious component of early reperfusion might prevent the potentially beneficial effects of a reduced tissue damage on survival or late arrhythmias.

Coronary vasodilation induced by captopril and zofenoprilat: evidence for a prostaglandin-independent mechanism

In this study, the vasodilating properties of captopril and zofenoprilat, two angiotensin-converting enzyme (ACE) inhibitors containing the sulfhydryl group, are investigated in the isolated rat heart. It is demonstrated that both compounds increase coronary flow in a dose-dependent manner. However, the mean pD2 of zofenoprilat appears to be significantly higher than the mean pD2 of captopril (4.55 +/- 0.06 and 3.35 +/- 0.02 respectively), indicating that zofenoprilat is about ten times more potent in increasing coronary flow than captopril. Possibly this difference in potency between captopril and zofenoprilat can be explained by their physicochemical properties. Since zofenoprilat is more lipophilic than captopril, its concentration in cardiac and vascular tissues at distribution equilibrium is thought to be higher than the tissue concentration of captopril, which may result in a more pronounced vasodilatory action. The precise mechanism of coronary vasodilation induced by ACE inhibitors containing the sulfhydryl group is not yet understood. Several factors have been proposed, such as stimulation of prostacyclin production. However, in this study, concomitant administration of 10(-6) mol/l acetylsalicylic acid shows no antagonism, indicating that under normoxic conditions the vasodilatory effects of captopril and zofenoprilat are independent of the production of vasodilating prostaglandins. Therefore, other factors than stimulation of prostacyclin synthesis seem to be involved, such as prevention of bradykinin breakdown and/or potentiation of endothelium derived relaxing factor (EDRF). Furthermore, despite a marked inhibition of prostacyclin production, 10(-6) mol/l acetylsalicylic acid itself has no effect on coronary flow. These results suggest that prostacyclin does not play an important role in the regulation of coronary flow, at least in the normoxic isolated rat heart.

Effects of bradykinin on inducible sustained ventricular tachycardia two weeks after myocardial infarction in pigs

We studied the in vivo effect of bradykinin infusion on inducible sustained ventricular tachycardia (VT) 2 weeks after myocardial infarction in pigs, based on the assumption that the antiarrhythmic effect of angiotensin-converting enzyme (ACE) inhibitors may, apart from their angiotensin-II lowering effect, also be due to elevation of endogenous bradykinin levels. Of the six pigs with inducible VT in the control state, four were noninducible during subsequent bradykinin infusion (p less than 0.05). The ventricular effective refractory period (VERP) did not change during bradykinin infusion (from 237 +/- 37 to 239 +/- 42 ms), nor did intraventricular conduction change (filtered QRS duration was 45 +/- 17 ms before and 43 +/- 19 ms during infusion). Bradykinin caused both a significant systolic blood pressure (SBP) decrease (from 79 +/- 14 to 49 +/- 4 mm Hg, p less than 0.001) and diastolic BP (DBP) decrease (from 41 +/- 10 to 27 +/- 4 mm Hg, p less than 0.01). In conclusion, exogenous bradykinin reduced the inducibility of sustained VT 2 weeks after myocardial infarction. Because refractory periods or conduction velocity were not affected, the mechanism of action might be associated with the BP decrease, which can decrease wall stress. The previously reported antiarrhythmic effect of ACE inhibitors may be due in part to elevation of endogenous bradykinin levels.

In vivo effect of bradykinin during ischemia and reperfusion: improved electrical stability two weeks after myocardial infarction in the pig

In this study, the effect of bradykinin or saline infusion during ischemia and reperfusion on electrical stability, 2 weeks after myocardial infarction, was assessed. Acute myocardial infarction was induced in 21 pigs by a transluminal occlusion of the left coronary artery with a catheter balloon, inflated for 45 min. Bradykinin was administered by a 30-min infusion that started after 30 min of coronary occlusion and was continued until 15 min after reperfusion. Although creatine kinase levels in bradykinin-treated animals were significantly lower (p less than 0.001), 2 week survival was not different between groups. In survivors, the filtered QRS (ventricular deflection) duration (detected using signal-averaged electrocardiography) was significantly prolonged in saline-treated pigs, whereas in bradykinin-treated pigs this prolongation was prevented. The terminal voltage of the QRS complex was significantly lower in saline-treated pigs than in bradykinin-treated pigs. These two parameters signify an improved electrical stability after bradykinin treatment. Refractory periods in saline-treated hearts were longer than in bradykinin-treated hearts (106 +/- 10% vs. 95 +/- 13%, p less than 0.05). Also, current thresholds in the infarct border zones showed a greater variance in saline-treated hearts (p less than 0.001), pointing toward more tissue heterogeneity of the infarct border zone. Programmed electrical stimulation showed a trend toward reduced inducibility of sustained ventricular tachycardia in bradykinin-treated hearts. Therefore, bradykinin improves electrical stability weeks after experimental myocardial infarction.

Beneficial effects of bradykinin on porcine ischemic myocardium

Exogenous bradykinin was administered to pigs in which an experimental infarction was evoked by ischemia and reperfusion. Ischemia (45 min) was induced in a closed-chest model with a balloon catheter in the left anterior descending artery, reperfusion by deflating and removing the balloon. The pigs were treated with saline (n = 11) or bradykinin (0.1 mg/kg in 30 min) infusion (n = 10) during the last 15 min of the ischemic period and the first 15 min of reperfusion. During ischemia, heart rate increased in the saline group to 120 +/- 9% of the initial value (p less than 0.05) and in the bradykinin group to 155 +/- 13% (p less than 0.05). After reperfusion, the rate-pressure product was increased in both groups. The increase of arterial creatine kinase levels was significantly less in the bradykinin-treated group. However, the catecholamine and purine levels were increased, as was the plasma renin activity when compared with the saline group. Two weeks after the infarction, six pigs had died in each group. In three out of five surviving saline-treated pigs and one out of four surviving bradykinin-treated pigs, a sustained ventricular tachyarrhythmia was inducible after programmed electrical stimulation. In conclusion, although systemically administered bradykinin caused a temporary increase in myocardial ischemia, it did reduce the (enzymatic indices of) infarct size. Therefore, the beneficial effects, previously found for ACE-inhibitors might at least partially be related to the potentiation of endogenous bradykinin.

The effects of oral pretreatment with zofenopril, an angiotensin-converting enzyme inhibitor, on early reperfusion and subsequent electrophysiologic stability in the pig

The effects of oral zofenopril pretreatment were investigated in a chronic closed-chest pig model of ischemia and reperfusion. Pigs (25-35 kg) were pretreated orally with zofenopril (15 mg/day) on the 2 days prior to ischemia, which was evoked by the inflation of a catheter balloon in the left anterior descending coronary artery over 45 minutes. The catheter was then removed and the myocardium was reperfused. After 2 weeks, infarct properties were assessed by signal averaging of the body surface electrocardiogram and the inducibility of malignant ventricular tachyarrhythmias was tested with a programmed electrical stimulation protocol. A significant increase in the pressure-rate product (43 +/- 11%, mean +/- SEM), indicating the oxygen demand of the heart, was prevented by zofenopril (19 +/- 8%, p less than 0.05). Zofenopril reduced the peak efflux of adrenaline (1302 +/- 213 vs. 3201 +/- 760 pg/ml; p less than 0.05), noradrenaline (402 +/- 54 vs. 902 +/- 282 pg/ml; p less than 0.05), and of the adenosine catabolites inosine and hypoxanthine (56 +/- 4 vs. 78 +/- 9, pg/ml; p less than 0.05) in the coronary venous effluent. The efflux of the cytoplasmatic enzyme creatine phosphokinase was not significantly reduced after zofenopril (p = 0.08). No difference in plasma renin levels between the groups were found. After 2 weeks, late potentials were found only in the surviving animals from the untreated group, i.e., the voltage vector magnitude was more reduced, and a prolongation of the QRS duration and of the terminal low-amplitude part of the high-frequency QRS were found.(ABSTRACT TRUNCATED AT 250 WORDS)

Basic pharmacology of ACE-inhibitors with respect to ischaemic heart disease: prostaglandins and bradykinin

Experimental evidence suggests that ACE-inhibitors possess cardioprotective properties. Since ACE-inhibitors can prevent bradykinin breakdown and can stimulate prostaglandin production, it is thought that these cardioprotective effects are mediated by bradykinin and prostaglandins. This article summarizes the results indicating that bradykinin and prostaglandins, although not the only factors, do play an important role in cardioprotection by ACE-inhibitors. Special attention is paid to the presence of the sulphydryl moiety of certain ACE-inhibitors. Probably, these sulphydryl group-containing ACE-inhibitors have an additional protective effect through an interaction with bradykinin or through scavenging of free radicals. However, these cardioprotective effects have not yet been shown in patients with ischaemic heart disease, although some studies indicate that ACE-inhibitors are also able to cause anti-ischaemic effects in patients. Further studies are required to establish the clinical importance of cardioprotection by ACE-inhibitors in ischaemic heart disease.

Effects of isradipine on hemodynamic parameters and ventricular tachycardia in healed myocardial infarction

The calcium-entry blocker isradipine was tested in a closed-chest pig model for chronic myocardial infarction. Ischemia was evoked in anesthetized pigs (25-35 kg) by inflating a catheter balloon in the left anterior descending coronary artery for at least 45 min. Hemodynamic monitoring and signal averaging of X, Y, and Z electrocardiographic leads were performed (150 beats, filtered at 50 Hz). After reperfusion, all animals developed an accelerated idioventricular rhythm and high creatine kinase (CPK) plasma levels. Coronary venous purines and catecholamines increased transiently. Two hours after reperfusion, heart rate was elevated from the initial 87.5 +/- 6.3 to 126 +/- 6.4 beats/min (p less than 0.01) and the pressure-rate product (PRP, an index of oxygen demand) from 9,530 +/- 630 to 11,950 +/- 790 mm Hg/min (p less than 0.05). After 2 weeks, six surviving pigs had a decreased stroke volume (98 +/- 18 versus the initial 124 +/- 14 microliters/kg, p less than 0.05), a prolonged high-frequency signal-averaged QRS duration (81.2 +/- 6.5 versus 65.7 +/- 2.9 ms, initially; p less than 0.05), and ventricular tachycardias (VTs), inducible by programmed electrical stimulation (PES). After the infusion of isradipine (1 microgram/kg/min for 30 min), the cardiac index increased from 92 +/- 14 to 133 +/- 8.7 ml/min.kg (p less than 0.02). Even at a higher heart rate, the PRP dropped from 12,600 +/- 1,900 to 10,560 +/- 1,400 mm Hg/min (p less than 0.05). Sustained monomorphic tachycardias were inducible in five pigs before and in three pigs after isradipine, and no deterioration of the signal-averaged electrocardiogram parameters was found.(ABSTRACT TRUNCATED AT 250 WORDS)

The haemodynamic effects of two angiotensin converting enzyme inhibitors, enalaprilat and zofenoprilat, in the rat: evidence for the involvement of bradykinin

Since angiotensin converting enzyme (ACE) metabolizes bradykinin, the hypotensive effect of ACE inhibitors could be partly due to an increased bradykinin activity. We therefore investigated the influence of HOE K86-4321 [D-Arg-(Hyp2-Thi5,8-DPhe7)-bradykinin], a selective bradykinin-2 receptor antagonist, on the effects of enalaprilat (0.3 and 3.0 mg/kg) and zofenoprilat (0.1 and 1.0 mg/kg) on the heart rate, mean arterial blood pressure, cardiac output and total peripheral resistance in rats. Both enalaprilat and zofenoprilat reduced mean arterial pressure (from 110 +/- 7 to 85 +/- 6 and from 108 +/- 9 to 72 +/- 9 mmHg, respectively; P less than 0.05) and total peripheral resistance (from 515 +/- 35 to 413 +/- 29 and from 495 +/- 45 to 310 +/- 25 x 10(-3) mmHg/litre per min per kg, respectively; P less than 0.05); the heart rate and cardiac output changed little. In the presence of HOE K86-4321, which by itself did not affect the haemodynamic variables measured, the effects of the two ACE inhibitors were significantly reduced. These results suggest that bradykinin-2 receptor-mediated vasodilation, although not involved in blood pressure regulation, influences the reduction in blood pressure induced by enalaprilat and zofenoprilat in normotensive rats. Furthermore, at comparable ACE-inhibiting doses, zofenoprilat was more effective in reducing mean arterial pressure, which might be related to the presence of a sulphydryl group.