Allopurinol and amlodipine improve coronary vasodilatation after myocardial ischaemia and reperfusion in anaesthetized dogs.

1. We have assessed the effect of allopurinol, amlodipine and propranolol pretreatment on both endothelium-dependent and endothelium-independent coronary vasodilatation in vivo, by comparing pre-ischaemic responses with those measured after 60 min of coronary artery occlusion and 30 min of reperfusion in anaesthetized dogs. 2. In 15 untreated dogs ischaemia and reperfusion attenuated the increases in coronary blood flow produced by either acetylcholine (0.01-0.05 micrograms kg-1, i.a.) or glyceryl trinitrate (0.05-0.2 micrograms kg-1, i.a.), to an average of 39 +/- 4% and 42 +/- 5% of the pre-ischaemic control response, respectively (both P < 0.05). 3. In 5 dogs treated with allopurinol (25 mg kg-1, orally, 24 h previously, plus 50 mg kg-1, i.v., 5 min before occlusion), the increases in coronary blood flow after ischaemia and reperfusion (acetylcholine: 78 +/- 12%, glyceryl trinitrate: 60 +/- 3% of pre-ischaemic response) were significantly larger than post-ischaemic responses in untreated dogs (both P < 0.05). 4. Similarly, amlodipine treatment (3 micrograms kg-1 min-1, i.v., starting 90 min before occlusion) in 5 dogs improved post-ischaemic increases in blood flow (acetylcholine: 58.5%, glyceryl trinitrate: 66 +/- 6% of pre-ischaemic response, significantly greater than post-ischaemic responses in untreated dogs, P < 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)     

Mechanisms underlying endothelium-dependent,nitric oxide- and prostanoid-independent relaxation in monkey and dog coronary arteries

We compared the mechanisms of vasorelaxation of acetylcholine and of substance P with reference to K(+) channels, and analyzed pharmacologically the nature of endothelium-derived substance(s) other than NO and prostanoids in monkey and dog coronary arteries. Coronary arteries were isolated from monkeys and dogs, and the isometric tension of the artery strips was measured. In canine coronary artery strips treated with indomethacin plus N(G)-nitro- L-arginine ( L-NA) and partially contracted with prostaglandin F(2alpha), acetylcholine induced concentration-related relaxation, which was abolished by removal of the endothelium. The relaxation was markedly suppressed but not abolished in the strips exposed to high K(+) media. Charybdotoxin plus apamin potently inhibited the relaxation to the similar extent to that by high K(+) media, whereas glibenclamide or iberiotoxin had no effect. The relaxation was markedly inhibited by quinacrine, a phospholipase A(2) inhibitor, and ketoconazole, a selective cytochrome P450 (CYP) 3A inhibitor, but not by sulfaphenazole, a selective CYP 2C inhibitor. In contrast to acetylcholine, endothelium-dependent and indomethacin-plus- L-NA-resistant relaxation induced by substance P was not inhibited by high K(+) media, charybdotoxin plus apamin, or ketoconazole. Quinacrine and AA861, a 5-lipoxygenase inhibitor, inhibited the relaxation induced by substance P. In monkey coronary artery, acetylcholine-induced relaxation resistant to indomethacin plus L-NA was abolished by endothelial denudation and by treatment with high K(+) media, charybdotoxin plus apamin, progesterone and ketoconazole, but was not affected by iberiotoxin or sulfaphenazole. Substance P did not relax monkey coronary arteries. It is concluded that endothelium-dependent, nitric oxide- and prostanoid-independent relaxation induced by acetylcholine in monkey and dog coronary arteries are mediated by charybdotoxin plus apamin-sensitive but iberiotoxin-insensitive Ca(2+)-activated K(+) channel opening substance(s), which may be CYP3A-derived arachidonic acid metabolite(s). Contrasting to the response to acetylcholine, endothelium-dependent, indomethacin-plus- L-NA-resistant relaxation induced by substance P in dog coronary artery is not associated with K(+) channel opening, and may be mediated by 5-lipoxygenase product(s).     

Enhanced role for the opening of potassium channels in relaxant responses to acetylcholine after myocardial ischaemia and reperfusion in dog coronary arteries

1. Anaesthetized dogs were subjected to 1 h occlusion of the left circumflex coronary artery followed by 2 h of reperfusion. Relaxant responses were examined in coronary artery rings removed proximal (nonischaemic) or distal (ischaemic) to the site of occlusion. 2. Relaxant responses to acetylcholine (ACh) were similar in nonischaemic and ischaemic artery rings. In addition ACh-induced relaxation of nonischaemic and ischaemic artery rings was equally susceptible to inhibition of nitric oxide (NO) synthase using L-N(G)-nitroarginine (L-NOARG, 10(-4) M), or to inhibition of soluble guanylate cyclase using 1H-[1,2,4]oxadiazolo[4,3-a]quinoxaline-1-one (ODQ, 10(-5) M). 3. In nonischaemic arteries, the relaxation to ACh was unaffected by high K+ (67 mM) but in ischaemic arteries, the maximum relaxation to ACh was significantly reduced from 113+/-6 to 60+/-2% (ANOVA, P<0.05). Tetraethylammonium (TEA, 10(-3) M), an inhibitor of large conductance calcium activated potassium (BK(Ca)) channels did not inhibit the response to ACh in nonischaemic arteries but in ischaemic arteries TEA significantly shifted the concentration response curve to ACh to the right (pEC(50); nonischaemic, 7.07+/-0.25; ischaemic, 6.54+/-0.21, P<0.01, ANOVA) without decreasing the maximum relaxation. TEA did not affect the responses to sodium nitroprusside in either nonischaemic or ischaemic arteries. 4. In conclusion, ischaemia/reperfusion did not change the sensitivity of endothelium-dependent relaxation to L-NOARG or ODQ indicating that ischaemia did not affect the contribution of NO or cyclic GMP to ACh-induced relaxation. However, in ischaemic arteries the opening of the BK(Ca) channels contributed to relaxation caused by ACh whereas TEA had no effect in nonischaemic arteries. The factor responsible for the opening of this potassium channel was a factor other than NO and may be endothelium derived hyperpolarizing factor (EDHF).     

Approaches to the prevention of coronary vascular dysfunction caused by myocardial ischaemia and reperfusion

The endothelium is an important regulator of coronary vascular tone due to its ability to release potent vasoactive substances such as the vasodilators nitric oxide (NO), endothelium-derived hyperpolarizing factor (EDHF), prostacyclin (PGI2) and the potent vasoconstrictor endothelin. Endothelial dysfunction has been associated with a number of pathological states such as atherosclerosis, hypertension, diabetes and congestive heart failure. A disturbance of endothelial function may also contribute to the adverse effects that ischaemia and reperfusion exerts on the coronary vasculature. After ischaemia and reperfusion there is usually a selective impairment of endothelium-dependent relaxation in isolated coronary arteries. However, in the intact coronary circulation, there is a general loss of vasodilator reserve as responses to both endothelium-dependent and endothelium-independent agonists are attenuated. The release of vasoconstrictor(s) and plugging of capillaries with leukocytes may contribute to that impairment of the capacity of the coronary circulation to dilate together with the reduction in basal blood flow (no-reflow phenomenon). Ischaemic preconditioning is able to prevent ischaemic damage to the myocardium but the vasculature is less well protected as reperfusion is enhanced but the vasodilator reserve continues to be limited. Pharmacological preservation of vascular function has proved more successful with inhibitors of leukocyte adhesion, calcium channel blockers, endothelin receptor antagonists and inhibitors of oxygen radical generation all offering protection. Further refinement of protocols to preserve endothelial and vascular function after ischaemia will aid reperfusion, enhance vasodilator reserve and maximise recovery of myocardial function.     

Impaired endothelium-dependent relaxation in isolated resistance arteries of spontaneously diabetic rats.

1. Previous studies have shown that endothelium-dependent relaxation in the aorta of spontaneously diabetic bio bred rats (BB) is impaired. 2. We have investigated noradrenaline (NA) contractility, endothelium-dependent acetylcholine (ACh) and bradykinin (BK) relaxation, and endothelium-independent sodium nitroprusside (SNP) relaxation in mesenteric resistance arteries of recent onset BB rats and established insulin treated BB rats, compared to their age-matched non diabetic controls. 3. There was no significant difference in the maximum contractile response or sensitivity to noradrenaline in either of the diabetic groups compared to their age-matched controls. 4. Incubation with the nitric oxide synthetase inhibitor NG-nitro-L-arginine (L-NOARG) resulted in a significant increase in maximum contractile response to noradrenaline in the recent onset age-matched control group (P < 0.05). Analysis of the whole dose-response curve (using ANOVA for repeated measures with paired t test) showed a significant left-ward shift following the addition of L-NOARG (P < 0.001). A similar but less marked shift (P < 0.01) was evident in vessels from recent onset diabetics. An overall shift in both sensitivity and maximum response was also evident in the age-matched non diabetic controls of the insulin-treated group (P < 0.05). However, by contrast, there was no significant change in sensitivity in the insulin-treated diabetic rats. 5. ACh-induced endothelium-dependent relaxation was significantly impaired in the recent onset diabetic rats compared to their age-matched controls (47 +/- 11% versus 92 +/- 2%, P < 0.05, n = 6), and in the insulin treated diabetic rats (34 +/- 5% versus 75 +/- 6%, P < 0.05, n = 6). The relaxation responses to BK also were significantly impaired in the diabetic rats compared to their age-matched controls (recent onset: 20 +/- 3% versus 72 +/- 7%, P < 0.05, n = 6; insulin treated: 12 +/- 9% versus 68 +/- 7%, P < 0.05, n = 7). 6. Incubation with either the nitric oxide synthetase substrate, U-arginine, or the free radical scavenging enzyme superoxide dismutase (150 mu ml-1) failed to improve the attenuated response of acetylcholine-induced relaxation in the diabetic vessels. 7. Endothelium-dependent relaxation mediated by ACh and BK was significantly attenuated in both the diabetic and control vessels after incubation with L-NOARG. 8. Pretreatment with a cyclo-oxygenase inhibitor, indomethacin, significantly enhanced the relaxation to ACh in both the recent onset and insulin treated diabetic rats (42 +/- 10%, n = 7 versus 64 +/- 7%, n = 7, P < 0.05, and 40 +/- 5%, n = 7 versus 65 +/- 9%, n = 6, P < 0.05). 9. Following endothelium removal, there was a marked impairment in endothelium-dependent relaxation responses to ACh and BK in both the diabetic and control vessels. 10. Incubation with the thromboxane A2 receptor antagonist SQ29548, did not significantly improve the ACh endothelium-dependent relaxation response in the diabetic vessels. 11. Endothelium-independent relaxation to sodium nitroprusside was significantly impaired in the first group of diabetic vessels studied; however, subsequent studies showed no impairment of the sodium nitroprusside response in the diabetic vessels. 12. In conclusion, the ability of the endothelium to regulate vascular contractility is reduced in recent onset diabetic vessels, and significantly impaired in established insulin treated diabetics. Relaxation to the endothelium-dependent vasodilators ACh and BK was impaired in both the recent onset and the established insulin treated diabetics, and the ACh response was significantly improved following pretreatment with indomethacin, suggesting a role for a cyclo-oxygenase-derived vasoconstrictor. Preliminary studies with a thromboxane A2, receptor antagonist, SQ29548 did not significantly improve the impaired relaxation to ACh, indicating that the vasoconstrictor prostanoid is not thromboxane A2.     

Inhibition of thrombin-induced endothelium-dependent relaxation after coronary ischemia in the dog: possible role of the coagulation cascade.

Myocardial ischemia inhibits endothelium-dependent relaxation stimulated by the coagulant peptide, thrombin. To investigate whether activation of endogenous thrombin contributed to this reduction in relaxant sensitivity, the effects of pretreatment of dogs with the coumarin anticoagulant, brodifacoum, were studied. Experiments were performed in both normal coronary vasculature and coronary vasculature exposed to 90 min of myocardial ischemia, with or without 60 min of subsequent reperfusion. Ischemia was induced in the left anterior descending artery (LAD); nonischemic vessels from the left circumflex (LCX) artery of the same animals were used as control. Thrombin caused dose-dependent relaxation in isolated LCX preconstricted with prostaglandin F2 alpha (Emax of 89.1 +/- 2.33%). Relaxation was reduced by 90 min of ischemia (Emax of 27.5 +/- 8.0%; p less than 0.05), and further reduced after subsequent reperfusion (Emax of 8.7 +/- 8.7%). However, maximum relaxations to acetylcholine, calcimycin, and isoproterenol were unchanged after ischemia (Emax greater than 90% in all groups). Brodifacoum had no effect on thrombin-induced relaxation in control vessels (Emax of 83.0 +/- 3.5%), or on relaxation in response to acetylcholine, calcimycin, or isoproterenol (Emax greater than 90%). In contrast, brodifacoum markedly reduced thrombin-induced relaxation after ischemia (Emax of 3.3 +/- 3.3%; p less than 0.05) yet significantly preserved the relaxant response to thrombin after ischemia and reperfusion (Emax of 36.6 +/- 4.3%). Infusion of the thrombin inhibitor, D-phenylalanyl-L-prolyl-L-arginine chloromethyl ketone (PPACK), during ischemia and reperfusion also preserved in part the relaxant response induced by thrombin (Emax of 30.0 +/- 5.1%; p less than 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)     

The effects of propranolol and acebutolol on left ventricular function and coronary haemodynamics in the conscious dog with myocardial ischaemia.

1 The cardiovascular effects of the beta-adrenoceptor blocking drugs, propranolol and acebutolol, on regional coronary blood flow and left ventricular function have been investigated in the conscious dog with developing myocardial infarction. 2 Propranolol (1 to 1.5 mg/kg) or acebutolol (4 to 5 mg/kg) were administered intravenously 2 to 3 h after occlusion of the left anterior descending coronary artery. 3 Propranolol or acebutolol administration resulted in a relative increase in flow to the ischaemic area of the myocardium, particularly to the subendocardium. 4 Propranolol produced a greater reduction in heart rate and myocardial contractility than acebutolol. 5 These results demonstrate that beta-adrenoceptor blocking drugs reduce myocardial oxygen consumption and increase coronary flow to the ischaemic area of the myocardium after coronary artery occlusion in the conscious dog.     

Effects of allopurinol on myocardial ischemic injury induced by coronary artery ligation and reperfusion

The effects of allopurinol pretreatment (1 mg/ml in the drinking water for 7 days at an estimated daily dose of 75 mg/kg) on biochemical and chemical changes occurring following left circumflex coronary artery ligation (40 min) and reperfusion (60 min) were examined in pentobarbital-anesthetized rabbits. During the ischemic phase, allopurinol pretreatment provided significant preservation of cellular ATP levels and of mitochondrial ATP generation as compared with untreated animals (P less than 0.05). During the reperfusion phase, allopurinol pretreatment significantly prevented the decrease in left ventricular pressure, sodium and calcium accumulation and decreases in sarcolemmal Na+,K+-stimulated and sarcoplasmic reticulum K+,Ca2+-stimulated ATPase activities as compared with untreated animals (P less than 0.05). In contrast, the decrease in mitochondrial (azide-sensitive) ATPase during ischemia and the partial recovery during reperfusion were unaffected by allopurinol pretreatment. Our results indicate that the myocardial protective effects of allopurinol may differ mechanistically in the ischemic and reperfusion phases of injury. The fact that rabbit hearts do not contain detectable xanthine oxidase activity would seem to preclude an obligatory role of this enzyme both in the generation of myocardial ischemic/reperfusion injury and in the protective actions of allopurinol.     

Stereospecific antiarrhythmic effects of naloxone against myocardial ischaemia and reperfusion in the dog.

1. The effects of both the (-)- and (+)-stereoisomers of naloxone in anaesthetized dogs with arrhythmias induced by acute coronary artery occlusion followed by reperfusion were investigated. 2. Following coronary artery occlusion and reperfusion, all dogs in the control group developed ischaemia- and reperfusion-induced cardiac arrhythmias, bradycardia and hypotension. 3. The opiate antagonist (-)-naloxone prevented the arrhythmias, bradycardia and hypotension due to myocardial ischaemia and reperfusion. 4. The (+)-stereoisomer of naloxone, which is inactive as an opiate antagonist, was without beneficial effects. 5. These results indicate a possible involvement of endogenous opioid peptides in the cardiac effects due to myocardial ischaemia and reperfusion, mediated by opiate receptors through opiate antagonism.     

Myocardial and coronary endothelial protective effects of acetylcholine after myocardial ischaemia and reperfusion in rats: role of nitric oxide.

1. Recent experiments suggest that acetylcholine (ACh) may exert myocardial protective effects during ischaemia (I) and reperfusion (R). The present study was designed (i) to assess whether ACh limits infarct size and protects coronary endothelial cells in a rat model of I and R, (ii) to evaluate the role of ATP-sensitive potassium (KATP) channels and nitric oxide (NO) in the beneficial effect of ACh (iii) to evaluate whether the protective effect of ACh also extends to coronary endothelial cells and (iv) to assess whether ACh contributes to the beneficial effect of preconditioning. 2. Anaesthetized rats were subjected to 20 min I (left coronary artery occlusion) and 2 h of R. Infarct size was assessed by triphenyltetrazolium (TTC) staining and expressed as a % of the area at risk (India ink injection). Vascular studies were performed on 1.5-2 mm coronary segments (internal diameter 250-300 micros) removed distal to the site of occlusion and mounted in wire myographs. 3. ACh limited infarct size (from 59 +/- 3 to 26 +/- 5%, P < 0.01), and this was prevented by atropine (46 +/- 7%; P < 0.05 vs ACh), but not by the inhibitor of KATP channels, glibenclamide (29 +/- 8%). The inhibitor of NO synthesis NG-nitro L-arginine did not affect infarct size (54 +/- 5%) but abolished the beneficial effect of ACh (59 +/- 8%; P < 0.05 vs ACh), whereas the NO donor 3-morpholinosydnonimine-N-ethylcarbamide (SIN-1 limited infarct size to the same extent as ACh (28 +/- 6%).(ABSTRACT TRUNCATED AT 250 WORDS)     

Antagonism by droperidol of dopamine-induced relaxation in isolated dog arteries.

Dopamine caused a dose-related relaxation in helically cut strips of dog coronary and renal arteries treated with phenoxybenzamine andcontracted with prostaglandin F2 alpha. The dose-response curve to dopamine was shifted to the right by droperidol in concentrations above 3 X 10(-5) M. Adenosine-induced relaxations were not attenuated by droperidol. The dose--relaxation curve to isoproterenol was also shifted to the right by droperidol. Propranolol (10(-6) M) failed to significantly alter the dose response curve to dopamine, and in propranolol-treated preparations the antagonism by droperidol of dopamine actions was practically identical with that in control preparations. Droperidol appears to act as a reversible, surmountable antagonist to dopamine actions on dog arterial smooth muscles, and such evidence supports the hypothesis of specific dopamine receptors in dog arteries.     

Involvement of nitric oxide in endothelium-dependent, phasic relaxation caused by histamine in monkey cerebral arteries.

Monkey cerebral artery strips partially contracted with prostaglandin F2 alpha responded to histamine with biphasic patterns of relaxation. The delayed and sustained relaxation was suppressed by cimetidine, whereas the phasic response was abolished by treatment with chlorpheniramine and NG-nitro-L-arginine (L-NA), a nitric oxide (NO) synthase inhibitor. The inhibition by L-NA was reversed by L-arginine. D-NA was without effect. Endothelium denudation abolished the phasic relaxation. We hypothesized that endothelium-dependent, phasic relaxations caused by histamine are mediated by NO that is released by H1-receptor stimulation, whereas the sustained relaxation is associated with the activation of H2-receptors in the smooth muscle of monkey cerebral arteries.     

Role of endogenous endothelin in myocardial and coronary endothelial injury after ischaemia and reperfusion in rats: studies with bosentan, a mixed ETA-ETB antagonist.

1. Previous studies suggested that endothelin-1 (ET-1) may play a role in myocardial ischaemia and reperfusion. This study was designed to test the effect of a new nonpeptide antagonist of endothelin ETA and ETB receptors, bosentan, on myocardial infarct size, ventricular arrhythmias, and coronary endothelial dysfunction after ischaemia and reperfusion. 2. Anaesthetized male Wistar rats were subjected to 20 min ischaemia (left coronary artery occlusion) followed by 1 h (for the evaluation of coronary endothelial dysfunction) or 2 h (for the evaluation of infarct size) reperfusion, or 5 min ischaemia followed by 15 min reperfusion (for the evaluation of reperfusion arrhythmias). Vascular studies were performed on 1.5-2 mm coronary segments (internal diameter 250-300 microns) removed distal to the site of occlusion and mounted in wire myographs for isometric tension recording. Area at risk and infarct size were determined by Indian ink injection and triphenyl tetrazolium staining, using computerized analysis of enlarged sections after colour video acquisition. 3. Bosentan, administered at a dose which virtually abolished the pressor response to big ET-1 (3 mg kg-1, i.v. before ischaemia) did not affect heart rate, arterial pressure or the rate pressure product before ischaemia, during ischaemia and during reperfusion. Bosentan did not affect the incidence of reperfusion-induced ventricular fibrillation (controls: 86%, n = 14; bosentan: 93%, n = 15), and did not modify infarct size (% of area at risk: controls: 63 +/- 4, n = 10; bosentan: 60 +/- 6, n = 8).(ABSTRACT TRUNCATED AT 250 WORDS)     

Endothelium-dependent relaxation induced by angiotensin II and histamine in isolated arteries of dog.

In helical strips of dog renal and mesenteric arteries pre-contracted with prostaglandin F2 alpha (PGF2 alpha), endothelium-dependent relaxations were investigated. Removal of the endothelium was shown histologically by staining with silver nitrate and functionally by testing the inability of acetylcholine to induce arterial relaxations. When the endothelium was removed, relaxation of renal arteries to angiotensin (Ang) II was markedly suppressed, whereas relaxations induced by PGI2 or isoprenaline were attenuated only slightly. Removal of the endothelium attenuated the relaxant response of mesenteric arteries to histamine but did not significantly alter the response to PGI2. Treatment with indomethacin caused an additional attenuation of the relaxant response to histamine or a reversal of the Ang II-induced relaxation to a contraction in the arterial strips, from which the endothelium had been removed. Relaxation of renal arteries induced by Ang II and of mesenteric arteries induced by histamine is postulated to result from PGI2 released from the arterial wall. Therefore, it appears that the endothelium is a major site but not the only site responsible for drug-induced release of PGI2.     

Endothelium-dependent relaxation and hyperpolarization evoked by bradykinin in canine coronary arteries: enhancement by exercise-training.

1. Kinins, which are produced locally in arterial walls, stimulate the release of endothelium-derived vasodilator substances. Therefore, they may participate in the metabolic adaptation to chronic exercise that occurs in the coronary circulation. Experiments were designed to compare the reactivity to bradykinin in coronary arteries isolated from sedentary and exercised-trained dogs (for 8-10 weeks). 2. The organ chambers used in this study were designed for measurement of isometric tension and cell membrane potential with glass microelectrodes. Rings of canine isolated coronary arteries with endothelium were suspended in the organ chambers filled with modified Krebs-Ringer bicarbonate solution (37 degrees C, gassed with 5% CO2 in 95 O2), and were all treated with indomethacin to prevent interference from prostaglandins. 3. Bradykinin evoked concentration-dependent relaxations of the coronary arteries. However, the kinin was significantly less potent in relaxing coronary arteries from the sedentary dogs than those from the trained ones. 4. In the presence of NG-nitro-L-arginine (an inhibitor of nitric oxide synthases), concentration-relaxation curves to bradykinin were shifted to the right in both types of preparations. Nonetheless, the peptide was still significantly more potent in arteries from exercise-trained animals. 5. In the electrophysiological experiments, concentration-hyperpolarization curves to bradykinin obtained in arteries from sedentary dogs were also significantly to the right of those in vessels from exercise-trained animals. Thus, in arteries from exercised animals, bradykinin more potently evoked the release of both nitric oxide (NO) and endothelium-derived hyperpolarizing factor (EDHF). 7. The angiotensin converting enzyme (ACE)-inhibitor, perindoprilat, shifted to the left the concentration-relaxation curves to bradykinin obtained under control conditions and in the presence of NG-nitro-L-arginine. The concentration-hyperpolarization curves to bradykinin were also shifted to the left by perindoprilat. The shift induced by the ACE-inhibitor in either type of preparation was not significantly different. 8. These findings demonstrate that exercise-training augments the sensitivity of the coronary artery of the dog to the endothelium-dependent effects of bradykinin. This sensitization to bradykinin may reflect an increased role of both NO and EDHF, and is not the consequence of differences in ACE activity in the receptor compartment.     

The prevention of myocardial ultrastructural changes by perindopril, atenolol and amlodipine in chronic alcohol administered rats.

The effects of perindopril, an angiotensin converting enzyme inhibitor, atenolol, a beta adrenergic receptor blocker and amlodipine, a calcium channel blocker were investigated in chronic alcohol administered rats. Adult male Wistar rats (240-320 g) were used in the present study. Alcohol was given to rats by a modified liquid diet for 21 days. Perindopril (2.5 and 5 mgkg(-1)), atenolol (5 and 10 mg kg(-1)) and amlodipine (5 and 10 mg kg(-1)) were injected to rats in different groups intraperitoneally for 21 days. Control rats were pair fed by an isocaloric liquid diet containing sucrose as a caloric substitute for alcohol. Saline was injected to control rats for 21 days. Rats were anesthetized with ether. Their hearts were removed and 1 mm3 samples from left ventricles were fixed. Five fields per heart were examined and photographed with transmission electron microscope. Blood alcohol levels were also measured spectrophotometrically. Daily alcohol consumption of the rats was in a range of 12.09-15.5 g kg(-1). Blood alcohol concentrations were found as 145.63 mg dl(-1) at 21st day of alcohol consumption. Chronic alcohol consumption caused some marked myocardial injuries. Perindopril and atenolol but not amlodipine produced some significant beneficial effects on alcohol-induced myocardial damages. Our results imply that perindopril and atenolol but not amlodipine have protective effects on heavy chronic alcohol consumption-induced myocardial injury in rats.     

NHE-1 inhibition: from protection during acute ischaemia/reperfusion to prevention/reversal of myocardial remodelling

The myocardial Na⁺/H⁺ exchanger isoform 1 (NHE-1) represents a major H⁺ extrusion mechanism for intracellular pH (pH_i) regulation especially during ischaemia and early reperfusion. Paradoxically, however, its activation contributes to induction of cell injury because Na⁺/H⁺ exchange is coupled closely to elevations in intracellular [Ca²⁺] through the Na⁺/Ca²⁺ exchanger. NHE-1 is exquisitely sensitive to intracellular acidosis but other factors may have also stimulatory effects via phosphorylation-dependent processes, like autocrine and paracrine agents as well as hormonal factors such as endothelin-1, angiotensin II and -1-adrenoceptor agonists. In addition, phosphorylation-independent NHE-1 activation mechanisms are known, e.g. cell shrinkage.To date at least 8 NHE isoforms have been identified and designated as NHE-1–8. All, except NHE-6 and NHE-7, which are located intracellularly, are restricted to the sarcolemmal membrane. The NHE-1 subtype is the predominant isoform in the heart, but NHE-6 is also expressed in the heart. Newly developed, selective NHE-1 inhibitors possess potent cardioprotective properties. The efficacy of NHE-1 inhibitors in experimental studies with ischaemia/reperfusion has led to clinical trials for the evaluation of these agents in high-risk patients with coronary artery disease (GUARDIAN Trial) and acute myocardial infarction (ESCAMI Trial). The GUARDIAN trial demonstrated only for the coronary artery by-pass graft (CABG) patient population a reduction in the primary cardiovascular endpoint (death and reoccurring myocardial infarction). However, recent evidence also suggests that NHE-1 inhibition may be conducive to attenuation of remodelling processes after myocardial infarction, independently of infarct size reduction and blood pressure. In addition, in separate preclinical studies, the NHE-1 inhibitor cariporide also prevented and/or caused regression of age-related and hypertension-induced myocardial fibrosis and hypertrophy.NHE-1 inhibitors thus offer substantial promise for clinical development for attenuation of both a) acute responses to myocardial injury, b) chronic post-infarct and hypertension- and age-related responses resulting in the development of heart failure.     

Mechanism of endothelium-dependent relaxation induced by substance P in the coronary artery of the pig.

1. Using front-surface fluorometry of fura-2-loaded porcine coronary arterial strips with the endothelium intact, we investigated the mechanisms of vasorelaxation induced by substance P (SP). Fura-2 fluorescence signals which indicated the cytosolic Ca2+-concentration ([Ca2+]i), were observed to arise exclusively from teh smooth muscle cells in these strips. 2. During the contractions induced by U46619 (100 nM), a thromboxane A2 analogue, an SP-induced endothelium-dependent, biphasic vasorelaxation was observed, which consisted of an initial rapid relaxation phase followed by a sustained phase, with a transient decrease in [Ca2+]i. Pretreatment with indomethacin (Ind) had no effect on the SP-induced relaxation; however, pretreatment with NG-nitro-L-arginine (L-NOARG) partially, but significantly inhibited the decrease in both the [Ca2+]i and tension abolished. Thus, part of the relaxation was considered to be mediated by L-NOARG-sensitive relaxing factor (endothelium-derived relaxing factor: EDRF). 3. During the 40 mM K+-depolarization-induced contraction which may eliminate the effects of endothelium-derived hyperpolarizing factor (EDRF), the vasorelaxation reduced by SP was completely inhibited by L-NOARG. 4. During the vasorelaxation induced SP, the [Ca2+]i-tension relationships shifted to the right of the contractions induced by either U46619 or high K+-depolarization. 5. Using front-surface fluorometry of fura-2 loaded porcine aortic valvular strips, we examined the effects of SP on [Ca2+]i in endothelial cells in situ. SP induced a rapid increase in [Ca2+]i of endothelial cells in situ followed by a small sustained phase in normal PSS (5.9 mM K+). The increase in extracellular K+ had no apparent effect on the SP-induced [Ca2+]i elevation of endothelial cells.     

Effects of nipradilol on myocardial ischaemia produced by coronary stenosis in dogs.

Effects of nipradilol which is a new beta-adrenoceptor blocking agent endowed with nitroglycerin-like vasodilator actions, its denitrated derivative (denitro nipradilol) and propranolol on abnormalities of regional myocardial shortening produced by partial occlusion of the left circumflex coronary artery (LCX) were studied in anaesthetized open-chest dogs. In the presence of LCX stenosis, nipradilol (0.1 mg kg-1, i.v.) produced marked decreases in heart rate and LVdP/dt without a significant increase in left ventricular end-diastolic pressure (LVEDP). It improved impaired myocardial segment shortening and restored normal cardiac lactate metabolism. Denitro nipradilol (0.2 mg kg-1 i.v.) and propranolol (0.2 mg kg-1 i.v.) both caused similar haemodynamic changes to nipradilol but also produced a significant increase in LVEDP. However, improvement by these two agents of regional dysfunction in the ischaemic myocardium was comparable to those seen with nipradilol. All three agents markedly inhibited isoprenaline-induced tachycardia, but vehicle did not. Atrial pacing abolished the beneficial effect of nipradilol on myocardial shortening in the ischaemic region without affecting other haemodynamic parameters. These results indicate that nipradilol alleviates acute myocardial ischaemia produced by coronary stenosis with similar efficacy to denitro nipradilol and propranolol suggesting, that a major part of the beneficial effect of nipradilol may be attributable to its beta-adrenoceptor blocking action.     

Neuropeptide Y inhibits relaxation of guinea pig cerebral, coronary, and uterine arteries: blockade by D-myo-inositol-1,2,6-triphosphate.

Interactions between neuropeptide Y and perivascular vasodilator agents were studied in guinea pig cerebral, coronary, and uterine arteries. In all three types of arteries, vessel segments precontracted with prostaglandin F2 alpha or histamine relaxed concentration dependently upon application of acetylcholine (ACh), substance P (SP), and vasoactive intestinal peptide (VIP). Neuropeptide Y (NPY: 10(-8)-10(-7) M) caused inhibition of relaxations produced by ACh, SP, and VIP in all three types of segments; however, the effective concentration varied between vessel type. Thus, cerebral and uterine arteries were approximately 10 times more sensitive to NPY than the coronary artery. D-myo-inositol-1,2,6-triphosphate (PP56) was a potent inhibitor of the NPY effect in all three vessel types. Thus, NPY, which is colocalized not only with norepinephrine in sympathetic perivascular fibers but also with VIP and ACh in some parasympathetic neurons, can greatly reduce the vasodilatory effect of ACh and VIP, as well as of the sensory peptide SP. This further illustrates the complex interactions NPY has with perivascular neuroeffector mechanisms.