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Biomedical subjects

W Linz

Publications and source records attributed to W Linz.

At least 91 records · Page 5Linked to original sources
PubMed1991

Experimental cardiovascular benefits of angiotensin-converting enzyme inhibitors: beyond blood pressure reduction.

In an attempt to separate the cardiac effects of converting-enzyme (CE) inhibition from those on blood pressure, experiments were performed in rats and dogs with nonantihypertensive (subhypotensive) doses of the CE inhibitor ramipril. (a) Left ventricular hypertrophy: Rats with aortic constriction treated with a nonantihypertensive dose of ramipril (10 micrograms/kg/day) for 6 weeks showed the same prevention and regression of cardiac hypertrophy as groups receiving the antihypertensive dose of 1 mg/kg/day. Comparable results were obtained in animals treated for 1 year. (b) Ischemia-reperfusion injuries: In rats, subchronic oral administration of ramipril in a subhypotensive dose (10 micrograms/kg/day) prevented ex vivo postischemic reperfusion arrhythmias and improved cardiodynamic and metabolic parameters. Almost complete inhibition of cardiac CE was achieved with this low dose. (c) Acute myocardial infarction: Ramiprilat (40 ng/kg/min) was infused for 6 h into the left coronary artery of anesthetized dogs with a ligation of the descending branch of this artery. This route and the low dose were chosen to achieve local cardiac effects without affecting systemic hemodynamics. Ramiprilat significantly reduced the infarct area expressed as a percentage of the area at risk. This cardioprotective effect of ramiprilat was mimicked by bradykinin and abolished by coadministration of a bradykinin antagonist. Thus, factors beyond blood pressure reduction and load changes may add to the cardiovascular benefits of CE inhibitors. This may indicate local (cardiac) paracrine and/or autocrine effects of the renin-angiotensin system and/or participation of kinins.

Angiotensin-Converting Enzyme Inhibitors↗
PubMed1991

[ACE inhibition: mechanisms of "cardioprotection" in acute myocardial ischemia].

Local inhibition of angiotensin-converting enzyme (ACE, kininase II) produces both-attenuation of angiotensin II generation and of bradykinin degradation. To delineate the participation of bradykinin in the cardioprotective actions of ACE inhibitors, experiments were performed in rats and dogs with cardiac ischemia-reperfusion injuries. In isolated perfused working rat hearts with regional myocardial ischemia, bradykinin in concentrations as low as 1 x 10(-9) M increases coronary flow and reduces the incidence and duration of reperfusion ventricular fibrillation. In addition, enzyme activities of lactate dehydrogenase and creatine kinase as well as lactate output were decreased in the venous effluent of bradykinin-perfused hearts, which also showed improved cardiodynamic and metabolic parameters. Even concentrations of bradykinin lower than 1 x 10(-10) M, which were without influence on coronary flow, exerted comparable beneficial metabolic effects connected with reduced incidence and duration of ventricular fibrillation. Combined perfusions with threshold concentrations of bradykinin (1 x 10(-12) M) and the ACE inhibitor ramiprilat (2,58 x 10(-9) M), which were ineffective given alone, resulted in a marked cardioprotective effect. Perfusion with angiotensin II (1 x 10(-9) M) aggravated reperfusion arrhythmias and worsened myocardial metabolism. Bradykinin perfusion prevented this deterioration in a concentration-dependent manner. The bradykinin antagonist D-Arg-[Hyp2, Thi5,8, D-Phe7]-bradykinin (1 x 10(-5)) completely abolished the cardioprotective effects of bradykinin or the ACE inhibitor. However, higher concentrations of bradykinin (1 x 10(-7) M) or ramiprilat (2,58 x 10(-5) M) reversed these properties of the bradykinin antagonist.(ABSTRACT TRUNCATED AT 250 WORDS)

Angiotensin-Converting Enzyme Inhibitors↗
PubMed1990

Local inhibition of bradykinin degradation in ischemic hearts.

Local inhibition of angiotensin-converting enzyme (ACE, kininase II) produces both attenuation of angiotensin (Ang) II generation and bradykinin (BK) degradation. To delineate the participation of BK in the cardioprotective actions of ACE inhibitors, experiments were performed in rats and dogs with cardiac ischemia-reperfusion injuries. (I) In rat isolated perfused working hearts with regional myocardial ischemia, BK in concentrations as low as 1 X 10(-9) M increased coronary flow (CF) and reduced the incidence and duration of reperfusion ventricular fibrillation (VF). In addition, enzyme activities of lactate dehydrogenase (LDH) and creatine kinase as well as lactate output were decreased in the venous effluent of BK-perfused hearts, which also showed improved cardiodynamic and metabolic parameters. Even concentrations of BK lower than 1 X 10(-10) M, which were without influence on coronary flow, exerted comparable beneficial metabolic effects connected with reduced incidence and duration of VF. Combined perfusions with threshold concentrations of BK (1 X 10(-12) M) and the ACE inhibitor ramiprilat (2.58 X 10(-9) M), which were ineffective given alone, resulted in a marked cardioprotective effect. Perfusion with Ang II (1 X 10(-9) M) aggravated reperfusion arrhythmias and worsened myocardial metabolism. BK perfusion prevented this deterioration in a concentration-dependent manner, whereas the Ang II receptor antagonist saralasin was only marginally effective. The BK antagonist D-Arg-[Hyp2, Thi5,8, D-Phe7]-BK (1 X 10(-5) M) completely abolished the cardioprotective effects of BK or the ACE inhibitor. However, higher concentrations of BK (1 X 10(-7) M) or ramiprilat (2.58 X 10(-5) M) competitively reversed these properties of the BK antagonist. (II) In anesthetized dogs, BK was infused into the coronary artery in a dose of 1 ng/kg/min during occlusion (90 min) and reperfusion (30 min) of the left descending coronary artery (LAD)--a dose without effects on cardiovascular parameters. In line with the findings in isolated ischemic rat hearts, BK infusion reduced LDH activities and lactate concentrations in the coronary sinus blood, whereas myocardial tissue levels of glycogen and energy-rich phosphates were increased in the infarcted area. The cardioprotective effects produced by perfusion with BK or by reduction of BK degradation through local interference with ACE favor a role for BK in ischemia-reperfusion injuries in rats and dogs.

Anesthesia↗
PubMed1990

Cardioprotective effects of ACE inhibitors: experimental proof and clinical perspectives.

Molecular, biochemical, and pharmacological data give evidence for a local renin angiotensin system (RAS). Infusion of angiotensin (ANG) I into the isolated perfused rat heart resulted in the appearance of ANG II in the venous effluent. In isolated working rat hearts with regional myocardial ischemia followed by reperfusion, angiotensin-converting enzyme (ACE) inhibitors were able to reduce the incidence and duration of ventricular fibrillation. Local ACE inhibition in the heart improved cardiodynamics, reduced enzyme release and increased the energy-rich phosphates in ischemic myocardial tissue. Bradykinin perfusion showed an identical fingerprint of effects, whereas ANG I or ANG II perfusion aggravated postischemic reperfusion arrhythmias and induced a deterioration of cardiodynamic and metabolic events. In different studies after myocardial infarction with congestive heart failure (animals and humans) it was demonstrated that long-term ACE inhibitor therapy prolonged survival. Furthermore, ACE inhibition increased exercise capacity in patients with myocardial infarction. In cardiac hypertrophy, ACE inhibitors capable of affecting tissue RAS can induce prevention and regression not only through their blood pressure lowering actions, but possibly also by direct cardiac effects, presumably by inhibition of local ANG II generation, a possible growth factor. These findings from experimental and clinical studies give evidence for cardioprotective effects of ACE inhibitors. Two to 3 days of pretreatment with 5 mg ramipril given as a once daily dose to hypertensive patients undergoing vascular surgery induced as increase in renin-like activity in carotid and renal arteries, as compared to normo- and hypertensives who did not receive ramipril medication before surgery.(ABSTRACT TRUNCATED AT 250 WORDS)

Angiotensin-Converting Enzyme Inhibitors↗
PubMed1989

Cardiac arrhythmias are ameliorated by local inhibition of angiotensin formation and bradykinin degradation with the converting-enzyme inhibitor ramipril.

We investigated the influence of the angiotensin-converting enzyme (ACE) inhibitor ramipril on cardiac arrhythmias in guinea pigs and rats. Ramiprilat, the active moiety of ramipril, did not influence action potentials of isolated guinea-pig papillary muscle or rabbit sinus node, thereby excluding cellular electrophysiological evidence of anti-arrhythmic properties. Ramipril protected against cardiac arrhythmias induced by digoxin infusion in guinea pigs. This effect was comparable with that of lidocaine. In isolated perfused ischemic working rat hearts, angiotensin (ANG) I (3 x 10(-9) M/l) and ANG II (1 x 10(-9) M/l) aggravated reperfusion arrhythmias, accompanied by deterioration of cardiodynamic and metabolic events. Bradykinin (BK) (1 x 10(-10)-1 x 10(-8) M/l), in contrast, protected against reperfusion arrhythmias, which corresponded to an increase in energy-rich phosphates and glycogen stores and a decrease in lactate levels in myocardial tissue. Identical changes were seen in hearts from rats pretreated with ramipril (1 mg/kg PO) or perfused with ramiprilat (2.58 x 10(-7)-2.58 x 10(-5) M/l). Local ACE inhibition in these ischemic hearts antagonized ANG I but not ANG II effects and enhanced BK effects. The BK antagonist D-Arg-(Hyp2, Thi5,8, D-Phe7)BK abolished the beneficial effects of BK, ramipril, and ramiprilat. Increased concentrations of BK or ramiprilat were able to reverse the antagonism. The antiarrhythmic agent nicainoprol, a fast-sodium-channel blocking drug (class Ib), also protected isolated rat hearts against reperfusion arrhythmias, but was without beneficial effects on cardiac hemodynamics and biochemical parameters, in contrast to the ACE inhibitor. These results suggest that the beneficial effects of the ACE inhibitor ramipril on digoxin and reperfusion arrhythmias are not mediated by their direct actions on ionic channels in the cell membrane. It seems that other factors are responsible for its beneficial effects on reperfusion arrhythmias, cardiac function, and metabolism, which are associated with a reduction in ANG II generation and BK degradation by local ACE inhibition in the heart.

Action Potentials↗
PubMed1989

Cardiac renin-angiotensin system.

Based on molecular, biological, biochemical, and pharmacological data, evidence is presented for a cardiac renin-angiotensin system. Using radiolabeled cRNA probes prepared from specific cDNA fragments, we were able to document renin and angiotensinogen gene expression in atria and ventricles of the rat heart by Northern blot and liquid hybridization analysis. Relative signal strength for both mRNAs was highest in the atria and next highest in the right and left ventricle. We also demonstrated the presence of both angiotensin I and angiotensin II in all anatomical regions of the monkey and rat heart using specific, high pressure liquid chromatography (HPLC) controlled radioimmunoassays (RIAs) for angiotensin peptides. The presence of converting-enzyme activity was also ascertained by direct in vitro determinations. Infusion of angiotensin I into the isolated perfused rat heart resulted in the prompt appearance of angiotensin II; the single pass fractional conversion was 6.42 +/- 0.33%. Dose-dependent inhibition of this effect by simultaneous infusion of converting-enzyme inhibitor supports the existence of a specific intracardiac pathway for the activation of angiotensin II. When the isolated, perfused rat hearts were exposed to infusions of purified renin, angiotensin I, undetectable before renin, was dose-dependently released into the coronary circulation at peak rates ranging from 2.4 +/- 0.7 fmol/min to 1.4 +/- 0.2 pmol/min, of which 7.2 +/- 1.1% was intracardially converted to angiotensin II. All renin effects were blocked in the presence of a specific pentapeptide renin inhibitor. Together, the results of these studies add support to the concept of a functionally active cardiac tissue renin-angiotensin system.

Animals↗
PubMed1989

Effects of endothelin on isolated ischaemic rat hearts during ramiprilat, bradykinin and indomethacin perfusion.

In isolated ischaemic rat hearts, endothelin induced a short transient increase, followed by a lasting decrease in coronary flow and an increase in the left ventricular dp/dt max in a concentration-dependent manner. Both enzyme activities and lactate output were increased in the venous effluent. Myocardial tissue levels of glycogen, ATP and creatine phosphate were reduced. Endothelin aggravated post-ischaemic reperfusion arrhythmias. Perfusion with ramiprilat and bradykinin increased coronary flow and left ventricular dp/dt max and reduced reperfusion arrhythmias; enzyme activities and lactate output were significantly reduced and in the myocardial tissue glycogen and energy-rich phosphates were preserved. In comparison, indomethacin prolonged reperfusion arrhythmias, decreased coronary flow and increased the enzyme activities with no changes in myocardial metabolism. When ramiprilat and bradykinin were combined with endothelin, reperfusion arrhythmias and the enzyme activities were reduced but the decrease in coronary flow could not be fully blocked. Indomethacin aggravated the endothelin-induced coronary flow reduction, enzyme release and reperfusion arrhythmias but had no effects on the other parameters.

Angiotensin-Converting Enzyme Inhibitors↗
PubMed1989

High-affinity binding of the converting enzyme inhibitor, ramiprilat, to isolated human glomeruli.

Evidence for effects of angiotensin converting enzyme (ACE) on isolated human glomeruli was provided using specific binding of tritium-labeled ramiprilat, a potent inhibitor of ACE. [3H]ramiprilat bound to isolated glomeruli, depending on time and temperature, displaying a KD of 3.8 nmol/L and a Bmax of 853 fmol/mg protein. Specific binding represented more than 90% of total binding. Dissociation occurred rapidly after dilution of the sample with incubation buffer or after addition of an excess of unlabeled inhibitor. Binding of [3H]ramiprilat was also inhibited by increasing concentrations of enalaprilat, another ACE inhibitor. ACE is a zinc-containing enzyme. Addition of EGTA to the assay, which chelates zinc ions, completely prevented binding. This was reversed by divalent Zn2+ and Ca2+ ions, but not by magnesium. Binding of [3H]ramiprilat to isolated glomeruli was maximal at pH 8, which also is optimal for ACE activity. The binding of [3H]ramiprilat to isolated human glomeruli is specific, and resembles the characteristics which have been found earlier for enzyme activity of ACE. Thus, binding of [3H]ramiprilat to isolated glomeruli can be assumed to be directed to ACE.

Adult↗
PubMed1989

Converting enzyme inhibition specifically prevents the development and induces regression of cardiac hypertrophy in rats.

Antihypertensive agents have been shown to differ markedly in their effects on the development and regression of cardiac hypertrophy. In view of possible trophic properties of angiotensin II (ANG II), we compared the effects of equipotent antihypertensive doses of the converting enzyme (CE) inhibitor ramipril (1 mg/kg), the calcium antagonist nifedipine (30 mg/kg), and the arterial vasodilator dihydralazine (30 mg/kg) on cardiac mass in rats subjected to banding of the abdominal aorta. Treatment was started either immediately after banding ("prevention experiments") or after hypertension and hypertrophy had already developed ("regression experiments"). Groups of untreated animals with aortic constriction and sham-operated animals served as controls. In the prevention experiments heart weight, myocardial protein content and ANG II plasma levels were significantly increased in untreated animals and in those receiving nifedipine and dihydralazine. In contrast, values obtained in animals treated with ramipril were not different from those seen in normotensive, sham operated controls with the exception of plasma ANG II levels which were lower. Similar results were observed in the second series of studies which examined the effect of antihypertensive agents on the "regression" of cardiac hypertrophy. Treatment was started 6 weeks after aortic banding and continued for another 6 weeks. While all three drugs lowered blood pressure equally well, only ramipril induced a significant and complete regression of cardiac hypertrophy to values not different from sham-operated controls. In addition we studied a group of animals treated with a nonantihypertensive low dose of ramipril (10 micrograms/kg). Remarkably, these animals showed the same complete regression of cardiac hypertrophy as seen in the group receiving the antihypertensive dose of CE inhibitor. Our study indicates a selective advantage of CE inhibitors over other antihypertensive drugs in the prevention and regression of hypertensive cardiac hypertrophy. Importantly, the dissociation between effects on blood pressure and cardiac mass demonstrated in the experiments with a low dose of ramipril stresses the role of factors other than blood pressure and afterload on the development of hypertensive cardiac hypertrophy. One such peptide, thus, may be ANG with its known potential as a growth factor.

Angiotensin II↗
PubMed1989

Pharmacological interference with the cardiac renin-angiotensin system.

Biochemical, pharmacological, and molecular biological data provide evidence for the presence of a cardiac renin-angiotensin system. Tissue angiotensins were demonstrated in all regions of the mammalian heart. Reduction of cardiac angiotensin II formation after oral administration of converting enzyme (CE) inhibitors in nephrectomized animals points to local generation of these peptides. Functional studies in isolated working rat hearts subjected to transient regional ischemia and reperfusion showed that there is aggravation of arrhythmias as well as exhaustion of energy status by angiotensins. This was prevented by CE inhibition and/or perfusion with bradykinin (BK), which in turn could be competitively antagonized with a BK antagonist. Intracoronary infusion of low-dose bradykinin attenuated ischemia-reperfusion injuries and reduced enzyme and lactate release in anesthetized dogs. Oral pretreatment with the CE inhibitor ramipril in rats, in doses that did not affect the elevation of blood pressure caused by aortic constriction, could prevent induction of as well as cause regression of established cardiac hypertrophy. In contrast, pure vasodilation was without effect on cardiac enlargement despite lowering blood pressure, pointing to a possible trophic influence of angiotensin II. Thus, apart from afterload reduction and euvolumia produced by CE inhibition, the outstanding efficacy of this therapeutic approach in congestive heart failure and cardiac hypertrophy and its potential usefulness in myocardial ischemia may also be explained by intracardiac suppression of angiotensin II generation and bradykinin degradation.

Angiotensin-Converting Enzyme Inhibitors↗
PubMed1989

Potentiation of the effects of atrial natriuretic factor on the cardiovascular system by amiloride.

Amiloride has previously been shown to facilitate receptor binding of atrial natriuretic factor (ANF) to membranes of adrenal cortex and to enhance ANF induced inhibition of steroid secretion in vitro. This interaction of amiloride and ANF also holds true for the cardiovascular system. In precontracted rabbit aortic strips the relaxing effect induced by the combination of ANF (10(-10) mol/l) and amiloride (10(-5) mol/l) was overadditional. The production of cyclic guanosine monophosphate (cGMP), which parallels ANF induced relaxations of vascular strips, was not affected by amiloride alone up to 10(-3) mol/l, but was concentration-dependently increased in the presence of ANF (10(-8) mol/l). In spontaneously hypertensive rats ANF-induced decreases in blood pressure were potentiated by amiloride. Post ischemia reperfusion arrhythmias in isolated rat hearts were reduced by ANF. Amiloride increased this effect. The binding experiments revealed an interaction of amiloride and ANF on the receptor level. Binding of labeled ANF to aortic tissue was concentration-dependently increased by amiloride. Addition of ATP had the opposite effect. Therefore it can be suggested that amiloride and ATP interfere with a mechanism regulating the sensitivity of the vascular ANF-receptor for its ligand regarding binding and signal transforming presumably by a kinase mediated phosphorylation/dephosphorylation process.

Amiloride↗
PubMed1988

High affinity binding of ramiprilat on isolated human glomeruli.

Evidence for angiotensin-converting enzyme (ACE) on isolated human glomeruli was furnished by specific binding of tritium-labeled ramiprilat, a potent inhibitor of ACE. 3H-ramiprilat bound to isolated glomeruli, depending on time and temperature displaying a KD of 3.8 nmol/l and a Bmax of 853 fmol/mg protein. Specific binding represented more than 90% of total binding. Dissociation occurred rapidly after dilution of the sample with incubation buffer or after addition of an excess of unlabeled inhibitor. Binding of 3H-ramiprilat was also inhibited by increasing concentrations of enalaprilat, another ACE-inhibitor or by preincubation of the glomeruli with polyclonal antibodies against ACE. ACE is a zinc-containing enzyme. Addition of EGTA to the assay, which chelates zinc ions, completely inhibited binding. This inhibitory effect of EGTA was reversed by divalent Zn2+ and Ca2+ ions but not by magnesium. Binding of 3H-ramiprilat to isolated glomeruli was maximal when the pH of the assay medium was brought to pH 8. In conclusion, the binding of 3H-ramiprilat to isolated human glomeruli is specific and resembles the characteristics which have been found earlier for enzyme activity of ACE. Thus, binding of 3H-ramiprilat to isolated glomeruli can be assumed to be directed to ACE.

Angiotensin-Converting Enzyme Inhibitors↗
PubMed1988

Evidence for a distinct Ca2+ antagonist receptor for the novel benzothiazinone compound HOE 166.

The pharmacological and binding properties of the novel enantiomerically pure benzothiazinone (R)-(+)-3,4-dihydro-2-isopropyl-4-methyl-2-[2-[4-[4-[2-(3,4,5-tri- methoxyphenyl)-ethyl]-piperazinyl]-butoxyl-phenyl]-2H-1,4- benzothiazine-3-one dihydrochloride (HOE 166), are described. HOE 166 stereoselectively inhibited KCl-but not noradrenaline-induced contractions of guinea-pig pulmonary arteries, rabbit aorta, rat mesenteric artery preparations and k-strophantin-induced enhancement of guinea-pig papillary muscle contraction in a dose-dependent manner. KCl-induced smooth muscle contraction was inhibited by HOE 166 with IC50-values of approximately 70 nM (5-11 times less potent than nifedipine, 2-16 times more potent than verapamil), the respective S-(-)-enantiomer being approximately 10-fold less potent. HOE 166 decreased the upstroke velocity of the slow action potential in partially depolarized guinea-pig papillary muscle at similar concentrations than nifedipine. To investigate possible interactions with the calcium channel, HOE 166 and its S-(-)-enantiomer were characterized by radioligand binding studies in heart, brain and skeletal muscle transverse-tubule membranes. HOE 166 was a 4-15 times more potent inhibitor of reversible (+)-[3H]PN200-110, (-)-[3H]desmethoxyverapamil and d-cis [3H]diltiazem binding compared to its pharmacologically less active (S)-(-)-enantiomer, with IC50 values in the low nanomolar range. Extensive equilibrium and kinetic studies suggest that HOE 166 exerts its Ca2+-antagonistic effect by binding to a Ca2+-channel-associated drug receptor which is distinct from the 1,4-dihydropyridine, phenylalkylamine or benzothiazepine-selective domain. This HOE 166-selective site is, however, allosterically linked to the other sites of the Ca2+ antagonist receptor complex. We conclude that HOE 166 is a novel calcium antagonist.

Action Potentials↗
PubMed1988

Local inhibition of angiotensin II formation and bradykinin degradation in isolated hearts.

The interaction of the converting enzyme (CE)-inhibitor ramipril and the bradykinin (BK)-antagonist D-Arg-[Hyp2, Thi5,8, D-Phe7]BK with angiotensin I (ANG), ANG II and BK were studied in isolated hearts of rats and guinea pigs. In isolated working rat hearts perfusion with ANG I and ANG II reduced cardiac function and coronary flow, increased the activities of lactate dehydrogenase (LDH) and creatine kinase (CK) in the perfusate, decreased high-energy rich phosphates and glycogen in the myocardium and increased duration and incidence of post-ischemic reperfusion arrhythmias. BK on the other hand reduced LDH and CK activities, improved metabolic parameters in the myocardium and reduced reperfusion arrhythmias. In isolated rat hearts pretreatment with ramipril protected against reperfusion arrhythmias and reduced enzyme activities of LDH and CK in the coronary effluent. Cardiodynamic parameters and coronary flow improved and myocardial tissue levels of glycogen, ATP and creatine phosphate (CP) were elevated. Almost identical changes were seen during perfusion with BK. The cardioprotective effects produced by both, the CE-inhibitor and BK, were completely abolished when the BK-antagonist was added to the perfusate, while a smaller inhibition was obtained by indomethacin perfusion. In isolated guinea pig hearts BK increased coronary flow. Single-dose oral pretreatment with ramipril potentiated, whereas perfusion with the BK-antagonist abolished this effect. These data add support to the hypothesis that local inhibition of CE = kininase II contributes to the beneficial effects of CE-inhibitors in the heart.

Angiotensin-Converting Enzyme Inhibitors↗
PubMed1988

Effects of the angiotensin converting enzyme inhibitor, ramipril, in isolated ischaemic rat heart are abolished by a bradykinin antagonist.

To elucidate the role of bradykinin in the cardiac actions of angiotensin converting enzyme (ACE) inhibitors, experiments were performed in isolated ischaemic hearts from guinea pigs and rats treated with the ACE inhibitor ramipril and the bradykinin-antagonist D-Arg[Hyp2,Thi5,8,D-Phe7]BK. In guinea pig hearts bradykinin increased coronary flow. Single oral pretreatment with ramipril (10 mg/kg) potentiated but perfusion with the bradykinin antagonist abolished this effect. In ischaemic working rat heart preparations perfusion with ramiprilat (2.58 x 10(-7) mol/l) or single oral pretreatment with ramipril (1 mg/kg) protected the heart from the ventricular fibrillations that invariably occurred upon reperfusion after ischaemia. Lactate dehydrogenase and creatine kinase activities, as well as lactate formation, were decreased in the venous effluent of pretreated hearts. Moreover, ACE inhibition in the heart improved cardiodynamic and metabolic parameters; left ventricular pressure, (dp/dt)max and coronary flow were increased and myocardial tissue levels of glycogen, ATP and creatine phosphate were elevated. A comparable array of changes was seen when rat hearts were perfused with bradykinin (1 x 10(-10) mol/l), which reduced enzymatic activities in the perfusate and improved the metabolic parameters in the myocardium. These cardioprotective effects produced by both the ACE inhibitor ramipril and bradykinin were completely abolished when the bradykinin-antagonist (1 x 10(-5) mol/l) was added to the perfusate. They were only partially attenuated when indomethacin (1 x 10(-6) mol/l) was perfused. Higher concentrations of bradykinin (1 x 10(-7) mol/l) or ramiprilat (2.58 x 10(-5) mol/l) overcame the actions of the bradykinin-antagonist.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗