15-hydroxy-11-alpha-9-alpha-(epoxymethano)prosta-5-13-dienoic-acid and ramiprilat

1. To examine the possibility that angiotensin-converting enzyme (ACE) inhibitors modulate the action of bradykinin at the receptor level, their effect on the dilator response to bradykinin was studied in the isolated saline-perfused heart of the rabbit. 2. Continuous infusion of bradykinin (10 nM) elicited a transient decrease in coronary perfusion pressure (CPP) and increased prostacyclin (PGI2) release which returned to baseline values within 30 min. 3. Subsequent co-infusion of ramiprilat (> or = 10 nM) or moexiprilat, but not of the less potent ACE inhibitor n-octyl-ramipril (RA-octyl), caused another fall in CPP and an increase in PGI2 release, the magnitude and time course of which were almost identical to the first response to bradykinin. No change in CPP or PGI2 release was observed when the ACE inhibitors were administered in the absence of exogenous bradykinin. 4. Infusion of D-Arg[Hyp3]-bradykinin (10 nM), a specific B2-receptor agonist which was significantly more resistant to degradation by ACE than bradykinin, produced virtually identical changes in CPP and PGI2 release when compared to bradykinin. Subsequent co-infusion of ramiprilat was similarly effective in restoring the fall in CPP and increase in PGI2 release elicited by D-Arg[Hyp3]-bradykinin as in the presence of bradykinin. 5. In concentrations which should block the degradation of bradykinin by ACE in the coronary vascular bed, two ACE substrates, hippuryl-L-histidyl-L-leucine (0.2 mM) and angiotensin I (0.3 microM), were unable to elicit a significant change in CPP or PGI2 release while ramiprilat and another ACE inhibitor, quinaprilat, were still active in the presence of these substrates. 6. To reveal the potential B2-receptor action of ramiprilat, its effect on the constrictor response to bradykinin was studied in the rabbit isolated jugular vein. Ramiprilat (0.1 MicroM), but not RA-octyl (1 MicroM),potentiated the endothelium-independent, B2-receptor-mediated constrictor response to bradykinin, but not that to the thromboxane-mimetic U46619 (9,11-dideoxy-ll alpha,9 alpha-epoxymethano-prostaglandin F2.).Moreover, ramiprilat but not RA-octyl caused a concentration-dependent, B2-receptor antagonist sensitive increase in tone when administered alone.7. These findings suggest that an interaction of ACE inhibitors with the B2-receptor or its signal transduction pathway rather than an accumulation of bradykinin within the vascular wall is responsible for the restoration of the endot

Topics: 15-Hydroxy-11 alpha,9 alpha-(epoxymethano)prosta-5,13-dienoic Acid; Angiotensin-Converting Enzyme Inhibitors; Animals; Bradykinin; Coronary Vessels; Epoprostenol; Female; In Vitro Techniques; Isoquinolines; Jugular Veins; Male; Oligopeptides; Prostaglandin Endoperoxides, Synthetic; Rabbits; Ramipril; Receptors, Bradykinin; Tetrahydroisoquinolines; Thromboxane A2; Vasoconstriction; Vasoconstrictor Agents; Vasodilation

We reported earlier that the vasodilator response to acetylcholine (ACh) in lungs exposed to indomethacin and preconstricted with an analog of thromboxane (U46619) is converted to vasoconstriction by brief electrolysis of inflowing perfusion medium and suggested that this effect reflected endothelial injury. The purpose of our present study was 2-fold. First, because captopril, a sulfhydryl-containing inhibitor of angiotensin-converting enzyme inhibitor, prevented this effect (we assumed by scavenging electrolysis generated free radicals of oxygen), we determined whether two angiotensin-converting enzyme inhibitors lacking this moiety, namely lisinopril and ramiprilat, provided similar protection. Second, we studied whether electrolysis, like other forms of experimental lung injury, impaired uptake of serotonin (5-HT) by the endothelium. Our study confirmed that within 5 min of electrolytic injury, the ACh response is converted to vasoconstriction. This effect was completely prevented by lisinopril (18 microM) or ramiprilat (30 microM), neither of which affected ACh vasodilatation in control lungs. Lower concentrations of either drug exerted lesser degrees of protection. Five or 20 min after electrolysis, single-pass uptake of [14C]5-HT was significantly (P less than .01; N = 11) lower than control (82.4 +/- 3.4% vs. 71 +/- 3.2 and 46.5 +/- 6%, respectively). In contrast, 5-HT uptake was unaltered by electrolysis in the presence of 18 microM lisinopril. We conclude that loss of ACh vasodilation is an early reflection of lung endothelial injury that is accompanied by reduced [14C]5-HT uptake. Also, the protective property of nonsulfhydryl-containing angiotensin-converting enzyme inhibitors may be related to unexpected antioxidant actions.

Topics: 15-Hydroxy-11 alpha,9 alpha-(epoxymethano)prosta-5,13-dienoic Acid; Angiotensin-Converting Enzyme Inhibitors; Animals; Enalapril; Endothelium, Vascular; Free Radicals; Lisinopril; Lung; Male; Prostaglandin Endoperoxides, Synthetic; Pyrroles; Rabbits; Ramipril; Serotonin; Vasoconstrictor Agents