BRADYKININ-INDUCED CORONARY VASODILATION - EVIDENCE FOR AN ADDITIONAL PROSTACYCLIN-INDEPENDENT MECHANISM

1. The action of bradykinin on prostacyclin (PGI2) release and the coronary artery tone was studied in the isolated guinea pig heart and the bovine coronary artery. Myocardial force of concentration and oxygen consumption were monitored continuously. 2. Addition of bradykinin to the guinea pig heart was followed by a dose-dependent decrease in the coronary perfusion pressure, while myocardial contractile force and oxygen consumption remained unchanged, indicating a direct effect on the coronary vascular resistance. There was no evidence for tachyphylaxis. 3. Long-term treatment of the hearts with indomethacin at low concentrations (5×10-7 g/ml) did not influence the bradykinin-induced coronary dilation. Increasing the indomethacin (5×10-6 g/ml) produced a partial (repetitive application) or complete inhibition (cumulative dose-response curves). 4. Application of bradykinin to coronary artery strip also produced relaxation. Indomethacin (2×10-6 g/ml) did only attenuate this effect although it completely prevented the response to arachidonic acid. 5. The release of PGI2-like material from the heart by bradykinin was studied using the cascade-technique of Vane (1969). There was a dose-dependent release of a substance, which relaxed the bovine coronary artery. Pretreatment of the hearts with 15-hydroperoxy arachidonic acid or indomethacin (5×10-6 g/ml) produced a partial or complete inhibition of this response. However, there was no significant inhibition of the bradykinin-induced relaxation of the coronary vascular bed. 6. It is suggested that the inhibitory effect of high dose indomethacin is not due to inhibition of prostaglandin biosynthesis, which is already completely blocked at low doses. According to this, two different actions of indomethacin on the coronary vessels could be established. 7. The results indicate that bradykinin produces a pronounced release of PGI2 from the coronary vessels, which, however, can be blocked without abolition of the coronary relaxing activity. This provides evidence for an additional, PGI2-independent coronary action of this substance. © 1979 Springer-Verlag.