| Abstract: | The relation between pO2 and beta adrenergic responsiveness was studied in isolated bovine and porcine coronary artery rings. Isoproterenol elicited a concentration-dependent relaxation of bovine and porcine coronary artery rings precontracted with KCI (2 X 10(-2) M) or histamine (10(-6) M); beta adrenergic responsiveness was significantly lower in K+-depolarized coronary arteries. A decrease of bath pO2 from 95 to 40% significantly reduced beta adrenergic responsiveness in both coronary preparations precontracted with either KCI or histamine. Similarly, exogenous arachidonic acid (3 X 10(-6) to 3 X 10(-5) M) depressed isoproterenol-induced relaxations in both tissues. Indomethacin (5 X 10(-6) M) augmented beta adrenergic responsiveness in the presence of 95% O2 and prevented the inhibitory effects of the decrease in bath pO2 and arachidonic acid in both preparations. The experimental data suggest that the demonstrated O2-sensitivity of beta adrenergic responsiveness is mediated by vascular prostaglandin synthesis in isolated large coronary arteries. |
