Prostacyclin (PGI2) mediates hypoxic relaxation of bovine coronary arterial strips

Bovine coronary arterial strips (BCA) exhibiting spontaneous tone, relax in response to a decrease in the pO2 of the bathing medium. Experiments were performed to determine if prostaglandins (PGs) mediate the oxygen-induced changes in tension. BCA were equilibrated in Krebs-bicarbonate solution at 37 degrees C gassed with 95% O2, 5% CO2 and tension was measured isometrically. When the pO2 of the bathing medium was decreased, BCA exhibited reversible reductions in tension. Switching from 95% O2, 5% CO2 to 95% N2, 5% CO2 (anoxia) elicited an initial relaxation followed by a contraction. In contrast, a change to 5% O2, 5% CO2, 90% N2 (hypoxia) was followed by a sustained relaxation. Re-introduction of O2 to anoxic strips produced a biphasic response: relaxation followed by contraction. Indomethacin or eicosatetraynoic acid (EYA) increased tone and inhibited the relaxation produced by anoxia or hypoxia. Indomethacin or EYA did not inhibit the relaxation of anoxic strips during re-introduction of O2, but did inhibit the contraction partially. Relaxation of arterial strips to arachidonic acid (AA) was similar to relaxation to prostacyclin (PGI2). Anoxia limited the relaxation to AA but not to PGI2. We conclude that PG synthesis contributes to the basal tone and the hypoxia-induced relaxation of BCA. In addition, hypoxia, unless severe, does not prevent the conversion of AA to PGI2.