The effect of hypoxia on prostaglandin output and on tone in isolated coronary arteries.

The relationship between bath Po2, intramural prostaglandin synthesis, and vessel tone in isolated coronary arteries of cattle was studied. The basal output of prostaglandin under 95% O2-5% CO2 (580 mmHg) was elevated markedly when the Po2 was decreased to 47 mmHg but extreme hypoxia (9 mmHg) sharply curtailed output. The coronary vessels responded to 47 mmHg with relaxation but they contracted when the Po2 was decreased further to 9 mmHg. Known inhibitors of prostaglandin synthesis attenuated both the hypoxia-induced relaxations and contractions. Analysis of the effects of extreme hypoxia and of inhibitors of prostaglandin synthesis on tone indicated that both suppress prostaglandin production. It is concluded that coronary prostaglandin synthesis is accelerated by hypoxia unless the oxygen deprivation is so severe as to limit the availability of oxygen for synthesis.