Modulation of prostacyclin synthetase and unmasking of PGE2 isomerase in bovine coronary arterial microsomes.

Prostacyclin (PGI2), a major product of prostaglandin endoperoxide (PGH2) metabolism in blood vessels, has potent vasodilator and platelet activity. Therefore, modulation of PGI2 synthetase activity is of prime physiological importance in the regulation of blood vessel function. In this study, PGI2 synthetase activity of bovine coronary arterial microsomes could be altered over a 2-3 fold range by GSH or dithiothreitol in a concentration-dependent manner and over a microsomal protein range of 10-200 micrograms. Modulation of coronary artery PGI2 synthetase activity was also seen in vessels from sheep, dog and man. These data suggest that coronary artery PGI2 synthetase activity is unusually sensitive to the redox state or sulfhydryl oxidation of the enzyme. The present data also unmask an active PGE2 isomerase, previously reported to be absent in bovine coronary arterial microsomes.