PROSTACYCLIN INCREASES CAMP IN CORONARY-ARTERIES

Abstract

Whether prostacyclin (PG[prostaglandin]I2)-induced relaxation in circular strips of coronary arteries might be mediated by c[cyclic]AMP was studied. Partially depolarized circular strips of bovine coronary arteries were used and PGI2-induced changes in length were compared with tissue concentrations of cAMP and cGMP, measured by RIA [radioimmunoassay]. PGI2 produced significant and concentration-dependent increases in cAMP levels which were associated with the relaxant effects produced by the same concentrations (0.3-26.7 .mu.M). cGMP was not changed by these concentrations. The relaxant effects of PGI2 were not antagonized by propranolol. There was a significant linear correlation between log increases in cAMP and percent relaxation produced by PGI2 which was almost identical with similar correlations obtained with isoprenaline or adenosine. Apparently the relaxant effects of PGI2 are, like isoprenaline and adenosine, probably mediated by cAMP.