Phospholipase A activity in the skin. Modulators of arachidonic acid release from phosphatidylcholine.

The distribution of the hydrolysis of 1-acyl-2-[1-14C]arachidonoyl-sn-glycero-3-phosphocholine and the simultaneous biosynthesis of prostaglandins by subcellular fractions from human and rat skin membrane preparations were determined. The phospholipase A2 activity was distributed among the subcellular particulate preparations with the highest specific activity in the 105000g particulate fraction. The activity was optimal at pH 7.5 in the presence of 1.0 mM-CaCl2 and was inhibited by EDTA. The hydrolysis of phosphatidylcholine by the skin 105000g particulate fraction was inhibited by cortisol and triamcinolone acetonide and it was stimulated by histamine, bradykinin, retinoic acid and cholera enterotoxin (freeze-dried Vibrio cholerae). Furthermore hydrolysis of phosphatidylcholine by the skin phospholipase A was also enhanced by low concentrations of prostaglandin E2 and prostaglandin F2 alpha. These last results suggest that the amplication of the hydrolysis of phosphatidylcholine by prostaglandin E2 and prostaglandin F2 alpha, with the consequent release of arachidonic acid (the substrate of prostaglandin synthesis) is likely a positive-feedback regulation of the arachidonic acid-prostaglandin cascade.