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

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Abstract
The distribution of the hydrolysis of 1-acyl-2-[1-14C]arachidonoyl-sn-glycero-3-phosphocholine and the simultaneous biosynthesis of prostaglandins [PG] 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 105,000 g 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 105,000 g 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). Hydrolysis of phosphatidylcholine by the skin phospholipase A was also enhanced by low concentrations of PGE2 and PGF2.alpha.. These last results suggest that the amplification of the hydrolysis of phosphatidylcholine by PGE2 and PGF2.alpha., with the consequent release of arachidonic acid (the substrate for PG synthesis) is likely a positive-feedback regulation of the arachidonic acid-PG cascade.