An enzyme isolated from arteries transforms prostaglandin endoperoxides to an unstable substance that inhibits platelet aggregation

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Abstract
Microsomes prepared from rabbit or pig aortas transformed endoperoxides (PG[prostaglandin]G2 or PGH2) to an unstable substance (PGX) that inhibited human platelet aggregation. PGX was 30 times more potent in this respect than PGE1. PGX contracted some gastrointestinal smooth muscle and relaxed certain isolated blood vessels. PG endoperoxides cause platelet aggregation possibly through the generation by platelets of thromboxane A2. Generation of PGX by vessel walls could be the biochemical mechanism underlying their unique ability to resist platelet adhesion. A balance between formation of anti- and pro-aggregatory substances by enzymes could also contribute to the maintenance of the integrity of vascular endothelium and explain the mechanism of formation of intra-arterial thrombi in certain physiopathological conditions.
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