Metabolism of 20-hydroxyeicosatetraenoic acid by cyclooxygenase. Formation and identification of novel endothelium-dependent vasoconstrictor metabolites.

We recently demonstrated that 20-hydroxyeicosatetraenoic acid (20-HETE) constricts rat aortic rings. The contractile response was partially dependent on the presence of endothelium and was abolished by pretreatment of the rings with either indomethacin or the endoperoxide/thromboxane receptor antagonist, SQ29548. Addition of GSH or SnCl2 to the organ bath diminished the contractile response of 20-HETE, whereas preincubation of the rings with a thromboxane synthase inhibitor did not affect the 20-HETE induced contractions. Short time incubation (2 min) of 20-HETE with ram seminal vesicle microsomes in the presence of p-hydroxymercurybenzoate yielded metabolites which migrated similarly on thin layer chromatography to the known arachidonate endoperoxides prostaglandin (PG) G2 and PGH2 and possess vasoconstrictory properties. The vasoconstriction was dose-dependent with a half-life of approximately 6.3 +/- 0.6 min. Addition of SQ29548 to the aortic ring bath 1 min after metabolite elicited vasoconstriction produced immediate relaxation. Furthermore, pretreatment of the rings with SQ29548 totally abolished the contraction. SnCl2 reduction of the metabolites produced in incubation of rat seminal vesicles with 20-HETE and p-hydroxymercurybenzoate resulted in a single radioactive peak which was further identified by gas chromatography/mass spectrometry as 20-hydroxy-PGF2 alpha. The inhibitory effect of SQ29548, the appearance of labile metabolites with a half-life of approximately 6 min and the production of 20-hydroxy-PGF2 alpha by SnCl2 reduction clearly indicate that the vasoconstrictor metabolites of 20-HETE are the labile endoperoxides of 20-HETE, 20-hydroxy-PGG2, and 20-hydroxy-PGH2.