sq-29548 and 20-hydroxy-5-8-11-14-eicosatetraenoic-acid

We recently demonstrated that endothelin-1-induced medullary vasodilation despite a potent cortical vasoconstriction in the rat kidney may be accounted for by 20-hydroxyeicosatetraenoic acid (20-HETE) production. This study characterized the effects of 20-HETE and its metabolites, 20-hydroxy prostaglandin E(2) (20-OH PGE(2)) and 20-hydroxy prostaglandin F(2alpha) (20-OH PGF(2alpha)), and the contribution of nitric oxide (NO) and prostanoids to the changes evoked in cortical blood flow (CBF) and medullary blood flow (MBF). We tested the hypothesis that 20-HETE produces qualitatively different regional hemodynamic effects in the kidney with 20-OH PGF(2alpha) or 20-OH PGE(2), accounting for the vasoconstriction or vasodilation, respectively, in the cortex and medulla. Renal intra-arterial infusion of 1, 2.5, 5, and 10 ng/min 20-HETE decreased CBF by 10 +/- 3, 24 +/- 4, 40 +/- 7, and 58 +/- 9 perfusion units (PU), respectively, but increased MBF by 4 +/- 2, 16 +/- 4, 27 +/- 3, and 41 +/- 10 PU, respectively. 20-OH PGF(2alpha) mimics the effects of 20-HETE, as did PGF(2alpha). However, 20-OH PGE(2) increased both CBF and MBF, as did PGE(2). Indomethacin (5 mg/kg) blunted the effects of 20-HETE but not that of 20-OH PGE(2) and 20-OH PGF(2alpha). However, SQ29548 ([1S-[1alpha,2alpha(Z),3alpha,4alpha]]-7-[3[[2-[(phenylamino)carbonyl[hydrazino]methyl]-7-oxabicyclo]2.2.1]hept-2-yl]-5-heptenoic acid) (0.1 mg/kg), a prostaglandin H(2)/thromboxane A(2) receptor antagonist, blunted the cortical and medullary hemodynamic effects elicited by 20-HETE, 20-OH PGE(2), 20-OH PGF(2alpha), and PGF(2alpha) but not PGE(2). N(omega)-L-nitro arginine methyl ester (5 mg/kg), the inhibitor of NO synthase, exacerbated the cortical constrictor effects of 20-HETE and 20-OH PGF(2alpha) without affecting the medullary perfusion produced by 20-HETE or its metabolites. These findings suggest that 20-HETE, through its hydroxyl metabolites, produced differential effects in the kidney. The medullary perfusion appears to be independent of NO.

Topics: Animals; Bridged Bicyclo Compounds, Heterocyclic; Cerebrovascular Circulation; Dinoprostone; Dose-Response Relationship, Drug; Fatty Acids, Unsaturated; Hydrazines; Hydroxyeicosatetraenoic Acids; Indomethacin; Kidney Medulla; Male; Nitric Oxide; Rats; Rats, Sprague-Dawley; Renal Circulation; Vasoconstriction

1. The cytochrome P-450 metabolite of arachidonic acid, 20-hydroxyeicosatetraenoic acid (20-HETE), was found to be a potent, dose-dependent inhibitor of platelet aggregation and inhibitor of thromboxane biosynthesis induced by arachidonic acid (IC50 5.2 +/- 1.5 microM), A23187 (IC50 16.2 +/- 5.4 microM), and U46619 (IC50 7.8 +/- 2.4 microM). 20-HETE did not inhibit thrombin-induced aggregation. 2. The human platelet metabolized 20-HETE to a series of novel metabolites formed by cyclo-oxygenase as well as lipoxygenase pathways. The structures of the metabolites were identified by mass spectrometry as 20-hydroxy-thromboxane B2, 12,17-dihydroxyheptadecatrienoic acid, 12,20-dihydroxyeicosatetraenoic acid, and 11,20-dihydroxyeicosatetraenoic acid. 3. The identification of the 11-hydroxy metabolite of 20-HETE suggests that 20-HETE is less efficiently cyclized to an endoperoxide intermediate by cyclo-oxygenase than is arachidonate. 4. Although some biological activity of 20-HETE may be related to competition with endogenous arachidonate for cyclo-oxygenase metabolism, the predominant mechanism of action of 20-HETE appears to be through antagonism of the prostaglandin H2/thromboxane A2 receptor.

Topics: Adult; Arachidonate 12-Lipoxygenase; Blood Platelets; Bridged Bicyclo Compounds, Heterocyclic; Cyclic AMP; Fatty Acids, Unsaturated; Humans; Hydrazines; Hydroxyeicosatetraenoic Acids; In Vitro Techniques; Platelet Activation; Platelet Aggregation; Platelet Aggregation Inhibitors; Prostaglandin H2; Prostaglandin-Endoperoxide Synthases; Prostaglandins H; Thromboxane A2

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.

Topics: Animals; Aorta; Bridged Bicyclo Compounds, Heterocyclic; Chromatography, Thin Layer; Cyclooxygenase Inhibitors; Endothelium, Vascular; Fatty Acids, Unsaturated; Hydrazines; Hydroxyeicosatetraenoic Acids; In Vitro Techniques; Indomethacin; Male; Mass Spectrometry; Microsomes; Muscle Contraction; Prostaglandin-Endoperoxide Synthases; Rats; Rats, Inbred Strains; Seminal Vesicles; Sheep; Vasoconstrictor Agents