Renal vasodilator activity of 5,6-epoxyeicosatrienoic acid depends upon conversion by cyclooxygenase and release of prostaglandins.
The 5,6-epoxyeicosatrienoic acid (5,6-EET), a renal vasodilator metabolite of arachidonic acid via cytochrome P450 (P450) requires cyclooxygenase for expression of its vasoactivity as the responses are inhibited by indomethacin and other aspirin-like drugs. We now report on the metabolism of 5,6-EET by rabbit kidneys in order to characterize those metabolites that may account for its vasoactivity. The 5,6-EET was injected close-arterially into the rabbit isolated Krebs-Henseleit perfused kidney, preconstricted with phenylephrine, and the effluent collected throughout the response period. Basal collections, following injection of 100 microliters of vehicle, were made at 20-min intervals before each 5,6-EET injection. Prior to acidic extraction, deuterated 6-keto-prostaglandin (PG) F1 alpha and PGE2 were added as internal standards. The extracts were separated by TLC and prostaglandins were derivatized for gas chromatography-mass spectrometry analysis using a negative ion chemical ionization mode. Injection of 0.5, 1, 5, 10, and 20 micrograms of 5,6-EET (n = 4) resulted in dose-related decreases in perfusion pressure of 6 +/- 2, 12 +/- 4, 21 +/- 4, 26 +/- 4, and 27 +/- 7 mm Hg, respectively. Basal perfusates contained 6-keto-PGF1 alpha and PGE2, levels of which were increased by 2-fold or more by 5,6-EET. Perfusates, collected during 5,6-EET administration, also contained 5-hydroxy-PGI1 and 5,6-epoxy-PGE1, cyclooxygenase metabolites of 5,6-EET. This is the first report of the recovery and identification of these 5,6-EET metabolites from an intact organ. Since the responses to 5,6-EET are endothelial-dependent, we also studied the profile of eicosanoids formed following incubation of 5,6-EET with cultured bovine pulmonary endothelial cells. Endothelial cells metabolized 5,6-EET to products with a similar radioactive profile on reverse-phase high pressure liquid chromatography compared to kidney perfusates. We compared the vasodilator activity of 5,6-epoxy-PGE1 and 5-hydroxy-PGI1, chemically synthesized by us from PGE2 and PGF2 alpha, respectively, with PGE2 and PGI2 in the rabbit kidney. The 5,6-epoxy-PGE1 was equipotent to PGE2 as a vasodilator. The ED50 values for 5,6-EET, 5,6-epoxy-PGE1, and PGE2 were 4.69, 0.43, and 0.42 nmol, respectively. Although PGI2 was a potent vasodilator (ED50, 0.24 nmol), 5-hydroxy-PGI1 was devoid of activity. Thus, the cyclooxygenase-dependent vasoactivity of 5,6-EET in the rabbit kidney has two components: release of vasodilator prostaglandins, PGE2 and PGI2, and metabolism of 5,6-EET to a prostaglandin analog, 5,6-epoxy-PGE1.
Department of Pharmacology, New York Medical College, Valhalla 10595.
M A
MA
Carroll
M
M
Balazy
P
P
Margiotta
J R
JR
Falck
J C
JC
McGiff
D015126:8,11,14-Eicosatrienoic Acid / Q000031:analogs & derivatives* / Q000378:metabolism / Q000494:pharmacology; D000818:Animals; D002417:Cattle; D002478:Cells, Cultured; D003577:Cytochrome P-450 Enzyme System / Q000378:metabolism; D004730:Endothelium, Vascular / Q000378:metabolism*; D008401:Gas Chromatography-Mass Spectrometry; D066298:In Vitro Techniques; D007668:Kidney / Q000378:metabolism*; D008297:Male; D010477:Perfusion; D011451:Prostaglandin-Endoperoxide Synthases / Q000378:metabolism*; D011453:Prostaglandins / Q000378:metabolism* / Q000494:pharmacology; D011817:Rabbits; D012079:Renal Circulation / Q000187:drug effects*; D014664:Vasodilation / Q000187:drug effects; D014665:Vasodilator Agents / Q000494:pharmacology*
D011453:Prostaglandins; D014665:Vasodilator Agents; C040776:5,6-epoxy-8,11,14-eicosatrienoic acid; D003577:Cytochrome P-450 Enzyme System; D011451:Prostaglandin-Endoperoxide Synthases; D015126:8,11,14-Eicosatrienoic Acid