Vasorelaxation by an endothelium-derived metabolite of arachidonic
acid.
Pfister, Sandra L., Nancy Spitzbarth, William Edgemond, and William B.
Campbell.
Department of Pharmacology and Toxicology, Medical College of
Wisconsin, 8701 Watertown Plank Road, Milwaukee, Wisconsin 53226
APStracts 2:0389H, 1995.
Arachidonic acid elicited relaxation responses in normal rabbit aorta
precontracted with norepinephrine. The relaxation response was
enhanced by the cyclooxygenase inhibitor, indomethacin and inhibited
by lipoxygenase inhibitors, including nordihydroguaiaretic acid and
cinnamyl-3,4-dihydroxy-[alpha]-cyanocinnamate. The cytochrome P450
epoxygenase inhibitor metyrapone had no effect on arachidonic acid
-induced relaxations. The present study hypothesized that a
lipoxygenase metabolite of arachidonic acid mediated the response.
Incubation of rabbit aorta with 14C-arachidonic acid resulted in the
synthesis of a previously unidentified 14C-labeled metabolite and was
called the unknown factor. The production of the unknown factor was
not inhibited by indomethacin and decreased by lipoxygenase
inhibitors. Both the production of the unknown factor and arachidonic
acid-induced relaxations were dependent on an intact endothelium
indicating that the cellular source of the unknown relaxant factor
was the endothelial cell. This was confirmed by demonstrating the
ability of cultured rabbit aortic endothelial cells to produce the
unknown factor from 14C-arachidonic acid. Feeding rabbits a 2%
cholesterol diet for two weeks induced hypercholesterolemia without
causing atherosclerosis. In the cholesterol-fed rabbits, indomethacin
enhanced arachidonic acid-induced relaxations in norepinephrine
precontracted aortas (maximal relaxation, 49.0 +/- 2.5% vs 35.5 +/-
1.7%, cholesterol-fed vs normal), and increased the production of the
unknown factor as compared to normal rabbits. The partially purified
unknown factor elicited an approximate 26% inhibition of the
vasoconstrictor response to norepinephrine in intact rabbit aorta.
Further purification of the unknown factor by reverse phase high
pressure liquid chromatography system resulted in the isolation of a
radioactive product that relaxed precontracted rabbit aorta.
Therefore, these data suggest that in both normal and
hypercholesterolemic rabbit aorta, the endothelium produces an
unknown metabolite of arachidonic acid that causes vasorelaxation and
may regulate vascular tone.
Received 22 May 1995; accepted in final form 21 August 1995.
APS Manuscript Number H481-5.
Article publication pending Am. J. Physiol. (Heart Circ. Physiology).
ISSN 1080-4757 Copyright 1995 The American Physiological Society.
Published in APStracts on 23 September 1995.