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      17beta-estradiol decreases vascular tone in cerebral arteries by shifting COX-dependent vasoconstriction to vasodilation.

      American Journal of Physiology - Heart and Circulatory Physiology

      drug effects, Vasodilation, pharmacology, Vasoconstrictor Agents, Vasoconstriction, Uterus, Rats, Inbred F344, Rats, biosynthesis, Prostaglandins, physiology, Prostaglandin-Endoperoxide Synthases, Prostaglandin Antagonists, Pressure, Organ Size, Muscle, Smooth, Vascular, Muscle Tonus, Muscle Contraction, Membrane Proteins, Isoenzymes, metabolism, Intramolecular Oxidoreductases, Female, Estradiol, Cytochrome P-450 Enzyme System, Cyclooxygenase 1, Cerebral Arteries, Body Weight, Arachidonic Acid, Animals, 15-Hydroxy-11 alpha,9 alpha-(epoxymethano)prosta-5,13-dienoic Acid

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          We have previously shown that estrogen treatment increases cerebrovascular cyclooxygenase-1, prostacyclin synthase, and production of prostacyclin. Therefore, vascular tone and prostanoid production were measured to investigate functional consequences of estrogen exposure. Middle cerebral arteries were isolated from ovariectomized female Fischer-344 rats with or without chronic in vivo 17beta-estradiol treatment. In vivo 17beta-estradiol treatment increased cerebral artery diameter; functional endothelium was required for expression of these differences. The nonspecific cyclooxygenase inhibitor indomethacin constricted, whereas arachidonic acid dilated, cerebral arteries from estrogen-treated animals. Estrogen exposure increased production of prostacyclin by cerebral arteries. Conversely, in estrogen-deficient animals, indomethacin dilated and arachidonic acid constricted cerebral blood vessels. This correlated with vasorelaxation following inhibition of the thromboxane-endoperoxide receptor with SQ-29548 but not after selective blockade of thromboxane synthase with furegrelate, suggesting prostaglandin endoperoxide (i.e., PGH2) activity. Removal of the endothelium or selective blockade of cyclooxygenase-1 with SC-560 abolished estrogen-mediated differences in the effects of arachidonate on vessel diameter and on prostacyclin production by cerebral arteries. These data suggest 17beta-estradiol decreases cerebrovascular tone by shifting the primary end product of the endothelial cyclooxygenase-1 pathway from the constrictor prostaglandin PGH2 to the vasodilator prostacyclin. These effects of estrogen may contribute to the heightened thromboresistance and enhanced cerebral blood flow documented in pre-versus postmenopausal women.

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