Estrogen and Lipopolysaccharide Stimulation of Prostacyclin Production and the Levels of Cyclooxygenase and Nitric Oxide Synthase in Ovine Uterine Arteries¹

^a Department of Animal, Dairy, and Veterinary Sciences, Utah State University, Logan, Utah 84322 ^b Departments of Obstetrics/Gynecology, Perinatal Research Laboratories, and Meat/Animal Science, University of Wisconsin-Madison, Madison, Wisconsin 57311

Several enzymes play a role in vasodilation, including cyclooxygenase, which converts arachidonic acid into prostaglandins, and nitric oxide synthase, which converts arginine to citrulline and yields nitric oxide. The effects of endogenous and exogenous estrogen and lipopolysaccharide on uterine artery production of prostacyclin, and levels of cyclooxygenase and nitric oxide synthase were examined. Uterine arteries collected from ewes during the follicular (Day -1 to 0, Day 0 = estrus) or luteal (Day 10) phase were treated in vitro with lipopolysaccharide. In addition, ovariectomized ewes were treated in vivo with estradiol-17ß (5 µg/kg; 120 min) or a vehicle control; arteries from the uteri were treated in vitro with lipopolysaccharide. After 24 h of lipopolysaccharide treatment, culture media were collected for measurement of 6-keto-prostaglandin F₁ (the stable metabolite of prostacyclin). These uterine arteries were homogenized, and the level of cyclooxygenase and nitric oxide synthase was determined by Western analysis. Lipopolysaccharide stimulated (p < 0.02) prostacyclin production by uterine arteries from both follicular- and luteal-phase sheep although phase of the estrous cycle did not affect prostacyclin responses (p = 0.56) to lipopolysaccharide. In contrast, uterine arteries from ovariectomized sheep treated with estradiol-17ß produced more prostacyclin (p < 0.001) in response to lipopolysaccharide than did uterine arteries from ovariectomized sheep treated with the vehicle control. There was no effect of phase (follicular or luteal) of the estrous cycle on either cyclooxygenase-1 or -2 gene expression. Lipopolysaccharide increased (p = 0.0002) gene expression of cyclooxygenase-2, but not cyclooxygenase-1, in both follicular- and luteal-phase ewes, which was significantly correlated (r² = 0.91, p = 0.003) with uterine artery production of prostacyclin. Uterine arteries from follicular-phase sheep expressed significantly more nitric oxide synthase-III after lipopolysaccharide exposure than did uterine arteries from luteal-phase ewes (p = 0.03). In contrast, nitric oxide synthase-II was not detected in uterine arteries after lipopolysaccharide exposure. These results suggest that estrogen plays a role in regulating uterine artery responses to lipopolysaccharide.

¹ Research was supported by the United States Department of Agriculture grants #95372032647 and #9735044912 and National Institutes of Health grants HL49210, HD33225, and HL57653, and by the Utah Agricultural Experiment Station, Utah State University, Logan, UT. Approved as paper no. 7045.

² Correspondence. FAX: 435 797 2118; kvagnoni{at}cc.usu.edu

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