Endothelial Vasodilator Production by Uterine and Systemic Arteries. IV. Cyclooxygenase Isoform Expression During the Ovarian Cycle and Pregnancy in Sheep1

Abstract

Uterine artery endothelial production of the potent vasodilator, prostacyclin, is greater in pregnant versus nonpregnant sheep and in whole uterine artery from intact versus ovariectomized ewes. We hypothesized that uterine artery cyclooxygenase (COX)-1 and/or COX-2 expression would be elevated during pregnancy (high estrogen and progesterone) and the follicular phase of the ovarian cycle (high estrogen/low progesterone) as compared to that in luteal phase (low estrogen/high progesterone) or in ovariectomized (low estrogen and progesterone) ewes. Uterine and systemic (omental) arteries were obtained from nonpregnant luteal-phase (LUT; n = 10), follicular-phase (FOL; n = 11), and ovariectomized (OVEX; n = 10) sheep, as well as from pregnant sheep (110-130 days gestation; term = 145 +/- 3 days; n = 12). Endothelial and vascular smooth muscle (VSM) COX-1 protein levels and uterine artery endothelial cell COX-1 mRNA levels were compared. Using immunohistochemistry and Western analysis, the primary location of COX-1 protein was the endothelium; that is, we observed 2.2-fold higher COX-1 protein levels in intact versus endothelium-denuded uterine artery and a 6.1-fold higher expression in the endothelium versus VSM (P < 0.05). COX-2 protein expression was not detectable in either uterine artery endothelium or VSM. COX-1 protein levels were observed to be higher (1.5-fold those of LUT) in uterine artery endothelium from FOL versus either OVEX or LUT nonpregnant ewes (P < 0.05), with substantially higher COX-1 levels seen in pregnancy (4.8-fold those of LUT). Increases in uterine artery endothelial COX-1 protein were highly correlated to increases in the level of COX-1 mRNA (r(2) = 0.66; P < 0.01) for all treatment groups (n = 6-8 per group), suggesting that increased COX-1 protein levels are regulated at the level of increased COX-1 mRNA. No change in COX-1 expression was observed between groups in a systemic (omental) artery. In conclusion, COX-1 expression is specifically up-regulated in the uterine artery endothelium during high uterine blood flow states such as the follicular phase and, in particular, pregnancy.

17β-Estradiol Increases Rat Cerebrovascular Prostacyclin Synthesis by Elevating Cyclooxygenase-1 and Prostacyclin Synthase

“…14 In another study treatment of fetal ovine pulmonary artery endothelial cells with 17␤-estradiol in vitro increased COX-1 mRNA and protein with a concomitant elevation of both basal and stimulated PGI 2 synthesis. 11 This was shown to be due to increased transcription and translation and not to changes in stability of mRNA or protein.…”

“…13 Moreover, fluctuating estrogen levels that occur during the menstrual cycle cause parallel changes in PGI 2 synthesis in uterine blood vessels. 14 Given that cyclooxygenase-dependent pathways are important in the regulation of cerebral blood flow, 15 it is interesting that the effects of 17␤-estradiol on PGI 2 production in the cerebral vasculature have not previously been studied.…”

Estrogen and Cerebrovascular Physiology and Pathophysiology

“…However, this action of estrogen may vary according to the vascular bed being studied. For example, increases in COX-1 expression or prostacyclin synthesis were seen in uterine (107,111), aortic (110), pulmonary (109) and umbilical (108) tissue, but not omental (107) and vascular tissue. In mesenteric vessels, one study reported E 2 to be associated with a diminished prostanoid-dependent vasodilating function (112), while another provided evidence for an E2-related capacity to repress prostanoid-associated vasoconstrictor function (113).…”

Estradiol Regulation of Prostanoids Production in Endothelium

“…In the vast majority of experiments, cells were exposed to estradiol during 24-48 hours, and the increase of prostacyclin above control values ranged from 16 % to 78 % (Table 1). In addition, it has been shown that estradiol stimulates production of prostaglandins in a variety of preparations of arteries, including ovine uterine arteries (Vagnoni & Magness, 1998;Janowiak et al, 1998;Habermehl et al, 2000), mesenteric arteries from ovariectomized rats (Davidge & Zhang, 1998;Armstrong et al, 2002), rat cerebral blood vessels (Ospina et al, 2002;Ospina et al, 2003), and aorta from ovariectomized monkeys (O'Sullivan et al, 2001). The increase of prostacyclin production is of a similar magnitude to that obtained with cultured endothelial cells.…”

“…In this way, COX-1 protein content is increased in rat (Ospina et al, 2002) and mice (Geary et al, 2001) cerebral blood vessels, and in ovine uterine arteries in response to treatment with estrogen (Rupnow et al, 2002). Indeed, COX-1 (but not COX-2) expression is increased in the endothelium of the ovine uterine artery during the follicular phase of the ovarian cycle and during pregnancy, where estrogen levels are highest (Janowiak et al, 1998;Habermehl et al, 2000). In spite of the classic consideration of COX-2 as an inducible enzyme, it seems that COX-2 does not contribute to the estradiol-increased prostacyclin production.…”