Endothelial vasodilator production by uterine and systemic arteries. II. Pregnancy effects on NO synthase expression

Abstract

Pregnancy is characterized by elevations in uterine but not omental artery nitric oxide synthase (NOS)-specific activity. We hypothesized that increases in NO production during pregnancy are associated with elevations in protein expression of the constitutive isoform, endothelial cell NOS (ecNOS), in uterine but not systemic arteries. Arterial NOS-specific activity and guanosine 3',5'-cyclic monophosphate (cGMP) production were tested in pregnant sheep in the presence or absence [+5 mM ethylene glycol-bis(beta-aminoethyl ether)-N,N,N',N'-tetraacetic acid] of Ca2+. With the use of Western analysis, ecNOS and neuronal NOS (nNOS) constitutive isoform expressions were evaluated in intact and denuded [vascular smooth muscle (VSM)] uterine and systemic (omental and renal) arteries as well as in isolated endothelium-derived proteins from nonpregnant and pregnant sheep. Uterine and omental artery NOS activity and cGMP production were inhibited 75-85% by Ca2+ removal. ecNOS was localized only in uterine and systemic artery endothelium (not VSM) by immunohistochemistry and Western analysis; nNOS was not detected. Compared with nonpregnant ewes, pregnancy increased expression of ecNOS in uterine [2.1- to 4.2-fold (P < 0.0001)] and omental [1.3- to 2.2-fold (P = 0.032)] but not renal (P = 0.1367) artery endothelium. Increases in uterine were greater than in omental artery endothelium. Levels of plasma and urinary cGMP were elevated (P < 0.01) proportionally (1.8- to 2.0-fold) in pregnant versus nonpregnant ewes. During pregnancy, expression of uterine artery endothelium-derived (not VSM) ecNOS constitutive isoform is increased, whereas expression in systemic vessels shows little or no change.

Transcriptional regulation of endothelial nitric oxide synthase expression in uterine artery endothelial cells by c-Jun/AP-1

“…In the uterine circulation, numerous studies have shown that NO produced locally by uterine artery endothelial cells (UAEC) is the most important, though not the only, factor to regulate uterine vasodilatation during normal pregnancy and the follicular phase of the estrous cycle as well as estrogen replacement therapy (Chen et al, 2006;Magness et al, 1997;Weiner et al, 1994). Uterine vasodilatation as shown by dramatic rises in uterine blood flow during pregnancy is required for delivering nutrients and oxygen to the developing fetus and thus is detrimental to fetal development (Lang et al, 2003).…”

“…The regulation of NOS3 expression in endothelial cells can take place at the levels of transcription (i.e., NOS3 promoter activity) and post-transcription (i.e., mRNA stability) (Fleming and Busse, 2003). Despite a large body of evidence accumulated showing that increased uterine artery endothelial NOS3 protein coincides with the pregnancy-associated and estrogen-induced uterine vasodilatation (Chen et al, 2006;Magness et al, 1997;Weiner et al, 1994), the mechanisms by which NOS3 expression is controlled in the UAEC are generally unknown. Uterine artery endothelial NOS3 mRNA is increased in ovariectomized sheep receiving estrogen replacement therapy (Rosenfeld et al, 2003), suggesting that uterine artery endothelial NOS3 expression might be regulated at the level of gene transcription.…”

Simultaneous imaging of [Ca2+]iand intracellular NO production in freshly isolated uterine artery endothelial cells: effects of ovarian cycle and pregnancy

“…The follicular phase of the ovarian cycle is partially characterized by elevation in UBF, and both pregnancy and follicular phase are associated with both increased estrogen levels and eNOS expression in UA endothelium (UAE) (34), as well as estrogen enhancement of flow-induced vasodilation (19,20). To date, only indirect measures have implied an increase in UA NO production (33,34,46), and there has been no direct demonstration of NO production in UA or evaluation of whether NO production increases in parallel with increased eNOS expression in these physiological states. This is not only important for the reasons stated above but also because more recent studies in sheep have implied that the pregnancyassociated increase in the endothelium-dependent relaxation of the UA via NO release may not only occur by way of increases in eNOS expression but also by way of reprogramming of kinase signaling (3).…”

“…During pregnancy, the uterine artery (UA) shows increased vasodilation in response to a number of agonists, including ATP, which in turn contributes to the increase in uterine blood flow (UBF) necessary to meet the needs of the growing fetus (3,(32)(33)(34). The follicular phase of the ovarian cycle is partially characterized by elevation in UBF, and both pregnancy and follicular phase are associated with both increased estrogen levels and eNOS expression in UA endothelium (UAE) (34), as well as estrogen enhancement of flow-induced vasodilation (19,20).…”

Expression of Nitric Oxide Synthase Isoforms in the Human Placenta Is Not Altered by Labor

“…Nitric oxide is hypothesized to contribute to the maintenance of pregnancy, by increasing uterine blood flow [2,3], maintaining myometrial quiescence [4][5][6], and others. The major effect of nitric oxide on cell function is mediated through the activation of soluble guanylyl cyclase, which generates guanosine 3',5'-cyclic monophosphate (cGMP) as an intracellular second messenger [7].…”