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1 Department of Obstetrics and Gynecology, Perinatal Research Laboratories and 2 Department of Animal Sciences, University of Wisconsin-Madison, Madison, Wisconsin 53715
Normal pregnancy and the follicular phase of the ovarian
cycle are both estrogen-dominated physiological states that are characterized by elevations in uterine blood flow and endothelial nitric oxide synthase (eNOS) protein expression in the uterine artery
(UA) endothelium. It is unknown if elevations in mRNA level account for
the changes in protein or eNOS activity. We tested the hypothesis that
pregnancy and the follicular phase are associated with increases in
eNOS mRNA and the consequent elevated expression of eNOS protein
results in increased circulating nitric oxide (NO) levels. UA were
obtained from pregnant (PREG; n = 8; 110-130 days
gestation; term = 145 ± 3 days), nonpregnant luteal (LUT; n = 6), nonpregnant follicular (FOL; n = 6), and nonpregnant ovariectomized (OVEX; n = 6)
sheep. Circulating NO levels were analyzed as total NO2-NO3 (NOx). Western analysis
performed on UA endothelial-isolated proteins demonstrated that eNOS
protein levels were OVEX = LUT
FOL < PREG
(P < 0.05), whereas eNOS mRNA expression (RT-PCR) in
UA endothelial cells obtained by limited collagenase digestion was
OVEX < LUT < FOL < PREG (P < 0.05).
Pregnancy dramatically elevated eNOS protein (4.1- to 6.9-fold) and
mRNA (2.4- to 6.9-fold) over LUT controls (P < 0.01).
Circulating NOx levels were not altered by ovariectomy or
the ovarian cycle but were elevated from 4.4 ± 1.1 µM in LUT to
12 ± 4, 22 ± 3, and 41 ± 3 µM at 110, 120, and 130 days gestation (P < 0.01). Systemic NOx
levels in singleton (12.5 ± 1.6 µM) were less
(P < 0.01) than in multiple (twin 27.6 ± 6.5 µM; triplet = 46 ± 10 µM) pregnancies. Therefore, the
follicular phase and, to a much greater extent, pregnancy are
associated with elevations in UA endothelium-derived eNOS expression,
although significant increases in systemic NOx levels were
only observed in the PREG group (multiple > singleton). Thus, although UA endothelial increases in eNOS protein and mRNA levels are
associated with high estrogen states, increases in local UA NO
production may require additional eNOS protein activation to play its
important role in the maintenance of uterine blood flow in pregnancy.
endothelial nitric oxide synthase; nitric oxide; ovarian cycle; uterus; estrogen; vasodilator
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