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Estradiol-17ß Inhibits Nitric Oxide Synthase (NOS)-II and Stimulates NOS-III Gene Expression in the Rat Uterus¹

^a Departments of Obstetrics and Gynecology and Anatomy and Neurosciences, The University of Texas Medical Branch, Galveston, Texas 77555

ABSTRACT

Nitric oxide (NO) is synthesized by NO synthases (NOS) from L-arginine in a variety of tissues, including rat uterus. Progesterone was shown to be required for maintaining elevated NOS II expression in pregnant rat uterus. However, effects of estrogens on uterine NOS II expression remains unclear. In the present study, we examined whether 17ß-estradiol regulates NO production and NOS II expression in the rat uterus during pregnancy and in nonpregnant rats treated with lipopolysaccharide (LPS). Rats on Day 18 of pregnancy received 17ß-estradiol (0.5 or 5 µg/rat). Groups of ovariectomized (ovx) rats received 17ß-estradiol (5 µg/rat) or LPS (1 mg/rat) or a combination of the two or received vehicle only. All rats were sacrificed 24 h after treatments. Nitrite concentrations in uterine cultures were measured by Greiss reaction. Uterine NOS II and NOS III proteins and mRNA levels were determined by Western blotting and reverse transcription polymerase chain reaction, respectively. In the pregnant rat, estradiol administration caused inhibition in total NO production, suppression of both mRNA and protein levels of NOS II enzyme, and increase in NOS III mRNA and protein levels in the uterus in a dose-dependent manner. The data indicate that estradiol inhibits NOS II and total NO generation and stimulates NOS III expression. In ovx rats, LPS stimulated NOS II mRNA and NO production by the uterus. Coadministration of 5 µg estradiol profoundly suppressed NOS II mRNA and NO generation but elevated NOS III mRNA. Thus, estradiol inhibited LPS-induced increases in NOS II mRNA. Estradiol inhibits NO production by NOS II through the inhibition of NOS II expression in the rat uterus. This inhibition of NOS II expression occurs whether NOS II expression is constitutive (pregnancy) or induced (LPS-treated nonpregnant). Estradiol inhibition of NOS II expression occurs in the presence (pregnancy) or absence (ovx) of progesterone. Estradiol may play a role in regulating NOS II expression and NO production and uterine contractility during pregnancy and labor.

FOOTNOTES

First decision: 24 September 1999.

¹ This work was supported in part by NIH grants HD 30273 and HL 58144 to C.Y.

² Correspondence: Chandra Yallampalli, Department of Obstetrics and Gynecology, The University of Texas Medical Branch, 301 University Boulevard, Route 1062, Galveston, TX 77555. FAX: 409 747 0475; chyallam{at}utmb.edu

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