Increased expression of nitric oxide synthase in the myometrium of the pregnant rat uterus

R. Kirk Riemer, Cori Buscher, Raj K. Bansal, Stephen M. Black, Youping He, Eileen S. Natuzzi

Research output: Contribution to journalArticlepeer-review

47 Scopus citations


Nitric oxide (NO) relaxes uterine smooth muscle and is produced by the pregnant uterus. Our previous studies revealed an increase in rat uterine NO synthase (NOS) activity in pregnancy and a decline at term. In the present study, we have examined the distribution of NOS isoform expression to determine whether their regulation is consistent with a role in the inhibition of uterine contractions before term. At day 17-18 of pregnancy, NOS immunohistochemistry revealed expression of two isoforms: endothelial constitutive form of NOS (ecNOS) in vascular endothelium and inducible form of NOS (iNOS) in myometrial and vascular smooth muscle and in decidual epithelium. Immunoblotting revealed that expression of iNOS declined nearly fivefold, whereas ecNOS declined twofold in laboring rats at term. We conclude that iNOS is expressed in myometrium of pregnant rat uterus but not the virgin rat and that iNOS expression declines at term when labor is present. The pattern of changes in myometrial iNOS expression with advancing gestation suggests that NO could act in an autocrine and/or paracrine manner to inhibit uterine contractions before term.

Original languageEnglish (US)
Pages (from-to)E1008-E1015
JournalAmerican Journal of Physiology - Endocrinology and Metabolism
Issue number6 35-6
StatePublished - Jun 1997
Externally publishedYes


  • Immunohistochemistry
  • Inducible nitric oxide synthase
  • Labor
  • Pregnancy maintenance
  • Ribonuclease protection assay

ASJC Scopus subject areas

  • Endocrinology, Diabetes and Metabolism
  • Physiology
  • Physiology (medical)


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