Riemer R K, Buscher C, Bansal R K, Black S M, He Y, Natuzzi E S
Department of Surgery, University of California, San Francisco 94143, USA.
Am J Physiol. 1997 Jun;272(6 Pt 1):E1008-15. doi: 10.1152/ajpendo.1997.272.6.E1008.
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.
一氧化氮（NO）可使子宫平滑肌舒张，由妊娠子宫产生。我们之前的研究显示，大鼠子宫一氧化氮合酶（NOS）活性在妊娠期间升高，足月时下降。在本研究中，我们检测了NOS同工型表达的分布，以确定其调节是否与足月前抑制子宫收缩的作用一致。在妊娠第17 - 18天，NOS免疫组化显示两种同工型的表达：血管内皮中的内皮型组成性NOS（ecNOS）以及子宫肌层、血管平滑肌和蜕膜上皮中的诱导型NOS（iNOS）。免疫印迹显示，足月分娩的大鼠中，iNOS的表达下降近五倍，而ecNOS下降两倍。我们得出结论，iNOS在妊娠大鼠子宫肌层中表达，但未在未孕大鼠子宫肌层中表达，并且在足月分娩时iNOS表达下降。随着妊娠进展，子宫肌层iNOS表达的变化模式表明，NO可能以自分泌和/或旁分泌方式在足月前抑制子宫收缩。
