Constitutive and inducible nitric oxide synthases in mouse uterus and their changes following treatment with ovarian steroids. Immunocytochemical and histoenzymological studies.

: Previous studies showed that different nitric oxide synthase isoforms are present in the uterus of laboratory mammals and that their expression is influenced by ovarian steroids. However, the results of these studies are not univocal, probably owing to the different hormonal treatments and techniques applied to reveal nitric oxide synthases. In this study we investigated the distribution and expression of constitutive and inducible nitric oxide synthase isoforms by immunocytochemistry and their changes following treatment of the mice with 17 beta-estradiol alone or in combination with medroxyprogesterone. Moreover, we compared the immunoreactivities for nitric oxide synthases with the histochemical reaction for NADPH-diaphorase, an enzyme that may be associated with nitric oxide synthase. The results obtained show that the two nitric oxide synthase isoforms are differently expressed in surface epithelium, glands, stromal cells and myometrium and that, as compared with the uteri from mice treated with estrogen alone, those from mice treated with estrogen plus progestin showed enhanced expression of constitutive nitric oxide synthase in the myometrium and of the inducible isoform in surface epithelium, glands, stromal cells and myometrium. The results obtained with NADPH-diaphorase reaction show that there is not a colocalization of nitric oxide synthase isoforms and NADPH-diaphorase, apart from a partial colocalization in part of the stromal cell population and myometrium. This provides evidence that NADPH-diaphorase histochemistry is not a valid technique to localize the sites of nitric oxide synthesis in the mouse uterus and that the use of this technique may generate misleading in the interpretation of the effect of ovarian steroids in regulating nitric oxide production by the different components of the uterine wall.