CELLULAR-LOCALIZATION AND HORMONAL-REGULATION OF INDUCIBLE NITRIC-OXIDE SYNTHASE IN CYCLING MOUSE UTERUS

Nitric oxide (NO), a potent and versatile free radical, is synthesized in macrophages and mast cells as well as in other types of cells by t he inducible form of nitric oxide synthase (iNOS). In this study, cell s containing iNOS were identified in the uteri of cycling mice by usin g a rabbit antibody generated to an iNOS-specific peptide. Macrophages were identified in semiserial sections of the same tissues with the m onoclonal antibody, F4/80, and mast cells were identified by toluidine blue staining. In tissue sections of uteri obtained from mice in the four stages of the estrous cycle (8 to 11 mice per stage), iNOS immuno reactivity was strongest in diestrus-I uteri and weakest in diestrus-I I uteri. Myometrial mast cells and endometrial epithelial cells were p rominent locations of iNOS, and specific protein was also present in m yometrial smooth muscle and macrophage-like cells in the endometrial s troma. Because cyclic variations suggested regulation of iNOS expressi on by ovarian steroid hormones, studies were done using ovariectomized mice. Seven days after ovariectomy, immunoreactive iNOS was low but d etectable in mast cells and luminal epithelial cells. In the uteri of ovariectomized, estradiol-17 beta (E(2))-treated mice, mast cells were iNOS(+) after 24 h whereas epithelial cells were negative; the revers e was observed in progesterone (P-4)-treated mice. Both mast cells and epithelial cells were iNOS(+) in the uteri of mice that had received a combination of E(2) + P-4. These results indicate that several types of uterine cells produce iNOS and that expression of this enzyme in s pecific cell lineages is governed by ovarian steroid hormones. The dat a are consistent with the postulate that NO derived from uterine leuko cytes and other types of cells plays a role in uterine cyclicity and p reparation for pregnancy.