Nitric oxide participates in the corpus luteum regression in ovaries isolated from pseudopregnant rats

In previous reports we found that nitric oxide is involved in corpus luteum regression in the rat by increasing prostaglandin F2 alpha synthesis during the luteolytic phase. In the present study we were interested in determining whether nitric oxide synthase activity is modulated with the corpus luteum development. For this purpose ovarian tissues obtained from pseudopregnant rats at different stages of pseudopregnancy, early, middle, and late, were used. Working with different doses of two competitive nitric oxide synthase inhibitors, NG-monomethyl-L-arginine (L-NMMA) and aminoguanidine (AG), we investigated the possible role of endogenous nitric oxide in the regulation of prostaglandin F2 alpha production by rat ovaries in the three different phases mentioned. We found that nitric oxide synthase activity diminishes with the corpus luteum development and that the calcium-independent activity was the predominant form of this enzyme in all stages studied. Endogenous nitric oxide increased prostaglandin F2 alpha synthesis only during the late phase of the corpus luteum. In the study of the possible role of nitric oxide regulating ovarian steroidogenesis, we found that L-NMMA increased progesterone production and diminished prostaglandin F2 alpha synthesis in ovarian tissue from pseudopregnant rats in the late phase. These results suggest that nitric oxide could participate in the corpus luteum demise in the rat by modulating part of prostaglandin F2 alpha and progesterone production.