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 l uteum regression in the rat by increasing prostaglandin F-2 alpha synt hesis during the luteolytic phase. In the present study we were intere sted in determining whether nitric oxide synthase activity is modulate d with the corpus luteum development. For this purpose ovarian tissues obtained from pseudopregnant rats at different stages of pseudopregna ncy, early, middle, and late, were used. Working with different doses of two competitive nitric oxide synthase inhibitors, N-G-monomethyl-L- arginine (L-NMMA) and aminoguanidine (AG), we investigated the possibl e role of endogenous nitric oxide in the regulation of prostaglandin F -2 alpha production by rat ovaries in the three different phases menti oned. We found that nitric oxide synthase activity diminishes with the corpus luteum development and that the calcium-independent activity w as the predominant form of this enzyme in all stages studied. Endogeno us nitric oxide increased prostaglandin F-2 alpha synthesis only durin g the late phase of the corpus luteum. In the study of the possible ro le of nitric oxide regulating ovarian steroidogenesis, we found that L -NMMA increased progesterone production and diminished prostaglandin F -2 alpha synthesis in ovarian tissue from pseudopregnant rats in the l ate phase. These results suggest that nitric oxide could participate i n the corpus luteum demise in the rat by modulating part of prostaglan din F-2 alpha and progesterone production.