EFFECT OF PROSTAGLANDIN-F2-ALPHA (PGF(2-ALPHA)) ON OVIDUCTAL NITRIC-OXIDE SYNTHASE (NOS) ACTIVITY - POSSIBLE ROLE OF ENDOGENOUS NO ON PGF(2-ALPHA)-INDUCED CONTRACTIONS IN RAT OVIDUCT

In this paper, we evaluated the hypothesis that prostaglandin F-2 alph a (PGF(2 alpha)) regulates NOS activity and we also investigated, by m eans of nitric oxide inhibitors (N-monomethyl-L-arginine monoacetate, L-NMMA) the role of endogenous NO on PGF(2 alpha)-induced contractions in rat oviduct. NOS activity was determined by measuring the conversi on of (14)[C]-L-arginine to (14)[C]-L-citrulline on oviductal homogena tes from estrogenized rats (1 mu g/rat). The presence of PGF(2 alpha) (10(-8) M) in the incubation medium produced an increase in NOS activi ty (p less than or equal to 0.05). The effect of the prostanoid was bl ocked completely by the presence of two NOS inhibitors: N-nitro-L-argi nine methyl ester (L-NAME, 0.6 mill) and aminoguanidine (Ag, 0.5 mill) . These results suggested that PGF(2 alpha) could be modulating the Ca 2+-independent NOS activity. We determined NOS activity using 1 mM EGT A, a chelator of Ca2+ in a free Ca2+ medium. These results indicated t hat PGF(2 alpha) produces an increase in Ca2+-independent NOS activity (p less than or equal to 0.05). PGF(2 alpha) induces contraction of t he oviductal smooth muscle in a concentration dependent manner. L-NMMA enhanced PGF(2 alpha) induced contraction of the oviduct, providing i ndirect evidence that there is a basal release of NO in the oviduct, w hich may reduce and/or modulate the contractile effects of PGF(2 alpha ).