Effect of prostaglandin F2 alpha (PGF2 alpha) on oviductal nitric oxide synthase (NOS) activity: possible role of endogenous NO on PGF2 alpha-induced contractions in rat oviduct.

In this paper, we evaluated the hypothesis that prostaglandin F2 alpha (PGF2 alpha) regulates NOS activity and we also investigated, by means of nitric oxide inhibitors (N-monomethyl-L-arginine monoacetate, L-NMMA) the role of endogenous NO on PGF2 alpha-induced contractions in rat oviduct. NOS activity was determined by measuring the conversion of 14[C]-L-arginine to 14[C]-L-citrulline on oviductal homogenates from estrogenized rats (1 microgram/rat). The presence of PGF2 alpha (10(-8) M) in the incubation medium produced an increase in NOS activity (p < or = 0.05). The effect of the prostanoid was blocked completely by the presence of two NOS inhibitors: N-nitro-L-arginine methyl ester (L-NAME, 0.6 mM) and aminoguanidine (Ag, 0.5 mM). These results suggested that PGF2 alpha could be modulating the Ca(2+)-independent NOS activity. We determined NOS activity using 1 mM EGTA, a chelator of Ca2+, in a free Ca2+ medium. These results indicated that PGF2 alpha produces an increase in Ca(2+)-independent NOS activity (p < or = 0.05). PGF2 alpha induces contraction of the oviductal smooth muscle in a concentration dependent manner. L-NMMA enhanced PGF2 alpha induced contraction of the oviduct, providing indirect evidence that there is a basal release of NO in the oviduct, which may reduce and/or modulate the contractile effects of PGF2 alpha.