Abstract
In this paper, we evaluated the hypothesis that prostaglandin F 2α (PGF 2α) 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 PGF 2α-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 μg/rat). The presence of PGF 2α (10 −8M) in the incubation medium produced an increase in NOS activity ( p ≤ 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 PGF 2α could be modulating the Ca 2+-independent NOS activity. We determined NOS activity using 1 mM EGTA, a chelator of Ca 2+, in a free Ca 2+ medium. These results indicated that PGF 2α produces an increase in Ca 2+-independent NOS activity ( p ≤ 0.05). PGF 2α induces contraction of the oviductal smooth muscle in a concentration dependent manner. l-NMMA enhanced PGF 2α 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 PGF 2α.
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