Converting enzyme activity in sow oviducts at different stages of the sex cycle. Influence of inhibitors of prostaglandin synthesis and its possible role in the inotropic effects of bradykinin.

The existence of angiotensin I converting enzyme (CE) activity in isolated sow Fallopian tubes and the "in vitro" influences of exogenous bradykinin (BK) on the spontaneous motility of sow oviducts, were explored. Independently of the stage of the sex cycle, the ampullary region of sow Fallopian tubes presented a higher basal CE activity than the isthmic one. On the other hand a greater CE activity was found in the isthmus at estrus and metestrus than at proestrus. Acetylsalicylic acid and mefenamic acid, two inhibitors of prostaglandin synthesis, reduced the CE activity only in ampullary segments obtained at metestrus. BK (0.06 microgram.ml-1) stimulates the spontaneous contractions of isthmic and ampullary tubal segments, triggering tonic responses. The positive inotropism had a longer duration in the isthmus than in the ampulla; presented at estrus a higher magnitude than at proestrus and was enhanced by captopril (50 microgram.ml-1). The data suggest that the low CE activity found in the isthmic tubal region could be subserving the positive inotropic action of BK in the isthmus, long lasting in comparison to that evoked in the ampulla. Moreover, at metestrus some tissue eicosanoid might be modulating the CE activity of ampullary tubal segments. Alternatively the foregoing results could be explained assuming the presence of a carboxy-peptidase different than CE in one region of the oviducts and not in the other, i.e., either one with different sensitivity towards sex hormones and prostaglandin synthesis blockers.