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The effect of the inhibition of nitric oxide synthase (NOS) on ovum transport and oviductal motility in rats was investigated. Three different NOS inhibitors were injected into the ovarian bursa at oestrus or day 3 of pregnancy. Oviducts and uteri were flushed 24 h later and the presence of ova was recorded. In oestrous and pregnant rats, treatment resulted in accelerated egg transport, as shown by a decrease in the number of ova present in the oviducts. In cyclic rats, intrabursal injection of 1 mg kg-1 of either N-monomethyl-L-arginine (L-NMMA) or N omega nitro-L-arginine methyl ester (L-NAME) elicited a 30% reduction in the number of ova present in the oviducts, whereas in pregnant animals, the same dose of L-NMMA produced a reduction of 40%. Simultaneous administration of the NO donor spermine NONOate (5 mg kg-1) completely reversed the effect of L-NMMA. Tubal motility was assessed by microsphere displacement analysis within the oviduct. Surrogate ova were transferred to the oviductal lumen at oestrus and 24 h later the effect of intraoviductal injection of 1 microgram L-NMMA or vehicle was assessed. The microspheres in the isthmus showed an oscillating motion, and periods in which movement was not detectable. However, L-NMMA treatment produced a 3.6-fold increase in the maximum instant velocities and a significant reduction in the resting periods of the microspheres compared with the control group (P < 0.001). These results provide evidence that NO inhibition increases tubal motility that results in accelerated ovum transport, and indicate that NO could act as a paracrine signal between different layers of the oviductal wall, providing a role for endogenous NO in regulation of tubal function.

The present study was performed in order to explore the influence of ova present within rat oviducts on: a) tubal spontaneous motility and b) oviduct prostaglandin production. It was found that the isometric developed tension (IDT) of tubes isolated from proestrous rats (preovulatory oviducts) was significantly higher (P less than 0.01) than the IDT of tubes from rats at estrus and at metestrus (postovulatory oviducts). After flushing the oviducts with KRB solution (i.e., after removing existing ova) the IDT of the oviducts obtained from estrous rats increased significantly (P less than 0.01), whereas the IDT of tubes isolated from proestrous rats (i.e., preparations without ova) was not modified. On the other hand, isolated tubes containing their corresponding ova released into the suspending solution significantly more PGE1 than PGE2 or PGF2 alpha (P less than 0.005). It was particularly interesting to find that after flushing the oviducts, tissue production of PGE1, PGE2 and PGF2 alpha was similar. Finally, when dose response curves for PGE1 and for PGE2 on the spontaneous contractions of oviducts isolated from rats at proestrus, estrus and metestrus were constructed, both PGs evoked an inhibitory inotropic action. The ED50 for PGE1 in tubes from estrous rats was significantly smaller (P less than 0.01) than that for metestrous animals but significantly greater (P less than 0.01) than that observed in oviducts from proestrous rats. The ED50 for PGE2 did not change in the different tested periods of the sex cycle. Results reported herein suggest the possibility that the ova present within rat oviducts, may influence their own transport along the tubes by modifying the amount of prostaglandins produced by the oviducts or via their own prostaglandin synthesis.

Dose-response curves for norepinephrine (NE), dopamine (DA) and 2-bromo-alpha-ergocryptine (BEC) in the isthmic and ampullary regions isolated from proestrous sow oviducts, were drawn. NE, DA and BEC depressed the contractile activity of ampullary segments in dose-dependent fashion. In the isthmic region, NE induced a dose-related stimulation whereas DA and BEC evoked relaxation. Propranolol (10(-6)M) did not modify significantly the effect of DA on the ampulla, whereas spiperone, chlorpromazine and haloperidol, shifted to the right DA dose-response curves. Haloperidol and spiperone were able to partially antagonize responses to DA of the isthmus. The catecholamine contents of the ampullary (a) and isthmic (i) regions of sow oviducts during proestrus (P), estrus (E) and metestrus (M) proved to be quite different and differently affected by the variations of the sex cycle: NE, DA and epinephrine (EPI) in (i) higher than in (a); NE in (i) and (a) during M higher than during E; NE in (i) lower during E than during P. The probable presence of specific dopamine receptors in sow oviducts as well as their eventual role in modulating tubal motility are discussed in this paper.

The output of prostaglandins (PGs) E1, E2 and F2 alpha, from ampullary and isthmic portions of sow oviducts isolated during proestrus, estrus and metestrus, was explored. Moreover, in vitro cumulative dose-response curves for the contractile effect of these three PGs, on identical oviductal segments, were constructed. Isthmic preparations from proestrous and metestrous animals released more PGE1 and PGF2 alpha than PGE2 "like material". During estrus, the outputs of PGE1, PGE2 and PGF2 alpha were similar, whereas, oviducts from proestrous and metestrous sows released less PGE1 and PGF2 alpha than during estrus. Although the output of PGE2 "like material" from isthmic and ampullary segments did not differ significantly during the three stages of the sex cycle, ampullary metestrous preparations released more PGE1 and PGF2 alpha, than estrous or proestrous ones. The addition of PGE1, PGE2 or PGF2 alpha, consistently stimulated the amplitude of contractions of isthmic oviductal segments isolated from proestrous and metestrous sows. Within the concentration-range explored, dose-response curves for PGE2 and PGE1 were to the left of those for PGF2 alpha in the isthmus obtained before ovulation (proestrus) but not in segments isolated at later times (2-3 days) of the cycle (metestrus). The stimulatory dose-response curves for PGE1, or PGE2, in isthmic segments of metestrous preparations incubated with phentolamine (10(-6)M) were shifted to the right of controls not exposed to the adrenoreceptor blocker, whereas, the curve for PGF2 alpha without phentolamine, was identical to that obtained in its presence. PGE1 and PGE2 did not evoke significant contractile effects on oviductal ampullary portions from proestrous sows, whereas, PGF2 alpha was clearly stimulatory at concentrations of 10(-9)M and higher. In ampullary segments isolated after ovulation (metestrus) the threshold for contractile enhancement following PGF2 alpha was greater than during proestrus, whereas, PGE1 elicited a significant inhibition of contractions. The spontaneous contractile pattern exhibited by isthmic and ampullary oviductal regions, prior to and after ovulation, is discussed in terms of tissue PG generation and output and is compared with results regarding tubal motility following the exposure to exogenous PGs.

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.