Effects of in vitro, acute and chronic treatment with fluoxetine on the sympathetic neurotransmission of rat vas deferens.

It is described that fluoxetine treatment is able to induce ejaculatory disorders. However, the exact mechanism is still not fully understood. Therefore, this study was carried out to further evaluate the anti-ejaculatory effects of fluoxetine, using different approaches (in vitro or in vivo treatments), on the sympathetic neurotransmission of the rat vas deferens. Vas deferens from male Wistar rats were used to check the in vitro effects of fluoxetine 10-6M, 3.10-6M or 10-5M. Animals were also acutely (20mg/kg, i.p. 4h or 24h) or chronically (10mg/kg, i.p., 30days) treated with fluoxetine or drug-free vehicle. The vas deferens from non-treated and treated animals were isolated and mounted in an isolated organ bath for the study of the contractions induced by adrenergic agonists, tyramine, 5-HT, Ca2+ or electrical field stimulation. In vitro or acute treatment with fluoxetine decreased the contraction induced by agonists, Ca2+ or electrical field stimulation. The chronic treatment with fluoxetine decreased the contractions induced agonists, tyramine or Ca2+, but did not modify the contractions induced by electrical field stimulation. We have shown that in vitro or in vivo fluoxetine treatment is able to alter the sympathetic neurotransmission of the rat vas deferens which could be related to alterations in the calcium signalling.

Influence of acute treatment with sibutramine on the sympathetic neurotransmission of the young rat vas deferens.

The effects of acute treatment with sibutramine on the peripheral sympathetic neurotransmission in vas deferens of young rats were still not evaluated. Therefore, we carried out this study in order to verify the effects of acute sibutramine treatment on the neuronal- and exogenous agonist-induced contractions of the young rat vas deferens. Young 45-day-old male Wistar rats were pretreated with sibutramine 6 mg/kg and after 4h the vas deferens was used for experiment. The acute treatment with sibutramine was able to increase the potency (pD2) of noradrenaline and phenylephrine. Moreover, the efficacy (Emax) of noradrenaline was increased while the efficacy of serotonin and nicotine were decreased. The maximum effect induced by a single concentration of tyramine was diminished in the vas deferens from treated group. Moreover, the leftward shift of the noradrenaline curves promoted by uptake blockers (cocaine and corticosterone) and ß-adrenoceptor antagonist (propranolol) was reduced in the vas deferens of treated group. The initial phasic and secondary tonic components of the neuronal-evoked contractions of vas deferens from treated group at the frequencies of 2 Hz were decreased. Moreover, only the initial phasic component at 5 Hz was diminished by the acute treatment with sibutramine. In conclusion, we showed that the acute treatment with sibutramine in young rats was able to affect the peripheral sympathetic nervous system by inhibition of noradrenaline uptake and reduction of the neuronal content of this neurotransmitter, leading to an enhancement of vas deferens sensitivity to noradrenaline.

A comparison of histamine effects on the sympathetic neurotransmission of testicular capsule and rat vas deferens.

Histamine is an important modulatory agent of the sympathetic neurotransmission, but its exact action on the testicular capsule or rat vas deferens is not fully understood. The present study sought to further investigate the functional effects of histamine on the neuronal and exogenous noradrenaline-induced contraction of the testicular capsule and rat vas deferens as well as to evaluate the contractile properties of this drug. The testicular capsule or vas deferens from Wistar rats, 3-4 months old, weighing 300-400 g, was isolated and mounted in organ baths for functional experiments. The results indicated that the neuronally evoked contraction of the testicular capsule was affected by histamine (10(-10) to 10(-8) M) with participation of inhibitory (H3 receptors) and excitatory (H1 receptors) receptors. Histamine (10(-7) to 10(-4) M) modulated the field-stimulated vas deferens by excitatory (H2 receptors) and inhibitory (H1 receptors) receptors. Histamine was able to decrease the tonic response for noradrenaline-induced contractions with participation of H1 receptors (testicular capsule) and H3 receptors (vas deferens) followed by nitric oxide generation. At high concentration, histamine exerts contractile effects in both tissues. In the testicular capsule, the histamine-induced contractions were related to H1 receptor activation followed by release of prostaglandins. In contrast, the contractile effects of histamine in the vas deferens were related to H2 receptor activation followed by release of catecholamines from sympathetic nerve endings. Therefore, our results indicate that histamine induced several effects on the sympathetic neurotransmission of rat testicular capsule and vas deferens. These effects are dependent on the concentration used and with participation of multiple histamine receptors.

Functional characterization of acetylcholine receptors and calcium signaling in rat testicular capsule contraction.

The motor activity of mammalian testicular capsule (TC) contributes to male fertility and infertility, but the acetylcholine receptors related to the contractions induced by cholinergic drugs are poorly known. Indeed to characterize the acetylcholine receptors and cellular signaling by Ca(2+) involved in TC motor activity of rats, the potency of agonists (pD2) and antagonists (pA2) of acetylcholine receptors, and effects of Ca(2+) cellular transport blockers on the cholinergic contractions were evaluated. pD2 values of acetylcholine (5.98) were ten-fold higher than that of carbachol (4.99). Efficacy (Emax) of acetylcholine and carbachol to induce contractions corresponded to 95% and 97% of Emax for KCl, but Emax for nicotine was very low (8% of Emax for KCl). Further, physostigmine did not affect the acetylcholine potency. Contractions induced by acetylcholine or carbachol were antagonized by muscarinic but not nicotinic antagonist. The order of pA2 values obtained for muscarinic antagonists, namely atropine>4-DAMP>AF-DX116>pirenzepine, corresponded to a typical profile of M3 receptors. Contractions induced by acetylcholine or carbachol were inhibited by blockers of Ca(2+) influx through voltage-dependent calcium channels (nifedipine and Ni(2+)), Ca(2+) reuptake by sarco-endoplasmic reticulum (cyclopiazonic acid) and mitochondria (FCCP). The protein kinase C (PKC) inhibitor chelerythrine only affected the acetylcholine-induced contraction. These results suggest that TC motor activity of rats are mediated mainly by M3 receptors followed by the increase of cytosolic Ca(2+) concentration regulated by voltage-dependent calcium channels, sarco-endoplasmic reticulum and mitochondria. Furthermore, the differential effects of chelerythrine in the acetylcholine or carbachol-induced contractions are discussed.

Changes of cytosolic calcium and contractility of young rat vas deferens by acute treatment with amphetamine, fluoxetine or sibutramine.

Previous studies conducted in our laboratory indicated that administration of amphetamine, fluoxetine or sibutramine affects the sympathetic nervous system of the rat vas deferens. Therefore, our goal was to verify the role of calcium in vasa deferentia from young rats pretreated with a single dose of these drugs. Young 40-day-old male Wistar rats were pretreated with amphetamine 3 mg/kg, fluoxetine 10 mg/kg or sibutramine 6 mg/kg for 4 h before the experiments. CaCl(2) (10 mM) was used to induce contraction through time-effect curves in calcium-free solution to measure phasic and tonic components. We also evaluated the calcium-induced fluorescence of vas deferens cut into thin slices. In rats pretreated with amphetamine, we found an increase of the tonic contraction component which was reduced by verapamil. The phasic and tonic responses were increased in the group treated with fluoxetine, but only the tonic response was more sensitive to the antagonism by verapamil. The group treated with sibutramine showed an increase of phasic response whereas the tonic component was decreased. In this group an increase of the affinity for verapamil antagonism was found. In the calcium fluorescence study it was observed that the group treated with amphetamine, fluoxetine or sibutramine showed higher basal Ca(2+) fluorescence after stimulus with KCl (70 mM), noradrenaline (10(-4)M) or acetylcholine (10(-4)M). In all pretreated groups the calcium fluorescence was diminished by nifedipine 10(-7)M. Therefore, the pretreatment with amphetamine, fluoxetine or sibutramine seems to affect the calcium contractility and homeostasis in young rat vas deferens.