Nitric oxide synthase/guanylate cyclase pathway modulates the rat vas deferens contractility induced by phenylephrine

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 β-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.

Efficacy of sildenafil citrate (Viagra) in men with premature ejaculation

OBJECTIVES

Premature ejaculation (PE) is the most common ejaculatory dysfunction. We assessed the efficacy of sildenafil to increase the time to ejaculation, improve ejaculatory control, and decrease the postejaculatory erectile refractory time in men with PE.

DESIGN AND METHODS

The main study was an 8-week, double-blind, placebo-controlled, parallel group study in men between 18 and 65 years of age with diagnosed PE. A substudy was also conducted using a subset of patients (two-way crossover, one center) before entry to the main study. The primary study measured intravaginal ejaculatory latency (IELT) and responses to the Index of Premature Ejaculation (IPE) questionnaire. The substudy measured vibrotactile stimulation ejaculatory latency time (VTS-ELT) and postejaculatory erectile refractory time. Differences between treatment groups were determined by ancova at the 5% level of significance.

RESULTS

The change in IELT (1.6 +/- 6.08 vs. 0.6 +/- 2.07 minutes) and VTS-ELT (2.9 +/- 0.4 vs. 2.4 +/- 0.4 minutes) were higher after taking sildenafil, compared with placebo, but did not reach statistical significance. However, patients who took sildenafil (vs. placebo) reported significantly (P < 0.05) increased ejaculatory control (1.8 +/- 0.3 vs. 1.5 +/- 0.3), increased ejaculatory confidence (2.2 +/- 0.2 vs. 1.9 +/- 0.2), and improved overall sexual satisfaction scores (3.1 +/- 0.2 vs. 2.8 +/- 02) on the IPE, and had a decreased postejaculatory erectile refractory time (3.2 +/- 0.7 vs. 6.4 +/- 0.7 minutes). The most common adverse events for sildenafil (vs. placebo) were headache (15% vs. 1%), flushing (15% vs. 0%), dyspepsia (5% vs. 1%), abnormal vision (5% vs. 0%), and rhinitis (5% vs. 0%).

CONCLUSIONS

Although IELT and VTS-ELT were not significantly improved, sildenafil increased confidence, the perception of ejaculatory control, and overall sexual satisfaction, and decreased the refractory time to achieve a second erection after ejaculation in men with PE.

Phenylephrine Induces Endogenous Noradrenaline Release in the Rat Vas deferens through Nitric Oxide Synthase Pathway

We have previously observed that in the rat vas deferens nitric oxide synthase pathway potentiated phenylephrine-induced contractility raising the possibility of a facilitatory role on neurotransmission by nitric oxide. To confirm this hypothesis we studied the effect of phenylephrine on the concentration response curves obtained in preparations from reserpine-treated rats in the absence and presence of the nitric oxide synthase inhibitor NG-monomethyl-L-arginine (L-NMMA). The endogenous noradrenaline released by normal preparations (without reserpine) was measured in the perfusion fluid of preparations stimulated with phenylephrine, in the absence and presence of L-NMMA, L-NMMA + the nitric oxide donor 3-morpholinosydnonimine hydrochloride (SIN-1), the alpha1-adrenoceptor antagonist prazosin and the blocker of noradrenaline carrier desipramine. The phenylephrine-induced noradrenaline release in a calcium-free medium was also measured. L-NMMA decreased the Emax of phenylephrine concentration response curves obtained in preparations from normal (reserpine-untreated) but not from reserpine-treated rats. In the perfusion fluid of preparations incubated with phenylephrine, a concentration-dependent increase of noradrenaline was observed which was reversed by L-NMMA and restored when SIN-1 was added together with the nitric oxide synthase inhibitor. The concentration-dependent phenylephrine-induced noradrenaline increase was not modified by desipramine but was abolished by 10 microM prazosin. In calcium-free medium, phenylephrine failed to increase the noradrenaline concentration. These results suggest that in the rat vas deferens, nitric oxide pathway potentiates the phenylephrine-induced contractility through a mechanism which involves calcium-dependent release of endogenous noradrenaline and seems to depend, at least partially on the activation of alpha1-adrenoceptors.