INHIBITORY EFFECT OF SEROTONERGIC DRUGS ON CONTRACTILE RESPONSE OF THE RAT VAS DEFERENS TO ELECTRICAL NERVE STIMULATION: IN VIVO STUDY

Peripheral Effects of Serotonin on the Contractile Responses of Rat Seminal Vesicles and Vasa Deferentia

With the central effects of serotonin (5-HT) on ejaculation having been relatively established, we investigated the peripheral effects of serotonin on the contractile responses of rat seminal vesicles and vasa deferentia. Male Sprague-Dawley rats were grouped on the basis of the agents administered: serotonin, clomipramine, or fluoxetine. The intraluminal pressures of the seminal vesicles and of the vasa deferentia were measured simultaneously. Control responses to hypogastric nerve stimulation (HNS) were recorded in each animal, and HNS was repeated after drug administration. Expression of the mRNAs of the 5-hydroxytryptamine (5-HT) receptors (5-HT1A, 5-HT1B, and 5-HT2C), which have been suggested to be involved in the ejaculation process, were examined by semiquantitative reverse-transcriptase polymerase chain reaction (RT-PCR). Serotonergic agents resulted in the concentration-dependent inhibition of HNS-induced seminal vesicle pressure increases (clomipramine > serotonin > fluoxetine). Vasal pressure responses were effectively inhibited by clomipramine and serotonin, but fluoxetine had no effect. No significant difference was observed in the relative expression levels of 5-HT1A receptor mRNA in seminal vesicles and in the vasa deferentia. However, the expression levels of 5-HT1B and 5-HT2C receptor mRNAs were lower in the vasa deferentia than in the seminal vesicles. These in vivo and in vitro experimental results provide evidence for the peripheral role of 5-HT in the regulation of contractile responses of the seminal tract. Regional differences in the distribution of the 5-HT receptor subtypes of the seminal vesicles and the vasa deferentia might contribute to the different responses to serotonergic agents shown by these organs.

Dapoxetine, a novel selective serotonin transport inhibitor for the treatment of premature ejaculation

Premature ejaculation (PE) is the most common male sexual disorder, estimated to affect up to 30% of men. Over the past one or two decades, clinical investigators have participated in an increasing number of studies that are helping in our understanding of PE, which will undoubtedly facilitate future treatments. Apart from a number of behavioral approaches, the treatment of PE consists of primarily off-label use of oral selective serotonin reuptake inhibitors (SSRIs) via either on-demand or daily delivery. However, various undesirable side-effects of these medications have led researchers to search for and develop new therapeutic approaches for PE. Dapoxetine is a short-acting SSRI developed specifically for the treatment of PE. Early trials with dapoxetine have documented successful outcomes without serious short- or long-term side-effects. This review addresses the definition, classification, diagnosis, physiology, and neurobiopathology of PE, and evaluates therapeutic strategies with novel treatments for PE.

Effects of chronic paroxetine pretreatment on (+/-)-8-hydroxy-2-(di-n-propyl-amino)tetralin induced c-fos expression following sexual behavior

Chronic treatment with the selective serotonin reuptake inhibitor paroxetine impairs the functioning of 5-HT(1A) receptors involved in ejaculation. This could underlie the development of delayed ejaculation often reported by men treated with paroxetine. The neurobiological substrate linking the effects of selective serotonin reuptake inhibitor-treatment and 5-HT(1A) receptor activation with ejaculation was investigated. Male Wistar rats that were pretreated with paroxetine (20 mg/kg/day p.o.) or vehicle for 22 days and had received an additional injection with the 5-HT(1A) receptor agonist 8-OH-DPAT ((+/-)-8-hydroxy-2-(di-n-propyl-amino)tetralin; 0.4 mg/kg s.c.) or saline on day 22, 30 min prior to a sexual behavior test, were perfused 1 h after the sexual behavior test. Brains were processed for Fos-, and oxytocin immunohistochemistry. The drug treatments markedly changed both sexual behavior and the pattern and number of Fos-immunoreactive cells in the brain. Chronic pretreatment with paroxetine caused delayed ejaculation. Acute injection with 8-OH-DPAT facilitated ejaculation in vehicle-pretreated rats, notably evident in a strongly reduced intromission frequency, whereas 8-OH-DPAT had no effects in paroxetine-pretreated rats. Chronic treatment with paroxetine reduced Fos-immunoreactivity in the locus coeruleus, and prevented the increase in Fos-immunoreactive neurons induced by 8-OH-DPAT in the oxytocinergic magnocellular part of the paraventricular nucleus as well as in the locus coeruleus. Since oxytocin and noradrenalin facilitate ejaculation, the alterations in Fos-IR in these areas could connect selective serotonin reuptake inhibitor treatment and 5-HT(1A) receptor activation to ejaculation. Chronic paroxetine treatment and 8-OH-DPAT changed c-fos expression in a number of other brain areas, indicating that Fos-immunohistochemistry is a useful tool to find locations where selective serotonin reuptake inhibitors and 8-OH-DPAT exert their effects.

In vivo rat model to measure hypogastric nerve stimulation-induced seminal vesicle and vasal pressure responses simultaneously

This study presents a modified in vivo model in which the intraluminal pressures of the seminal vesicle and vas deferens can be measured simultaneously. Male Sprague-Dawley rats were grouped based on agent administered: serotonin, clomipramine, fluoxetine, sertraline, paroxetine, prazosin, terazosin, and tamsulosin. The control responses to hypogastric nerve stimulation (HNS) were recorded in each animal, and HNS was repeated after each drug administration. Serotonergic agents resulted in concentration-dependent inhibition of the HNS-induced seminal vesicle pressure increases (clomipramine>serotonin>fluoxetine>sertraline approximately paroxetine). On the other hand, only serotonin and clomipramine significantly inhibited vasal pressure responses. alpha-Adrenergic blockers inhibited both intraluminal pressure responses in a concentration-dependent manner. This model illustrates the importance of the hypogastric nerve for the stimulation of the seminal tract, with attention focused on the seminal vesicle. This model may be useful for the evaluation of drugs for the treatment of premature ejaculation.

Calcium channel blocking activity of thioridazine, clomipramine and fluoxetine in isolated rat vas deferens: a relative potency measurement study

PURPOSE

We evaluated the calcium channel blocking activity of thioridazine, clomipramine and fluoxetine in isolated rat vas deferens and determined their relative order of potency.

MATERIALS AND METHODS

Cumulative control concentration-response curves to calcium chloride were obtained in isolated rat vas deferens incubated in depolarizing calcium-free Krebs-Henseleit solution. Tissues were washed to baseline length and equilibrated with a given concentration of test drugs. After a 30-minute period a calcium concentration-response curve was repeated. The resulting rightward displacement of the concentration-response curve to calcium provided a dose ratio. The dose ratio was used in the Schild equation and the antagonism of calcium induced contractions was quantified by Schild analysis.

RESULTS

The calcium channel blocking activity of thioridazine, clomipramine and fluoxetine was compared with nifedipine. All 4 drugs produced parallel rightward displacement of concentration-response curves to calcium. The potency of this effect was quantified by Schild analysis showing pA estimates, namely nifedipine 7, thioridazine 6.2, clomipramine 5.65 and fluoxetine 5.

CONCLUSIONS

A characteristic profile of calcium channel blocking activity on the vas deferens was obtained for all test drugs. The relative order of potency was determined as thioridazine greater than clomipramine greater than fluoxetine. Differences in the potency of calcium entry blockade at peripheral end organs may contribute to differential effects of these drugs on delaying ejaculatory latency in patients with premature ejaculation.

COMPARISON OF PERIPHERAL INHIBITORY EFFECTS OF CLOMIPRAMINE WITH SELECTIVE SEROTONIN RE-UPTAKE INHIBITORS ON CONTRACTION OF VAS DEFERENS:

PURPOSE

We compared the peripheral inhibitory effects of the tricyclic antidepressant clomipramine with those of various selective serotonin re-uptake inhibitors on the contractile response of the vas deferens.

MATERIALS AND METHODS

The contractile responses of 17 circular smooth muscle strips of human vas deferens to 10-4 M. norepinephrine were observed in the absence and presence of clomipramine, and the selective serotonin re-uptake inhibitors fluoxetine, sertraline and paroxetine. The intraluminal pressure response of rat vas deferens to electrical stimulation of the hypogastric nerve was measured in 5 rats in the central plus peripheral effect group before and after the intravenous injection of 4.2 mg./kg. clomipramine or 8.3 mg./kg. sertraline. The pressure response to each agent was also observed after the transection of all proximal sympathetic input to the hypogastric nerve in 5 animals in the peripheral effect group.

RESULTS

Clomipramine was about 100-fold more potent than sertraline, fluoxetine or paroxetine for inhibiting the norepinephrine induced contraction of human vasal muscle strips. The inhibitory effect of sertraline on rat intravasal pressure in the peripheral effect group was significantly lower than in the central plus peripheral effect group (p <0.05), while no significant difference was noted in the 2 groups regarding clomipramine. The effect of clomipramine was significantly higher than that of sertraline in the central plus peripheral and peripheral effect groups (p <0.01).

CONCLUSIONS

Differences in potency of the peripheral inhibitory effects of the selective serotonin re-uptake inhibitors and clomipramine may contribute to their differential effects on delaying ejaculatory latency in patients with premature ejaculation.