Effect of potassium channel modulators on male sexual behavior

Potential activity of Aframomum daniellii (Zingiberaceae) dry seeds: A case study of its action mechanism on the Wistar rat strain with testicular deficiency

This work was undertaken to evaluate the biological activity of the aqueous extract of the dry seeds of Aframomum daniellii seeds on the copulatory performance of rats with testicular deficiency. Hypogonadal adult male rats (30) were divided into 6 groups: group I received distilled water (10 ml/kg), group II received sildenafil citrate (5 mg/kg), group III received intramuscular injections of testosterone enanthate (3. 6 mg/kg), group IV, V, and VI received the aqueous extract of A. daniellii at the respective doses of 100, 200, and 400 mg/kg/po/day for 14 days. The copulatory performance of the animals were assessed on days 1, 7 and 14 through the following copulation parameters: Mount, intromission, and ejaculation latency (ML, IL, and EL) and frequency (MF, IF and EF), average interval of copulation (AIC) and post-ejaculatory interval (PEI)). We noticed a significant decrease of ML (p < 0.05), IL (p < 0.01), EL (p < 0.001) and the increase of MF, IF and EF (p < 0.01) particularly at doses of 100 and 400 mg/kg when compared to group I and II. In addition, we noticed a significant increase of AIC from day 7 (p < 0.05) to day 14 (p < 0.001) at the same two doses while the PEI significantly decreased from the 1st (p < 0.01) to the 14th day (p < 0.001) when compared to group I and II. These findings demonstrated that A. daniellii aqueous extract of seeds enhanced pro-sexual potential and pro-sexual desire in male rats with testicular deficiency.

Sodium nitroprusside impairs sexual competence of male rats

Recently, sodium nitroprusside (SNP), a potent nitric oxide (NO) donor and a clinically used antihypertensive, has been introduced as a penile self-injection medical therapy for erectile dysfunction. However, it is known that many antihypertensives impairs sexual competence; NO regulates sexual competence and NO is cytostatic and cytotoxic for human sperm. Thus, a possibility exists that SNP may impair male reproductive competence. Testing this aspect is the aim of this study. This was assessed in male rats (using three I.P. doses: 60, 30 or 20 g/kg) using noncompetitive copulation tests. The results show that the highest dose of SNP was toxic and caused rapid mortality of treated rats (within 30 min). The mid and low doses of SNP reversibly impaired several parameters of sexual competence in a dose-related fashion: sexual arousability, libido and sexual vigour. Some parameters of sexual behaviour remained unaltered: sexual motivation and intromission ratio, whilst one parameter was improved: sexual performance. In complete contrast, the ejaculatory competence and fertility remained unchanged. The SNP-induced impairments in sexual competence may be attributable to lowered testosterone levels and sedation mediated via its specific action and/or side effect. Further, this impairment of sexual function was not due to general toxicity, inhibition of penile sensitivity, penile erection or analgesic activity. It is concluded that SNP impairs male sexual competence, at least, in rats although it promotes penile erection.

A role for ATP-sensitive potassium channels in male sexual behavior

ATP-sensitive potassium (K(+)(ATP)) channels regulate cell excitability and are expressed in steroid-responsive brain regions involved in sexual behavior, such as the preoptic area (POA) and medial basal hypothalamus (MBH). We hypothesized that K(+)(ATP) channels serve as a mechanism by which testosterone can control the electrical activity of neurons and consequently elicit male sexual responsiveness. RT-PCR analysis indicated that castration induces, while testosterone inhibits, mRNA expression of the K(+)(ATP) channel subunit Kir6.2 in both the POA and MBH of adult male rats. Intracerebral infusion of the pharmacological K(+)(ATP) channel inhibitor tolbutamide increased the proportion of long-term castrates displaying sexual behavior and restored mount frequency, intromission frequency, and copulatory efficacy to values observed in testes-intact animals. Infusions of tolbutamide, but not vehicle, also decreased latencies to mount and intromit in castrated males. Unilateral tolbutamide infusion directly into the POA significantly reduced mount latency of castrates; however, it did not affect other copulatory measures, suggesting that blockade of K(+)(ATP) channels in additional brain regions may be necessary to recover the full range of sexual behavior. These data indicate that blockade of K(+)(ATP) channels is sufficient to elicit the male sexual response in the absence of testosterone. Our observations are consistent with the hypothesis that testosterone modulates male sexual behavior by regulating K(+)(ATP) channels in the brain. Decreased channel expression or channel blockade may increase the excitability of androgen-target neurons, rendering them more sensitive to the hormonal, chemical, and somatosensory inputs they receive, and potentially increase secretion of neurotransmitters that facilitate sexual behavior.

Effect of black tea brew of Camellia sinensis on sexual competence of male rats

AIM

In Sri Lankan traditional medicine black tea brew (BTB) of Camellia sinensis (L.) O. Kuntze (Theaceae) is claimed to have male sexual stimulant activity. As this claim is not scientifically tested and proven, this study was undertaken to evaluate the effects of BTB on male sexual competence.

MATERIAL AND METHODS

Different doses of BTB made from Sri Lankan high grown dust grade no 1 tea (84, 167 and 501 mg/ml) or water were orally administered to separate groups of rats (n=9 per group) and 3h later their sexual behaviour were monitored (for 15 min) using receptive females.

RESULTS

The overall results showed that BTB possesses marked aphrodisiac activity (in terms of prolongation of latency of ejaculation shortening of mount- and intromission latencies and elevation of serum testosterone level). The aphrodisiac action had a rapid onset and appears to be mediated via inhibition of anxiety and elevation of serum testosterone level. Further, this aphrodisiac action was not associated with impairment of other sexual parameters like libido, sexual motivation, sexual arousal, sexual vigour or penile erection. BTB was also nontoxic (in terms of overt signs, liver and renal toxicity).

CONCLUSIONS

It is concluded that BTB can function as a quick acting, safe, oral aphrodisiac which may also be useful in certain forms of sexual inadequacies such as premature ejaculation and impaired libido and other sexual functions.

Effects of aqueous extract of Alpinia calcarata rhizomes on reproductive competence of male rats

This study examined the effects of rhizomes of Alpinia calcarata Roscoe (Zingiberaceae) on male sexual competence and fertility, using a hot water extract (HWE) and rats. Different doses of HWE (150, 250 and 500 mg/kg) were orally administrated to male rats and their sexual behaviour was monitored (for 15 min) 3 h later using receptive females. Fertility was determined in a separate group (with the highest dose) using a noncompetitive copulation test. In the sexual behaviour study, the HWE impaired the number of rats ejaculating and markedly prolonged the latency for ejaculation. Further, the number of rats mounting and intromitting, and the latencies for mounting and intromission were inhibited. Collectively, these observations indicate a strong aphrodisiac action. The other parameters remained unchanged indicating non-impairment in libido, sexual arousability, sexual vigour and sexual performance or penile erectile ability. However, a slight impairment was evident in sexual motivation (with the highest dose) in a partner preference test. In the fertility test, HWE induced profound oligozoospermia but fertility was uninhibited. The highest dose of HWE also elevated the serum testosterone level and the number of spontaneous penile erections rapidly and markedly. Further, the HWE was nontoxic. It is concluded that A. calcarata rhizomes possess a strong and safe oral aphrodisiac activity.

Preserved inhibitory effect of recurrent hypoglycaemia on the male gonadotrophic axis

OBJECTIVE

Hypoglycaemia-induced decreases in male LH and testosterone concentrations are possibly mediated by activation of the hypothalamus-pituitary-adrenal (HPA) axis or by an increase in PRL. As counterregulatory stress hormone release is attenuated during recurrent hypoglycaemia, we questioned whether the gonadotrophic axis and PRL adapt similarly.

DESIGN

We performed two consecutive hypoglycaemic clamps on day 1 and one clamp on the following day in 15 healthy men. Blood concentrations of gonadotrophins, PRL, testosterone, ACTH and cortisol were measured during the first and the third clamp, taking place at the same time of day.

RESULTS

During hypoglycaemia, serum concentrations of LH and testosterone decreased (P < 0.003 for both), PRL, ACTH and cortisol increased (P < 0.001), and FSH remained unchanged (P = 0.90). The hypoglycaemia-induced decreases in LH and testosterone concentrations were similar during the first and the last clamp (P > 0.28 for both) whereas the increase in PRL, ACTH and cortisol was markedly attenuated during the third clamp (P < 0.001).

CONCLUSIONS

LH and testosterone responses do not adapt to recurrent hypoglycaemia, whereas the increase in PRL is attenuated, indicating adaptation. Considering the marked decrease in the responses of PRL and the HPA axis after antecedent hypoglycaemia, the data suggest that the hypoglycaemia-induced decreases in LH and testosterone concentrations, not adapting to recurrent hypoglycaemia, are mediated independently, probably by blood glucose itself.