Effects of a selective alpha 1-adrenoceptor agonist, methoxamine, on sexual behavior and penile reflexes

Bioactive metabolites reveal the therapeutic consistency of epimedii folium from multi-plant sources for the treatment of kidney-yang deficiency

ETHNOPHARMACOLOGICAL RELEVANCE

Epimedii Folium (Yin-yang-huo in Chinese), a traditional and commonly used herbal medicine (HM), is a representative of multi-plant sources. To date, little is known about the reasons for similar therapeutic effects of this HM from multi-plant sources.

AIM OF THE STUDY

To investigate the underlying reasons for the similar pharmacological effects of Epimedii Folium from two botanical sources (Epimedium koreanum Nakai and Epimedium wushanense T. S. Ying).

MATERIALS AND METHODS

Firstly, the phytochemicals of the extracts of E. koreanum and E. wushanense were systematically analyzed. Meanwhile, their pharmacological effects on kidney-yang deficiency (KYD) syndrome were evaluated in rats induced by hydrocortisone. Subsequently, we proposed a combined effect index (CEI) to assess the effects of two plants on the secretion of testosterone by combing the system exposure of twelve active components in vivo with their regulation activities of testosterone production in vitro. Moreover, the label-free proteomics and Western blot analysis were conducted to evaluate the possible mechanism of Epimedii Folium from two botanical sources.

RESULTS

E. koreanum and E. wushanense exhibited similar pharmacological effects on KYD syndrome with promoting the mating behaviors and testosterone levels of rats, although there is a certain difference in the main components between two plants. The CEI analysis showed that there was no difference (P > 0.05) in the sum of CEIs of two Epimedium, indicating that their similar therapeutic effects are attributed to bioactive metabolites in vivo. Furthermore, Epimedii Folium can regulate testosterone production in rat Leydig cell via reversing expressions of key steroidogenic enzymes, such as steroidogenic acute regulatory protein (StAR) and 3β-hydroxysteroid dehydrogenase (3β-HSD).

CONCLUSION

Our results supply critical evidence for the similar pharmacological effects of two Epimedium species, acting by consistent bioactive components directly exposing in vivo, not chemical compositions presenting in herbs. It provides a reasonable scientific basis for understanding of the HMs originated from multi-plant sources for the same clinical application.

Taurine Improves Sexual Function in Streptozotocin-Induced Diabetic Rats

Previous studies have identified that diabetic erectile dysfunction is associated with androgen and nitric oxide deficiency resulting from hyperglycemia. It has been demonstrated that taurine can stimulate testosterone secretion, increase nitric oxide synthase (NOS) activity and nitric oxide (NO) production, and reduce blood glucose levels in the diabetic animals. Furthermore, recent studies have found that taurine relaxes both the corpus cavernosum and the vasculature. Accordingly, we hypothesized that taurine might exert beneficial effects on erectile function of the diabetic rats. Here, we assessed the effects of taurine on sexual function in streptozotocin (STZ) -induced diabetic male rats. We observed that taurine treatment could markedly increase sexual response and mating ability of STZ-diabetic rats. The serum concentration of gonadotropin-releasing hormone (GnRH), luteinizing hormone (LH), follicle-stimulating hormone (FSH) and testosterone (T) were also significantly increased by taurine administration. Importantly, taurine supplementation notably increased mRNA levels and activity of endothelial NOS (eNOS) and neuronal NOS (nNOS), as well as NO and cGMP content, in the corpus cavernosum of the diabetic rats. In conclusion, the present data indicate that taurine can increase sexual function of STZ-induced diabetic male rats mainly by correcting the diabetes, increasing sexual desire, which is implicated in ameliorating the hypothalamic-pituitary-testicular axis function, and by improving penile erection, which requires increased signaling from the penile endothelial- and neuronal-dependent NO-cGMP pathway.

Effects of velvet antler polypeptide on sexual behavior and testosterone synthesis in aging male mice

Twenty-four-month-old male C57BL/6 mice with low serum testosterone levels were used as a late-onset hypogonadism (LOH) animal model for examining the effects of velvet antler polypeptide (VAP) on sexual function and testosterone synthesis. These mice received VAP for 5 consecutive weeks by daily gavage at doses of 100, 200, or 300 mg kg⁻¹ body weight per day (n = 10 mice per dose). Control animals (n = 10) received the same weight-based volume of vehicle. Sexual behavior and testosterone levels in serum and interstitial tissue of testis were measured after the last administration of VAP. Furthermore, to investigate the mechanisms of how VAP affects sexual behavior and testosterone synthesis in vivo, the expression of steroidogenic acute regulatory protein (StAR), cytochrome P450 cholesterol side-chain cleavage enzyme (P450scc), and 3β-hydroxysteroid dehydrogenase (3β-HSD) in Leydig cells was also measured by immunofluorescence staining and quantitative real-time PCR. As a result, VAP produced a significant improvement in the sexual function of these aging male mice. Serum testosterone level and intratesticular testosterone (ITT) concentration also increased in the VAP-treated groups. The expression of StAR, P450scc, and 3β-HSD was also found to be enhanced in the VAP-treated groups compared with the control group. Our results suggested that VAP was effective in improving sexual function in aging male mice. The effect of velvet antler on sexual function was due to the increased expression of several rate-limiting enzymes of testosterone synthesis (StAR, P450scc, and 3β-HSD) and the following promotion of testosterone synthesis in vivo.

A herbal medicine, saikokaryukotsuboreito, improves serum testosterone levels and affects sexual behavior in old male mice

Late-onset hypogonadism (LOH) is a clinical syndrome characterized with aging and declined serum testosterone levels. Sexual symptoms are also essential for the diagnosis of LOH. Testosterone replacement therapy is used widely to treat LOH. However, the side effects of it should not be ignored, such as fluid retention, hypertension and spermatogenic suppression. Therefore, alternate treatment modalities have been pursued. Herbal medicines used widely in China have achieved satisfying results with little side effects. Nonetheless, there are few pharmacological researches on them. In this study, 24-month-old mice were used as LOH animal models to explore the pharmacological effects of a herbal medicine, saikokaryukotsuboreito (SKRBT), on serum testosterone levels and sexual functions. Furthermore, the expression of steroidogenic acute regulatory (StAR) protein, a kind of rate-limiting enzyme of testosterone synthesis, was also examined. As a result, SKRBT improved the serum testosterone levels of these mice at a dose of 300 and 450 mg/kg. Multiple measures of sexual behavior were enhanced. The expression of StAR was also increased. Therefore, this study suggested that SKRBT can improve the serum testosterone levels by activating the expression of StAR and might be a viable option to treat sexual symptoms caused by LOH.

alpha-Adrenergic agents modulate the activity of the spinal pattern generator for ejaculation

Spinal cord transection at a thoracic level activates fictive ejaculation (FE) in the male rat. It has earlier been demonstrated that fictive motor patterns may be activated by pharmacological means and that the noradrenergic system seems to be particularly efficient in triggering locomotor fictive patterns in spinal animals. In the present study, the hypothesis was tested that the spinal noradrenergic system participates in the activation of the spinal generator for ejaculation (SGE). To this aim, the effect of the adrenergic agents, methoxamine, prazosin, clonidine, and yohimbine, upon FE was evaluated in spinal male rats using electromyographic techniques. The results obtained show that ejaculatory rhythmic patterns, accompanied by the expulsion of urethral contents and phasic penile movements, can be elicited by the intravenous (i.v.) injection of methoxamine or yohimbine. These drug-induced motor sequences appear superimposed to the intrinsic ejaculatory spinal rhythm. By contrast, i.v. injection of prazosin or clonidine blocked the expression of the spontaneous ejaculatory rhythmic pattern without inducing any other genital response. These data suggest that an increased noradrenergic tone, either by blockade of presynaptic alpha2-adrenoceptors or by stimulation of postsynaptic alpha1-adrenoceptors, results in the activation of the SGE. Present findings provide the evidence that the SGE might be importantly influenced by the noradrenergic system, which exerts a facilitatory control on the expression of the genital motor pattern of ejaculation.

Ultrasonic vocalization production of preweanling rats: effects of central and peripheral administration of alpha2-adrenoceptor agonists

Stimulation of alpha2-adrenoceptors increases the ultrasonic vocalization production of preweanling rats, however it is not known whether these critical alpha2-adrenoceptors are located peripherally or centrally. In a series of three experiments, ultrasonic vocalizations were measured after 11-day-old rats had been administered clonidine or 2-[2,6-diethylphenylamino]-2-imidazole (ST-91) either systemically (i.p.) or into the third ventricle (i.c.v.). These particular alpha2-adrenoceptor agonists were chosen because clonidine is lipophilic and enters the central nervous system, while ST-91 is hydrophilic and does not readily cross the blood-brain barrier. In the third experiment, clonidine- (1 microg, i.c.v.) and ST-91-induced (15 microg, i.c.v.) ultrasonic vocalizations were measured after systemic injection of the alpha2-adrenoceptor antagonist yohimbine (0.5 or 1 mg/kg, i.p.). Results showed that central administration of both clonidine and ST-91 increased the ultrasonic vocalization production of 11-day-old rats, whereas peripheral administration of only clonidine, and not ST-91, increased ultrasonic vocalizations. These results indicate that the alpha2-adrenoceptors mediating ultrasonic vocalization production are located in the central nervous system. Yohimbine fully attenuated clonidine-induced ultrasonic vocalizations but only partially attenuated ST-91-induced vocalizations. This pattern of results may have been due to the differential selectivity of clonidine and ST-91 for alpha2-adrenoceptor subtypes (alpha2A, alpha2B, and alpha2C) or imidazoline receptors. When combined with past research, the present results are consistent with the hypothesis that centrally located alpha2-adrenoceptors are a component of a neural system that mediates ultrasonic vocalization production.

Noradrenergic System Interacts With Genital Reflexes Induced by Cocaine in Paradoxical Sleep-Deprived Male Rats

Different doses of alpha-1, alpha-2, beta-1, and beta-2 adrenoceptor agonists or antagonists were administered to paradoxical sleep-deprived (PSD) rats prior to cocaine administration. Methoxamine reduced the percentage of rats displaying erection, whereas prazosin did not. Yohimbine significantly decreased this percentage. For beta-1 adrenoceptor drugs, both compounds reduced the percentage of rats displaying erection at the highest dose; beta-2 adrenoceptor drugs had no effect. Except for clonidine, all drugs significantly reduced the frequency of erection. Ejaculation was significantly decreased following yohimbine and beta-1 drugs, whereas it was completely abolished by prazosin. The results showed that noradrenergic drugs inhibited genital reflexes in PSD rats, with distinct responses in relation to their respective action over the adrenoceptor.

Modulatory activity of sildenafil on copulatory behaviour of both intact and castrated male rats

The first experiment of the present study investigates the effects induced by sildenafil (1 or 10 mg/kg po) on the copulatory behaviour of intact male rats, categorized, on the basis of seven consecutive mating pretests, as sluggish or normal ejaculators (SE or NE, respectively). The data obtained show that sildenafil modifies both sexual arousal and the ejaculatory mechanisms of copulation, diminishing ejaculation latency in both categories and increasing copulatory efficacy in SE rats; in addition, it reduced the inter-intromission interval in both SE and NE animals and the post-ejaculatory interval only in SE animals. The second experiment, conducted on rats 3 weeks after their castration, shows that sildenafil alone (1 or 10 mg/kg) did not modify copulatory failure. However, 3 months after castration, and 24 h after the last injection of testosterone (25 microg/kg sc) given twice weekly for 4 weeks, sildenafil (1 or 10 mg/kg) ameliorated rat copulatory performance.

Influence of sildenafil on copulatory behaviour in sluggish or normal ejaculator male rats: a central dopamine mediated effect?

The present study investigates the effects induced by sildenafil (1 mg/kg, p.o.) and the dopamine agonist, SND 919 (0.1 mg/kg, i.p.) on copulatory behaviour of male rats, categorized, on the basis of seven consecutive mating pre-tests, as sluggish and normal ejaculators (SE and NE, respectively). The data obtained show that sildenafil modifies both sexual arousal and ejaculatory mechanisms of copulation. It appears that, although it induced a facilitatory effect on ejaculation of all rats, similarly to SND 919, the lowering of ejaculatory threshold was achieved by means of a reduction of mount frequency and intromission frequency in SE and NE groups, respectively. Differently from SND 919, sildenafil increased sexual arousal, diminishing post ejaculatory interval in SE animals and inter-intromission interval in both SE and NE rats. As the dopamine antagonist, (-)eticlopride (0.02 mg/kg, s.c.), significantly inhibited sildenafil-induced enhancement of sexual arousal in SE rats, it is suggested that the drug acts both peripherally and centrally.

Ketanserin attenuates the behavioural effects of corticosterone: implications for 5-HT(2A) receptor regulation

The effects of chronic corticosterone treatment on sexual behaviour and wet-dog shakes were investigated in both female and male rats. The serotonergic type 2A (5-HT(2A)) receptor antagonist ketanserin was administered to test the hypothesis that the behavioural effects of corticosterone were mediated by increased 5-HT(2A) receptor activity. Rats were randomly assigned to one of four chronic treatment groups: control, ketanserin alone, corticosterone alone, or ketanserin and corticosterone. Ketanserin attenuated the corticosterone-induced changes in both sexual behaviour and wet-dog shakes. Ketanserin alone had no effect on these behaviours. Results suggest that increased 5-HT(2A) receptor activity mediates the effects of corticosterone on sexual behaviour and wet-dog shakes.

Exhaustion of the coital reflex in spinal male rats is reversed by the serotonergic agonist 8-OH-DPAT

Previous studies from our laboratory have shown that the genital motor pattern associated to the coital reflex in spinal male rats becomes exhausted when repeatedly evoked. Exhaustion of the genital motor pattern could be related to the sexual exhaustion phenomenon observed in copulating male rats. The present study was aimed to describe the features of coital reflex exhaustion and to determine if the 5-HT1A agonist 8-OH-DPAT was able to reverse exhaustion of this ejaculatory-like response. Additionally, the effect of pre-treatment with the 5-HT1A antagonist WAY 100635 on the 8-OH-DPAT induced motor response was evaluated. Results revealed that development of coital reflex exhaustion initiated with a progressive increase in the latency of response and was characterised by a change in the properties of the motor pattern itself. Once exhausted, i.v. administration of 8-OH-DPAT provoked the immediate expression of a potent motor pattern similar to the coital reflex, but in the absence of urethral stimulation. Injection of WAY 100635 induced, per se, expression of the coital reflex after exhaustion. Notwithstanding, pre-treatment with WAY 100635 was able to block the 8-OH-DPAT-induced motor response implying that its effect was exerted upon 5-HT1A receptors. Data suggest that the sexual exhaustion phenomenon might possess a spinal component.

Differential behavioural effect of quinpirole in neuroleptic-pretreated rats - role of alpha(1)-adrenoceptor

This paper presents the effect of 14-day intraperitoneal (i.p.) neuroleptic treatment on the behavioural response of Wistar rats to (-)-quinpirole hydrochloride (3 mg/kg, i.p.) administered 24 h after the last neuroleptic dose. Chlorpromazine hydrochloride (10 mg/kg), haloperidol (2 mg/kg) or (+/-)-sulpiride (100 mg/kg) increased the effect of quinpirole; however, there were qualitative and quantitative differences between the neuroleptics. Chlorpromazine and haloperidol, but not sulpiride, pretreatment enhanced quinpirole-induced locomotor hyperactivity. Prazosin (0.5 mg/kg, i.p. ) given to chlorpromazine-treated rats 1 h before quinpirole attenuated the quinpirole-induced hyperlocomotion. In chlorpromazine-pretreated rats, quinpirole elicited defensive aggressive behaviour with vocalization, copulatory attempts, intense rearing and head-down sniffing. When prazosin was given before quinpirole, head-down sniffing and object-directed oral activity were mainly observed. In haloperidol-pretreated rats, quinpirole induced intense head-down sniffing, rearing, grooming and object-directed oral activity. In sulpiride-pretreated rats, quinpirole induced intense head-down sniffing, grooming and object-directed oral activity. The results of the study suggest that differences in the behavioural expression of dopamine D(2) receptor supersensitivity induced by neuroleptics may be, at least in part, caused by concurrent stimulation of alpha(1)-adrenoceptors.

Sexual impotence is associated with a reduced production of oxytocin and with an increased production of opioid peptides in the paraventricular nucleus of male rats

Oxytocin plays a physiological stimulatory role on sexual behavior. Conversely, opioid neuropeptides play a physiological inhibitory role. Here we show that in sexually impotent rats there is a reduced expression of oxytocin mRNA and an increased expression of proenkephalin and pro-dynorphin mRNA in the paraventricular nucleus of hypothalamus (PVN), a brain structure of key importance for sexual behavior. These data suggest that an imbalance in the production of oxytocin and of opioid peptides in the PVN, with prevalence of opioid peptides, may underlie a condition of sexual impotence.

Effect of potassium channel modulators on male sexual behavior

In the adult sexually experienced male rat, the intracerebroventricular (i.c.v.) injection of pinacidil, a KATP channel opener, at the dose of 100-150-300 micrograms/rat worsened the copulatory performance in the presence of a receptive female, whereas the administration of glibenclamide, a KATP channel blocker, at the dose of 0.5 and 3 mg/kg intraperitoneally (i.p.) had an improving effect. These data indicate that KATP channels in target neurons may play an important role in the physiology of male sexual behavior.

Nitric oxide is involved in male sexual behavior of rats

In male rats, whether sexually experienced or sexually naive, the intraperitoneal administration of L-arginine (the natural substrate for nitric oxide synthase) (10, 25, 50 mg/kg) both increased the percentage of copulating in sexually naive rats and improved the indexes of sexual performance in sexually experienced rats, whereas the intraperitoneal administration of N(G)-nitro-L-arginine methyl ester (L-NAME) (a potent inhibitor of nitric oxide synthase) (10, 25, 50 mg/kg) had opposite effects. In contrast, after intracerebroventricular administration, L-arginine (25, 50, 100 microg/rat) had no effect - whether in naive or in experienced rats - whereas L-NAME completely prevented ejaculation in naive rats, at the dose of 100 microg/rat, but had no effect at all in experienced rats, up to the dose of 300 microg/rat. Finally, a direct relationship seems to exist between male copulatory performance and nitric oxide synthase activity in a discrete and defined brain area, the paraventricular nucleus of the hypothalamus: indeed, nitric oxide synthase mRNA expression in this nucleus in sexually potent rats is about twice that in sexually impotent rats. It is concluded that nitric oxide synthase is involved in the expression of male sexual activity, in spite of some inconsistencies that are hard to interpret.

The inhibitory effects of propranolol on genital reflexes in male rats

We have previously reported that propranolol adversely affects sexual behavior in male rats. To elucidate whether the effects of propranolol might involve decrements in ability, we examined two components of sexual function ex copula--ejaculatory reflex capacity and erectile reflexes. In the first study, we examined the effects of various doses of (+/-)-propranolol (1.25-10 mg/kg) administered subcutaneously. Marked inhibition was observed, evidenced by increases in the latency to ex copula ejaculation and to initial erection and decrements in the number of seminal emissions and in the number of erectile reflexes. Analyses of dose-response relationships indicated that the degree of inhibition increased with increasing dose. In the second study, we evaluated the stereo-selectivity of the responses. Both (+)- and (-)-propranolol (1.25 mg/kg) significantly inhibited ejaculatory reflex potential, and although (+)- and (-)-propranolol significantly inhibited erectile reflexes, (-)-propranolol had a greater effect. The data are interpreted to indicate that a) propranolol-induced sexual dysfunction involves both motivational and ability aspects; and b) propranolol-induced inhibition of genital reflexes may be due, at least in part, to mechanisms other than beta-adrenoceptor blockade.

Sexual function in altered physiological states: comparison of effects of hypertension, diabetes, hyperprolactinemia, and others to "normal" aging in male rats

In this review, we examine the changes in sexual function that accompany deviations from "normal" physiological states. We propose that the changes one observes in many altered physiological states should not be viewed in isolation. We describe our paradigms for assessing sexual function, and proceed to evaluate how sexual function changes with hormonal deprivation and aging, in rat models for hypertension, in severe hyperprolactinemia, in streptozotocin-induced diabetes, after chronic alcohol intake, after chronic morphine administration, and after exposure to the heavy metal, cadmium. We will provide evidence for the involvement of adrenergic transmitters and two neuropeptides, neuropeptide Y and somatostatin, in the neuroendocrine regulation of sexual behavior. Finally, we compare and contrast the changes observed relative to the changes seen in "normal" aging in rats. The sequence of age-related changes in sexual function is distinct. The first change observed is a decrement in ex copula erectile reflexes. Next are decreases in ejaculatory threshold, followed shortly by increases in initiation and reinitiation of copulation after ejaculation. This is followed by a decrement in the number of males copulating to ejaculation. Finally, there is a failure to initiate the copulatory process. This sequelae is relatively common, being evident after castration, with hyperprolactinemia, and after exposure to cadmium. The data available for sexual function in hypertension is incomplete and modified by the etiology, but a suggestion for this sequelae is seen in SHR. In contrast, sexual dysfunction associated with chronic morphine administration appears to be due to an initial deficit in motivational aspects. Testosterone reverses sexual dysfunction associated with castration, but not with idiopathic sexual inactivity, nor with sexual dysfunction associated with aging, diabetes, or chronic morphine administration. Comparing sexual function in rat models for hypertension, diabetes and chronic ethanol leads to the conclusion that increases in blood pressure, like decreases in testosterone, cannot be the primary causal factor for sexual dysfunction. Age, hormonal history of the subject, and the age at castration influence changes in sexual function. Age-related sexual dysfunction appears to be contributed to by changes in adrenergic-neuropeptidergic, to include sympathetic, systems. Site-specific administration of NPY induces alterations in parameters of copulatory behavior which mimic those seen in aging and the retention of ejaculatory behavior with aging is associated with site-selective attenuation (or reversal) of age-associated changes in NPY content. Yohimbine enhances copulatory activity in castrated and aging rats, and attenuates or reverses the antisexual effects of clonidine, epinephrine and somatostatin.(ABSTRACT TRUNCATED AT 400 WORDS)

Benextramine, an NPY antagonist, improves sexual behavior in male rats

In adult, sexually-experienced male rats, the NPY-antagonist benextramine--at the doses of 5 and 10 mg/kg i.p. and of 50 micrograms/rat i.c.v.--significantly and specifically improved several parameters of copulatory activity. These data may further support the idea that NPY plays a role in the complex regulation of male sexual function, seemingly at the brain level.

Suppression of copulatory behavior in male rats following central administration of clonidine

Adrenergic transmitters have been implicated in the regulation of male sexual behavior. In the present study the contribution of alpha 2-adrenoceptors, located within the central nervous system, was evaluated. Sexually experienced male Long-Evans rats were implanted with a permanent cannula in either the third cerebral ventricle or, unilaterally, in the medial preoptic area. Baseline mating tests were administered 4, 7 and 10 days after surgery and only males ejaculating (at least) in the 7 and 10 day tests were used. Clonidine-evoked dose-dependent decrements in the number of males mounting, intromitting and ejaculating, with administration into the medial preoptic area more effective than into the 3rd ventricle. In those animals mating, administration of 20 nmol into the 3rd ventricle was associated with decreases in the latency to ejaculation and intercopulatory interval, whereas administration of 2 nmol into the medial preoptic area was associated with increases in these parameters and decreases in the ejaculatory threshold. Administration of yohimbine into the medial preoptic area attenuated the effects of systemically-administered clonidine and the systemic administration of yohimbine completely prevented the copulatory suppression induced by administration of clonidine into the medial preoptic area. It is suggested that central alpha 2-adrenoceptors are important in the control of male sexual behavior and that alterations in adrenergic mechanisms in the medial preoptic area may underlie sexual dysfunction of various etiologies.

A rapidly reversible effect of a single dose of phenoxybenzamine on the fertility of male rats

Male Sprague-Dawley rats received a single subcutaneous injection of phenoxybenzamine and each was allowed to mate with an untreated receptive female at 5, 29 or 53 h post-injection. At 5 h the number of males ejaculating was reduced and fertility virtually abolished; at 29 h all males ejaculated, but fertility was still low; at 53 h the performance of the males was normal.

Central effect of yohimbine on sexual behavior in the rat

A large range of doses of yohimbine (Y) was administered intracerebroventricularly (ICV) (5-100 micrograms/rat) or intraperitoneally (IP) (0.35-10 mg/kg) to male rats and the effects on sexual, locomotor and general behavior were evaluated. For both routes there was a clear-cut inverted-U effect (stimulating/depressing), calculable as parabolic regressions on the log of administered doses. The maximal stimulating doses (15 micrograms/rat ICV and 1 mg/kg IP) significantly shortened mount, intromission and ejaculation latencies and the mean interintromission interval. These data indicate the importance of CNS mechanisms in the sexual effect of Y.