Contraction of Rat Cauda Epididymis Smooth Muscle to α1-Adrenoceptor Activation Is Mediated by α1A-Adrenoceptors

Extracellular cAMP elicits contraction of rat vas deferens: Involvement of ecto-5'-nucleotidase and adenosine A1 receptors

AIMS

It is well established that intracellular cAMP contributes to the relaxation of vas deferens smooth muscle. In many tissues, intracellular cAMP is actively transported to the extracellular space, where it exerts regulatory functions, via its metabolite adenosine. These actions take place through the cAMP conversion to adenosine by ectoenzymes, a process called "extracellular cAMP-adenosine pathway". Herein, we investigated whether, in addition to ATP, extracellular cAMP might be an alternative source of adenosine, influencing the contraction of vas deferens smooth muscle.

MAIN METHODS

The effects of cAMP, 8-Br-cAMP and adenosine were analyzed in the isometric contractions of rat vas deferens. cAMP efflux was analyzed by measuring extracellular cAMP levels after exposure of vas deferens segments to isoproterenol and forskolin in the presence or absence of MK-571, an inhibitor of MRP/ABCC transporters.

KEY FINDINGS

While 8-Br-cAMP, a cell-permeable cAMP analog, induced relaxation of KCl-precontracted vas deferens, the non-permeant cAMP increased the KCl-induced contractile response, which was mimicked by adenosine, but prevented by inhibitors of ecto-5'-nucleotidase or A1 receptors. Our results also showed that isoproterenol and forskolin increases cAMP efflux via an MRP/ABCC transporter-dependent mechanism, since it is inhibited by MK-571.

SIGNIFICANCE

Our data show that activation of β-adrenoceptors and adenylyl cyclase increases cAMP efflux from vas deferens tissue, which modulates the vas deferens contractile response via activation of adenosine A1 receptors. Assuming that inhibition of vas deferens contractility has been proposed as a strategy for male contraception, the extracellular cAMP-adenosine pathway emerges as a potential pharmacological target that should be considered in studies of male fertility.

Effects of histamine on the contractility of the rat distal cauda epididymis

The motor activity of the epididymis duct is an essential process for male fertility and it is regulated by hormonal, neuronal and epithelial mechanisms. However, although there is evidence for the presence of histamine in the epididymis, its effects on epididymal motor activity are unknown. This study sought to evaluate the contractile effects of histamine on the rat distal cauda epididymis duct. Segments of the distal cauda epididymis duct from male Wistar rats were isolated and used in isolated organ bath experiments to evaluate the contractile effects of histamine in the absence or presence of antagonists of histamine receptors, α₁-adrenoceptors and muscarinic acetylcholine receptors. The effects of histamine on noradrenaline induced contractions were also investigated. Histamine was able to induce phasic contractions on rat distal cauda epididymis duct which were prevented by promethazine 10-1000 nM (H₁ receptor antagonist), ranitidine 1-100 μM (H₂ receptor antagonist), atropine 100 nM (muscarinic antagonist), and prazosin 100 nM (α₁-adrenoceptor antagonist). In addition, histamine was also able to modify noradrenaline-induced contractions possibly via activation of H₁ and H₂ receptors. In conclusion, this study demonstrates that histamine can induce phasic contractions of rat distal cauda epididymis via H₂ receptors and autonomic neurotransmitters. Histamine may also exert modulatory actions on contractions of rat distal cauda epididymis duct induced by adrenergic receptor agonists. Further studies are necessary to unveil the localization of histamine receptors within the epididymal duct and the consequences of manipulation of the histaminergic system on epididymal function and male fertility.

Treatment of benign prostatic hyperplasia and abnormal ejaculation: live imaging reveals tamsulosin - but not tadalafil - induced dysfunction of prostate, seminal vesicles and epididymis

In brief

One of the most commonly prescribed benign prostatic hyperplasia (BPH) pharmacotherapies, the alpha1-adrenergic blocker tamsulosin, is frequently discontinued, especially by younger patients due to ejaculatory disorders, often without feedback to the attending physician. Using a newly developed ex vivo system simulating sympathetic effects on the most relevant structures for the emission phase of ejaculation, that is seminal vesicles, prostate and the most distal part of the cauda epididymidis, we elucidated that tamsulosin fundamentally disturbed the obligatory noradrenaline-induced contractions in each of these structures which differed to an alternative pharmacotherapy, the PDE5 inhibitor tadalafil.

Abstract

Structures responsible for the emission phase of ejaculation are the seminal vesicles, the most distal part of the cauda epididymidis and the newly characterized prostate excretory ducts. The emission phase is mainly regulated by the sympathetic nervous system through alpha1-adrenergic receptor activation by noradrenaline at the targeted organs. BPH treatment with alpha1A-adrenergic antagonists such as tamsulosin is known to result in ejaculation dysfunction, often leading to discontinuation of therapy. Mechanisms of this disturbance remain unclear. We established a rodent model system to predict drug responses in tissues involved in the emission phase of ejaculation. Imitating the therapeutic situation, prostate ducts, seminal vesicles and the distal cauda epididymal duct were pre-incubated with the smooth muscle cell-relaxing BPH drugs tadalafil, a novel BPH treatment option, and tamsulosin in an ex vivo time-lapse imaging approach. Afterwards, noradrenergic responses in the relevant structures were investigated to simulate sympathetic activation. Noradrenaline-induced strong contractions ultimately lead to secretion in structures without pre-treatment. Contractions were abolished by tamsulosin in prostate ducts and seminal vesicles and significantly decreased in the epididymal duct. Such effects were not observed with tadalafil pre-treatment. Data visualized a serious dysfunction of each organ involved in emission by affecting alpha1-adrenoceptors localized at the relevant structures but not by targeting smooth muscle cell-localized PDE5 by tadalafil. Our model system reveals the mechanism of tamsulosin resulting in adverse effects during ejaculation in patients treated for BPH. These adverse effects on contractility do not apply to tadalafil treatment. This new knowledge translates directly to clinical medicine.

Mechanisms underlying spontaneous phasic contractions and sympathetic control of smooth muscle in the rat caudal epididymis

Here we investigate mechanisms underlying spontaneous phasic contractions (SPCs) and sympathetic control of contractility in the rat epididymis, a long tubular duct involved in transportation and maturation of sperm. Longitudinal contractions of short segments (~ 1.5 mm) of rat proximal and distal caudal epididymal duct were measured + / - nerve stimulation. The extent of sympathetic innervation of these duct regions was determined by immunohistochemistry. Proximal caudal duct segments (150-300 μm dia.) exhibited SPCs, while distal segments (350-500 μm) were quiescent in ~ 80% of preparations. SPC amplitude and frequency were reduced by the L-type voltage-dependent Ca²⁺ channel (LVDCC) blocker nifedipine (1 μM), with the T-type voltage-dependent Ca²⁺ channel (TVDCC) blocker ML218 (1 μM) specifically decreasing SPC frequency. SPCs were inhibited upon blockade of the SR/ER Ca²⁺-ATPase (CPA 10 μM). SPCs were also inhibited by caffeine (1 μM), 2-APB (100 μM), niflumic acid (100 μM), or by lowering extracellular [Cl^-] from 134.4 to 12.4 mM but not by ryanodine (25 μM) or tetracaine (100 μM). Electrical field stimulation (EFS) at 2 Hz for 60 s caused a sustained α₁-adrenoceptor-sensitive contraction in distal segments and enhanced and/or induced α₂-adrenoceptor-sensitive oscillatory phasic contractions in proximal and distal segments, the latter mimicked by application of the α₂-adrenoceptor agonist clonidine. We hypothesise that SPCs in the proximal cauda are triggered by pacemaker mechanisms involving rhythmic IP₃ receptor-operated SR/ER store Ca²⁺ release and resultant activation of CaCC with TVDCCs and possibly LVDCCs subserving in this process. Sympathetic nerve-released noradrenaline induces α₂-adrenoceptor-mediated phasic contractions in the proximal and distal cauda. These findings provide new pharmacological targets for male infertility and contraception.

Sexual Incentive Motivation and Copulatory Behavior in Male Rats Treated With the Adrenergic α2-Adrenoceptor Agonists Tasipimidine and Fadolmidine: Implications for Treatment of Premature Ejaculation

BACKGROUND

Premature ejaculation is the most common sexual dysfunction in young men, and it often leads to reduced relationship satisfaction and quality of life.

AIM

To determine the role of central and peripheral α₂-adrenoceptors in the control of ejaculation and sexual incentive motivation in rats.

METHODS

Sexual incentive motivation was studied in a large arena in which a male subject could choose between approaching and remaining close to a sexually receptive female or another male. Sexual behavior was studied in standard observation cages in which a male was allowed to freely interact with a receptive female for 30 minutes. Two highly selective agonists at the α₂-adrenoceptors, tasipimidine and fadolmidine, were administered before the tests. Low peripheral doses of fadolmidine have been reported to have effects mainly outside of the central nervous system, whereas at large doses also the central effects are evident.

OUTCOMES

The time spent close to the receptive female in relation to the time spent with the male and measures of ambulatory activity were obtained from the test for sexual incentive motivation, while the habitual parameters of sexual behavior were recorded with the copulation test.

RESULTS

Tasipimidine prolonged ejaculation latency and the interintromission interval at the dose of 200 µg/kg when data from fast-ejaculating rats were used. No other sexual parameter was modified. A dose of 100 µg/kg was ineffective. There was no consistent effect on sexual incentive motivation, although modest sedation was observed. Fadolmidine, a drug that does not easily penetrate the blood-brain barrier, had no effect on sexual incentive motivation at any of the doses used (3, 30, and 100 µg/kg). The largest dose had clear sedative effects. The lower doses had no systematic effect on sexual behavior, not even when only fast or very fast ejaculating males were analyzed.

CLINICAL TRANSLATION

The findings are relevant to the search for treatments for premature ejaculation that are specific enough to selectively delay ejaculation.

STRENGTHS & LIMITATIONS

The procedures used here are standard in the field and yield the most reliable data. Whether the effects observed in male rats are directly transferrable to men can only be determined through clinical studies.

CONCLUSION

The observation that drugs acting at central but not peripheral α₂-adrenoceptors prolong ejaculation latency without affecting any other parameter of sexual behavior or sexual incentive motivation suggests that this kind of drug may be suitable for treating premature ejaculation. Jyrki L., Elisa V.-A., Xi C., et al. Sexual Incentive Motivation and Copulatory Behavior in Male Rats Treated With the Adrenergic α₂-Adrenoceptor Agonists Tasipimidine and Fadolmidine: Implications for Treatment of Premature Ejaculation. J Sex Med 2021;18:1677-1689.

Effects of dipyrone and acetylsalicylic acid on contractions of distal cauda epididymis duct, serum testosterone and sperm count in rats

The effects of dipyrone and acetylsalicylic acid (ASA) on male fertility are still not fully understood, mainly considering the epididymis as a putative target for their anti-fertility effects. Therefore, this study aimed to investigate the effects of dipyrone and ASA on the contractions of distal cauda epididymis duct, serum testosterone levels and sperm parameters in rats. Firstly, we checked the in vitro effects of dipyrone and ASA (10-1000 μM) on the contractions of distal cauda epididymis duct by pharmacological experiments. We also evaluated the effects of in vivo treatment with dipyrone and ASA 100 mg/kg (p.o.) for 15 days on epididymal duct contractions, serum testosterone levels and sperm parameters. In vitro dipyrone or ASA decreased the epididymal duct contractions induced by phenylephrine or carbachol. We observed that in vivo treatment with both drugs decreased the daily sperm production, serum testosterone levels and sperm count through epididymis without altering the epididymal duct contractions and sperm transit time through epididymis. In conclusion, in vitro dipyrone and ASA were able to diminish the contractions of epididymal duct, whilst in vivo administration decreased the sperm count throughout epididymis as a consequence of a low sperm production caused by reduced testosterone levels.

Immunolocalization of Adrenoceptors in the Reproductive Tract of Male Domestic Cats in Comparison to Rats

Simple Summary

In cats, semen is collected by pharmacological stimulation. The administration of a drug that stimulates α2-adrenoceptors causes the expulsion of spermatozoa into the urethra. However, as the results are not always satisfactory, this method needs to be improved. There are nine subtypes of adrenoceptors that are involved in the contraction of smooth muscle, including those in the reproductive tract, so adrenoceptors other than the α2-subtype are potential targets in any new, optimized protocol. The aim of this study was to analyze the immunolocalization of the adrenergic receptors in the reproductive tract of the male cat for the first time in this species. The expression of all adrenoceptor subtypes was noted in the peritubular smooth muscle in cats, indicating a potential clinical application for agonists of these receptors for the optimization of the pharmacological semen collection in felids. In a broader context, the development of a new procedure for semen collection in the male cat, using active substances from groups other than those currently used, will support the wider application of reproductive biotechnologies in felids.

Abstract

Adrenoceptors mediate the action of the sympathetic nervous system, including the contraction of the epididymis and vas deferens. The aim of this study was to immunolocalize the adrenergic receptors in the reproductive tract of the male cat, as this information is not yet available. The epididymis and vas deferens of domestic cats and rats (the biological controls) were analyzed by immunohistochemistry to determine the localization of the α1A-, α1B-, α1D-, α2A-, α2B-, α2C-, β1-, β2-, and β3-adrenoceptors. All the receptors were expressed in the peritubular smooth muscles of the cat, but the α1D-, α2C-, and β1-adrenoceptors were not detected in this tissue in the rat. For the α2A-adrenoceptor, the intensity of immunostaining differed significantly between the caput epididymis (weakest staining) and the vas deferens (strongest staining). The presence of all the types of the receptors was also detected in the cytoplasm of the epithelial cells in all the regions of the reproductive tract. The strong expression of the α2A-adrenoreceptor suggests it has a leading role in the contraction of the reproductive tract in the cat. The presence of other adrenergic receptors in the smooth muscle of the epididymis and vas deferens indicates a potential clinical application for α1-mimetics in the optimization of pharmacological semen collection in felids.

Lorcaserin Administration has Pro-Ejaculatory Effects in Rats via 5-HT2C Receptors Activation: A Putative Pharmacologic Strategy to Delayed Ejaculation?

BACKGROUND

Lorcaserin is an anti-obesity drug whose weight loss effect results from 5-hydroxytryptamin (5-HT)_2C receptors activation. The 5-HT_2C receptor was shown to participate in the physiological control of ejaculation, but no data addressing a putative effect of lorcaserin on ejaculation exist.

AIM

To investigate the effects of lorcaserin in different in vitro and in vivo experimental models of ejaculation in rats.

METHODS

Contractile responses to lorcaserin in rat seminal emission organs in vitro (prostatic and epididymal vas deferens, cauda epididymis, and seminal vesicles), analysis of male rat copulatory behavior, and electromyographic recording of bulbospongiosus muscle in anesthetized animals were studied.

MAIN OUTCOME MEASURES

The main outcome measures included in vitro contraction of seminal emission organs and evaluation of the male rat copulatory behavior. The male rat sexual behavior in terms of copulation latency, ejaculation latency, mount and intromission frequency, and ejaculation frequency of sexually experienced adult male rats with a receptive female were also recorded.

RESULTS

Lorcaserin (1.0 nM to 1.0 mM) had no significant effects on the in vitro contractility of seminal emission organs smooth muscle (cauda epididymis, vas deferens, and seminal vesicles). On the other hand, lorcaserin administration (0.3-1.0 mg/kg, intravenous) induced ejaculation in anesthetized rats, which was prevented by the 5-HT_2C-selective antagonist SB 242084 (0.1 and 0.3 mg/kg, intravenous). Single-dose treatment of non-anesthetized male rats with lorcaserin (1.0, 4.0, or 10 mg/kg, per os) induced non-copulating ejaculations in sexually naïve rats. Lorcaserin also had pro-ejaculation effects by decreasing the ejaculation threshold of copulating rats by half. The pro-ejaculatory effects of lorcaserin were reversible as the ejaculation threshold of treated rats recovered after a 1-week washout period.

CLINICAL IMPLICATIONS

Due to its reported clinical safety, repurposing lorcaserin for the treatment of delayed ejaculation may be suggested.

STRENGTHS & LIMITATIONS

The pro-ejaculatory effect of lorcaserin administration and the role of 5-HT_2C were demonstrated in different experimental models of ejaculation in rats. The lack of studies in putative experimental models of delayed ejaculation is a limitation of this study.

CONCLUSION

Our results demonstrate that the clinically approved 5-HT_2C agonist lorcaserin is a strong facilitator of ejaculation in rats. de Almeida Kiguti LR, Pacheco TL, Antunes E, et al. Lorcaserin Administration has Pro-Ejaculatory Effects in Rats via 5-HT2C Receptors Activation: A Putative Pharmacologic Strategy to Delayed Ejaculation? J Sex Med 2020;17:1060-1071.

Pupo A. Updates in the function and regulation of α1 -adrenoceptors

α1 -Adrenoceptors are seven transmembrane domain GPCRs involved in numerous physiological functions controlled by the endogenous catecholamines, noradrenaline and adrenaline, and targeted by drugs useful in therapeutics. Three separate genes, whose products are named α1A -, α1B -, and α1D - adrenoceptors, encode these receptors. Although the existence of multiple α1 -adrenoceptors has been acknowledged for almost 25 years, the specific functions regulated by each subtype are still largely unknown. Despite the limited comprehension, the identification of a single class of subtype-selective ligands for the α1A - adrenoceptors, the so-called α-blockers for prostate dysfunction, has led to major improvement in therapeutics, demonstrating the need for continued efforts in the field. This review article surveys the tissue distribution of the three α1 -adrenoceptor subtypes in the cardiovascular system, genitourinary system, and CNS, highlighting the functions already identified as mediated by the predominant activation of specific subtypes. In addition, this review covers the recent advances in the understanding of the molecular mechanisms involved in the regulation of each of the α1 -adrenoceptor subtypes by phosphorylation and interaction with proteins involved in their desensitization and internalization. LINKED ARTICLES: This article is part of a themed section on Adrenoceptors-New Roles for Old Players. To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v176.14/issuetoc.

Contractile Effects of Serotonin (5-HT) in the Rat Cauda Epididymis: Expression and Functional Characterization of 5-HT Receptors

Serotonin [5-hydroxytryptamine (5-HT)] exerts multiple central and peripheral functions. High concentrations of 5-HT have been found in the epididymis, a ductal organ that plays pivotal roles in sperm transport and maturation. The contraction of the epididymal smooth muscle is essential for sperm transport and emission during ejaculation. The contributions of the epididymal 5-HT system to these events are poorly understood. Here, we assessed the contractile function of 5-HT in the rat cauda epididymis (CE), pharmacologically targeting the receptor(s) and the reuptake mechanism involved in this system. Segments of CE duct from adult Wistar rats were set up in an organ bath system for isometric tension recordings, and concentration-response curves to 5-HT and norepinephrine were obtained. 5-HT elicited concentration-dependent contractions of the CE duct (pEC₅₀ = 6.5 ± 0.1) that were potentiated with high potency by the norepinephrine transporter (NET) inhibitor desipramine and with low potency by the highly selective serotonin transporter inhibitor paroxetine, indicating that the NET is the major mediator of 5-HT reuptake in vitro. CE contractions to 5-HT were antagonized by the α ₁-adrenoceptor (α ₁-AR) antagonist prazosin (pA ₂ ≅ 8.9), 5-HT_2A/2C antagonists ketanserin (pA ₂ ≅ 9.4) and fluoxetine (pA ₂ ≅ 7.4), and 5-HT_1A ligands WAY 100635 (pA ₂ ≅ 8.9) and buspirone (pA ₂ ≅ 7.3). Reverse transcriptase polymerase chain reaction analysis demonstrated that 5-HT_1A and 5-HT_2A transcripts are highly abundant in the cauda epididymis, whereas 5-HT_2C transcript was not found. Altogether, our results reveal that contractions of the CE duct to 5-HT encompasses at least activation of α ₁-ARs and 5-HT_1A and 5-HT_2A receptors, providing new insights into the roles of 5-HT on the epididymal function.

Epididymal approaches to male contraception

Today, a vast arsenal of contraceptive methods interfering at different levels of the female reproductive axis is available. This is not the case for men for whom, until now, there is no reliable male reversible method and for whom vasectomy, condom and withdrawal are the only options available. Despite this limited supply, more than one third of all contraceptive methods used worldwide rely on the cooperation of the male partner. Besides developing hormonal approaches to stop sperm production, there may be attractive approaches that will interfere with sperm functions rather than production. Sperm functions are primarily established during post-testicular maturation, with the epididymis accounting for the majority. The purpose of this review is to present some of the promising and/or already abandoned leads that emerge from research efforts targeting the epididymis and its activities as potential means to achieve male post-meiotic contraception.