Quantification and distribution of alpha 1-adrenoceptor subtype mRNAs in human vas deferens: comparison with those of epididymal and pelvic portions

Characteristics of α1-adrenoceptor antagonists-induced ejaculatory dysfunction on spontaneous seminal emission in rats

Although α1-adrenoceptor (α1-AR) antagonists used to treat benign prostatic hyperplasia can cause ejaculation disorders, the aetiology of this adverse event is still controversial. Therefore, we investigated the effects of antagonists with different affinities for α1-AR subtypes on ejaculatory function and their mechanisms of action in normal rats. In the spontaneous seminal emission (SSE) test, systemically administered prazosin, terazosin, tamsulosin and naftopidil decreased the weight of ejaculated seminal material in a dose-dependent manner; the potency order was as follows: tamsulosin > terazosin > prazosin > naftopidil. The selective α1D-AR antagonist BMY7378 had no effect on SSE. Intrathecal tamsulosin and naftopidil did not inhibit SSE. Tamsulosin, the most potent, was ineffective as a single dose and significantly increased seminal vesicle fluid in rats treated for 2 weeks but did not significantly change retrograde ejaculation. These results indicated that the difference in inhibitory potency of the five α1-AR antagonists against SSE was due to the involvement of α1A-AR subtypes. Our results further suggested that α1-AR antagonist-induced ejaculatory dysfunction at the peripheral level was mainly due to the loss of seminal emission, although some retrograde ejaculation may also be involved.

Evolving Role of Silodosin for the Treatment of Urological Disorders – A Narrative Review

Use of α-androgenic receptor blockers remains a mainstay therapeutic approach for the treatment of urological diseases. Silodosin is recommended over other α-blockers for the treatment of lower urinary tract symptoms (LUTS) and benign prostate hyperplasia (BPH), due to its high α_1A uroselectivity. Current research data suggest that silodosin is efficacious in the management of various urological diseases. Thus, we herein review the current evidence of silodosin related to its efficacy and tolerability and appraise the available literature that might ultimately aid in management of various urological conditions at routine clinical practice. Literature reveals that silodosin is beneficial in improving nocturia events related to LUTS/BPH. Silodosin exerts effect on relaxing muscles involved in detrusor obstruction, therefore prolonging the need for patients undergoing invasive surgery. Silodosin treatment, either as a monotherapy or combination, significantly improves International Prostate Symptom Score (IPSS) including both storage and voiding symptoms in patients with BPH/LUTS. Patients on other treatment therapies such as phosphodiesterase 5 inhibitors or other α-blockers are well managed with this drug. Steadily, silodosin has proved beneficial in the treatment of other urological disorders such as chronic prostatitis/chronic pelvic pain syndrome (CP/CPPS), overactive bladder/acute urinary retention (AUR), premature ejaculation (PE), and prostate cancer post brachytherapy-induced progression. In patients with distal ureteral stones, silodosin treatment is beneficial in decreasing stone expulsion time without affecting stone expulsion rate or analgesic need. Moreover, there were significant improvements in intravaginal ejaculation latency time, quality of life scores, and decrease in PE profile among patients with PE. Silodosin has also demonstrated promising results in increasing the likelihood of successful trial without catheter in patients with AUR and those taking antihypertensive drugs. Reports from Phase II studies have shown promising role of silodosin in the treatment of CP/CPPS as well as facilitating ureteral stone passage. From the robust data in this review, further silodosin treatment strategies in the management of different urological conditions need to be focused on.

Spontaneous Ejaculation: A Focused Review for the Clinicians

INTRODUCTION

The process of ejaculation has important meanings not only for its association with orgasm but also for the timing to ejaculate in the context of sexual activity. Spontaneous (involuntary) ejaculation (SE) without any sexual stimulation is a distressing symptom. Our understanding of SE is limited. Unfortunately, many physicians are not aware of these cases.

OBJECTIVES

The objective of this study is to describe the etiopathogenesis, clinical features, diagnosis, and treatment options for SE.

METHODS

We searched the literature for publications on "SE," "spontaneous emission" or "involuntary ejaculation," and factors influencing SE in the PUBMED/MEDLINE, Scopus, Cochrane Library, EMBASE, PsycINFO, ProQuest, Academic Search Complete database, Google Scholar, and CINAHL databases from inception to August 2020.

RESULTS

The literature search yielded 36 relevant publications reporting on 43 patients with SE. Attempts to explain the cause of pathologic SE have included 4 etiological groups (spinal cord lesions, psychological causes, rabies, and drug-induced). The underlying mechanisms responsible for induction of SE may include increased adrenergic activity, overactivity in dopaminergic system, decreased serotonergic activity, damage of descending inhibitory pathway, or penile hyperexcitability. SE may occur in the absence of an identifiable trigger or may be triggered by non-sexual circumstances (micturition, defecation, glans touch, anxiety, panic attack, or school examinations). Treatment options include psychoanalytic treatment, paroxetine, citalopram, sertraline, silodosin, and anxiolytics. In drug-induced SE, dose reduction and drug withdrawal with or without switching to another drug may relief SE.

CONCLUSIONS

SE is one of the least reported ejaculatory dysfunction. The key feature shared in common by these men is SE without any sexual thoughts or fantasies, may be triggered by non-sexual contexts, rarely associated with orgasm or erection. Treatment by psychoanalytic treatment and pharmacotherapy may be helpful. Further research might explore the definite underlying mechanisms. Abdel-Hamid IA, Ali OI. Spontaneous Ejaculation: A Focused Review for the Clinicians. Sex Med Rev 2021;9:406-422.

Comparison of the Effects of Tadalafil and α1-Adrenoceptor Antagonists on Spontaneous Seminal Emission and Electrical Field Stimulation-Induced Seminal Vesicle Contraction in Rats

BACKGROUND

Although numerous reports have shown that α₁-adrenoceptor (α₁-AR) antagonists, which are used to treat benign prostatic hyperplasia (BPH), can cause ejaculatory disorders, few studies have investigated whether the phosphodiesterase 5 (PDE5) inhibitor tadalafil has such adverse effects. In this study, we compared the effects of tadalafil and α₁-AR antagonists on seminal emission and their mechanisms of action.

AIM

To evaluate in normal rats the possible effects of tadalafil on spontaneous seminal emission (SSE) and seminal contraction evoked by hypogastric nerve stimulation.

METHODS

Male Sprague-Dawley rats were used. To assess SSE, plastic corsets were fitted around the thorax and upper abdomen of male Sprague-Dawley rats to prevent genital autogrooming. Rats were treated orally with tadalafil or an α₁-AR antagonist (silodosin, naftopidil, or tamsulosin) for 3 days and housed in wire-bottomed cages. Ejaculatory plugs dropped on the bottoms of the cages were counted and weighed. To assess the intraluminal pressure of seminal vesicles, the hypogastric nerve of urethane-anesthetized rats was isolated and electrically stimulated. After stabilization of seminal vesicle contraction, the rats were intravenously administered test drugs. The expression of PDE5, endothelial nitric oxide synthetase (eNOS), and neuronal NOS (nNOS) in the seminal vesicle and vas deferens were measured by reverse-transcription polymerase chain reaction.

MAIN OUTCOME MEASURE

The number and weight of the ejaculatory plugs produced by corset-fitted rats and the intraluminal pressure of the seminal vesicle were evaluated.

RESULTS

Tadalafil did not affect the number or weight of the ejaculatory plugs of corset-fitted rats, whereas all α₁-AR antagonists decreased both in a dose-dependent manner. The α₁-AR antagonists, but not tadalafil, inhibited the seminal vesicle contraction evoked by electrical stimulation of the hypogastric nerve. The seminal vesicle and vas deferens expressed higher levels of PDE5 and eNOS mRNA and lower levels of nNOS mRNA relative to the urethra.

CLINICAL IMPLICATIONS

Tadalafil can be a treatment option in cases where there is concern about negative effects on seminal emission.

STRENGTHS AND LIMITATIONS

We demonstrated different effects of tadalafil and 3 α₁-AR antagonists on rat SSE and their mechanisms of action by measuring seminal vesicle contractility in vivo. A limitation is that we used normal rats, not BPH model rats, and so our results might not apply to human BPH patients.

CONCLUSION

Tadalafil did not inhibit spontaneous seminal emission or electrical field stimulation-induced seminal vesicle contraction in normal rats. The NO-cyclic guanosine monophosphate pathway is unlikely to be involved in the inhibition of seminal vesicle contraction in normal rats. Yoshinaga R, Fukui T, Yoshifuji M, et al. Comparison of the Effects of Tadalafil and α₁-Adrenoceptor Antagonists on Spontaneous Seminal Emission and Electrical Field Stimulation-Induced Seminal Vesicle Contraction in Rats. J Sex Med 2019;16:680-690.

The impact and management of sexual dysfunction secondary to pharmacological therapy of benign prostatic hyperplasia

Benign prostatic hyperplasia (BPH) is one of the most common genitourinary complications in men over 50 years of age and typically presents with lower urinary tract symptoms (LUTS). Classes of medications include α1-adrenoceptor blockers, 5α-reductase inhibitors, and phosphodiesterase 5 inhibitors. Today, α1-adrenoceptor blockers and 5α-reductase inhibitors are often combined to give a synergistic effect. A review of the current literature identified several adverse sexual side effects, including erectile dysfunction (ED), decreased libido, orgasmic disorders, and ejaculatory disorders. We believe it is important to know the extent of these side effects, as the clinician and patient will need to decide the cost of improved voiding symptoms. The chief adverse effect is ejaculatory disorders, including the absence of ejaculation. Clinical consideration for BPH should include the elements of male sexual function, patients’ age, and the characteristics and comprehensive effects of each group of drugs. Methodological bias in clinical studies, such as the subjective evaluation of the sexual side effect, makes it difficult to determine the ideal drug for treatment.

Sexual Side Effects of Medical and Surgical Benign Prostatic Hyperplasia Treatments

Treatments for lower urinary tract symptoms due to benign prostatic hyperplasia can be evaluated by multiple metrics. A balance within the confines of patient expectations is key to determining the ideal treatment. A troubling adverse event for some patients is sexual dysfunction. Because the cohort of men who seek treatment of sexual dysfunction and lower urinary tract symptoms is essentially identical, these disease processes frequently overlap. This article considers potential pathophysiologic causes of dysfunction with treatment and attempts to critically review the available data to assess the true incidence of sexual adverse events with treatment.

Impact of alpha blockers, 5-alpha reductase inhibitors and combination therapy on sexual function

Medical treatments for lower urinary tract symptoms due to benign prostatic hyperplasia are frequently associated with changes in sexual function. While these medications are generally well-tolerated and have both reduced and delayed more invasive surgical options, the ramifications of long-term chronic use are largely unknown. Sexual side effects of these medications are frequently either reported as part of a short-term initial drug study or have inflexible endpoints that are not able to gauge more subtle changes in sexual performance. This review will delineate the currently known effects of these medications on sexual function and will consider mechanisms of dysfunction.

Physiological and pharmacological aspects of the vas deferens-an update

The vas deferens, a muscular conduit conveying spermatozoa from the epididymis to the urethra, has been used as a model tissue for smooth muscle pharmacological and physiological advancements. Many drugs, notably α-adrenergic antagonists, have effects on contractility and thus normal ejaculation, incurring significant side effects for patients that may interfere with compliance. A more thorough understanding of the innervation and neurotransmitter pharmacology of the vas has indicated that this is a highly complex structure and a model for co-transmission at the synapse. Recent models have shown clinical scenarios that alter the vas contraction. This review covers structure, receptors, neurotransmitters, smooth muscle physiology, and clinical implications of the vas deferens.

Withdrawal symptoms and rebound syndromes associated with switching and discontinuing atypical antipsychotics: theoretical background and practical recommendations

With the widespread use of atypical or second-generation antipsychotics, switching treatment has become current practice and more complicated, as the pharmacological profiles of these agents differ substantially despite their similarity in being 'atypical'. All share the ability to block dopamine D₂ receptors, and most of them also block serotonin 5-HT2A receptors. Apart from these common features, some atypical antipsychotics are also able to block or stimulate other dopamine or serotonin receptors, as well as histaminergic, muscarinergic or adrenergic receptors. As a result of the varying receptor affinities, in switching or discontinuing compounds several possible pitfalls have to be considered, including the occurrence of withdrawal and rebound syndromes. This article reviews the pharmacological background of functional blockade or stimulation of receptors of interest in regard to atypical antipsychotics and the implicated potential withdrawal and rebound phenomena. A MEDLINE search was carried out to identify information on withdrawal or rebound syndromes occurring after discontinuation of atypical antipsychotics. Using the resulting literature, we first discuss the theoretical background to the functional consequences of atypical antipsychotic-induced blockade or stimulation of neurotransmitter receptors and, secondly, we highlight the clinical consequences of this. We then review the available clinical literature on switching between atypical antipsychotics, with respect to the occurrence of withdrawal or rebound symptoms. Finally, we offer practical recommendations based on the reviewed findings. The systematic evaluation of withdrawal or rebound phenomena using randomized controlled trials is still understudied. Knowledge of pharmacological receptor-binding profiles may help clinicians in choosing adequate switching or discontinuation strategies for each agent. Results from large switching trials indicate that switching atypical antipsychotics can be performed in a safe manner. Treatment-emergent adverse events during or after switching are not always considered to be, at least in part, associated with the pre-switch antipsychotic. Further studies are needed to substantiate the evidence gained so far on different switching strategies. The use of concomitant medication, e.g., benzodiazepines or anticholinergic drugs, may help to minimize symptoms arising from the discontinuation or switching of antipsychotic treatment.

Efficacy of alfuzosin after shock wave lithotripsy for the treatment of ureteral calculi

PURPOSE

We evaluated the efficacy of alfuzosin for the treatment of ureteral calculi less than 10 mm in diameter after extracorporeal shock wave lithotripsy (ESWL).

MATERIALS AND METHODS

A randomized, single-blind clinical trial was performed prospectively by one physician between June 2010 and August 2011. A total of 84 patients with ureteral calculi 5 to 10 mm in diameter were divided into two groups. Alfuzosin 10 mg (once daily) and loxoprofen sodium 68.1 mg (as needed) were prescribed to group 1 (n=41), and loxoprofen sodium 68.1 mg (as needed) only was prescribed to group 2 (n=44). The drug administration began immediately after ESWL and continued until stone expulsion was confirmed up to a maximum of 42 days after the procedure.

RESULTS

Thirty-nine of 41 (95.1%) patients in group 1 and 40 of 43 (93.0%) patients in group 2 ultimately passed stones (p=0.96). The number of ESWL sessions was 1.34±0.65 and 1.41±0.85 in groups 1 and 2, respectively (p=0.33). The patients who required analgesics after ESWL were 8 (19.5%) in group 1 and 13 (30.2%) in group 2 (p=0.31). Visual analogue scale pain severity scores were 5.33±1.22 and 6.43±1.36 in groups 1 and 2, respectively (p=0.056). The time to stone expulsion in groups 1 and 2 was 9.5±4.8 days and 14.7±9.8 days, respectively (p=0.005). No significant adverse effects occurred.

CONCLUSIONS

The use of alfuzosin in combination with ESWL seems to facilitate stone passage and to reduce the time of stone expulsion but does not affect the stone-free rate.

Silodosin is effective for treatment of LUTS in men with BPH: a systematic review

The aim of this study was to systematically review the evidence on the efficacy and safety of silodosin treatments on lower urinary tract symptoms (LUTS) in men with benign prostatic hyperplasia (BPH) from randomized controlled trials. We searched PubMed (1966-December 2011), Embase (1974-December 2011) and the Cochrane Library Database (2011, Issue 12). The assessed outcome measures were the change from baseline for the International Prostate Symptom Score (IPSS), quality of life (QoL) score, peak urine maximum flow rate (Q(max)), QoL related to urinary symptoms and adverse effects. Two authors independently assessed the study quality and extracted data. All data were analysed using RevMan 5.1. The meta-analysis included four randomized controlled trials with a total of 2504 patients. The study durations were each 12 weeks. At the follow-up end points, the pooled results showed that the change from baseline for the silodosin group was significantly higher than the placebo group for the IPSS, QoL score and Q(max)(mean difference (MD)=-2.78, P<0.00001; MD=-0.42, P=0.004; MD=1.17, P<0.00001,respectively) and patients felt more satisfied with QoL related to urinary symptoms in the silodosin group than the placebo group. Ejaculation disorder was the most commonly reported adverse effect. The pooled results also showed that the silodosin group was superior to the 0.2 mg tamsulosin group with respect to the IPSS and QoL score (IPSS: MD=-1.14, P=0.02; QoL score: MD=-0.26, P=0.02) and inferior to the 0.2 mg tamsulosin group with respect to Q(max) (MD=-0.85, P=0.01). In contrast, there was no significant difference in the incidence of ejaculation disorder and dizziness between the silodosin and 0.2 mg tamsulosin groups. The current meta-analysis suggested that silodosin is an effective therapy for LUTS in men with BPH and is not inferior to 0.2 mg tamsulosin.

Investigation of ejaculatory disorder by silodosin in the treatment of prostatic hyperplasia

BACKGROUND

To assess the ejaculatory disorder caused by silodosin in the prostatic hyperplasia patients who carry out sexual actions (sexual intercourse, masturbation).

METHOD

The subjects of this study were 91 patients who had been clinically diagnosed to have LUTS/BPH at this hospital, who were administered silodosin at 4 mg twice a day, and who gave response to a questionnaire survey related to ejaculatory disorder. Sexual intercourse and masturbation were regarded as sexual actions in this study.

RESULTS

Ejaculatory disorder occurred in 38 (42%) of the 91 silodosin administration cases. Forty (44%) of the 91 patients answered that they carried out sexual actions after oral intake of silodosin. When the investigation was conducted only in those who exercised sexual actions, ejaculatory disorder was observed in 38 (95%) of these 40 patients, indicating a high incidence. When asked if disturbed by the ejaculatory disorder, 29 (76%) of the 38 patients who had ejaculatory disorder answered yes. Oral silodosin was discontinued due to the ejaculatory disorder in 2 (5%) of these patients. On the whole, the discontinuation rate of oral silodosin was 2% (2/91 patients).

CONCLUSION

It was demonstrated that the administration of silodosin induced ejaculatory disorder at a high incidence. Since it is possible that the high frequency of ejaculatory disorder by silodosin may reduce QOL, it is considered necessary to provide sufficient information related to ejaculatory disorder at the time of treatment with silodosin.

Assessment of tamsulosin as a potential male contraceptive in healthy volunteers

OBJECTIVE

To investigate the efficacy and safety of tamsulosin, an α(1A)-adrenoceptor antagonist, as a potential male contraceptive.

METHODS

Forty healthy male volunteers were equally divided into 2 groups, each of which received placebo and tamsulosin sequentially in a crossover manner. Ejaculatory profile was examined 4 to 6 hours after administration and adverse effects were noted.

RESULTS

Anejaculation occurred in all subjects after taking 0.8-mg of tamsulosin. Total functional sperm count was significantly reduced in subjects after taking 0.4-mg of tamsulosin. Six subjects receiving 0.8-mg of tamsulosin complained of tolerated discomfort, which disappeared 10 hours after administration.

CONCLUSION

When administered at 0.8 mg, tamsulosin can cause anejaculation with some transient side effects. Our results imply that tamsulosin and related drugs might potentially be used as male contraceptive agents in the future, which needs more studies to verify.

Comparison of the effects of four α1-adrenoceptor antagonists on ejaculatory function in rats

OBJECTIVE

To compare the effects of four α(1)-adrenoceptor (AR) subtype-selective antagonists on ejaculatory function in rats to investigate whether the differences in their modes of action-based on their selectivities for the α(1A)-AR subtype-would be related to the prevalence of ejaculation disorder (EjD).

METHODS

The effects of α(1)-AR antagonists on noradrenaline-induced contractions were studied in rat isolated seminal vesicles, vas deferens, bladder trigone, and prostate. Male rats were given α(1)-AR antagonists orally and, 1 hour after the drug administration they were cohoused in pairs for 1 hour with untreated female rats certified to be in estrus. The number of copulatory plugs (NP) present after mating was measured as a marker of EjD. Drug effects on ejaculatory function (ie, on NP) were compared with those on the prostatic urethra (ie, phenylephrine-induced increase in intraurethral pressure [IUP]).

RESULTS

All α(1)-AR antagonists concentration-dependently inhibited noradrenaline-induced contraction in all 4 tissues, and there were no differences in the rank order of potencies (tamsulosin > silodosin > alfuzosin > naftopidil) among the tissues. All α(1)-AR antagonists dose-dependently decreased NP and inhibited the phenylephrine-induced increase in IUP. There was little difference in the dose ratio ID(50) value (dose required to produce 50% inhibition) for NP/ID(50) value for IUP response among the four drugs. Drug potencies associated NP and IUP correlated closely with affinities for the human α(1A)-AR.

CONCLUSION

α(1)-AR antagonists cause EjD as a class effect that depends on affinity for α(1A)-AR. Differences in α(1A)-AR selectivity would be unlikely to be related to the incidence of EjD.

Correlation between lower urinary tract symptoms and premature ejaculation in Korean men older than 40 years old [corrected]

PURPOSE

To evaluate the correlation between lower urinary tract symptoms (LUTS) and premature ejaculation (PE) in Korean men older than 40 years.

MATERIALS AND METHODS

In total, 258 men older than 40 years completed the International Prostate Symptom Score (IPSS; total score, storage symptoms [ST], and voiding symptoms [VD]), a 5-item version of the International Index of Erectile Function (IIEF-5), and the Premature Ejaculation Diagnostic Tool (PEDT). The study examined the relationship between LUTS and PE. In the PEDT, PE is defined as a score ≥11.

RESULTS

The prevalence of PE was 29.1% with the PEDT versus a self-reported value of 49.5%. The prevalence of PE was 30.9% in 40 to 59-year-old men (21.3%) and 28.1% in 60 to 79 year-old men (78.7%). In men 40 to 59 and 60 to 79 years old, the mean PEDT, IPSS, and IIEF-5 scores were 8.65 and 7.88, 13.5 and 12.38, and 15.83 and 13.69, respectively. No significant correlations were observed between the total and subscale scores of the IPSS (p=0.204) and the PEDT (p=0.309) with increasing age, whereas a significant negative correlation was detected between the IIEF-5 and age (p=0.002). The PEDT score was significantly correlated with the IPSS-ST (r=0.326, p<0.001), IPSS-VD (r=0.183, p=0.005), IPSS-total (r=0.310, p<0.001), and IIEF-5 total (r=-0.248, p<0.001).

CONCLUSIONS

LUTS, especially storage symptoms, were related to PE. In elderly men, control of both erectile dysfunction and LUTS may play an important role in managing PE.

Silodosin in the treatment of benign prostatic hyperplasia

Benign prostatic hyperplasia (BPH)-associated lower urinary tract symptoms (LUTS) are highly prevalent in older men. Medical therapy is the first-line treatment for LUTS due to BPH. Alpha-adrenergic receptor blockers remain one of the mainstays in the treatment of male LUTS and clinical BPH. They exhibit early onset of efficacy with regard to both symptoms and flow rate improvement, and this is clearly demonstrated in placebo-controlled trials with extensions out to five years. These agents have been shown to prevent symptomatic progression of the disease. The aim of this article is to offer a critical review of the current literature on silodosin, formerly known as KMD-3213, a novel alpha-blocker with unprecedented selectivity for α(1A)-adrenergic receptors, as compared with both α(1B)- and α(1D) -adrenoceptors, exceeding the selectivity of all currently used α(1)-blockers, and with clinically promising effects.

Subtypes of functional alpha1-adrenoceptor

In this review, subtypes of functional alpha1-adrenoceptor are discussed. These are cell membrane receptors, belonging to the seven-transmembrane-spanning G-protein-linked family of receptors, which respond to the physiological agonist noradrenaline. alpha1-Adrenoceptors can be divided into alpha1A-, alpha1B- and alpha1D-adrenoceptors, all of which mediate contractile responses involving Gq/11 and inositol phosphate turnover. A fourth alpha1-adrenoceptor, the alpha1L-, represents a functional phenotype of the alpha1A-adrenoceptor. alpha1-Adrenoceptor subtype knock-out mice have refined our knowledge of the functions of alpha-adrenoceptor subtypes, particuarly as subtype-selective agonists and antagonists are not available for all subtypes. alpha1-Adrenoceptors function as stimulatory receptors involved particularly in smooth muscle contraction, especially contraction of vascular smooth muscle, both in local vasoconstriction and in the control of blood pressure and temperature, and contraction of the prostate and bladder neck. Central actions are now being elucidated.

Ejaculatory dysfunction caused by the new alpha1-blocker silodosin: A preliminary study to analyze human ejaculation using color Doppler ultrasonography

OBJECTIVES

In order to clinically investigate the mechanism of ejaculatory dysfunction attributable to the alpha1-blocker silodosin, a real-time observation of ejaculation by healthy males was performed.

METHODS

Following intake of silodosin, a newly developed selective alpha1-blocker for benign prostatic hypertrophy, ejaculation was dynamically observed using color Doppler ultrasound in three healthy males. Normal ejaculation was also investigated in the same manner.

RESULTS

With silodosin intake, no antegrade ejaculation was observed in cases 1 or 2. In case 1, seminal fluid slowly but continuously flowed out from the seminal vesicles into the bladder. In case 2, only a small amount of seminal fluid flowed into the bladder during the ejaculatory sensation. In case 3, ejection of a small amount of semen from the external urethral orifice was observed and inflow of a small amount of seminal fluid into the bladder was also captured. Without silodosin intake, all three subjects exhibited antegrade ejaculation.

CONCLUSIONS

The mechanism of ejaculatory dysfunction is intricately related to retrograde ejaculation (retrograde inflow of seminal fluid), insufficient contraction of the seminal vesicles, and insufficient rhythmic contraction of the muscles of the pelvic floor.

Short- and long-term effects of silodosin, a selective alpha 1A-adrenoceptor antagonist, on ejaculatory function in rats

OBJECTIVE

To investigate the short- and long-term effects of silodosin, a selective alpha(1A)-adrenoceptor antagonist, on spontaneous seminal emission by isolated rats and on the properties of alpha(1)-adrenoceptor subtypes in the rat seminal vesicle, as silodosin produces a relatively high incidence rate of abnormal ejaculation and chronic administration of receptor antagonists causes an up-regulation in the targeted receptor.

MATERIALS AND METHODS

Rats were treated with two doses (0.1 and 3 mg/kg/day) of silodosin orally for 3 or 30 days. Spontaneous seminal emission was studied during the 3-day observation period before completing treatment. The expression levels of alpha(1A), alpha(1B) and alpha(1D)-adrenoceptor mRNAs in the rat seminal vesicle and prostate were quantified by real-time reverse transcription-polymerase chain reaction using SYBR Green I.

RESULTS

The administration of two doses of silodosin for 3 or 30 days caused a significant dose-dependent reduction in the number of ejaculatory plugs and in their dry weight. However, in rats receiving the low dose of silodosin the inhibitory effect of the drug on spontaneous seminal emission diminished significantly with chronic usage over time. Although short-term administration of silodosin did not affect expression levels of any alpha(1)-adrenoceptor subtype mRNAs in the rat seminal vesicle and prostate, long-term administration of silodosin caused a significant up-regulation in the mRNA expression of alpha(1A)-adrenoceptor in a tissue-dependent manner.

CONCLUSION

Silodosin-induced up-regulation of alpha(1A)-adrenoceptor mRNA in the rat seminal vesicle might indicate potential differences in the inhibitory effect of this drug on ejaculatory function with chronic usage over time.

Human epididymal and prostatic tracts of vas deferens: Different contraction response to noradrenaline stimulation in isolated organ bath assay

In the present study epididymal and prostatic portions of human vas deferens were separately isolated and stimulated with exogenous noradrenaline to study their contractile properties. The results displayed that the epididymal tract produced a phasic-tonic response, while the prostatic strip produced only a phasic response suggesting a different functional role of each vas deferens segment. Moreover, it has been verified if alpha(1)-adrenoceptor antagonists doxazosin, alphuzosin and terazosin could differently block the noradrenaline response in each segment. Doxazosin, the most potent antagonist, displayed similar potency in epididymal and prostatic tract (pA(2)=8.51 and 8.42, respectively). Analogously, alphuzosin, although less potent than doxazosin, displayed in the same tracts a superimposed potency (pA(2)=7.25 and 7.30, respectively). In contrast with doxazosin and alphuzosin, terazosin displayed higher potency in blocking the contractile response in prostatic tract (pA(2)=7.67) than in epididymal segment (pA(2)=6.43). These results showed that alpha(1)-adrenoceptor antagonists doxazosin and alphuzosin, although with a different potency, did not discriminate between epididymal and prostatic segment while terazosin showed high potency in prostatic tract and only a moderate activity in epididymal section. Moreover, the biological model employed in our experiments could be a valid screening method to test the potential interferences of drugs indicated for bladder outlet obstruction with the peristaltic activity or the global tone of the human vas deferens.

Pharmacology of α1-adrenoceptor antagonists in the lower urinary tract and central nervous system

The main use of alpha(1)-adrenoceptor (AR) antagonists in urology has been to treat lower urinary tract symptoms (LUTS) in men with benign prostatic obstruction (BPO). The beneficial effects of these agents are primarily assumed to be because of relaxation of prostatic and urethral smooth muscle. The weak correlation between LUTS and prostatic enlargement, outflow obstruction, or both, however, has refocused interest on the role of extraprostatic alpha-ARs in the pathogenesis of LUTS and their treatment. The alpha(1)-ARs present in the bladder, urethra, vas deferens, peripheral ganglia, nerve terminals, and in the central nervous system could all potentially influence LUTS and, when the receptors are blocked, contribute to both the therapeutic and adverse effects of alpha(1)-AR antagonists. The relevance of alpha(1)-AR-subtype selectivity on the clinical usefulness of existing drug therapies has not been firmly established but it seems that blockade of both alpha(1A/L)- and alpha(1D)-ARs is necessary for the optimum balance between clinical efficacy and adverse effects.

Ejaculatory disorder caused by alpha-1 adrenoceptor antagonists is not retrograde ejaculation but a loss of seminal emission

AIM

The etiology of the ejaculatory disorder induced by alpha-1 blockers is still controversial, although it has been suggested to be retrograde ejaculation. The aim of this study was to investigate the distribution of alpha-1 adrenoceptor subtype mRNA in human seminal vesicles, and to analyze the prevalence and etiology of the disorder in healthy men.

METHODS

Experimental Study. Seminal vesicles from 10 surgical specimens (eight radical prostatectomy, two radical cystectomy) were dissected. Real-time PCR was conducted for quantification of mRNA expression of each alpha-1 adrenoceptor subtype. Clinical Study. Ejaculatory disorder was investigated using 17 healthy male volunteers. Tamsulosin (0.2 mg and 0.4 mg) and naftopidil (50 mg and 100 mg) were administered in a crossover manner for 3 days. The ejaculatory volume, sperm count in midstream urine after ejaculation, and fructose concentration in seminal plasma were investigated.

RESULTS

Real-time PCR revealed that alpha-1a mRNA was significantly predominant in seminal vesicles (P < 0.001; 1a, 75.0%; 1b, 11.7%; 1d, 13.3%). Ejaculatory volume (baseline 2.72 +/- 0.28 mL) significantly decreased in the tamsulosin group (0.2 mg, 1.75 +/- 0.31 mL; 0.4 mg, 1.51 +/- 0.39 mL; P < 0.05), but not in the naftopidil group (50 mg, 2.70 +/- 0.24 mL; 100 mg, 2.48 +/- 0.26 mL; P = NS). There was no sperm in midstream urine after any ejaculation.

CONCLUSIONS

The current study demonstrates that alpha-1a mRNA is predominant among the adrenoceptor subtypes in human seminal vesicles. Decreased capacity of contraction of the seminal vesicles is proposed as the cause of the ejaculatory disorder induced by alpha-1 blockers.

Silodosin, a new alpha1A-adrenoceptor-selective antagonist for treating benign prostatic hyperplasia: results of a phase III randomized, placebo-controlled, double-blind study in Japanese men

OBJECTIVE

To verify the efficacy and safety of the new alpha1A-adrenoceptor-selective antagonist silodosin compared with tamsulosin and placebo in patients with lower urinary tract symptoms (LUTS) associated with benign prostatic hyperplasia (BPH).

PATIENTS AND METHODS

This randomized, double-blind, placebo-controlled study was conducted at 88 centres in Japan. Men aged > or = 50 years with an International Prostate Symptom Score (IPSS) of > or = 8, a quality-of-life (QoL) score of > or = 3, a maximum urinary flow rate (Qmax) of < 15 mL/s, a prostate volume of > or = 20 mL and a postvoid residual urine volume of < 100 mL were eligible for enrolment. Patients were randomized to receive silodosin 4 mg twice daily, tamsulosin 0.2 mg once daily, or placebo, for 12 weeks. The primary endpoint was the change in IPSS from baseline. Safety was assessed by adverse events, physical examination, vital signs and laboratory tests.

RESULTS

In all, 457 patients were randomized (silodosin 176, tamsulosin 192 and placebo 89). The change in the total IPSS from baseline in the silodosin, tamsulosin and placebo groups was -8.3, -6.8 and -5.3, respectively. There was a significant decrease in the IPSS vs placebo in the silodosin group from 1 week. In the early-stage comparison, silodosin showed a significant decrease in IPSS vs tamsulosin at 2 weeks. The change in QoL from baseline was -1.7, -1.4 and -1.1 in the silodosin, tamsulosin and placebo groups, respectively; silodosin showed a significant improvement in the QoL score vs placebo. In the subgroup of patients with severe symptoms (IPSS > or = 20) silodosin also gave a significantly better improvement than placebo (-12.4 vs -8.7). The incidence rates of adverse events and drug-related adverse events were, respectively, 88.6%, 82.3% and 71.6% and 69.7%, 47.4% and 36.4%, respectively. The most common adverse event in the silodosin group was abnormal ejaculation, which occurred more often in the silodosin than in the tamsulosin group (22.3% vs 1.6%). However, only five men (2.9%) discontinued treatment for abnormal ejaculation.

CONCLUSION

Silodosin was generally effective in the absence of obtrusive side-effects. This study suggests that silodosin is clinically useful for treating LUTS associated with BPH.

Lower urinary tract symptoms/benign prostatic hyperplasia: minimizing morbidity caused by treatment

The beneficial effects of treatment for lower urinary tract symptoms (LUTS) suggestive of benign prostatic hyperplasia (BPH), or LUTS/BPH, have to be balanced against the morbidity associated with treatment. Invasive surgery, such as transurethral resection of the prostate, has been associated with irreversible complications (eg, impotence and retrograde ejaculation). Alpha(1)-adrenoceptor antagonists provide effective and fast relief of LUTS/BPH. In contrast to finasteride, they are not associated with sexual dysfunction (eg, decreased libido or impotence). Alpha(1)-adrenoceptor antagonists induce adverse events associated with interference with blood pressure regulation. The alpha(1A)/alpha(1D)-adrenoceptor antagonist tamsulosin has the lowest potential to interfere with blood pressure regulation and induce related adverse events. In addition, tamsulosin seems to be as well tolerated as phytotherapy, except for a higher incidence of abnormal ejaculation. Abnormal ejaculation occurs in 4% to 11% of patients receiving a alpha(1)-adrenoceptor antagonist, which is, however, well tolerated; <1% of patients discontinue because of this adverse event. In placebo-controlled trials, abnormal ejaculation has been predominantly reported for tamsulosin, but in most direct comparative studies, the incidence was comparable to that of other alpha(1)-adrenoceptor antagonists. Men with LUTS/BPH have an increased risk of impaired sexual function. However, alpha(1)-adrenoceptor antagonists, such as tamsulosin, may slightly improve sexual dysfunction together with LUTS problems. Combination therapy of an alpha(1)-adrenoceptor antagonist and finasteride has a similar adverse-event profile as each monotherapy, except for an increased risk of abnormal ejaculation. The discontinuation rate because of adverse events does not seem to be higher than with monotherapy. Medical therapies, and particularly alpha(1)-adrenoceptor antagonists such as tamsulosin, can be considered a first-line treatment option for LUTS/BPH because they provide effective relief of bothersome LUTS with excellent tolerability.

Safety and efficacy of alfuzosin 10 mg once-daily in the treatment of lower urinary tract symptoms and clinical benign prostatic hyperplasia: a pooled analysis of three double-blind, placebo-controlled studies

OBJECTIVES

To examine the efficacy and safety of a once-daily formulation of alfuzosin in a pooled analysis of three parallel, randomized, double-blind, placebo-controlled 3-month studies of patients with lower urinary tract symptoms (LUTS) consistent with clinical benign prostatic hyperplasia.

PATIENTS AND METHODS

Patients were randomized to receive alfuzosin, 10 mg once-daily (473) or placebo (482) for 12 weeks. Primary efficacy criteria were improvements in the International Prostate Symptom Score (IPSS) and peak urinary flow rate (PFR).

RESULTS

Alfuzosin significantly improved the mean (sd) IPSS, by - 6.0 (5.1) vs - 4.2 (5.7) with placebo (P < 0.005) and the PFR, by + 2.3 (3.8) vs + 1.1 (3.1) ml/s with placebo (P < 0.001), irrespective of prostate size. The significant improvement in LUTS included the irritative and the obstructive subscore of the IPSS and the nocturia criterion; the PFR increased rapidly and significantly, from the first visit (14 days). The quality-of-life score also improved significantly in alfuzosin-treated patients. Alfuzosin was well tolerated; the number of withdrawals for adverse events was comparable in both treatment groups. The most frequently reported adverse event was dizziness (placebo 2.9%, alfuzosin 6.1%). There were no significant changes in blood pressure with alfuzosin compared with placebo, including in elderly and hypertensive patients. Sexual adverse events were rare (abnormal ejaculation, 0.6%).

CONCLUSIONS

The once-daily formulation of alfuzosin, administered at 10 mg with no dose titration is effective, with a good safety profile, especially in elderly and hypertensive patients.

Contractile actions of imidazoline alpha-adrenoceptor agonists and effects of noncompetitive alpha1-adrenoceptor antagonists in human vas deferens

The contractile actions of imidazoline alpha-adrenoceptor agonists were investigated in human vas deferens longitudinal and circular muscle. The effects of phenoxybenzamine were studied in comparison to dibenamine and SZL-49 (4-amino-6,7-dimethoxy-2-quinazolinyl-4-(2-bicyclo[2,2,2]octa-2,5-dienylcarbonyl-2-piperazine), an alkylating prazosin analogue that discriminates between alpha(1H)- and alpha(1L)-adrenoceptor subtypes. The imidazoline alpha-adrenoceptor agonist, A-61603 (N-[5-(4,5-dihydro-1H-imidazol-2yl)-2-hydroxy-5,6,7,8-tetrahydronaphthalen-1-yl]methanesulfonamide hydrobromide), was a potent agonist (pD(2); longitudinal muscle 6.9, circular muscle 6.4) and cirazoline a partial agonist (pD(2); longitudinal muscle 6.1, circular muscle 5.1). Oxymetazoline was less effective, indanidine and clonidine were ineffective. SZL-49 produced a differential inhibition of contractions evoked by A-61603 in circular (alpha(1H)) compared to longitudinal (alpha(1L)) muscle and phenoxybenzamine had the opposite effect. Dibenamine inhibited the contractions comparably in both muscle types and analyses of its partial alkylation of receptors yielded identical estimates of equilibrium dissociation constant (pK(d)) for A-61603 in longitudinal (5.82) and circular (5.84) muscle. Receptor occupancy-response relationships revealed that whilst the muscle types are not different in receptor reserves for A-61603, contraction to the potent imidazoline is more efficiently coupled in longitudinal than in circular muscle. This underlies the markedly different responsiveness of the muscle types to cirazoline or oxymetazoline (alpha-adrenoceptor agonists with lower efficacies relative to A-61603). The differential inhibitory actions of phenoxybenzamine and SZL-49 are discussed.

Discrimination by SZL49 between contractions evoked by noradrenaline in longitudinal and circular muscle of human vas deferens

The effects of irreversible alpha1-adrenoceptor antagonists, SZL-49 (an alkylating analogue of prazosin), dibenamine and benextramine on contractions to noradrenaline (NA) in longitudinal and circular muscle of human epididymal vas deferens were investigated. Competitive alpha1-adrenoceptor antagonists were also used to further characterize the alpha1-adrenoceptor subtype stimulated by NA in longitudinal and circular muscle. NA evoked concentration-dependent contractions of both muscle types (pD2; 5.4 and 5.2 respectively). The contraction of circular muscle was comparatively more sensitive than that of longitudinal muscle to pretreatment with SZL-49. In contrast, dibenamine or benextramine produced comparable effects in both muscle types. The relationship between receptor occupancy and contraction in either longitudinal or circular muscle was nonlinear, with half-maximal response requiring similar receptor occupancy (longitudinal muscle 14%, circular muscle 16%). Maximal response in both muscle types occurred with little or no receptor reserve (<10%). The competitive alpha1-adrenoceptor antagonists produced dextral shifts of the dose-response curves to NA in longitudinal and circular muscle. The inhibitory potencies, estimated from the apparent pKB values were significantly different in longitudinal and circular muscle respectively for either WB 4101 (pKB, 8.6 and 9.5) or RS-17053 (pKB, 7.1 and 9.0) but not for Rec 15/2739 (pKB, 9.2 and 9.8) or HV 723 (pKB, 8.3 and 8.4). In conclusion, the potency profile of the competitive alpha1-adrenoceptor antagonists and the lack of different receptor reserves for NA in the muscle types suggest that the discriminatory effects of SZL-49 is primarily due to a predominance of the alpha1L-adrenoceptor subtype in longitudinal muscle and alpha1A-subtype in circular muscle.

Alpha1-adrenoceptor subtypes in rat epididymis and the effects of sexual maturation

We have characterized the expression of alpha1-adrenoceptor in epididymis from rats in different stages of sexual maturation: 40 (immature), 60 (young adult), and 120 (adult) days of age. Plasma testosterone levels were low in the immature animals but increased significantly in the 60- and 120-day-old animals. These changes were followed by a progressive increase in rat body weight and in caput and cauda epididymis relative weight. Reverse transcription polymerase chain reaction assay indicated that alpha1a-, alpha1b-, and alpha1d-adrenoceptor transcripts were present in both caput and cauda epididymis from adult rats. Ribonuclease protection assays further indicated that the expression of these alpha1-adrenoceptor transcripts differed with age and epididymal region analyzed. Prazosin (nonselective alpha1 antagonist), 5-methyl urapidil (alpha1A-selective), and BMY 7378 (alpha1D-selective) displaced [3H]prazosin binding curves in caput and cauda epididymis from 40- and 120-day-old rats. The potency order for these antagonists, as calculated from the negative logarithm of the inhibition constant (pK(i)) values for the high-affinity sites, indicated a predominant population of alpha1A-adrenoceptor subtype in caput and cauda epididymis from adult animals. Differences in pK(i) values in caput and cauda epididymis from immature and adult animals also suggested that the relative amount of alpha1-adrenoceptors, at the protein level, is modulated by sexual maturation. Taken together, the changes in alpha1-adrenoceptor expression during sexual maturation may suggest specific roles for these receptors in epididymal function.

Long-term safety and efficacy of a once-daily formulation of alfuzosin 10 mg in patients with symptomatic benign prostatic hyperplasia: open-label extension study

OBJECTIVES

To evaluate the long-term safety and efficacy of a new, once-daily (o.d.) prolonged-release formulation of the clinically uroselective alpha1-blocker, alfuzosin, in patients with symptomatic benign prostatic hyperplasia (BPH).

METHODS

This is a 9-month open-label extension of a 3-month double-blind, placebo-controlled evaluation of alfuzosin 10 mg o.d. and standard alfuzosin 2.5 mg, three times daily (t.i.d.), administered without dose titration in both cases. A total of 311 patients continued in the extension phase and all received alfuzosin 10 mg o.d. Efficacy was evaluated in all patients enrolled in the extension phase (n = 311). Safety was assessed in all patients exposed to alfuzosin, whether in the double-blind or extension phase (n = 360).

RESULTS

Mean international prostate symptom score (IPSS) improved significantly, from 17.1 to 9.3 (P < 0.0001), and mean peak flow rate (PFR) (assessed at through plasma levels) increased significantly, from 9.1 to 11.3 ml/s (P < 0.0001), between baseline (i.e. beginning of the double-blind phase) and the endpoint of the extension phase. Quality of life (QOL) index also improved significantly, from 3.3 to 2.1 (P < 0.0001). Alfuzosin was well tolerated, with only 16 of 360 patients (4.4%) reporting adverse events potentially related to alpha-blockade (mainly dizziness). Ejaculation disorders were infrequent (0.6%) and did not show a relationship to treatment. The incidence of asymptomatic orthostatic hypotension was low (2.8%), and no age effect was identified.

CONCLUSIONS

Alfuzosin 10 mg o.d. provides effective relief from BPH, and clinical benefits are maintained up to 12 months. This study also demonstrates the satisfactory long-term safety of this formulation, and its safe use even in at-risk populations.

Efficacy and safety of once-daily alfuzosin in the treatment of lower urinary tract symptoms and clinical benign prostatic hyperplasia: a randomized, placebo-controlled trial

OBJECTIVES

To assess the efficacy and safety, and determine the optimal dosage, of a once-daily (OD) formulation of the clinically uroselective alpha(1)-blocker, alfuzosin, in patients with lower urinary tract symptoms and symptomatic benign prostatic hyperplasia.

METHODS

Five hundred thirty-six patients were randomized to receive alfuzosin (10 mg OD or 15 mg OD), without initial dose titration, or placebo in a 3-month double-blind trial conducted in North America. The primary efficacy criteria were improvement in symptoms (International Prostate Symptom Score) and peak urinary flow rate.

RESULTS

Alfuzosin was significantly more effective than placebo in improving the symptoms and peak urinary flow rate from the first follow-up visit (day 28). The mean change in the International Prostate Symptom Score from baseline at endpoint was -3.6 and -3.4 with alfuzosin 10 mg and 15 mg, respectively, compared with -1.6 with placebo (alfuzosin 10 mg versus placebo, P = 0.001; alfuzosin 15 mg versus placebo, P = 0.004). The median increase in the peak urinary flow rate was +1.1 mL/s and +1.0 mL/s with alfuzosin 10 mg and 15 mg, respectively, compared with 0.0 mL/s with placebo (P = 0.0006 versus placebo for both dose groups). The patients' quality of life also significantly improved with both alfuzosin doses. Overall, alfuzosin at both doses was well tolerated. The incidence of orthostatic hypotension as determined by systematic blood pressure measurements with both doses of alfuzosin was similar to placebo. No clinically relevant ejaculation disorders were observed with alfuzosin.

CONCLUSIONS

Alfuzosin 10 mg OD, administered without dose titration, provides effective relief from the symptoms of benign prostatic hyperplasia with no additional benefit from a 15-mg dose. It is well tolerated from a cardiovascular viewpoint and is not associated with abnormal ejaculation.

Alpha-adrenoceptor subtypes

Different studies have led to our present knowledge of the membrane receptors responsible for mediating the responses to the endogenous catecholamines. These receptors were initially differentiated into alpha - and beta-adrenoceptors. Alpha-adrenoceptors mediate most excitatory functions, and were in turn differentiated in the 1970s into alpha(1)- and alpha(2)-adrenoceptors. The alpha(1)-adrenoceptor type usually mediates responses in the effector organ. The alpha(2)-adrenoceptor type is located presynaptically and regulates the release of the neurotransmitter but it is also present in postsynaptical locations. Both alpha-adrenoceptors are important for the control of vascular tone, but we now know that neither alpha(1)- nor alpha(2)-adrenoceptors constitute homogeneous groups. Each alpha-adrenoceptor type can be subdivided into different subtypes and in this review we have turned our attention to these. The alpha(1)- and the alpha(2)-adrenoceptor subtypes were previously defined pharmacologically by functional and binding studies, and later they were also isolated and identified using cloning methods. In fact, the study of alpha-adrenoceptors was revolutionized by the techniques of molecular biology which permitted us to establish the present classification. The present classification of alpha(1)-adrenoceptors stands as follows: alpha(1A)-adrenoceptor subtype (cloned alpha(1c) and redesignated alpha(1a/c)), alpha(1B)-adrenoceptor subtype (cloned alpha(1b)) and alpha(1D)-adrenoceptor subtype (cloned alpha(1d) and redesignated alpha(1a/d)). It has not been easy to establish the distribution of these alpha(1)-adrenoceptor subtypes in the various organs and tissues, or to define the functional response mediated by each one in the different species studied. Nevertheless it seems that the alpha(1A)-adrenoceptor subtype is more implicated in the maintenance of vascular basal tone and of arterial blood pressure in conscious animals, and the alpha(1B)-adrenoceptor subtype participates more in responses to exogenous agonists. It has also been observed that the expression of the alpha(1B)-adrenoceptor subtype can be modified in pathological situations and particular attention has been paid to the regulation of expression of this receptor. The present classification of alpha(2)-adrenoceptors stands as follows: alpha(2A/D)-adrenoceptor subtype (today it is accepted that the alpha(2A)-adrenoceptor subtype and the alpha(2D)-adrenoceptor subtype are the same receptor but they were identified in different species: the alpha(2A) in human and the alpha(2D) in rat); alpha(2B)-adrenoceptor subtype (cloned alpha(2b)) and alpha(2C)-adrenoceptor subtype (cloned alpha(2c)). Today we know that the alpha(2A/D)- and alpha(2B)-adrenoceptor subtypes in particular control arterial contraction, and that the alpha(2C)-adrenoceptor subtype is responsible above all for venous vasoconstriction. We also know that the alpha(2 A/D)-adrenoceptor subtype fundamentally mediates the central effects of the alpha(2)-adrenoceptor agonists. Despite the validity of the above-mentioned classification of the alpha(1)- and alpha(2)-adrenoceptors, it seems clear that the contractions of a large number of tissues including smooth muscle are mediated by more than one alpha-adrenoceptor subtype. Moreover, few ligands recognise only one alpha-adrenoceptor subtype and the lack of specifity in the different drugs for each one limits their administration in vivo and their therapeutic use.

Distribution of alpha1-adrenoceptor subtype mRNA and identification of subtype responsible for renovascular contraction in human renal artery

This study was intended to quantify the amounts of the alpha1-adrenoceptor subtype mRNAs in human renal artery and to demonstrate the distribution of receptor subtypes responsible for the contraction of the renal artery. RNase protection assay showed that the mean amount of alpha1a mRNA was much greater than that of alpha1b or alpha1d mRNAs in both the main and branch renal arteries. However, the abundance of alpha1a mRNA in human renal artery was much less than in our previous data in the prostate. In situ hybridization showed that all alpha1 subtype mRNAs were localized in the smooth muscle cells of the tunica media of the artery, and the distribution pattern of these three mRNAs in the main artery was the same as in the branch artery. However, the intensity of signals for alpha1d and alpha1b antisense RNAs probes was lower than that for the alpha1a antisense RNA probe. In the functional study, concentration-response curves to noradrenaline pretreated with KMD-3213, an alpha1A/L-adrenoceptor selective antagonist, seemed to be biphasic in nature. Chloroethyclonidine (CEC) failed to inactivate the noradrenaline-induced contraction, and prazosin showed relatively low affinity with a pA2 value of 8.8. These data suggest that the alpha1A/L-adrenoceptor mediates primarily those responses to noradrenaline in this artery. The other alpha1-adrenoceptor subtypes could also mediate the secondary contractile response to noradrenaline in this artery.

Distribution of alpha1-adrenoceptor subtype mRNAs in human renal cortex

OBJECTIVE

To determine the quantity and distribution of alpha1-adrenoceptor subtype mRNAs in human renal cortex.

MATERIALS AND METHODS

Specimens of renal cortex tissue were obtained at the time of radical nephrectomy or total nephroureterectomy from 46 patients (mean age 59.0 years, sd 14.7) with renal cell carcinoma, renal pelvic or ureteric tumour. Using the reverse-transcriptase polymerase chain reaction (RT-PCR), the RNase protection assay and in situ hybridization, the presentation, quantity and distribution of alpha1-adrenoceptor subtype mRNAs were determined.

RESULTS

Expression of the three alpha1-adrenoceptor subtype mRNAs (alpha1a, alpha1b and alpha1d) was confirmed in the arteries of the renal cortex (arciform, interlobular, arteriole), but among the three subtypes, the alpha1b was less apparent by in situ hybridization. Intense alpha1-mRNA staining was apparent especially in the smooth muscle of arterial walls. In both proximal and distal renal tubules, each of the alpha1-mRNAs was less marked in cytoplasm than in the arteries. In the glomeruli weak staining was detected in the endothelium but there was no obvious staining in the veins. RT-PCR showed all three subtypes of alpha1-adrenoceptor. The RNase protection assay showed that the predominant alpha1-adrenoceptor subtype mRNA in human renal cortex was alpha1a. However, the abundance of alpha1a-mRNA in human kidney was much less than in the prostate.

CONCLUSION

Three alpha1-adrenoceptor subtype mRNAs were recognized in human renal cortex and detected particularly in the smooth muscle of the arteries. There was more alpha1a-adrenoceptor subtype in human renal cortex than the other subtypes. It is not known how each subtype operates against adrenergic stimulation; further studies are needed to examine receptor density or receptor function.

Subtypes of functional alpha1- and alpha2-adrenoceptors

In this review, subtypes of functional alpha1- and alpha2-adrenoceptors are discussed. These are cell membrane receptors, belonging to the seven transmembrane spanning G-protein-linked family of receptors, which respond to the physiological agonists noradrenaline and adrenaline. Alpha1-adrenoceptors can be divided into alpha1A-, alpha1B- and alpha1D-adrenoceptors, all of which mediate contractile responses involving Gq/11 and inositol phosphate turnover. A 4th alpha1-adrenoceptor, the alpha1L-, has been postulated to mediate contractions in some tissues, but its relationship to cloned receptors remains to be established. Alpha2-adrenoceptors can be divided into alpha2A-, alpha2B- and alpha2C-adrenoceptors, all of which mediate contractile responses. Prejunctional inhibitory alpha2-adrenoceptors are predominantly of the alpha2A-adrenoceptor subtype (the alpha2D-adrenoceptor is a species orthologue), although alpha2C-adrenoceptors may also occur prejunctionally. Although alpha2-adrenoceptors are linked to inhibition of adenylate cyclase, this may not be the primary signal in causing smooth muscle contraction; likewise, prejunctional inhibitory actions probably involve restriction of Ca2+ entry or opening of K+ channels. Receptor knock-out mice are beginning to refine our knowledge of the functions of alpha-adrenoceptor subtypes.