Alpha-blockers and lower urinary tract function: more than smooth muscle relaxation?

Silodosin improves functional consequences of lower urinary tract obstruction secondary to benign prostate hypertrophy, a proof of concept study in the spontaneously hypertensive rat supplemented with testosterone

Background

The main purpose of this study is to investigate the effect of silodosin on the urodynamic consequences in a previously established model of lower urinary tract symptoms associated with benign prostate hyperplasia, the spontaneously hypertensive rats (SHR) supplemented with testosterone.

Methods

Three groups of animals (8-week-old; n = 10/group) were considered: Wistar Kyoto (control) rats (WKY), SHR supplemented with testosterone at 3 mg/kg/day and treated with either vehicle (SHR-T, n = 10) or silodosin at 0.1 mg/kg/day (SHR-T + silodosin, n = 10) by oral gavage for 6 weeks. Cystometry experiments were performed. The bladder was harvested, weighed and paraffin-embedded for morphometric analysis. The prostate was also harvested and weighed.

Results

The number of animals included in the analysis were n = 10/10 for WKY and n = 7–8/10 for each SHR rats supplemented with testosterone group. SHR-T displayed a significant decrease in the intercontraction interval, infused volume and mean flow rate whereas the frequency of non-voiding contractions was increased. Silodosin improved the voiding behavior of SHR-T by significantly increasing the intercontraction interval, the infused volume and the mean flow rate and decreasing the number of non-voiding contractions. SHR-T displayed a significant increase in prostate and bladder weights and a 15% increase in the detrusor wall area compared to WKY.

Conclusions

Chronic silodosin treatment relieved storage symptoms in SHR supplemented with testosterone and decreased the frequency of non-voiding detrusor contractions during the filling phase.

Naftopidil for the treatment of lower urinary tract symptoms compatible with benign prostatic hyperplasia

BACKGROUND

Benign prostatic hyperplasia (BPH) is a common condition in ageing men that may cause lower urinary tract symptoms (LUTS). Treatment aims are to relieve symptoms and prevent disease-related complications. Naftopidil is an alpha-blocker (AB) that has a high affinity for the A1d receptor that may have advantages in treating LUTS in this setting. This is an update of a Cochrane Review first published in 2009. Since that time, several large randomised controlled trials (RCTs) have been reported, making this update relevant.

OBJECTIVES

To evaluate the effects of naftopidil for the treatment of LUTS associated with BPH.

SEARCH METHODS

We performed a comprehensive search using multiple databases (the Cochrane Library, MEDLINE, Embase, Scopus, LILAC, and Web of Science), trials registries, other sources of grey literature, and conference proceedings with no restrictions on the language of publication or publication status up to 31 May 2018 SELECTION CRITERIA: We included all parallel RCTs. We also included cross-over design trials.

DATA COLLECTION AND ANALYSIS

Two review authors independently classified and abstracted data from the included studies. We performed statistical analyses using a random-effects model and interpreted them according to the Cochrane Handbook for Systematic Reviews of Interventions. Primary outcomes were urological symptom scores, quality of life (QoL) and treatment withdrawals for any reason; secondary outcomes were treatment withdrawals due to adverse events, acute urinary retention, surgical intervention for BPH, and cardiovascular and sexual adverse events. We considered outcomes measured up to 12 months after randomisation as short term, and later than 12 months as long term. We rated the certainty of the evidence according to the GRADE approach.

MAIN RESULTS

We included 22 RCTs with 2223 randomised participants across four comparisons for short-term follow-up. This abstract focuses on only two of four comparisons for which we found data since two comparators (i.e. propiverine and Eviprostat (phytotherapy)) are rarely used. One study comparing naftopidil to placebo did not report any relevant outcomes and was therefore excluded. There were no trials that compared to combination therapy with naftopidil or any 5-alpha reductase inhibitors (5-ARIs) to combination therapy with other ABs and any 5-ARIs.All included studies were conducted in Asian countries. Study duration ranged from four to 12 weeks. Mean age was 67.8 years, prostate volume was 35.4 mL, and International Prostate Symptom Score was 18.3. We were unable to perform any of the preplanned subgroup analyses based on age and baseline symptom score.Naftopidil versus tamsulosinBased on 12 studies with 965 randomised participants, naftopidil may have resulted in little or no difference in urological symptom score (mean difference (MD) 0.47, 95% confidence interval (CI) -0.09 to 1.04 measured on a scale from 0 to 35 with higher score representing increased symptoms), QoL (MD 0.11, 95% CI -0.09 to 0.30; measured on a scale from 0 to 6 with higher scores representing worse QoL), and treatment withdrawals for any reason (risk ratio (RR) 0.92, 95% CI 0.64 to 1.34; corresponding to 7 fewer per 1000 participants, 95% CI 32 fewer to 31 more). Naftopidil may have resulted in little to no difference in sexual adverse events (RR 0.54, 95% CI 0.24 to 1.22); this would result in 26 fewer sexual adverse events per 1000 participants (95% CI 43 fewer to 13 more). We rated the certainty of evidence as moderate for urological symptom score and low for the other outcomes.Naftopidil versus silodosinBased on five studies with 652 randomised participants, naftopidil may have resulted in little or no difference in the urological symptom scores (MD 1.04, 95% CI -0.78 to 2.85), QoL (MD 0.21, 95% CI -0.23 to 0.66), and treatment withdrawals for any reason (RR 0.80, 95% CI 0.52 to 1.23; corresponding to 26 fewer per 1000 participants, 95% CI 62 fewer to 32 more). We rated the certainty of evidence as low for all these outcomes. Naftopidil likely reduced sexual adverse events (RR 0.15, 95% CI 0.06 to 0.42; corresponding to 126 fewer sexual adverse events per 1000 participants, 95% CI 139 fewer to 86 fewer). We rated the certainty of evidence as moderate for sexual adverse events.

AUTHORS' CONCLUSIONS

Naftopidil appears to have similar effects in the urological symptom scores and QoL compared to tamsulosin and silodosin. Naftopidil has similar sexual adverse events compared to tamsulosin but has fewer compared to silodosin.

Noradrenergic targets for the treatment of alcohol use disorder

The role of norepinephrine (NE) in the development of alcohol use disorder (AUD) has been studied over the past several decades. However, the NE system has been largely ignored for many years as a potential target for medication development for AUD. More recently, preclinical and clinical studies have demonstrated the potential value of targeting NE signaling for developing new pharmacological treatments for AUD. This review contributes to a special issue of Psychopharmacology focused on promising targets for alcohol addiction. Specifically, this review coalesces preclinical and clinical neuroscience that re-evaluate the noradrenergic system, and in particular the alpha-1 receptor, as a potential target for AUD.

New alpha blockers to treat male lower urinary tract symptoms

PURPOSE OF REVIEW

To date it is unclear whether the selectivity of new alpha-blockers to alpha-adrenergic receptor subtypes translates into more clinical benefits and less adverse effects in clinical practice. We performed a systematic review of the two new Abs silodosin and naftopidil. With the availability of numerous alpha-blockers to treat lower urinary tract symptoms secondary to benign prostatic hyperplasia, the findings of this review will be highly relevant to the field of urology.

RECENT FINDINGS

Silodosin was found to be more effective than placebo in improving International Prostate Symptom Score (IPSS) and quality of life scores and as effective as other alpha-blockers. Although the incidence of cardiovascular adverse events of silodosin was similar compared with placebo and other alpha-blockers (tamsulosin, naftopidil, alfuzosin), the sexual adverse events were more common with silodosin. No placebo-controlled randomized trial exists investigating the effects of naftopidil in men with lower urinary tract symptoms secondary to benign prostatic hyperplasia. Naftopidil had similar efficacy with regards to IPSS and quality of life compared with tamsulosin. The rate of adverse events was similar compared with tamsulosin.

SUMMARY

The two new selective alpha-blockers, silodosin, and naftopidil showed similar efficacy in IPSS and quality of life compared with other alpha-blockers. However, silodosin has more sexual adverse events.

The Role of α1-Adrenoceptor Antagonists in the Treatment of Prostate and Other Cancers

This review evaluates the role of α-adrenoceptor antagonists as a potential treatment of prostate cancer (PCa). Cochrane, Google Scholar and Pubmed were accessed to retrieve sixty-two articles for analysis. In vitro studies demonstrate that doxazosin, prazosin and terazosin (quinazoline α-antagonists) induce apoptosis, decrease cell growth, and proliferation in PC-3, LNCaP and DU-145 cell lines. Similarly, the piperazine based naftopidil induced cell cycle arrest and death in LNCaP-E9 cell lines. In contrast, sulphonamide based tamsulosin did not exhibit these effects. In vivo data was consistent with in vitro findings as the quinazoline based α-antagonists prevented angiogenesis and decreased tumour mass in mice models of PCa. Mechanistically the cytotoxic and antitumor effects of the α-antagonists appear largely independent of α 1-blockade. The proposed targets include: VEGF, EGFR, HER2/Neu, caspase 8/3, topoisomerase 1 and other mitochondrial apoptotic inducing factors. These cytotoxic effects could not be evaluated in human studies as prospective trial data is lacking. However, retrospective studies show a decreased incidence of PCa in males exposed to α-antagonists. As human data evaluating the use of α-antagonists as treatments are lacking; well designed, prospective clinical trials are needed to conclusively demonstrate the anticancer properties of quinazoline based α-antagonists in PCa and other cancers.

Commentary: Doxazosin for alcoholism

Recent preclinical and clinical evidence using prazosin indicates that α(1) -blockade may represent a new approach to treat alcohol dependence (AD). While most of the alcohol research on α(1) -blockade has been conducted testing prazosin, O'Neil and colleagues recently performed a set of preclinical experiments testing another α(1) -blocker, doxazosin, which has a longer half-life that may enhance clinical utility. Doxazosin and prazosin share the same chemical structure, in which the central element is a piperazine ring. O'Neil and colleagues' main results are that doxazosin significantly reduced alcohol intake without affecting locomotor activity. As such, O'Neil and colleagues provide the first preclinical evidence of the possible role of doxazosin in AD. Additional translational research is needed to further test this hypothesis.

Comparisons of the responses of anterior and posterior human adult male bladder neck smooth muscle to in vitro stimulation

OBJECTIVE

To evaluate differing methods of stimulation on strips of human bladder neck smooth muscle and compare muscle taken from the anterior and posterior aspects.

MATERIALS AND METHODS

Samples of adult human male bladder neck muscle were obtained from patients undergoing open radical prostatectomy. Muscle was taken from either the anterior or posterior (nine and six patients, respectively) aspects of the bladder neck. Muscle strips dissected from these samples were suspended in the Brading-Sibley organ bath. The strips were superfused with 100 mm KCl-enriched Krebs' solution for 4 min to determine viability. This allowed experimentation on 17 strips from the anterior aspect of the bladder neck and 13 from the posterior bladder neck. These remaining strips were then superfused either with various concentrations (x10(-7) to x10(-3)m) of carbachol or noradrenaline in Krebs' solution, for 15 s. A further set of strips (eight from anterior, six from posterior) was suspended and responses to electrical field stimulation (EFS) with varying parameters were measured. Each EFS experiment was repeated after a 15 min exposure to 10(-3)m atropine, and again after a 15 min exposure 10(-7)m tetrodotoxin (TTX). Tension responses produced in these series of experiments were measured using strain gauges and analysed using data acquisition software. Student's t-test was used for the statistical analysis.

RESULTS

All muscle strips included in the study responded to EFS. The magnitude of this contraction is frequency dependent. The contractions were abolished by superfusion of the muscle strips with atropine. There was no further suppression of the contractile response on addition of TTX. Posterior bladder neck samples had a greater mean contractile response per unit mass than anterior strips at all frequencies of >1 Hz, and significantly more at 20 and 30 Hz. There was a concentration-dependent response in bladder neck contraction to carbachol but only in the strips from the anterior bladder neck at concentrations of <10(-3)m. Posterior bladder neck strips did not significantly contract upon application of carbachol. Similarly, there was a concentration-dependent response to noradrenaline. Responses to noradrenaline were not uniform around the bladder neck, but not significantly different. Carbachol was the more 'potent' stimulator in anterior smooth muscle strips, but again the differences between agonists were not statistically significant.

CONCLUSION

These experiments show physiological variability around the circumference of the human male bladder neck. The posterior bladder neck shows significantly stronger contraction to alpha-adrenergic agonists compared with cholinergic agonists; the anterior bladder neck does not have a similarly significant differential response. The uniform response to noradrenaline may underlie the bladder neck's role in the prevention of retrograde ejaculation. The differential responses to carbachol may reflect differences in the embryological derivation of the anterior and posterior bladder neck fibres or in their innervation. Some of these differences may have clinical importance through the action of therapeutic agents.

Do α1-adrenoceptor antagonists improve lower urinary tract symptoms by reducing bladder outlet resistance?

AIMS

To test the hypothesis that improvements of lower urinary tract symptoms (IPSS) upon treatment with an alpha-blocker are due to reduction of bladder outlet obstruction (assessed as the bladder outlet obstruction index, BOOI); relationships of either with free flow Q(max) were also explored.

METHODS

The database of a large placebo-controlled, randomized, double-blind study with the alpha-blocker tamsulosin was analyzed retrospectively. Patients were stratified into lower and upper halves according to baseline IPSS, Q(max) or BOOI and treatment-associated alterations thereof. In these strata differences between values for the other two parameters were analyzed, for example, improvement of IPSS and Q(max) were compared in patients with below and above median improvement of BOOI.

RESULTS

Patients with below and above median baseline for one parameter, for example, IPSS had rather similar values for the other two parameters, for example, Q(max) and BOOI. Likewise, patients based upon baseline strata for one parameter had rather similar improvements of the other two parameters. Most importantly, patients with below and above median treatment-associated improvements of one parameter, for example, BOOI exhibited only small if any difference for alterations of the other two parameters, for example, IPPS and Q(max).

CONCLUSIONS

We conclude that IPSS, free flow Q(max) and BOOI are only loosely related at baseline. More importantly, treatment-induced improvements of these parameters are also only loosely related. These data do question the hypothesis that alpha-blockers largely improve lower urinary tract symptoms by reducing bladder outlet obstruction and suggest that they may also act independent of prostatic smooth muscle tone.

Alpha1-, alpha2- and beta-adrenoceptors in the urinary bladder, urethra and prostate

1 We have systematically reviewed the presence, functional responses and regulation of alpha(1)-, alpha(2)- and beta-adrenoceptors in the bladder, urethra and prostate, with special emphasis on human tissues and receptor subtypes. 2 Alpha(1)-adrenoceptors are only poorly expressed and play a limited functional role in the detrusor. Alpha(1)-adrenoceptors, particularly their alpha(1A)-subtype, show a more pronounced expression and promote contraction of the bladder neck, urethra and prostate to enhance bladder outlet resistance, particularly in elderly men with enlarged prostates. Alpha(1)-adrenoceptor agonists are important in the treatment of symptoms of benign prostatic hyperplasia, but their beneficial effects may involve receptors within and outside the prostate. 3 Alpha(2)-adrenoceptors, mainly their alpha(2A)-subtype, are expressed in bladder, urethra and prostate. They mediate pre-junctional inhibition of neurotransmitter release and also a weak contractile effect in the urethra of some species, but not humans. Their overall post-junctional function in the lower urinary tract remains largely unclear. 4 Beta-adrenoceptors mediate relaxation of smooth muscle in the bladder, urethra and prostate. The available tools have limited the unequivocal identification of receptor subtypes at the protein and functional levels, but it appears that the beta(3)- and beta(2)-subtypes are important in the human bladder and urethra, respectively. Beta(3)-adrenoceptor agonists are promising drug candidates for the treatment of the overactive bladder. 5 We propose that the overall function of adrenoceptors in the lower urinary tract is to promote urinary continence. Further elucidation of the functional roles of their subtypes will help a better understanding of voiding dysfunction and its treatment.

ASSOCIATION OF HYPERTENSION WITH SYMPTOMS OF BENIGN PROSTATIC HYPERPLASIA

PURPOSE

We determined whether the intensity of benign prostatic hyperplasia (BPH) symptoms and arterial hypertension are associated.

MATERIALS AND METHODS

Baseline data from a large sample of men seeking treatment for BPH symptoms were analyzed retrospectively. BPH symptom intensity (assessed by the International Prostatic Symptom Score [I-PSS] or urinary flow rate [Qmax]) and blood pressure were determined in 9,857 patients with BPH. Normotension was defined as a diastolic blood pressure of 90 mm Hg or less, the absence of the diagnosis hypertension and the lack of antihypertensive medication (in 4,725). Hypertension was concomitantly defined as a diastolic blood pressure of greater than 90 mm Hg (in 1,727), being diagnosed with hypertension (1,950) or the current prescription of anti-hypertensive drugs (3,360 patients).

RESULTS

When age and presence of hypertension were used as the independent explanatory variables, each year of age contributed 0.13 points and measured hypertension 1.60 points to I-PSS as the dependent response variable. Similar results were obtained with Qmax as the dependent response variable. In a logistic regression procedure using age, I-PSS and Qmax as the independent explanatory variables, each year of age and each I-PSS point significantly increased the risk of being hypertensive by 5.3% and 5.0%, respectively, while Qmax did not yield a statistically significant contribution to that risk.

CONCLUSIONS

We conclude that a significant, age independent association exists between BPH symptoms and hypertension. This finding indicates a common pathophysiological factor for both disease states such as increased sympathetic activity.

Pathophysiological aspects of bladder dysfunction: a new hypothesis for the prevention of ‘prostatic’ symptoms

This article reviews the literature on the pathophysiology of male lower urinary tract symptoms (LUTS) with the intention of developing a new preventive intervention for this bothersome disease. Traditionally, male voiding dysfunction has been thought to arise from bladder outlet obstruction (BOO) caused by prostatic enlargement. Many years of research, however, have shown that a clear relationship between the size of the prostate and the occurrence or severity of symptoms is doubtful. Because of its crucial role in urination, it is increasingly being accepted that the clinical manifestation of voiding dysfunction relies on the functional behaviour of the bladder. Several animal studies have shown that bladder performance can be improved by increasing urine output. Contrary to alterations observed in pathologic situations, an increased urine output provides a physiologic stimulus for animal bladder function improvement. We hypothesise that a trained bladder should be less susceptible to the harmful effects of ageing and obstruction. Future symptoms may thus be prevented. In humans an increased urine output can be achieved by drinking additional water, which could be an adequate preventive intervention.

Systemic alpha 1A-adrenoceptor antagonist inhibits neointimal growth after balloon injury of rat carotid artery

Previous in vitro and in vivo studies have shown that norepinephrine, acting through alpha(1A)-adrenoceptors, stimulates hypertrophy, proliferation, and migration of vascular smooth muscle cells and adventitial fibroblasts and may contribute to neointimal growth, lumen loss, and inward remodeling caused by iatrogenic wall injury and vascular disease. Our present aim was to determine whether intravenous administration of the alpha(1A)-adrenoceptor antagonist KMD-3213, at dosages without systemic hemodynamic effects, inhibits wall growth after injury. Inhibition of alpha(1A)-adrenoceptors with 12.8 and 32 microg/kg KMD-3213 had no effect on arterial pressure or renal and hindquarter resistances in anesthetized rats. A second group then received carotid balloon injury and continuous intravenous KMD-3213 at 4 and 10 microg x kg(-1) x h(-1) for 2 wk. Mean, systolic, and diastolic arterial pressures and heart rate of conscious unrestrained rats were unaffected. KMD-3213 reduced neointima growth by approximately 30 and 46% at the two doses (P < 0.01). These data support the novel hypothesis that a direct alpha(1A)-adrenoceptor-dependent trophic action of catecholamines is augmented by injury and may contribute significantly to hypertrophic vascular disease.

Alfuzosin in the treatment of high leak-point pressure in children with neurogenic bladder

OBJECTIVE

To decrease the detrusor leak-point pressure (LPP) of > 40 cmH2O in children with a neurogenic bladder, using the alpha1-adrenergic blocking agent alfuzosin.

PATIENTS AND METHODS

Videocystometry was used to measure the detrusor LPP and several other variables before and 3 weeks after the oral administration of alfuzosin (2.5-7.5 mg/day) in 17 children (mean age 6.3 years) with an upper motor neurone lesion.

RESULTS

The mean (sd) detrusor LPP decreased from 68 (37) to 46 (31) cmH2O (P < 0.01), reflex volume (defined as the volume at the first uninhibited bladder contraction of > 15 cmH2O) increased from 78 (69) to 112 (118) mL (+ 44%), bladder compliance increased from 9.3 (6.1) to 19.6 (14.6) mL/cmH2O (+ 111%), maximal vesical pressure decreased from 84 (40) to 70 (47) cmH2O (- 17%), and the mean number of uninhibited bladder contractions decreased from 6.3 to 3.5 (- 44%). The therapy was well tolerated; side-effects were rare and not severe. Intermittent catheterization could be avoided in six children.

CONCLUSION

Alfuzosin decreases the detrusor LPP in children with a neurogenic bladder caused by an upper motor neurone lesion, significantly and therapeutically, and should be considered as an alternative or addition to intermittent catheterization and anticholinergic drugs in selected patients.

Alpha(1)-adrenoceptor stimulation directly induces growth of vascular wall in vivo

Previous studies suggesting that norepinephrine is directly trophic for the vascular wall have been confounded by concomitant hemodynamic disturbances. Herein, a microcatheter connected to an osmotic minipump was implanted adjacent to the rat carotid for 2-wk perivascular suffusion of agents at systemic levels ~1,000 times below the threshold for altering arterial pressure. Norepinephrine decreased lumen and adventitial areas and circumference by 10, 14, and 5%, respectively (all P < 0.05); a nonsubtype-specific alpha(1)-adrenoceptor (AR) antagonist had no effect. When begun at the time of balloon injury, 2-wk norepinephrine increased lumen loss by 45%, increased neointimal area by 64% and collagen content by 33%, and reduced vessel circumference by 5% (all P < 0.05). alpha(1)-AR antagonists decreased neointimal area by 33% (all P < 0.05). alpha(1)A-AR antagonist reduced lumen loss by 70%, neointimal area by 54%, circumference decline by 84%, and adventitial thickening by 87% (all P < 0.05), whereas alpha(1B)-, alpha(1D)-, alpha(2)- and beta-AR antagonists were without effect. These are the first in vivo studies demonstrating that norepinephrine is directly trophic for the vascular wall and augments injury-induced intimal lesion growth.

Preclinical pharmacology of fiduxosin, a novel alpha(1)-adrenoceptor antagonist with uroselective properties

Benign prostatic hyperplasia (BPH), common in aging males, is often treated with alpha(1)-adrenoceptor antagonists. To minimize hypotensive and other side effects, compounds with selective antagonist activity at alpha(1A)- and alpha(1D)- (compared with alpha(1B)-) adrenoceptors were evaluated that would block lower urinary tract alpha(1)-adrenoceptors in preference to cardiovascular alpha(1B)-adrenoceptors. Fiduxosin (3-[4-((3aR,9bR)-cis-9-methoxy-1,2,3,3a,4,9b-hexahydro-[1]-benzopyrano[3,4-c]pyrrol-2-yl)butyl]-8-phenyl-pyrazino[2',3':4,5] thieno-[3,2-d]pyrimidine-2,4(1H,3H)-dione; ABT-980) was tested in radioligand binding assays, isolated tissue bioassays, intraurethral pressure (IUP) tests in isoflurane-anesthetized dogs, and blood pressure analyses in spontaneously hypertensive rats (SHR). Fiduxosin had higher affinity for cloned human alpha(1a)- (0.16 nM) and alpha(1d)-adrenoceptors (0.92 nM) in radioligand binding studies compared with alpha(1b)-adrenoceptors (25 nM) or in isolated tissue bioassays [pA(2) values of 8.5-9.6 for alpha(1A)-receptors in rat vas deferens or canine prostate strips, 8.9 at alpha(1D)-adrenoceptors (rat aorta), compared with 7.1 at alpha(1B)-adrenoceptors (rat spleen)]. Furthermore, the compound antagonized putative alpha(1L)-adrenoceptors in the rabbit urethra (pA(2) value of 7.58). Fiduxosin blocked epinephrine-induced increases in canine IUP (pseudo-pA(2) value of 8.12), eliciting only transient decreases in mean arterial blood pressure (MAP) in SHR. The area under the curve (AUC(0-->60) min) for the hypotensive response was dose related with a log index value for fiduxosin of 5.23, indicating a selectivity of 770-fold comparing IUP to MAP effects. Preferential antagonism of alpha(1A)- and alpha(1D)- versus alpha(1B)-adrenoceptors in vitro, blockade of putative alpha(1L)-sites in vitro, and selective effects on lower urinary tract function versus blood pressure in vivo by fiduxosin suggest the potential utility of this compound for the treatment of BPH.

Effect of fiduxosin, an antagonist selective for alpha(1A)- and alpha(1D)-adrenoceptors, on intraurethral and arterial pressure responses in conscious dogs

Fiduxosin is an alpha(1)-adrenoceptor antagonist with higher affinity for alpha(1A)-adrenoceptors and for alpha(1D)-adrenoceptors than for alpha(1B)-adrenoceptors. Our hypothesis is that such a compound with higher affinity for subtypes implicated in the control of lower urinary tract function and lower affinity for a subtype implicated in the control of arterial pressure could result in a superior clinical profile for the treatment of lower urinary tract symptoms suggestive of benign prostatic obstruction. The purpose of this study was to evaluate the potency and selectivity of fiduxosin for effects on prostatic intraurethral pressure (IUP) versus mean arterial pressure (MAP) relative to current clinical standards, terazosin and tamsulosin, in conscious dogs. Phenylephrine (PE)-induced increases in IUP and MAP were determined before and at various time points after an oral dose of each antagonist. Hypotensive potency was also determined. All three antagonists caused dose- and time-dependent blockade of the IUP and MAP pressor effects of PE. The IUP ED(50) values of fiduxosin, tamsulosin, and terazosin were 0.24, 0.004, and 0.23 mg/kg p.o., respectively. The corresponding MAP ED(50) values were 1.79, 0.006, and 0.09 mg/kg p.o. The rank order of IUP selectivity (ratio) was fiduxosin (7.5-fold), tamsulosin (1.5-fold), and terazosin (0.4 = 2.5-fold MAP-selective). Tamsulosin and terazosin caused dose-dependent hypotension, whereas no change in arterial pressure was seen after fiduxosin. These data, illustrating a superior selectivity profile of fiduxosin, are consistent with our hypothesis.

Terazosin, doxazosin, and prazosin: current clinical experience

Lower urinary tract symptoms (LUTS) suggestive of benign prostatic obstruction are common in aging men. Nearly 25% of men >40 years of age have LUTS. Medical therapy with alpha-blockade is the most common method of medical therapy for benign prostatic obstruction. Multiple methods of minimally invasive surgical therapies have been introduced in the last decade. These methods include balloon dilatation, temporary and permanent urethral stents, various laser techniques, microwave thermotherapy, transurethral needle ablation, electrovaporization, and high-intensity focused ultrasound. alpha-Receptor blockers to reduce the sympathetic tone of the prostate are considered as first-line therapy to relieve the symptoms of benign prostatic hyperplasia. Selective alpha(1)-receptor blockers relax prostatic smooth muscle, relieve bladder outlet obstruction, and enhance urine flow with fewer side effects. In addition, it was determined that treating patients with alpha-blockers increases prostatic apoptosis. Pharmacokinetic activity, mode of action, clinical efficacy, and side effects of the selective alpha(1)-receptor blockers terazosin, doxazosin, and prazosin are reviewed.