Pharmacological characteristics of smooth muscle in benign prostatic hyperplasia and normal prostatic tissue

Generation and Regulation of Spontaneous Contractions in the Prostate

Spontaneous myogenic contractions have been shown to be significantly upregulated in prostate tissue collected from men with Benign Prostatic Hyperplasia (BPH), an extremely common disorder of the ageing male. Although originally thought likely to be involved in 'housekeeping' functions, mixing prostatic secretions to prevent stagnation, these spontaneous myogenic contractions provide a novel opportunity to understand and treat BPH. This treatment potential differs from previous models, which focused exclusively on attenuating nerve-mediated neurogenic contractions. Previous studies in the rodent prostate have provided an insight into the mechanisms underlying the regulation of myogenic contractions. 'Prostatic Interstitial Cells' (PICs) within the prostate appear to generate pacemaker potentials, which arise from the summation of number of spontaneous transient depolarisations triggered by the spontaneous release of Ca²⁺ from internal stores and the opening of Ca²⁺-activated Cl^- channels. Pacemaker potentials then conduct into neighbouring smooth muscle cells to generate spontaneous slow waves. These slow waves trigger the firing of 'spike-like' action potentials, Ca²⁺ entry and contraction, which are not attenuated by blockers of neurotransmission. However, these spontaneous prostatic contractions can be modulated by the autonomic nervous system. Here, we discuss the mechanisms underlying rodent and human prostate myogenic contractions and the actions of existing and novel pharmacotherapies for the treatment of BPH. Understanding the generation of human prostatic smooth muscle tone will confirm the mechanism of action of existing drugs, inform the identification and effectiveness of new pharmacotherapies, as well as predict patient outcomes.

Novel drug targets for the pharmacotherapy of benign prostatic hyperplasia (BPH)

Benign prostatic hyperplasia (BPH) is the major cause of lower urinary tract symptoms in men aged 50 or older. Symptoms are not normally life threatening, but often drastically affect the quality of life. The number of men seeking treatment for BPH is expected to grow in the next few years as a result of the ageing male population. Estimates of annual pharmaceutical sales of BPH therapies range from $US 3 to 10 billion, yet this market is dominated by two drug classes. Current drugs are only effective in treating mild to moderate symptoms, yet despite this, no emerging contenders appear to be on the horizon. This is remarkable given the increasing number of patients with severe symptoms who are required to undergo invasive and unpleasant surgery. This review provides a brief background on prostate function and the pathophysiology of BPH, followed by a brief description of BPH epidemiology, the burden it places on society, and the current surgical and pharmaceutical therapies. The recent literature on emerging contenders to current therapies and novel drug targets is then reviewed, focusing on drug targets which are able to relax prostatic smooth muscle in a similar way to the α(1) -adrenoceptor antagonists, as this appears to be the most effective mechanism of action. Other mechanisms which may be of benefit are also discussed. It is concluded that recent basic research has revealed a number of novel drug targets such as muscarinic receptor or P2X-purinoceptor antagonists, which have the potential to produce more effective and safer drug treatments.

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.

Stimulation of epithelial CB1 receptors inhibits contractions of the rat prostate gland

BACKGROUND AND PURPOSE

This study investigated whether stimulation of cannabinoid receptors influences smooth muscle contractility in the rat prostate gland.

EXPERIMENTAL APPROACH

Immunohistochemistry was used to characterize and localize cannabinoid receptors in the rat prostate gland. Isolated organ bath experiments were carried out to investigate the effects of cannabinoids on prostate contractility.

KEY RESULTS

Immunohistochemical studies of the rat prostate yielded positive immunoreactivity for the CB(1) receptor, but not the CB(2) receptor. Double labelling revealed that CB(1) receptors were not colocalized with alpha-actin in the smooth muscle layer but were primarily expressed within the epithelial lining of the prostatic acini. The cannabinoid receptor agonist WIN 55,212-2 (10 nM - 10 microM) inhibited contractile responses to electrical-field stimulation (10 Hz, 0.5 ms, 60 V for 2 s per minute) in a concentration-dependent manner. The CB(1) selective antagonists, SR141716 (1 microM) and LY 320135 (1 microM), reversed the WIN 55,212-2-mediated inhibition but the CB(2) selective antagonist, SR144528 (1 microM), did not. Furthermore, the cyclooxygenase inhibitor indomethacin (0.1 microM) caused significant reversal of the WIN 55,212-2 mediated inhibition of contractile responses, whereas the nitric oxide synthase inhibitor N (omega)-nitro-L-arginine methyl ester hydrochloride (L-NAME, 1 mM) did not. Prostaglandin E(2) (10 nM - 10 microM), produced a similar concentration-dependent inhibition to WIN 55,212-2.

CONCLUSIONS AND IMPLICATIONS

WIN 55,212-2, an agonist at cannabinoid receptors, causes inhibition of smooth muscle contraction in the rat prostate by activating epithelial CB(1) receptors. This inhibition is mediated via the cyclooxygenase pathway.

Correlation between lower urinary tract symptoms and urethral function in benign prostatic hyperplasia

AIM

To examine the potential correlation between urethral function and lower urinary tract symptoms (LUTS) in men with benign prostatic hyperplasia (BPH).

METHODS

Thirty-one patients with clinical BPH, who were confirmed to have benign prostatic enlargement (BPE) of 20 ml or more, were enrolled into the study. A mark-sheet questionnaire was used for obtaining the LUTS history. Multichannel pressure-flow urodynamic studies were performed and external urethral sphincter pressure (PEUS), intravesical pressure (PVES), and bladder neck pressure (PBN) were recorded both at maximum cystometric capacity and during voiding with 5-microtip transducers, for the purpose of detecting BPE-specific urodynamic findings at different levels within the urethra.

RESULTS

There was a positive correlation between hesitancy and detrusor bladder neck dyssynergia (DBND) (P = 0.0011) and between incomplete emptying and low PBN at maximum cystometric capacity (P = 0.0425). The hesitancy proved to have no correlation with bladder neck opening time (TBNO).

CONCLUSION

Urodynamic evaluation of urethral function was beneficial for attributing LUTS to clinical BPH. Among various parameters, DBND was the most specific to clinical BPH, suggesting it to be a situation where a steep rise in PBN or prostatic urethral pressure remains greater than the increasing PVES, resulting in sustained difficulty in opening the bladder neck and subsequently the subjective sensation of hesitancy.

Hormonal effects of Z-350, possessing steroid 5alpha-reductase inhibitory and alpha1-adrenoceptor antagonistic actions, in the rat

We examined the hormonal effects of Z-350, (S)-4-[3-(4-[1-(4-methylphenyl)-3-[4-(2-methoxyphenyl)piperazine-1-yl]propoxy]benzoyl)indole-1-yl]butyric acid hydrochloride, which has both alpha1-adrenoceptor blocking activity and steroid 5alpha-reductase inhibitory activity, in male and female rats. Z-350 administered orally for 14 days at a dose of 30 mg/kg to normal male rats significantly reduced the weight of the prostate and seminal vesicles without affecting the weight of the testis, epididymis, adrenals, kidney or liver. Prostatic levels of dihydrotestosterone decreased dose-dependently, with a slight increase in the level of testosterone at a Z-350 dose of 100 mg/kg. We observed no effects on the weight of the prostate in castrated rats or on the weight of the uterus in normal or 17beta-estradiol-treated female rats. These results suggest that Z-350 inhibits prostatic growth via inhibition of steroid 5-reductase without other hormonal effects.

Effect of JTH-601, a novel alpha(1)-adrenoceptor antagonist, on prostate function in dogs

We examined the effect of JTH-601 (3-¿N-[2-(4-hydroxy-2-isopropyl-5-methylphenoxy)ethyl]-N-methylaminom ethyl¿-4-methoxy-2,5,6-trimethylphenol hemifumarate), a new alpha(1L)-adrenoceptor antagonist, on prostatic function in isolated canine prostate and in anesthetized dogs. In the contraction study, phenylephrine and noradrenaline produced concentration-dependent contractions in canine prostate and carotid artery, respectively. In these tissues, JTH-601, prazosin (a non-selective alpha(1)-adrenoceptor antagonist), and tamsulosin (an alpha(1A)-adrenoceptor antagonist) competitively antagonized contraction in a concentration-dependent manner. The pA(2) (pK(B)) values with prostate were 8.49+/-0.07 for JTH-601, 7.94+/-0.04 for prazosin and 9.42+/-0.22 for tamsulosin. The ratio of pA(2) (carotid artery/prostate), i.e. prostatic selectivity, was 10.471 for JTH-601, 0.008 for prazosin and 0.371 for tamsulosin, respectively. In anesthetized dogs, JTH-601 (1 mg/kg, i.d.) significantly decreased urethral pressure by 15% without affecting blood pressure or heart rate. Tamsulosin (0.1 mg/kg, i.d.) decreased urethral pressure to the same extent as did JTH-601, but with a significant effect on blood pressure and heart rate. JTH-601 showed higher selectivity for canine prostate both in vitro and in vivo. In prostate, an important role of the alpha(1L)-adrenoceptor is suggested in the smooth muscle contraction mediated by alpha(1)-adrenoceptors. JTH-601 is expected to be an effective alpha(1)-adrenoceptor antagonist for the treatment of urinary outlet obstruction by benign prostatic hypertrophy with a minimum effect on the cardiovascular system.

Investigation of the effects of some alkaloidal alpha1-adrenoceptor antagonists on human hyperplastic prostate

The effects of N-allylsecoboldine, (-)-discretamine, ( )-govadine and [(+/-)-2,3,10,11-tetrahydroxytetrahydroproto-berberine HBr] ((+/-)-THP) on contractile responses were investigated in human hyperplastic prostate. They all inhibited, concentration dependently, the tension responses to phenylephrine and electrical field stimulation, and the pA2 and pIC50 values were calculated. The relative potencies of these four agents with reference to prazosin were obtained. The results showed that N-allylsecoboldine exhibited greater potency (4.1-fold), whereas (-)-discretamine, (+/-)-govadine and (+/-)-THP had similar potencies, against contractions elicited by electrical field stimulation and against contractions elicited by phenylephrine in human hyperplastic prostate. In addition, the potency ratios of N-allylsecoboldine, (-)-discretamine, (+/-)-govadine and (+/-)-THP against phenylephrine-induced contractions in rat vas deferens/spleen were 7.78, 0.89, 0.57, and 0.96, respectively. In the presence of prazosin (0.3 +/-M) to block alpha1-adrenoceptor-mediated responses, nifedipine (10 microM), but not the above four agents, significantly blocked KCl (60 mM)-induced tension responses in human hyperplastic prostate. It is suggested that N-allylsecoboldine exhibits greater potency against nerve-mediated contraction than against phenylephrine-induced contraction in human hyperplastic prostate and that this antagonistic effect is due mainly to its high affinity for the alpha1A-adrenoceptor subtype.

Morphological and pharmacological characterization of guinea-pig prostatic smooth muscle cells in vitro

BACKGROUND

Prostatic smooth muscle is thought to play a major role in the pathogenesis of bladder outlet obstruction in patients with benign prostatic hypertrophy. However, the physiology of prostatic smooth muscle cells remains largely unknown, in part due to the lack of a suitable model system. We therefore sought to establish an in vitro culture of guinea pig prostatic smooth muscle cells.

METHODS

Immature guinea pig prostate was treated by enzymatic digestion and the cells obtained were used to initiate the primary culture. After 3 to 4 passages, cultured smooth muscle cells were examined morphologically by immunocytochemistry and electron microscopy. The contractile properties of cultured smooth muscle cells were also examined.

RESULTS

The cultured prostatic cells demonstrated hill and valley morphology, which is a hallmark of smooth muscle cells in vitro, and stained positively for desmin. In addition, electron microscopic examination of ultrastructural morphology revealed myofilaments. Confluent cultures of prostatic smooth muscle cells showed a clear, dose-dependent contractile response to phenylephrine. Furthermore, contraction of the prostatic smooth muscle cells by 10(-6) mol/L phenylephrine was completely inhibited by pretreatment with 10(-6) mol/L terazosin.

CONCLUSIONS

An in vitro culture of prostatic smooth muscle cells was established. This culture is likely to provide a powerful tool for elucidating the physiology and pathophysiology of prostatic smooth muscle.

Prostatic alpha 1-adrenoceptors and uroselectivity

BACKGROUND

alpha 1-adrenoceptor antagonists (blockers) are now commonly used in the treatment of the symptoms of lower urinary tract obstruction. Originally phenoxybenzamine, a non-selective antagonist at both alpha 1- and alpha 2-adrenoceptors, was used by Marco Caine. In an attempt to minimize side effects, selective alpha 1-antagonists, e.g. prazosin, were subsequently developed. More recently, agents such as alfuzosin, doxazosin, terazosin, and tamsulosin have been introduced and claims of "uroselectivity" and "prostate" selectivity have emerged.

METHODS

This review attempts to put these claims into perspective and represents a comprehensive analysis of all pre-clinical and clinical data including several papers from the Japanese literature. An attempt is made to define what is meant by selectivity at various levels including the test tube, in the laboratory animal and, most importantly, in the clinical context of the whole patient.

CONCLUSIONS

The conclusions are interpreted within the context of the subdivision of the alpha 1-adrenoceptor into alpha 1A, alpha 1B, and alpha 1D subtypes.

Ouabain-induced increases in resting tone of human hyperplastic prostate following repeated noradrenaline and electrical field stimulation

1. The effect of ouabain on contractions to repeated noradrenaline stimulation and electrical field stimulation of human hyperplastic prostate was examined. Ouabain (1 microM) did not induce contractile response per se but progressively increased the resting tone (i.e., the tone between one noradrenaline stimulation, or electrical field stimulation, and the following) of human hyperplastic prostate. 2. The increased tone by ouabain following repeated noradrenaline stimulations or electrical field stimulation was fully relaxed by the removal of external calcium, and recovered following restoration of calcium. 3. The effect of noradrenaline on NA+ uptake was measured. Noradrenaline (10 microM) significantly increased the rate of Na+ accumulation in the presence of ouabain (1 microM); this stimulatory effect was almost completely blocked by prazosin (0.1 microM) and ethylisopropylamiloride (100 microM). In contrast, tetrodotoxin (1 microM) had no effect on noradrenaline-stimulated Na+ transport in human hyperplastic prostate. 4. Intracellular Na+ loading by noradrenaline (10 microM) in the presence of ouabain (1 microM) significantly increased the transmembrane Ca2+ uptake as compared with the absence of ouabain; however, nifedipine (1 microM) was ineffective on Ca2+ uptake under this condition. 5. Transmembrane CA2+ efflux was stimulated by noradrenaline (10 microM) in human hyperplastic prostate; this effect was significantly decreased in the presence of ouabain (1 microM). 6. It is suggested that the increased tone of human hyperplastic prostate following repeated excitation in the presence of ouabain is due to increased Ca2+ entry and reduced efflux of Ca2+ through the Na+/Ca+ exchange system as a consequence of Na+ pump inhibition by ouabain.

Characterization of alpha 1-adrenoceptor subtypes in tension response of human prostate to electrical field stimulation

1. The effects of various alpha 1-adrenoceptor antagonists and nifedipine on tension responses of human prostate to electrical field stimulation were evaluated in this study. 2. Prazosin (3 x 10(-10) to 10(-8) M) and 5-methyl-urapidil (10(-9) to 3 x 10(-8) M) blocked concentration-dependently the tension responses to electrical field stimulation and completely abolished them in the maximal concentrations (10(-8) M and 3 x 10(-8) M, respectively); in contrast, chloroethylclonidine (CEC), in the maximal concentration of 100 microM, blocked these effects by only 50%. 3. The contractile responses of rat vas deferens and spleen to exogenously-applied alpha 1-adrenoceptor agonists were competitively inhibited by prazosin and 5-methyl-urapidil; in addition, the pA2 values were calculated and the relative potencies with reference to prazosin were obtained. The relative potency of 5-methyl-urapidil in human prostate (0.105) was close to that in rat vas deferens (0.257), which contains primarily putative alpha 1A-adrenoceptors. However, it was much more than that in rat spleen (0.011), which contains primarily putative alpha 1B-adrenoceptors. 4. Nifedipine (10(-8) to 10(-6) M) inhibited concentration-dependently the contractile responses to electrical field stimulation in human prostate; in addition, the inhibition percentages were similar to those to exogenously-applied noradrenaline in rat vas deferens. In contrast, CEC (10 microM), which almost flattened the concentration-response curve of the rat spleen to phenylephrine, only partially inhibited (by 33.1%) the nerve-mediated contraction of human prostate. 5. The involvement of prejunctional alpha 2-adrenoceptors situated on the sympathetic nerve terminals of human prostate was also examined. Clonidine (3 x 10-9 to 3 x 10- M) blocked concentration-dependently the contractile response to electrical field stimulation of human prostate and this inhibitory effect was reversed by yohimbine (10-7 M). Additionally, the inhibitory effect of CEC (3 x 10-6 to 3 x 10-4 M)to the nerve-mediated contraction was also partially reversed by yohimbine (10-7 M).6. It is suggested that the putative czA-adrenoceptors in human prostate may be functionally confined to the synaptic region whereas only minor populations of the putative alpha 1B- and/or alpha 1c-adrenoceptors exist in this region.

Functional identification of alpha 1-adrenoceptor subtypes in human prostate: comparison with those in rat vas deferens and spleen

The effects of some alpha 1-adrenoceptor antagonists (prazosin, nonselective for the alpha 1A- and alpha 1B-adrenoceptor subtypes; 5-methyl-urapidil, selective for the alpha 1A-adrenoceptor subtype; chloroethylclonidine, selective for the alpha 1B-adrenoceptor subtype) and nifedipine were compared on contractile responses to noradrenaline or phenylephrine in human prostatic tissues, rat vas deferens and spleen. In rat vas deferens, nifedipine (1 microM), but not chloroethylclonidine (100 microM), almost completely abolished noradrenaline-induced contraction, the pA2 values for prazosin and 5-methyl-urapidil against noradrenaline being 9.29 and 8.55, respectively. In rat spleen, chloroethylclonidine reduced (by 57%) the maximum contraction induced by phenylephrine; nifedipine was ineffective. The log concentration-response curve was shifted significantly to the right; the pA2 values of prazosin and 5-methyl-urapidil against phenylephrine were 9.45 and 7.21, respectively. In human prostatic tissues, both nifedipine and chloroethylclonidine produced significant inhibition of noradrenaline-induced contractions. Chloroethylclonidine produced a 44% reduction of the maximum contraction to noradrenaline and shifted the log concentration-response curve to the right. In contrast, nifedipine, while reducing the maximum response to a similar extent, produced a small rightward shift in the log concentration-response curve. The pA2 values for prazosin and 5-methyl-urapidil against noradrenaline were 9.21 and 7.74, respectively. The pA2 values for prazosin in these three tissues did not vary significantly, whereas that for 5-methyl-urapidil in human prostatic tissue was intermediate between that in rat vas deferens and that in rat spleen: these tissues contain primarily alpha 1A- and alpha 1B-adrenoceptor subtypes, respectively.(ABSTRACT TRUNCATED AT 250 WORDS)

Effect of alpha 1 adrenoceptor antagonists on prostatic pressure and blood pressure in the anesthetized dog

OBJECTIVES

In the current study we have profiled a range of compounds at alpha 1 adrenoceptor subtypes in vitro and have assessed their effects in vivo using the anesthetized dog in an attempt to elucidate the predominant alpha 1 adrenoceptor subtype mediating contractile responses of the canine prostate.

METHODS

The affinity of compounds for alpha 1 adrenoceptor subtypes was determined by displacement of [3H] prazosin binding from stably transfected rat 1 fibroblasts expressing alpha 1A, alpha 1B, and alpha 1C, adrenoceptor subtypes. The potency of these agents was then assessed in vivo using an anesthetized dog model allowing simultaneous measurement of prostatic pressure and blood pressure following intravenous (i.v.) administration of phenylephrine (1 to 128 micrograms/kg).

RESULTS

All compounds examined in this study showed high and similar affinity for alpha 1 adrenoceptor subtypes, with the exception of 5-Methyl-urapidil, which was selective for alpha 1C (pKi = 9.3) over alpha 1B (pKi = 7.2) and alpha 1A (pKi = 8.1). Doxazosin, terazosin, alfuzosin, and tamsulosin were potent antagonists of phenylephrine responses and in vivo derived "pseudo pA2" determinations showed that the drugs did not discriminate between prostatic and vascular receptors. 5-Methyl-urapidil was also a potent antagonist of phenylephrine-induced responses but was selective for prostatic pressure ("pseudo pA2" = 8.7) over blood pressure ("pseudo pA2" = 7.2).

CONCLUSIONS

Data in the present study suggest a predominant role of the alpha 1C adrenoceptor subtype in the contractile response of the canine prostate to phenylephrine in vivo. This model therefore provides a suitable means of assessing putative prostate-selective antagonists for the treatment of benign prostatic hyperplasia.

Effect of naftopidil on urethral obstruction in benign prostatic hyperplasia: assessment by urodynamic studies

Thirty-two patients with voiding dysfunction attributable to symptomatic benign prostatic hyperplasia were treated with naftopidil, an alpha 1-blocker, at doses of 25-75 mg/day for 4-6 weeks. The efficacy of the drug was assessed from the changes in urinary symptoms and urodynamic data. Total symptom scores were significantly reduced after treatment (P < 0.001). Average flow rate and maximum flow rate were significantly increased (P < 0.001 and P < 0.001, respectively), and residual urine volume, residual urine rate (ratio of residual urine volume/sum of voided volume and residual urine volume), and maximum urethral closure pressure were significantly (P < 0.05, P < 0.01, and P < 0.05, respectively) reduced, and at bladder capacity, the first desire to void was significantly (P < 0.05) increased. The pressure/flow study demonstrated no changes in intravesical pressure at maximum flow, but a significant (P < 0.05) reduction in minimum urethral resistance. A mild side effect (dizziness) was noted in one patient (3.3%), which soon disappeared after the dose was decreased. The efficacy was good or excellent in 21 of 30 patients (70.0%). The drug was evaluated to be promising in the treatment of bladder outlet obstruction due to benign prostatic hyperplasia.

Alfuzosin, a selective alpha 1-adrenoceptor antagonist in the lower urinary tract

1. Phenylephrine-induced contractions of rabbit isolated trigone and urethra were antagonized in a competitive manner by alfuzosin (pA2 7.44 and 7.30, respectively) and prazosin. 2. The characteristics of [3H]-prazosin binding to human prostatic adenoma tissue were evaluated. [3H]-prazosin was potently displaced by alpha 1-adrenoceptor specific agents including alfuzosin, its (+)- and (-)-enantiomers and prazosin (IC50 0.035, 0.023, 0.019 and 0.004 microM, respectively), but only weakly by alpha 2-adrenoceptor selective agents, for example, yohimbine (IC50 = 6.0 microM). 3. In the pithed rat, alfuzosin (0.03-0.3 mg kg-1, i.v.) markedly inhibited pressor responses produced by the alpha 1-selective agonist, cirazoline but inhibited only slightly responses to the alpha 2-selective agonist, UK 14,304. Alfuzosin (1 mg kg-1, i.v.) had minimal effects against responses mediated by stimulation of prejunctional alpha 2-receptors (UK 14,304-induced inhibition of sympathetic tachycardia). 4. In the anaesthetized cat, alfuzosin (0.001-1 mg kg-1, i.v.) and prazosin (0.001-0.3 mg kg-1, i.v.) produced dose-related inhibition of the increases in urethral pressure caused by stimulation of sympathetic hypogastric nerves. Prazosin was approximately 5 fold more potent than alfuzosin. When phenylephrine was employed to induce urethral and vascular alpha 1-mediated tone simultaneously, prazosin inhibited both stimuli with similar potency whereas alfusozin was 3-5 fold more potent against elevated urethral pressure. This functional uroselectivity of alfuzosin was more evident by the intraduodenal route, since doses of 0.03 and 0.1 mg kg-1 alfuzosin inhibited urethral pressure with minimal effects on arterial blood pressure. 5. Alfuzosin is a potent selective alpha1-adrenoceptor antagonist in tissues of the lower urinary tract including the human prostate. This provides a pharmacological basis for its use in the treatment of benign prostatic hypertrophy.

Medical management of benign prostatic hyperplasia: a canine model comparing the in vivo efficacy of alpha-1 adrenergic antagonists in the prostate

Medical management of benign prostatic hyperplasia (BPH) is an alternative to surgical treatment of this disease. A major target for pharmacologic therapy is the alpha-1 adrenergic receptor, since activation of this receptor by endogenous catecholamines is thought to contribute to outlet obstruction. In the present study, we compared the potency of various alpha-1 adrenergic antagonists against epinephrine-induced contraction of the canine prostate. The drugs tested were dibenzyline, prazosin, terazosin and YM617. The rank order of potency, comparing inhibitory constants (Ki's), was found to be YM617 >> prazosin > terazosin > dibenzyline. This study is the first to compare all of these drugs directly in the prostate in vivo. The rank order of potency of the drugs is similar to the rank order of potency at other alpha-1 receptors. These results demonstrate that 1) our model is useful in confirming activity of drugs at the alpha-1 receptor and 2) the prostate alpha-1 receptor is similar to other alpha-1 receptors. Whether activity at the alpha-1 adrenergic receptor is a sufficient determinant of clinical efficacy of these drugs remains to be determined.

Placebo-controlled study of terazosin in the treatment of benign prostatic hyperplasia with 2-year follow-up

This randomised, placebo-controlled, double-blind study was performed to evaluate the efficacy and safety of once-a-day terazosin (10 mg/d) in ambulatory patients (n = 57) with benign prostatic hyperplasia (BPH). After a 4-week placebo lead-in and a 24-week treatment period with terazosin (with both phases being single-blind), 30 patients who responded to terazosin were randomly assigned to either the terazosin or placebo treatment group for 12 weeks. During the single-blind treatment period, the peak urine flow rate increased 54% from a baseline average of 7.76 ml/s to 11.92 ml/s after terazosin administration; the mean flow rate increased 55% from a baseline of 4.90 ml/s to 7.59 ml/s; and the residual volume decreased 56% from 93.1 ml to 40.7 ml. The mean obstructive symptom score, irritative symptom score and physician global assessment score improved by 68%, 34% and 27%, respectively. All these changes were significant when compared with baseline values. During the double-blind period, the improvement in all the variables was sustained in the terazosin group but not in the placebo group. Peak and mean urinary flow rates, and physician assessment showed significant differences at the end of the double-blind period. Adverse events occurred only during the single-blind period. The most frequently experienced events were headache (n = 6), asthenia (n = 3) and hypotension (n = 3). A follow-up study that initially included 12 patients showed no significant loss of improvement in symptoms and no change in urodynamic parameters with the 5 mg terazosin dose at 1 year. At 2 years, the 9 remaining patients showed sustained improvement and no signs of tachyphylaxis.

Anti-desmin vs. anti-actin for quantifying the area density of prostate smooth muscle

Anti-desmin and anti-actin are commercially available antibodies that bind to smooth muscle. The present study was designed to compare the staining properties of anti-desmin and anti-actin in the human prostate in order to determine the optimal antibody for quantifying the smooth muscle content of the human prostate. Nineteen male subjects with symptomatic BPH underwent needle biopsy of the prostate. Double-immunoenzymatic staining was performed with peroxidase-anti-peroxidase (PAP) and alkaline phosphatase-anti-alkaline phosphatase (APAAP) techniques. Rabbit anti-desmin:mouse anti-human prostatic acid phosphatase and mouse anti-actin:rabbit anti-human prostatic acid phosphatase were utilized. Computer assisted color image analysis was performed using the Bioquant image analysis system. The percent area density of stroma and epithelium was independent of the antibodies used. The percent area density of smooth muscle in the anti-actin stained tissue sections was twofold greater than the anti-desmin stained tissue sections. A direct relationship was observed for the area density of smooth muscle (r = 0.71; P = 0.0006) and the area density of connective tissue (r = 0.82; P less than 0.001) determined from anti-desmin and anti-actin stained tissue sections. Anti-actin represents the optimal antibody for quantifying the area density of prostate smooth muscle. The reproducibility of the immunoenzymatic staining technique is inferred from the direct relationship observed for area density of epithelium between the different staining techniques.

Alfuzosin for treatment of benign prostatic hypertrophy. The BPH-ALF Group

To assess the long-term efficacy and safety of alfuzosin, a selective alpha 1-adrenergic antagonist, 518 symptomatic patients with benign prostatic hypertrophy (BPH) were randomised to received either alfuzosin (daily dose 7.5-10 mg) or placebo for 6 months. Obstructive and irritative symptoms, assessed according to the Boyarsky scale, significantly improved in the alfuzosin group compared with the placebo group (p = 0.0004). Fewer patients in the alfuzosin group than in the placebo group dropped out due to lack of efficacy (6.8% vs 14.6%, p = 0.004) and the prevalence of spontaneous acute urine retention was lower in the alfuzosin group (0.4% vs 2.6%, p = 0.04). By 6 months, mean urinary flow rates had increased (p less than 0.05) and residual volume had decreased (p = 0.017) in the alfuzosin group, although the two groups were broadly similar with respect to increase in peak flow rate. The overall incidence of adverse events was similar in the two groups, which led to the withdrawal of 10.8% and 9.0% of patients, respectively. The findings emphasise the magnitude of the placebo response in symptomatic patients with BPH and show that treatment with alpha 1 adrenergic antagonist drugs provides long-lasting improvement in such patients.

Characterisation of human prostatic adrenoceptors using pharmacology receptor binding and localisation

Benign prostatic enlargement is a common cause of bladder outlet obstruction. Recent work has demonstrated the important role played by the sympathetic nervous system in the control of prostatic muscle tone. Although isometric muscle strip studies and clinical trials have highlighted the influence of alpha-1 adrenoceptors, radioisotope ligand binding studies have demonstrated a relatively increased density of alpha-2 adrenoceptors in the muscle within prostatic tissue, the significance of which is as yet unexplained. Forty patients entered a study using pharmacological muscle strip experiments, radioligand binding assays and receptor autoradiography. Pharmacological data from these studies confirmed that contraction of prostatic muscle is mediated predominantly by alpha-1 adrenoceptor stimulation, with no evidence of significant alpha-2 adrenoceptor or cholinergic mediated effects. Radioligand binding studies confirmed that there is a higher concentration of alpha-1 binding sites as contrasted to alpha-2 within normal prostate, but that this relationship approaches equity in adenomatous prostate. Autoradiographic localisation demonstrated that alpha-1 adrenoceptor binding is predominant within prostatic stroma with only a small component of alpha-2 adrenoceptors in this compartment. This comprehensive study supports the suggestion that prostatic muscular contraction is controlled by the influence of the sympathetic nervous system acting via alpha-1 adrenoceptors. These findings support the therapeutic use of specific alpha-1 adrenoceptor blockade in the management of benign prostatic hyperplasia.

Effects of prazosin in men with symptoms of bladder neck obstruction and a non-hyperplastic prostate

In a double blind cross-over study, the selective alpha 1-adrenoceptor blocker prazosin was given to eleven men with a non-hyperplastic prostate and with symptoms of bladder neck obstruction. During prazosin treatment maximum and average flow rates increased and residual urine was reduced. Prazosin did not change any pressure variables recorded. All patients had antegrade ejaculation and no side effects were reported. It is concluded that in selected patients with bladder outlet obstruction, prazosin may be a therapeutic alternative to bladder neck incision.

Contractile properties of human prostate adenomas and the development of infravesical obstruction

The contractile response of human prostate adenomas to KCl, phenylephrine (alpha 1 adrenergic agonist), UK 14304 (alpha 2 adrenergic agonist), and carbachol (muscarinic cholinergic agonist) was evaluated in tissue specimens obtained from men with symptomatic and asymptomatic BPH. Prostate specimens were obtained from 5 men with asymptomatic BPH undergoing cystoprostatectomy, 11 men with symptomatic BPH undergoing open prostatectomy, and 11 men with symptomatic BPH undergoing transurethral resection of the prostate (TURP). Quantitative symptom score analysis and urinary flow rate determination documented the absence of bladder outlet obstruction in men undergoing cystoprostatectomy and confirmed the presence of bladder outlet obstruction in men undergoing prostatectomy. The magnitude of the contractile response (Emax) and the potency of phenylephrine-induced contractions (EC50) in prostatic preparations obtained from men with symptomatic and asymptomatic BPH were similar. The IC50 for the inhibition of phenylephrine-induced contractions by prazosin was 3.2 nM, confirming that phenylephrine-induced contraction in the human prostate is mediated by the alpha 1 adrenoceptor. The contractile responses of prostate adenomas to muscarinic cholinergic and alpha 2 agonists were negligible. This study demonstrates that the development of bladder outlet obstruction in men with BPH is not related to alterations in the functional response of the smooth muscle component of the prostate adenoma.