Effects of prazosin in patients with benign prostatic obstruction

Use of an alpha 1-blocker, YM617, in the treatment of benign prostatic hypertrophy. YM617 Clinical Study Group

A recently synthesized alpha 1-blocker, (R)(-)-5-[2-[[2-(o-ethoxyphenoxy)ethyl]amino]propyl]-2- methoxybenzenesulfonamide hydrochloride (YM617), was evaluated in 270 patients with benign prostatic hypertrophy in a double-blind study. After 2 weeks on placebo the patients were assigned at random to 4 groups: group P--placebo, group L--0.1 mg., group M--0.2 mg. and group H--0.4 mg. of YM617. Comparing the placebo to the treatment period, subjective symptoms, such as nocturia and urgency, were significantly decreased in group H (p less than 0.01). The sensation of incomplete voiding was significantly improved in groups M and H (p less than 0.01). However, the differences among the groups were statistically insignificant. Residual urine volume was significantly decreased in groups L, M and H after instillation of saline into the bladder (p less than 0.01) but not in group P. The maximum and average flow rates were significantly increased in groups L, M and H (p less than 0.01) but not in group P. Average flow rate showed significant differences between groups M or H versus group P. Neither orthostatic hypotension nor a decrease in blood pressure was noted. Adverse side effects and changes in laboratory data were all slight and disappeared when the second tests were performed. In summary, the irritative and obstructive symptoms caused by benign prostatic hypertrophy were decreased and urodynamic studies were markedly improved by the alpha 1-blocker, YM617. The drug seems to be useful in the treatment of patients with benign prostatic hypertrophy.

The efficacy of transurethral resection of the prostate in men with moderate symptoms of prostatism

Transurethral resection of the prostate represents the operation most commonly performed by urologists in the United States. The objective of this study was to determine the efficacy of transurethral prostatectomy in men with moderate symptoms of prostatism. The efficacy parameters evaluated included peak urinary flow rate, obstructive and irritative symptom scores, and the global assessment by the patient of the voiding symptomatology. The mean peak urinary flow rate improved 108% after transurethral prostatectomy, and the mean obstructive and irritative symptom scores decreased 88 and 65%, respectively. The observed changes in urinary flow rates and symptom scores were statistically and clinically significant. Over-all, 84% of the patients indicated that the voiding symptoms were markedly improved after prostatic resection. Baseline urodynamic parameters were of no value for prediction of postoperative outcome. Several investigators recently reported their clinical experience with various pharmacological approaches for the treatment of symptomatic benign prostatic hyperplasia. Over-all, the degree of improvement in urinary flow rates and symptom scores achieved after transurethral prostatectomy exceeds all other therapeutic options that presently are available for the treatment of benign prostatic hyperplasia.

Importance of the natural history of benign prostatic hyperplasia in the evaluation of pharmacologic intervention

The variable natural history of untreated symptomatic benign prostatic hyperplasia (BPH) and the fact that therapeutic intervention is based more on subjective than objective criteria of progressive disease have important consequences for appropriately evaluating the effects of pharmacologic intervention on clinical BPH. To evaluate accurately the success of drug therapy for symptomatic BPH, any trial must include a placebo treatment arm for comparison. However, for such a placebo control to be legitimate, it must not affect the natural history of BPH. To evaluate the effect of placebo treatment on BPH, a large body of data following the natural history of untreated clinical BPH from a variety of independent studies was combined and compared to those from a large variety of independent studies in which a placebo-treated group of patients with clinical BPH also followed. These comparisons demonstrate that 1) placebo treatment does not affect the natural history of the disease; 2) spontaneous improvement usually occurs within the first 6 months of initial presentation of symptoms, if it is to occur at all; and 3) 3-6 months of follow-up are needed to determine if a patient is going to get worse. Thus, to evaluate accurately the potential benefit of any medical intervention for symptomatic BPH, placebo-controlled clinical trials will be required and should be of at least 6 month's duration.

Multicentre controlled trial of indoramin in the symptomatic relief of benign prostatic hypertrophy

A group of 139 patients with symptoms of bladder outflow obstruction due to benign prostatic hypertrophy were entered into a double-blind, parallel group, multicentre study of 2 doses of indoramin versus placebo. There were 18 withdrawals or exclusions, leaving 121 patients for analysis. After 8 weeks, mean peak flow rates increased more in patients treated with indoramin 20 mg bd than in those with placebo. The difference between indoramin 20 mg nocte and placebo was not significant. The change in mean peak flow rate for the higher dose of indoramin represented an increase of 50%. Both patients and investigators reported that the patients' symptoms had improved significantly on both indoramin 20 mg bd and 20 mg nocte; 9 patients were withdrawn because of adverse events, 5 taking placebo and 2 in each of the treatment groups. It was concluded that indoramin 20 mg bd was both effective and well tolerated in the management of symptomatic benign prostatic hypertrophy.

Efficacy of once-a-day terazosin in benign prostatic hyperplasia: a randomized, double-blind placebo-controlled clinical trial

This randomized, placebo-controlled, double-blind study was performed to evaluate the efficacy and safety of once-a-day terazosin (10 mg/day) 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 (both 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/sec to 11.92 ml/sec after terazosin; the mean flow rate increased 55% from a baseline of 4.90 ml/sec to 7.59 ml/sec; and the residual volume decreased 56% from 93.1 ml to 40.7 ml. The mean obstructive symptom score, irritative symptom score and physician's global assessment score improved by 68%, 34% and 27%, respectively. All these changes were significant (P less than 0.05) when compared to 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's global assessment showed significant (P less than or equal to 0.05) differences at the end of the double-blind period. Adverse events occurred only during the single-blind period. The most frequent were headache (n = 6), asthenia (n = 3), and hypotension (n = 3). In summary, terazosin administered once-a-day improved the obstructive and irritative symptoms of BPH, urine flow rates and residual volume. Terazosin was well tolerated.

Medical outcomes research and benign prostatic hyperplasia

Increasing health care costs and growing interest in quality care have focused attention on medical outcomes research. With regard to symptomatic BPH, patients deciding between different treatment choices need to know the likely outcomes of these alternatives, including chances for symptom responses and improved functional health and well-being. There is a paucity of high-quality outcomes research in medicine, including research that would clarify treatment outcomes for BPH. The relationship between physiologic and anatomic bladder outlet obstruction due to BPH and its symptoms, as well as quality of life, needs further study to elucidate how BPH affects health. A number of ongoing studies should provide information on the outcomes of alternative treatment strategies for BPH, the relationship between anatomic and physiologic BPH, and higher-level outcomes, such as symptom levels and quality of life.

Autonomic receptors in human prostate adenomas

Radioligand receptor binding techniques were used to characterize alpha 1 adrenergic, alpha 2 adrenergic and muscarinic cholinergic (MCh) binding sites in human prostate adenomas obtained from men with symptomatic and asymptomatic benign prostatic hyperplasia (BPH). Prostate adenoma specimens were obtained from nine 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). A quantitative symptoms score analysis and urinary flow rate determinations documented the absence of bladder outlet obstruction in men undergoing cystoprostatectomy and confirmed the presence of bladder outlet obstruction in men undergoing prostatectomy. The mean equilibrium dissociation constants (Kd) and the mean densities of 125I-Heat (alpha 1 adrenergic) and 3H-NMS (MCh) binding sites were similar in tissue homogenates obtained from men with asymptomatic and symptomatic BPH. The mean Kd of 3H-Rauwolscine (3H-Ra) was significantly greater in the prostatectomy specimens obtained from men with symptomatic BPH compared to the specimens obtained from men with asymptomatic BPH (p less than 0.05). The density of 3H-Ra (alpha 2 adrenergic) binding sites was significantly greater in the prostate adenomas obtained from men with symptomatic BPH compared to the prostate adenomas obtained from men with asymptomatic BPH (p less than 0.05). The difference in alpha 2 adrenoceptor density was accounted for by an increased receptor density in the open prostatectomy specimens. There was no significant correlation between alpha 2 adrenergic, alpha 1 adrenergic, and MCh receptor densities and prostate weight or patient age. This study indicates that the development of infravesical obstruction in men with BPH is not related to upregulation or altered binding affinity of alpha 1 adrenergic or MCh receptor binding sites. The significance of the observed upregulation of alpha 2 adrenoreceptors in the prostate adenomas obtained from men undergoing open prostatectomy is unknown, and requires further investigation.

Role of alpha-adrenergic blockers in the treatment of benign prostatic hyperplasia

The dynamic component of infravesical obstruction in men with symptomatic benign prostatic hyperplasia (BPH) is determined by alpha 1-adrenoceptor-mediated contractions of the prostatic capsule, prostate adenoma, and bladder neck. Since alpha 1-adrenoceptors are sparse in the bladder, medical therapy aimed at blocking the alpha receptor will relieve bladder outlet obstruction without inhibiting bladder function. Numerous clinical studies have evaluated the use of various alpha blockers for the treatment of BPH. Although the majority of these trials involved limited numbers of patients treated for only short periods, their results have consistently shown that alpha blockers improve urinary flow rates. Adverse reactions appear to be more frequent and more serious with the use of nonselective alpha blockers than with selective alpha 1 blockers, such as terazosin or prazosin. Terazosin offers the additional advantage of once-daily dosing. The common association of hypertension, hyperlipidemia, and symptomatic BPH in the aging male population may provide further impetus for initiating treatment with alpha blockers because alpha blockers are effective antihypertensive agents and may favorably alter lipid profiles.

Electrical and mechanical activity of rabbit prostate smooth muscles in response to nerve stimulation

1. The rabbit prostate contains two smooth muscle bundles: one forms the capsule of the prostate and the other runs longitudinally in the outermost layer of the prostate. The former was contracted by exogenously applied noradrenaline (NA) and the latter by acetylcholine (ACh), and were therefore identified as NA-sensitive and ACh-sensitive muscles, respectively. 2. In the NA-sensitive muscle, exogenously applied NA, but not ACh, depolarized the smooth muscle membrane, and this action of NA was antagonized by prazosin but not by yohimbine. The membrane of the ACh-sensitive muscle was depolarized by ACh and hyperpolarized by NA. The former was antagonized by atropine and the latter by phentolamine. 3. In both bundles, electrical stimulation of intramural nerves elicited a biphasic junction potential: an excitatory junction potential (EJP) followed by an inhibitory junction potential (IJP). In the NA-sensitive muscle, the EJP was resistant to alpha-adrenoreceptor antagonists and sensitive to guanethidine, while the IJP was sensitive to apamin and resistant to alpha- or beta-adrenoreceptor antagonists or guanethidine. The EJP and IJP elicited in the ACh-sensitive muscle were inhibited by atropine and apamin, respectively, but both potentials were resistant to alpha- or beta-adrenoreceptor antagonists or guanethidine. 4. Transmural nerve stimulation elicited a twitch contraction in both muscle bundles, and the contractions in the NA-sensitive muscle were partially inhibited by prazosin and blocked completely by guanethidine. The contraction of the ACh-sensitive muscle was blocked by atropine. Contractions produced by exogenously applied NA and ACh were antagonized by prazosin and atropine, respectively. 5. It is concluded that in the rabbit prostate there are two smooth muscles bundles which are respectively contracted with associated depolarization by NA or ACh. The NA-sensitive muscle receives adrenergic excitatory and non-adrenergic non-cholinergic inhibitory innervation. The ACh-sensitive muscle receives cholinergic excitatory and non-adrenergic non-cholinergic inhibitory innervation.

Functional evaluation of sympathetically mediated responses in in vivo lower urinary tract of dogs

An in vivo procedure for evaluating local effects of alpha-adrenoceptor stimuli on the lower urinary tract was developed in anesthetized dogs. Electrical stimulation of hypogastric nerve at varied frequencies (1, 2, and 4 Hz) and intraarterial (i.a.) administration of an alpha 1-adrenoceptor agonist, phenylephrine (0.3, 1, and 3 micrograms) to the urethra and bladder through the cannulated right external iliac artery caused reproducible frequency- or dose-related increases in intraurethral pressure (IUP). Intrabladder pressure (IBP) was increased by the nerve stimulation but not by i.a. phenylephrine. Acetylcholine (10 micrograms) given i.a. elicited increases in both IUP and IBP. Prazosin (0.1, 1, and 10 micrograms/kg, i.v.) dose-dependently suppressed the urethral contractile responses to the nerve stimulation and i.a. phenylephrine, but it failed to affect the bladder contraction evoked by the nerve stimulation. The results suggest that the urethral contractile responses to hypogastric nerve stimulation as well as i.a. phenylephrine were mediated via alpha 1-adrenoceptors, whereas the IBP increasing effect of hypogastric nerve stimulation was not mediated via alpha 1-adrenoceptors.

Alpha-adrenoceptor inhibitors in the treatment of benign prostatic hyperplasia

Although benign prostatic hypertrophy is the most common cause of urinary tract symptoms in men, the cause is still unclear. Recently it has been suggested that treatment with alpha-adrenoceptor inhibitors may be helpful in this condition. Eighty patients with prostatic obstruction were entered into a double-blind parallel study of prazosin versus placebo. There were 25 withdrawals or exclusions, leaving 55 patients for analysis. Mean maximal flow rates increased significantly more in patients treated with prazosin than in patients treated with placebo (p less than 0.005), but there was no significant reduction in maximal voiding pressure. The mean number of voids, recorded on diary cards, was reduced from an initial 10.0/24 hours by 2.1 in the final week, a significantly greater reduction than in the placebo group (p less than 0.01). However, there were no statistically significant changes in the filling cystometrograms. When patients were classified as responders or nonresponders in terms of bladder filling, urine flow, bladder emptying, weekly average of voids/24 hours, and nocturia, the proportion of patients responding to prazosin was significantly greater in all categories except bladder filling and emptying. It was concluded that prazosin at a dose of 2 mg twice daily is a safe and effective treatment for prostatic obstruction and may be used in patients awaiting surgery and in those who are unfit for operation.

In vivo experiments for the evaluation of alpha 1-adrenoceptor antagonistic effects of SGB-1534 on canine urethra

The alpha 1-adrenoceptor blocking effects of SGB-1534 on the urethral smooth muscle were compared in in vivo lower urinary tract preparations of anesthetized dogs, with the effects of other alpha 1-adrenoceptor antagonists, prazosin and bunazosin. Hypogastric nerve stimulation and selective administration of phenylephrine to the urethra and bladder through the cannulated right external iliac artery (i.a.) elicited reproducible frequency- and dose-dependent increases in intra-urethral pressure. Intra-bladder pressure was increased by the nerve stimulation but not by i.a. phenylephrine. SGB-1534, prazosin or bunazosin (0.1-10 micrograms/kg i.v.) dose dependently suppressed the urethral contraction evoked by the nerve stimulation and i.a. phenylephrine but did not influence the bladder contraction elicited by nerve stimulation. The alpha 1-adrenoceptor blocking potency of SGB-1534 was approximately 2.3 and 8.1 times greater than that of prazosin and bunazosin, respectively. The results indicate that alpha 1-adrenoceptors may mediate mainly the urethral contraction induced by hypogastric nerve stimulation and i.a. phenylephrine, and that SGB-1534 was more potent alpha 1-adrenoceptor blocking activity than prazosin and bunazosin in the canine urethra.

Management of urinary retention due to benign prostatic hyperplasia using luteinizing hormone-releasing hormone agonist

A common affliction of older men is bladder outlet obstruction secondary to benign prostatic hyperplasia for which the standard treatment is surgical prostatectomy. We report on six men with urinary retention from benign prostatic hyperplasia who were not medically able to undergo surgical prostatectomy but were successfully treated with the luteinizing hormone-releasing hormone (LH-RH) agonist, leuprolide acetate. This therapy is exemplified by the case of a sixty-six-year-old man with hemophilia B and urinary retention. The patient was treated with daily subcutaneous injections of 1 mg of leuprolide acetate, and prostatic size decreased from 132 g to 42 g, with initiation of spontaneous micturition while on treatment. For patients with symptomatic benign prostatic hyperplasia who are not candidates for surgery, treatment with an LH-RH agonist, such as leuprolide acetate, should be considered as a possible alternative.

Autoradiographic analysis of alpha-adrenoceptors and muscarinic cholinergic receptors in the hyperplastic human prostate

Radioligand receptor binding and autoradiography were used to characterize, localize and compare alpha-1 and alpha-2 adrenoceptors and muscarinic cholinergic receptor populations in human benign prostatic hyperplastic tissue. The binding of selective alpha-1 and alpha-2 ligands, [3H]-prazosin and [3H]-UK 14,304, to homogenates of human central and peripheral prostate was saturable and of high affinity. Scatchard analysis produced an equilibrium dissociation constant (KD) of 0.51 +/- 0.10 nM for alpha-1 adrenoceptors, and 2.34 +/- 0.40 nM for alpha-2 adrenoceptors. The mean densities, Bmax, of alpha-1 and alpha-2 adrenoceptors identified in the human adenomatous prostate were 65.9 +/- 12.9 and 36.1 +/- 7.0 fmoles/mg. protein respectively. Receptor autoradiography was used to examine the distribution of muscarinic cholinergic receptors [( 3H]-QNB), alpha-1 adrenoceptors [( 3H]-prazosin]), and alpha-2 adrenoceptors [( 3H]-rauwolscine) on consecutive sections of benign hyperplastic prostatic tissue. Although both subtypes of adrenoceptor were seen in the stromal component of the hyperplastic prostate, there was a substantial predominance of alpha-1 adrenoceptors. A densitometric computer-assisted analysis was performed on the autoradiographic slides to determine the mean ratio of specific alpha-1: alpha-2 adrenoceptors in the stromal compartment of the hyperplastic tissue. The ratio, expressed as % grain occupancy/unit area, was 3.9 +/- 0.75, which is in agreement with a functional alpha-1 adrenoceptor predominance shown in previous studies. Although sparsely distributed in the stroma, a dense alpha-2 adrenoceptor population was seen in association with blood vessels, and in close proximity to the base of some of the [3H]-QNB-labelled prostatic glandular epithelial cells.(ABSTRACT TRUNCATED AT 250 WORDS)

Alpha-1 blockers. A new generation of antihypertensive agents

Alpha-1 blockers have certain disadvantages over conventional and antihypertensive therapies in their haemodynamic profile and metabolic effects. This paper reviews the development of alpha-blockade, the therapeutic efficacy of prazosin, the prototype alpha-1 blocker, and the rationale for the once-daily antihypertensive compounds, terazosin and doxazosin. These drugs offer a useful alternative to first- or second-line therapy in suitable hypertensive patients, particularly with their potentially beneficial effects on serum lipids.

Stimulation of postjunctional alpha-1 and alpha-2 adrenoreceptors increases proximal urethral perfusion pressure in the pithed rat

1. In pithed rats, the effects of postjunctional alpha-1 and alpha-2 adrenoreceptor stimulation on prostatomembranous urethral perfusion pressure (UPP) were characterized by using selective adrenoreceptor agonists and antagonists. 2. Dose-dependent increases in UPP were elicited by the intravenous administration of selective alpha-1 and alpha-2 adrenoreceptor agonists, phenylephrine (1.0-30.0 micrograms kg-1) and BHT-933 (10-3000 micrograms kg-1), respectively. 3. The effects of phenylephrine on UPP were antagonized, in a dose-related manner, by pretreatment with prazosin (0.1 and 0.5 mg kg-1, iv), a selective alpha-1 adrenoreceptor antagonist. In contrast, pretreatment with rauwolscine 0.1 and 0.5 mg kg-1, iv), a selective alpha-2 adrenoreceptor antagonist, did not alter phenylephrine-induced increases in UPP. 4. BHT-933 elicited increases in UPP that were antagonized, in a dose-related manner, by pretreatment with rauwolscine (0.1 and 0.5 mg kg-1, iv). Neither dose of prazosin altered the effects of BHT-933 on UPP. 5. These results demonstrate increases in the resistance to flow (constriction) through the proximal urethra following selective stimulation of postjunctional alpha-1 and alpha-2 urethral adrenoreceptors. 6. The role of urethral alpha-adrenoreceptor subtypes in the neurohumoral control of the urethra remains to be determined.

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.

Infravesical outflow obstruction in rats: a comparison of two models

1. A new model of infravesical outflow obstruction was developed in male rats by the repeated s.c. administration of testosterone for 5-15 days (3 mg/kg die). The effects of this treatment which produced a 65% increase of prostate weight (10 days) on bladder voiding was evaluated in urethane anesthetized rats by the transvesical infusion of saline and compared to the cystometric alterations produced by application of a silk ligature at urethral level in female rats (4-8 weeks before) as described by Malmgren et al. (1987a, b). 2. Testosterone-pretreatment for 10 days produced little changes in bladder weight, bladder capacity or amplitude of micturition contraction but determined a marked increase in residual volume, indicating that infravesical outflow obstruction impaired significantly bladder voiding. Furthermore, detrusor instability was observed in the majority of testosterone-treated rats. 3. The participation of an active component to voiding impairment in testosterone-treated rats was suggested by the effect of intravenous prazosin which improved voiding efficiency. 4. In urethra-ligated female rats there was a marked increase in bladder weight which was paralleled by a dramatic alteration in micturition reflex that is marked increase in bladder capacity and residual volume. 5. It is concluded that these two models of infravesical outflow obstruction produce cystometric patterns simulating the urodynamic alterations observed in patients with benign prostatic hyperplasia and are potentially suitable for development of drugs in this field.

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.

The alpha adrenergic binding properties of terazosin in the human prostate adenoma and canine brain

Clinical trials are currently underway to evaluate the efficacy of terazosin for the treatment of symptomatic benign prostatic hyperplasia (BPH). Terazosin is a potent and selective alpha 1 adrenergic blocking agent structurally similar to prazosin. The alpha adrenergic binding properties of terazosin were studied in human prostate adenomas and canine brains using radioligand receptor binding methods. Saturation analyses were performed at varying concentrations of [125I]-Heat and [3H]rauwolscine [( 3H]Ra) in human prostate adenomas and canine brains. The binding of [125I]-Heat and [3H]Ra in the human prostates and canine brains was consistently saturable and of high affinity. The equilibrium dissociation constant (Kd) for [125I]-Heat binding in the canine brains and human prostate adenomas was 84.4 +/- 4.3 pM and 65.4 +/- 19.2 pM, respectively (p greater than 0.05). The (Kd) for [3H]Ra binding in the human prostate adenomas and canine brains was 1.21 +/- 0.23 nM and 1.52 +/- 0.28 nM, respectively (p greater than 0.05). The density of alpha 1 (0.37 +/- 0.15 fmol/mg. wet wt.) and alpha 2 (0.29 +/- 0.09 fmol/mg. wet wt. adrenergic binding sites in the human adenomas were similar (p greater than 0.05). The IC50 corrected (IC50 corr) of terazosin for [125I]-Heat and [3H]Ra binding sites in the human prostate was 2.5 nM and 1.0 micron., respectively. The IC50 corr of terazosin for [125I]-Heat and [3H]Ra binding sites in the canine brain was 2.0 nM and 0.8 microM, respectively. The competitive binding assays indicate that terazosin binds selectively to alpha 1 adrenergic binding sites in the human prostate and canine brain.

The effect of electrocautery on neurotransmitter receptor binding assays in the canine prostate

The purpose of this study was to determine whether resection of the prostate with electrocautery alters the binding properties of various neurotransmitter ligands. Prostate glands were removed from four adult male dogs. The prostates were divided in the midsaggital plane and one half of the prostate was resected using a resectoscope. Saturation experiments were performed on the resected and control prostatic tissue using 3H-NMS, 125I-Heat, and 3H-rauwolscine. The mean equilibrium dissociation constants (Kd) and the mean densities of 3H-NMS, 125I-Heat, and 3H-Rauwolscine binding sites were similar in tissue homogenates obtained from control and resected portions of the prostate (p greater than 0.05). Resection of the prostate using electrocautery did not alter the binding properties of various neurotransmitter ligands for characterizing and quantifying muscarinic cholinergic, alpha 1 adrenergic, and alpha 2 adrenergic binding sites in the canine prostate. Approximately 90% of prostatectomies for symptomatic BPH (benign prostatic hyperplasia) are performed transurethrally. The ability to accurately measure neurotransmitter receptor densities in prostate tissues obtained following transurethral resection is imperative for our future studies designed to elucidate the role of alpha adrenergic receptors in the development of bladder outlet obstruction in men with BPH.

The stereospecificity of LY253352 for alpha 1-adrenoceptor binding sites in the brain and prostate

1. The stereospecificity of the enantiomers of LY253352, a potent and selective alpha 1-adrenoceptor antagonist, were studied in the human prostate and canine brain using radioligand receptor binding methods. 2. The mean equilibrium dissociation constant (KD) in the canine brain and human prostatic adenoma was 84.4 pM and 65.4 pM, respectively. 3. The alpha 1-adrenoceptor density in the canine brain was approximately eight fold greater than in the human prostatic adenoma. 4. The mean Ki values of (-)-LY253352 and (+)-LY253352 in the prostate were 0.19 nM and 5.79 nM, respectively. 5. The mean Ki values of (-)-LY253352 and (+)-LY253352 in the brain were 0.29 nM and 34.7 nM, respectively. 6. This study indicates that the stereochemical specificity of the optical isomers of LY253352 is a manifestation of differential affinities of the enantiomers for alpha 1-adrenoceptor binding sites. 7. The differential affinities of (+)-LY253352 in the brain and prostate are suggestive of subtle unique properties of adrenoceptor binding sites in these tissues.

Alpha-adrenergic blockers

alpha-Adrenergic blockers are important drugs in the treatment of hypertension and other cardiovascular and noncardiovascular disorders. The ability to selectively block alpha-receptor subtypes provides a greater margin of safety and efficacy for these drugs.

Electrical and mechanical properties of the capsular smooth muscles of the rabbit prostate in relation to the actions of the alpha 1-adrenoceptor blocker, YM-12617

1. Electrical and mechanical properties of smooth muscle cells of the rabbit prostate capsule and the actions of the alpha 1-adrenoceptor blocker, YM-12617, were investigated using microelectrode and isometric tension recording methods. 2. The capsular muscles comprised thick and thin muscle bundles. In the former, noradrenaline (NA; 0.1-10 microM) provoked the phasic and tonic mechanical responses, with twitch contractions superimposed on the tonic response. YM-12617, in concentrations over 1 nM inhibited the contraction evoked by any given concentration of NA. Yohimbine (up to 10 microM) slightly inhibited the NA-induced contraction whilst clonidine (up to 10 microM) and acetylcholine (ACh; up to 10 microM) produced no mechanical response. 3. In thin muscle bundles, NA (0.1-10 microM) produced a contraction but the phasic response was small and the tonic response was negligible. These changes were blocked by YM-12617. In contrast, ACh (0.1-10 microM) produced atropine-sensitive, large phasic and tonic responses similar to those observed on application of NA to thick muscle bundles. 4. In thin and thick muscle bundles, the mean resting membrane potentials were -54 and -56 mV, respectively, values which were not statistically different. However, in thick muscle bundles, NA (over 0.1 microM) depolarized the membrane in a concentration-dependent manner and produced repetitive spike generation; ACh (up to 1 microM) did not modify the membrane potential. In thin muscle bundles, the above concentrations of NA hyperpolarized the membrane but ACh produced a large depolarization with repetitive spike generation. 5. In thick muscle bundles, nifedipine (0.3 microM) blocked twitch contractions generated spontaneously or provoked by application of NA with no effect on phasic and tonic responses. The NA-induced depolarization persisted after superfusion with nifedipine up to a concentration of 1.0 microM. In a Ca-free solution containing 2 mM EGTA, NA produced only the phasic responses, and re-addition of Ca (2.6 mM) restored the generation of a tonic response. 6. After application of 0.3 microM nifedipine, the effects of YM-12617 and prazosin were observed on the tonic component of the NA-induced contraction of thick muscle bundles. The ID50 values for YM-12617 and prazosin were 1 nM and 15 nM, respectively (n = 4). YM-12617 shifted the NA concentration-response curve to the right in a concentration-dependent and parallel manner. The Schild plot yielded a straight line with slope of 0.97 +/- 0.05, (n = 4). The pA2 value for YM-12617 was 10.4 +/- 0.05, (n = 4). 7. In thiqk muscle bundles, the depolarization induced by NA (1O microM) was blocked by YM-12617 (over 1 nM) to a greater extent than by prazosin (0.1 microM). Half-inhibition of the NA (10 microM)-induced maximum depolarization by YM-12617 or prazosin occurred at concentrations of 2 nm and 100 nM, respectively. 8. From these mechanical and electrical responses, the heterogeneous nature and distribution of alpha-adrenoceptors and muscarinic receptors has been elucidated in capsular smooth muscles in the rabbit prostate. In both thick and thin muscle bundles, NA-induced electrical and mechanical responses were more potently inhibited by YM-12617 than by prazosin.

Partial cystectomy for the myogenic decompensated bladder with excessive residual urine. Urodynamics, histology and 2-13 years follow-up

Partial cystectomy was performed for myogenic decompensated bladder with excessive residual urine in 11 patients, in whom training instructions and pharmacological treatment were unsuccessful. Postoperatively, the patients were followed for 2-13 years (median 4 years). Both symptoms and residual urine were reduced permanently. Urodynamic testing had demonstrated underactive detrusor function in all. The supposed etiology was infravesical obstruction in 4, overdistension due to sensory bladder paresis in 3 and unknown in 4. Histological examination of the resected bladders showed focal degeneration of the smooth muscle cells (detrusor myopathy) in 7, transmural edema and vast deposits of collagen in 8, mastocytosis in 3 and eosinophilic cystitis in 1. In conclusion we regard partial cystectomy an alternative to clean intermittent self-catheterization in selected patients with excessive residual urine.

Effects of prazosin and carbachol in patients with benign prostatic obstruction

To eight patients with benign prostatic obstruction (BPO), prazosin and placebo were given in a double blind cross-over manner. Prazosin decreased significantly residual urine volume and increased maximum and average flow rates. Neither when treated with prazosin nor with placebo, did the patients improve their ability to empty the bladder after injection of carbachol (0.25 mg) s.c. The only significant effect of carbachol on urodynamic variables was an increase in intravesical premicturition pressure. This was observed both when the patients were treated with prazosin and with placebo. Fourteen patients with BPO were given oral carbachol in maximally tolerated doses (6 or 12 mg/day) during a 2 week period. Despite producing significant systemic side effects in all patients, carbachol did not change any of the urodynamic variables tested. It is concluded that carbachol does not further improve bladder emptying in BPO patients given prazosin. Oral carbachol has no effects on bladder emptying in these patients.

Alpha 1 adrenergic receptors in canine lower genitourinary tissues: insight into development and function

Radioligand receptor binding methods were used to characterize the alpha 1-adrenergic receptor in the bladder body, bladder base, prostate and urethra of the male dog. Saturation experiments were performed in tissue homogenates using [125iodine]-Heat, an alpha 1-adrenergic antagonist of high specific activity (2,200 Ci. per mmol.). The equilibrium dissociation constant Kd for [125iodine]-Heat binding in the bladder body (0.56 pM.), bladder base (0.81 +/- 0.11 pM.), prostate (0.86 +/- 0.19 pM.) and urethra (0.55 pM.) was similar, suggesting homogeneity of alpha 1-adrenergic binding sites in lower genitourinary tissues. The receptor density in the bladder body, bladder base, prostate and urethra, expressed as fmol. per mg. wet weight, was 0.22 +/- 0.02, 0.82 +/- 0.09, 0.55 +/- 0.06 and 0.27 +/- 0.06, respectively (mean +/- standard error of mean). Competitive binding experiments with [125iodine]-Heat and unlabeled prazosin and clonidine confirmed the selectivity of Heat for alpha 1-adrenergic binding sites. Anatomical dissections have revealed that a major component of the smooth muscle of the bladder base and prostate originates from the ureter, whereas a major component of the smooth muscle of the urethra originates from the bladder. The measured alpha 1-adrenergic receptor densities support these developmental theories.

Prazosin in the treatment of prostatic obstruction. A placebo-controlled study

Eighty patients with prostatic obstruction were entered into a double-blind parallel study of prazosin versus placebo. There were 25 withdrawals or exclusions, leaving 55 patients for analysis. Mean maximum flow rates increased significantly more in patients treated with prazosin than in those treated with placebo (P less than 0.005), but there was no significant reduction in maximum voiding pressure. The mean number of voids, recorded on diary cards, was reduced from an initial 10.0/24 h by 2.1 in the final week, a significantly greater reduction than in the placebo group (P less than 0.01). However, there were no statistically significant changes in the filling cystometrograms. When patients were classified as responders or non-responders in terms of bladder filling, urine flow, bladder emptying, weekly average of voids/24 h and nocturia, the proportion of patients responding to prazosin was significantly greater in all categories except bladder filling and emptying. It was concluded that prazosin at a dose of 2 mg bd is a safe and effective treatment for prostatic obstruction and may be used in patients awaiting surgery and those who are unfit for operation.

Alpha 2 adrenergic receptors in canine prostate: biochemical and functional correlations

The sympathetic innervation of human prostate adenomas has been previously demonstrated using fluorescence microscopy and in vitro isometric studies. A clinical implication of these observations is that bladder outlet obstruction in men with benign prostatic hypertrophy may be subject to pharmacologic manipulation using adrenergic drugs. Randomized clinical trials have demonstrated the efficacy of alpha adrenergic antagonists for symptomatic BPH. We have previously characterized the alpha1 and alpha2 adrenergic receptors in the human prostate using [3H]prazosin and [3H]rauwolscine, respectively. The mean alpha1 and alpha2 receptor densities in the adenomas studied were equivalent. The effect of alpha2 adrenergic drugs on prostatic urethral pressure has not been examined in the human or in an animal model. In this study a canine model was used to define the effect of alpha2 drugs on prostatic urethral pressure. Intravenous administration of clonidine, a selective alpha2 agonist, resulted in a dose dependent increase in prostatic urethral pressure. The maximal increase in urethral pressure ranged between 18 to 30 cm. H2O. The maximal response to clonidine was approximately 50% less than the response to epinephrine, indicating that clonidine acts as a partial agonist. Pretreatment with yohimbine, a selective alpha2 adrenergic antagonist, abolished the effects of clonidine and epinephrine. The alpha2 adrenergic receptors were then studied in the canine prostates using [3H]rauwolscine. The equilibrium dissociation constant, Kd, ranged between 0.68 to 1.80 nM and the receptor density ranged between 14.8 to 69.3 fmol./mg. protein. The receptor density was homogeneous in specimens obtained from the proximal, midportion, and distal canine prostate suggesting that the effect of alpha2 drugs is not sphincter mediated. These in vitro and in vivo studies provide the basis for investigating the effects of alpha2 antagonists in men with symptomatic BPH.

Alpha 2 adrenergic receptors in hyperplastic human prostate: identification and characterization using [3H] rauwolscine

[3H]Rauwolscine ([3H]Ra), a selective ligand for the alpha 2 adrenergic receptor, was used to identify and characterize alpha 2 adrenergic receptors in prostate glands of men with benign prostatic hyperplasia. Specific binding of [3H]Ra to prostatic tissue homogenates was rapid and readily reversible by addition of excess unlabelled phentolamine. Scatchard analysis of saturation experiments demonstrates a single, saturable class of high affinity binding sites (Bmax = 0.31 +/- 0.04 fmol./microgram. DNA, Kd = 0.9 +/- 0.11 nM.). The relative potency of alpha adrenergic drugs (clonidine, alpha-methylnorepinephrine and prazosin) in competing for [3H]Ra binding sites was consistent with the order predicted for an alpha 2 subtype. The role of alpha 2 adrenergic receptors in normal prostatic function and in men with bladder outlet obstruction secondary to BPH requires further investigation.

The value of permixon in benign prostatic hypertrophy

A double-blind trial comparing the effect of Permixon (160 mg bd) against placebo in the treatment of benign prostatic hypertrophy is described. In both groups a significant improvement in flow rate and subjective assessment of symptoms was seen. There was no significant difference between the results of treatment in either group.

Alpha-adrenoceptors and muscarinic receptors in the isolated human prostate

Prostatic specimens of adenomatous tissue (PA) were obtained from the lateral lobe of the prostate in patients with benign prostatic hyperplasia (BPH). Non-hyperplastic specimens of the outer prostatic tissue (PC) were taken from the dorsal part of the prostate in patients undergoing cystourethrectomy. Effects of alpha-adrenoceptor and muscarinic receptor active drugs were studied. Noradrenaline (NA) and the alpha 1-adrenoceptor agonist phenylephrine induced concentration-dependent contractions in PC and PA preparations. The alpha 2-adrenoceptor agonist clonidine was without effect on PC but contracted PA preparations; it was less potent and had less intrinsic activity than phenylephrine. In PC and PA strips, the alpha 1-adrenoceptor antagonist prazosin was more effective than the alpha 2-adrenoceptor antagonist rauwolscine to inhibit NA-induced contractions. Prazosin, but not rauwolscine, inhibited electrically induced contractions in PC strips. The muscarinic receptor agonists acetylcholine and carbachol were without effect in PC and PA preparations. In both PC and PA preparations, clonidine decreased and rauwolscine increased the electrically elicited 3H-efflux after pre-loading of the tissues with 3H-noradrenaline. Carbachol and scopolamine were without consistent effects. In radioligand receptor binding experiments, the occurrence of alpha 1- and alpha 2-adrenoceptor binding sites was demonstrated; the ratio between alpha 1- and alpha 2-adrenoceptor binding sites was 3/2 in PC, but 2/3 in PA tissue. By autoradiography, muscarinic receptors were found to be localized exclusively to the glandular epithelium, consistent with the lack of contractile effects of muscarinic receptor active drugs on PC and PA preparations. Our results thus suggest that the main alpha-adrenoceptor function in human prostatic smooth muscle is of the alpha 1-type and that muscarinic receptors in the prostate are involved in processes other than control of smooth muscle contraction.

In vitro characterization of the alpha-adrenoceptors in human prostate

The alpha-adrenoceptors of the human prostate gland were characterized in vitro by the use of antagonists selective for alpha 1- and alpha 2-adrenoceptor subtypes. The contractile response induced by norepinephrine in this tissue could be antagonized by prazosin, a selective alpha 1-antagonist, with a receptor dissociation constant (KB) of 4.0 +/- 0.9 nM. The selective alpha 2-antagonists rauwolscine and SK&F 86466 were less potent antagonists of this response, with KB values of 1020 +/- 400 nM and 2400 +/- 800 nM, respectively. The irreversible alpha-antagonists benextramine and phenoxybenzamine, both of which preferentially inactivate the alpha 1-subtype, produced marked depression of norepinephrine-induced contraction. These data would suggest that the alpha-receptors on prostatic smooth muscle are predominantly of the alpha 1-subtype.

Characterization of alpha1 adrenergic receptors in human benign prostatic hyperplasia

Bladder outlet obstruction in men with benign prostatic hyperplasia is decreased following administration of prazosin, a selective alpha1 adrenergic antagonist. Prazosin presumably binds and antagonizes alpha1 adrenergic receptors on the smooth muscle cells of the prostatic adenoma. This study represents the first identification and characterization of alpha1 adrenergic receptors in the prostate using radioligand receptor binding methods. The binding of [3H] prazosin in homogenates obtained from human prostatic adenomas was saturable and a single high affinity prazosin binding site was identified (Kd = 0.29 +/- 0.09 nM). The alpha1 adrenergic receptor concentration in these homogenates ranged between 0.28 to 2.05 fmol./ mg. wet wt. prostate. The equilibrium dissociation constant and density of prazosin binding sites were similar in different regions of an enucleated prostate suggesting homogeneity of receptor density and receptor binding sites within an adenoma. The receptor density was not directly proportional to the weight of the surgically removed adenoma. The pharmacology of the prazosin binding sites was characterized by competitive binding experiments using [3H] prazosin and several unlabelled adrenergic analogs. The IC50's determined from competitive binding experiments using [3H] prazosin and alpha-methylnorepinephrine, rauwolscine and corynanthine were characteristic of alpha1 adrenergic receptor binding.