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

Categorización de receptores α1-adrenérgicos en el detrusor de pacientes con hbp obstructiva. estudio inicial en modelo animal de experimentación

INTRODUCTION

The action of alpha 1-adrenergic receptor antagonists in ameliorating irritation and obstruction in patients with bladder outlet obstruction (due to Benign Prostatic Hyperplasia-BPH) has been demonstrated. Although it is well known that alpha 1-a receptors are responsible for prostate smooth muscle relaxation, the mechanism by which irritative bladder symptoms are improved is unknown. Different alpha 1 receptor subtypes may be involved. The objective of this study is to investigate the changes in the alpha-adrenergic receptor populations in the obstructed detrusor, and to determine which subtype is proportionally increased in this situation (bladder outlet obstruction).

MATERIAL AND METHODS

This was an in vivo study in an experimental model: male NZ (New Zealand) rabbits. The bladder neck of one group of rabbits was obstructed surgically using the technique proposed by Levin et al. Subsequent to bladder catherization with a 8Fr catheter, the bladder neck was exposed by means of a low medial abdominal incision. The bladder neck was tied with a 2/0 silk thread below the ureteral orifices. The catheter was taken out at the end of the intervention. The rabbits were sacrificed after 4 weeks using intracardiac pentothal and cystectomy was performed. A control group that did not undergo bladder obstruction were also sacrificed at this time, for the comparative study. Part of the detrusor was used for a pathological study and the rest for a physio-pharmacological study in which the organ was placed in a bath of adrenoceptor agonists (phenylephrine and noradrenaline) and antagonists WB101, AH11101A and BMY7378 (antagonists of the alpha 1a, b, d, respectively).

RESULTS

The findings of the pathological study show that the bladder wall was thicker in the rabbits that underwent bladder obstruction. The physio-pharmacological studies demonstrate that the detrusor response to the selective alpha-1 adrenergic agonist was greater in the rabbits that underwent bladder obstruction, however detrusor contractility was decreased (KPSS). With bladder obstruction the alpha 1d receptors were increased.

DISCUSSION AND CONCLUSIONS

Receptor-binding studies (Malloy et al) aim to differentiate the alpha-adrenoreceptor populations. These studies identify and quantitate the different receptor subtypes in tissue without taking into account their activity. The isometric and physio-pharmacological tests evaluate active receptors, i.e. those that respond to agonist and antagonist stimuli. This enables detrusor activity to be evaluated accurately. The results obtained in this investigational study support the hypothesis that there is a high statistically significant increase in the alpha 1 adrenergic receptors in the obstructed detrusor. Furthermore, in agreement with previous molecular studies, during prostate obstruction alpha 1d is the predominate sub-population in the bladder. These findings may have patho-physiological, clinical and pharmacological implications. If this hypothesis which has been demonstrated in an experimental model, is also demonstrated in studies in humans, pharmacological development should not only be focussed on selective alpha 1a receptor antagonists (prostate) but also on those of alpha 1d, for relieving symptoms in patients with bladder outlet obstruction (BPH and prostatism).

The medical management of lower urinary tract symptoms and benign prostatic hyperplasia

Prostatism is a widely used term assigned to the symptom complex of older men with voiding dysfunction. The cause of the syndrome has routinely been ascribed to an enlarged prostate. More recent thinking recognizes that many men with such symptoms do not, in fact, have prostate enlargement or benign prostatic hyperplasia (BPH) and that such symptoms are not a surrogate for BPH. Such recognition is essential if cost effective medical management of lower urinary tract symptoms (LUTS) is to be achieved. Prostate volume has emerged as a key factor in the selection of medical therapy of LUTS and BPH not only regarding symptom relief but also to the newer concept of the prevention of disease progression and the avoidance of future adverse events in those men with true BPH. In the United States, medical management is now first line therapy for LUTS. The proper selection of therapy based on the patient's individual pathophysiologic characteristics is now made possible by many new recent studies within the medical literature.

Current trends in management of men with lower urinary tract symptoms and benign prostatic hyperplasia

Management of lower urinary tract symptoms (LUTS) and benign prostatic hyperplasia (BPH) has been central to urology for decades. The urologic community has increasingly come to realize that many men with LUTS do not have prostate enlargement and do not need their prostates debulked surgically. Of all the factors that have emerged to alter the trends associated with management of LUTS and BPH, none has had more impact than the advent of medical therapy. The selective, long-acting, alpha1-blocking agents terazosin, doxazosin, and tamsulosin have become most popular because of their specificity in the urinary tract, reduced side effects, and simplicity of dosage. In addition, finasteride, a 5-alpha-reductase inhibitor, was found to be effective in men with prostates of > or = 40 g. Furthermore, the larger the prostate at baseline, the greater the efficacy of finasteride on symptom relief and flow rate improvement. In addition to medical therapy, an array of device therapies has emerged in the management of LUTS and BPH. Laser prostatectomy is the oldest of the device therapies and includes transurethral vaporization of the prostate (VLAP), transurethral evaporation of the prostate (TUEP), and transurethral interstitial laser prostatectomy (TILP). Studies report beneficial outcomes approaching those achieved with transurethral resection of the prostate (TURP) with less morbidity and a shorter hospital stay. Common diseases contribute the most to national healthcare expenditures. The management of LUTS and BPH are such disorders and result in the expenditure of vast healthcare resources worldwide. The surgical strategies have an established record of outcomes documenting their potential for symptom relief and the avoidance of future complications. Medical and device therapies, although currently promising and attractive, therefore must prove comparable durability.

Benign prostatic hyperplasia. Current pharmacological treatment

During the past decades, pharmacological treatment of symptomatic benign prostatic hyperplasia (BPH) has become a fairly established modality. Approaches include blockade of alpha-adrenoreceptors and suppression of androgens. Patients eligible for drug treatment are those with mild to moderate symptoms of BPH and no strong indications for surgery. alpha-Receptor blockers generally improve urinary symptoms and peak urinary flow rates 2 to 4 weeks after introduction of therapy. Because of minor adverse effects, selective alpha 1-blockers are preferred over nonselective drugs. Prazosin, terazosin and alfuzosin are extensively studied and widely used in BPH treatment. Terazosin might be preferred to prazosin and alfuzosin because it can be administered once daily, but a disadvantage is higher cost. Doxazosin and tamsulosin (amsulosin; YM 617) are drugs currently under clinical investigation in the treatment of BPH. Antiandrogen therapy induces reduction in prostate volume and relief in symptoms of bladder outlet obstruction. However, the only drug which seems to be of major interest in BPH treatment is finasteride. Other drugs [gonadotrophin-releasing hormone (GnRH) agonists, progestogens and flutamide] are associated with frequent and sometimes severe adverse effects, such as impotence, flushing and loss of libido. Finasteride has fewer adverse effects and is well tolerated, but needs to be administered for at least 6 to 12 months to obtain maximum effect. Future approaches in medical treatment of BPH might be combination therapy of alpha 1-blockers and finasteride.

Identification, quantification, and localization of mRNA for three distinct alpha 1 adrenergic receptor subtypes in human prostate

The dynamic component of bladder outlet obstruction caused by benign prostatic hyperplasia (BPH) is regulated by alpha 1 adrenergic receptors (alpha 1-AR) located in the prostatic stroma. Recently two alpha 1-AR subtypes (alpha 1A, alpha 1B) have been identified in the human prostate by both functional and pharmacological assays. However, the presence of the alpha 1C subtype has not been evaluated, presumably due to the lack of availability of selective ligands for this receptor subtype. We have used molecular techniques to investigate the mRNA expression of all three alpha 1-AR subtypes in the human prostate. RNA extracted from the prostate gland of 15 patients was used in ribonuclease protection assays to identify the expression of three alpha 1-AR subtype mRNAs. Quantitative solution hybridization assays further identify the predominant subtype of alpha 1-AR mRNA to be the alpha 1C, which represents approximately 70% of the total alpha 1-AR mRNA in the human prostate. Furthermore, in situ hybridization localizes the alpha 1C AR mRNA predominantly to the stromal compartment. The identification of a predominant alpha 1-AR mRNA in human prostate identifies a potential need for subtype selective pharmaceutical agents. These agents could be very important clinically in the treatment of diseases such as BPH.

Medical treatment of benign prostatic hyperplasia: 5 alpha-reductase inhibitors and alpha-adrenergic antagonists

Benign prostatic hyperplasia (BPH), a nonmalignant neoplasm of the prostatic epithelial and stromal tissue, occurs commonly in elderly men. The "gold standard" of care for symptomatic BPH has been and remains transurethral resection of the prostate. This operation, however, like any surgical procedure, has associated morbidity and imposes an appreciable expense on the health-care system; therefore, enthusiasm for the development of medical therapies for the management of symptomatic BPH has been substantial. Currently, practicing physicians have two types of medications for the treatment of symptomatic BPH: 5 alpha-reductase inhibitors and alpha-adrenergic antagonists. The former drugs inhibit the conversion of testosterone to the potent prostatic androgen dihydrotestosterone. As a result, the androgenic stimulation to the prostate gland is suppressed, and the size of the prostate is decreased by approximately 25%. In some patients, this outcome decreases the mechanical obstruction of the prostatic urethra and improves micturition. alpha-Adrenergic antagonists decrease the smooth muscle tone of the bladder neck, prostatic adenoma, and prostatic capsule. After these structures have been relaxed, resistance to urine flow through the prostatic urethra can be decreased, and obstructive voiding symptoms can be resolved. Although two distinctly different mechanisms are involved, both types of medications are effective for treating BPH. Thus, in 1993, transurethral resection of the prostate is no longer the only available therapeutic option. With the advent of medical therapies, internists and primary-care physicians will have more involvement in the care of patients with BPH than previously. Therefore, urologists and nonurologists must work together to serve the needs of patients with prostatism.

Terazosin. A review of its pharmacodynamic and pharmacokinetic properties, and therapeutic potential in benign prostatic hyperplasia

Terazosin selectively antagonises alpha 1-adrenoceptor-mediated contraction of the prostate, prostatic capsule, proximal urethra and bladder base, and consequently reduces urethral pressure, bladder outlet resistance and urinary symptoms associated with symptomatic benign prostatic hyperplasia. The efficacy of terazosin is reflected in increases in peak urinary flow rate, and reductions in obstructive and irritative symptom scores compared with placebo, and reductions in residual urinary volume from baseline. Clinical improvements begin to occur within 2 weeks and have been sustained for up to 2 years. The most marked treatment effects tend to occur in patients with more severe pretreatment urinary flow abnormalities. The relatively long duration of action of terazosin, allowing once-daily administration, offers a potential clinical advantage over other alpha 1-adrenoceptor antagonists although formal compliance studies have not been reported. Terazosin is generally well tolerated, but caution is recommended at treatment initiation and when dosage adjustments are made due to an increased risk of postural hypotension and related adverse effects at these times; such a risk has also been observed with several other alpha 1-adrenoceptor antagonists. Although publication of clinical trial results with terazosin is still evolving, this drug shows promise in the treatment of patients with mild to moderate symptomatic benign prostatic hyperplasia for whom surgery is not absolutely indicated. Terazosin also shows promise as a nonsurgical treatment alternative in patients with severe symptoms who are unfit for surgery and also in those who are on long waiting lists for surgery.

Alfuzosin. A review of its pharmacodynamic and pharmacokinetic properties, and therapeutic potential in benign prostatic hyperplasia

Alfuzosin, a new quinazoline derivative, acts as a selective and competitive antagonist of alpha 1-adrenoceptor-mediated contraction of prostatic, prostatic capsule, bladder base and proximal urethral smooth muscle, thereby reducing the tone of these structures. Consequently, urethral pressure and resistance, bladder outlet resistance, bladder instability and symptoms associated with benign prostatic hyperplasia are reduced. A limited range of clinical studies have shown oral alfuzosin to be more effective than placebo (in studies of < or = 6 months duration), to have sustained effects on long term administration (< or = 30 months), and to be comparable with the alpha 1-adrenoceptor antagonist prazosin, in the symptomatic treatment of benign prostatic hyperplasia. This is reflected in increases in urinary flow rate and decreases in symptom score and residual urinary volume. The most marked improvements occur in patients with severe pretreatment urinary flow abnormalities. Furthermore, preliminary results suggest a beneficial effect of alfuzosin on quality of life in patients with benign prostatic hyperplasia. The overall incidence of adverse effects appears similar to that with placebo, and the incidence of vasodilatory-related adverse effects appears lower than that with prazosin. The relative selectivity of alfuzosin for alpha 1-adrenoceptors in the genitourinary tract compared with receptors in the vasculature is a potential advantage over other alpha-adrenoceptor antagonists, including prazosin, as the symptoms of benign prostatic hyperplasia may be reduced by alfuzosin at doses that have minimal vasodilatory effects, thereby minimising postural hypotension and syncope. However, vasodilatory-related adverse effects are the most common adverse effects that occur with alfuzosin, and dose and first-dose hypotensive relationships, especially in the elderly, cannot be excluded at this stage in the clinical use of alfuzosin. The full potential of alfuzosin in the symptomatic treatment of benign prostatic hyperplasia will be clarified by further long term comparative studies (with large patient numbers) against placebo and other alpha 1-adrenoceptor antagonists. Nevertheless, oral alfuzosin 7.5 to 10 mg/day in divided doses appears to be a promising first-line agent for symptomatic treatment of noncomplicated mild to moderate benign prostatic hyperplasia in patients with a high dynamic component to their obstruction. In addition, alfuzosin offers an alternative to prostatectomy (the current 'gold standard') in patients who require surgery but are unfit for this treatment, and in patients requiring symptomatic relief while awaiting surgery.

Terazosin in the treatment of benign prostatic hyperplasia: the United States experience

The rationale for selective alpha 1 blockade in benign prostatic hyperplasia (BPH) is based upon the observations that the prostate adenoma contains between 20% and 40% smooth muscle and the contractile properties of prostatic smooth muscle are mediated by the alpha 1 adrenoceptor. Terazosin is a selective alpha 1 adrenoceptor antagonist that is currently under clinical investigation for the treatment of clinical BPH. The United States experience with this drug is reviewed in the present report. The outcome measures used to assess the efficacy of terazosin in BPH includes Boyarsky symptom scores and uroflowmetry. The total Boyarsky symptom score decreased 55% and the peak urinary flow increased 47% following terazosin therapy in the cumulative open-label and single-blind studies. Three hundred and thirteen subjects with clinical BPH were randomised into a phase III double-blind parallel-group 3-month placebo-controlled study of once-a-day administration of terazosin. The total Boyarsky symptom score decreased 43% and 21% in the 10 mg and placebo treatment groups, respectively. The peak urinary flow increased 37% and 12% in the 10 mg and placebo-treated groups, respectively. The adverse events associated with terazosin were relatively minor and reversible. The United States experience has unequivocally demonstrated the short-term safety and efficacy of terazosin therapy in BPH. Studies are currently under way to determine the long-term safety and efficacy associated with terazosin therapy in BPH.

A randomized, placebo-controlled multicenter study of the efficacy and safety of terazosin in the treatment of benign prostatic hyperplasia

The clinical manifestations of benign prostatic hyperplasia (BPH) are related primarily to bladder outlet obstruction resulting from enlargement of the prostate gland. Transurethral prostatectomy is the most common treatment currently offered for BPH in the United States. The primary objective of the present randomized placebo controlled multicenter study was to determine the efficacy and safety of terazosin, a selective long-acting alpha 1-blocker, for the treatment of symptomatic BPH. A total of 285 men with symptomatic BPH was randomly assigned in equal proportions to receive placebo, or 2, 5 or 10 mg. terazosin administered once daily. Of the patients 237 completed the 4-week single-blind placebo lead-in and 12-week double-blind treatment periods. The primary outcome parameters were changes in peak and mean urinary flow rates, and changes in the Boyarsky symptom scores. All terazosin treatment groups exhibited significantly greater decreases in total Boyarsky symptom score than the placebo group. The 10 mg. terazosin group exhibited significantly greater increases in peak and mean urinary flow rates than the placebo group. The improvements in symptom scores and urinary flow rates did not reach a plateau within the dose range evaluated, suggesting that further efficacy may be achieved with doses of terazosin exceeding 10 mg. This study unequivocally demonstrates the safety and efficacy of terazosin for the treatment of BPH. Selective alpha 1-blockade is likely to gain widespread acceptance for the treatment of BPH due to its safety and efficacy.

Binding and functional properties of alpha 1 adrenoceptors and area density of smooth muscle in the canine prostate

The present study was designed to compare the area density of smooth muscle, and the binding and functional properties of alpha 1 adrenoceptors in 8 different regions of the canine prostate. The area density of smooth muscle, alpha 1 adrenoceptor density, and contractile response to phenylephrine were investigated using immunoenzymatic staining with color assisted computer image analysis, radioligand receptor binding, and isometric tension studies, respectively. The equilibrium dissociation constants (Kd) for 125I-Heat binding and the alpha 1 adrenoceptor densities (Bmax) in the prostatic regions ranged between 138-230 pM and 0.32-0.52 fmol/wet wt., respectively. The maximal tension generated in the presence of phenylephrine (phenylephrine Emax) and phenylephrine EC50s ranged between 0.043-0.129 gm. force/mm.2 CSA and 4.0-11.0 microM, respectively. The differences between Kd, Bmax, Emax, and EC50 were not significantly different between the different regions of the prostate. The percent area density of smooth muscle ranged between 10.6-24.4%. A direct relationship was not observed between alpha 1 adrenoceptor density and phenylephrine Emax, or alpha 1 adrenoceptor density and percent area density of smooth muscle. A direct relationship was observed between the phenylephrine Emax and percent area density of smooth muscle (p = 0.003; r = 0.90). The phenylephrine Emax and percent area density of smooth muscle was threefold and 1.6-fold greater in the peripheral prostate relative to the central prostate, respectively. The morphometrical and isometric tension studies provides evidence that the canine prostate is a heterogeneous gland.

Mediation of contraction and relaxation by alpha- and beta-adrenoceptors in the ureterovesical junction of the sheep

The effects of alpha- and beta-adrenoceptor agonists and antagonists were studied in the sheep ureterovesical junction. Non-specific adrenergic agonists such as adrenaline and noradrenaline induced contraction in the sheep ureterovesical junction, suggesting a predominance of alpha-over beta-adrenoceptors in this functional unity. An inhibition of the noradrenaline-induced contraction was observed after prior blocking with prazosin (10(-7) M) and yohimbine (10(-7) M), the effect of prazosin being more potent than that of yohimbine. The effect of phenylephrine on alpha 1-adrenoceptors was more potent than that of B-HT 920 on alpha 2-adrenoceptors. Isoproterenol caused a concentration-dependent relaxation that was inhibited by propranolol (10(-6) M), pafenolol (10(-5) M) and butoxamine (10(-5) M). These results suggest that ureterovesical junction contraction is mediated by both alpha 1 and alpha 2-adrenoceptors, alpha 1 predominating over alpha 2. Relaxation is mediated by beta-adrenoceptors of the beta 1 and beta 2 subtypes.

Alpha- and beta-adrenoceptors in the sheep urinary bladder

A study was undertaken to determine the presence and distribution of alpha- and beta-adrenoceptors in the sheep bladder body and base. In the bladder body, noradrenaline and isoproterenol induced relaxation which was significantly inhibited by propranolol, pafenolol and butoxamine. In the presence of propranolol (10(-5) M), noradrenaline induced a small contraction, as well as phenylephrine, but B-HT 920 failed to cause any effect on the bladder body. In the bladder base, noradrenaline caused a contraction that was significantly inhibited by prazosin but not by yohimbine. Phenylephrine also induced a contractile response in this structure which was inhibited by prazosin. Isoproterenol caused a relaxation that was significantly inhibited by propranolol and pafenolol but not by butoxamine. Relaxation was mediated by both beta 1 and beta 2-adrenoceptors in the detrusor muscle and by beta 1-adrenoceptors in the bladder base. Alpha 1-adrenoceptors contributed to maintain the detrusor tone and contract the bladder base.

Medical management of benign prostatic hyperplasia

Medical management of clinical BPH is a reality. The only effective nonsurgical treatment now recommended is aimed at relieving the dynamic component of clinical BPH. Pharmacologic treatment using alpha-adrenoceptor antagonists may be used appropriately to manage patients with prostatism who are poor surgical risks but who could benefit from reduced sympathetic tone. In addition, alpha blockers are used to relieve acute retention, and to prevent retention when increased sympathetic discharge is expected. Thus far, nonsurgical therapy aimed at reducing the mechanical obstruction associated with BPH by prostatic size reduction has failed to produce consistent objective improvement. However, several drugs are now being investigated and may be effective for reducing prostatic size in patients with BPH. Clinical trials are complicated by a number of factors, especially very variable symptoms. Moreover, reduction in prostatic size induced by drugs is not permanent and regrowth occurs with drug withdrawal, necessitating chronic treatment. Ideally, future research should be aimed at the prevention of BPH at an early age. However, this presupposes a better understanding of the pathogenesis of BPH. BPH may not be a single, variable disease but a family of diseases with a number of predictable clinical courses. In the future, we should pay particular attention to histologic variability, to see if in fact different pathologic forms of BPH follow different clinical patterns. If urologists are to keep their predominant position in managing the patient with BPH, they will have to keep informed of medical treatment trials and of potential alternative treatment strategies to prostatectomy.

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.

Comparison of muscarinic cholinergic and alpha adrenergic receptors in canine ileum, colon, intestinal urinary reservoirs and bladder

The muscarinic cholinergic (MCh) and alpha 2 adrenergic receptor densities in canine ileum, colon, ileal and colonic urinary reservoirs and bladder were determined using radioligand receptor binding methods in order to provide a rational basis for pharmacologic management of urinary incontinence following bladder replacement with intestinal segments. Muscarinic cholinergic and alpha 2 adrenergic receptor binding sites were studied in these tissues using saturation experiments with 3H-NMS and 3H-rauwolscine, respectively. The mean equilibrium dissociation constants for 3H-NMS binding (0.13 to 0.17 nM) in these tissues were similar (p greater than 0.05) indicating homogeneity of muscarinic cholinergic binding sites. The mean equilibrium dissociation constants for 3H-rauwolscine binding (1.27 to 1.98 nM) in these tissues were also similar (p greater than 0.05). A substantial density of MCh (1.06 to 1.22 fmol/mg. wet wt.) and alpha 2 adrenergic (0.47 to 1.11 fmol/mg. wet wt.) binding sites was identified in the intestinal tissues assayed. The density of ileal and colonic MCh and alpha 2 adrenergic binding sites was not altered following construction of urinary intestinal reservoirs. The presence of a substantial density of MCh and alpha 2 adrenergic binding sites in the intestinal tissues suggests that MCh and alpha 2 adrenergic analogs may be utilized for the management of urinary incontinence following bladder replacement with intestinal urinary reservoirs.

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.

Exocrine secretion of epidermal growth factor by the rat prostate: effect of adrenergic agents, cholinergic agents, and vasoactive intestinal peptide

Perfusion of the rat prostatic urethra in vivo provided a means of collecting the rat prostatic secretory product. The secretion of the protein epidermal growth factor (EGF) was investigated by radioimmunoassay (RIA). Baseline secretion of EGF into prostatic fluid was less than .03 +/- .004 SEM ng/min. The alpha-adrenergic agonist phenylephrine caused an increase in EGF to 3.6 +/- .4 SEM ng per 30-min period. The stimulation was blocked completely by prazosin and only partially by yohimbine, indicating primarily alpha 1 control. One mg/kg IV phenylephrine produced a maximal response. The beta-adrenergic agonist isoproterenol caused no increased secretion of EGF. The cholinergic agonist pilocarpine stimulated EGF secretion to 3.2 +/- .6 SEM ng per 30-min period. Atropine blocked the cholinergic stimulation. The combination of phenylephrine and pilocarpine did not result in greater stimulation than either agent alone. Vasoactive intestinal peptide (VIP) did not stimulate EGF secretion, nor did it augment either pilocarpine or phenylephrine-stimulated secretion. EGF secretion into rat prostatic fluid is under both alpha 1-adrenergic and cholinergic control.