Introduction

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Benign prostatic hyperplasia (BPH), or the nonmalignant enlargement of the prostate gland, affects up to 80% of men more than 60 years old, with approximately 40% developing clinical symptoms of bladder outlet obstruction (Barry, 1990; Garraway et al., 1991). BPH is composed of static and dynamic components that contribute to the symptoms. The static component refers to the enlargement of the prostate gland, which may result in compression of the urethra and obstruction of urine flow from the bladder. The dynamic component reflects the smooth muscle tone of the bladder neck and prostate smooth muscle. Functional studies have established that prostate smooth muscle tone is maintained through ₁-adrenergic receptors (₁-ARs). The molecular clones of three human ₁-AR subtypes [_1a (Schwinn et al., 1990), _1b (Ramarao et al., 1992), and _1d (Bruno et al., 1991)] have been isolated. ₁-AR antagonists lacking in subtype selectivity, such as terazosin, doxazosin, and alfuzosin, were originally introduced as antihypertensive agents but have become increasingly important in the management of BPH (Eri and Tveter, 1995; Hieble and Ruffolo, 1996; Kenny et al., 1997). ₁-AR antagonists reduce smooth muscle tone in the prostate and lower urinary tract, thereby relaxing the bladder outlet and increasing urinary flow. The major disadvantage of nonselective ₁-AR antagonists is their adverse side effect profile, which includes symptoms of dizziness, postural hypotension, asthenia, and occasionally syncope; some of which may be attributed to relaxation of vascular smooth muscle tone. Dose titration on the initiation of treatment with these agents has become necessary to avoid the onset of side effects. It is also likely that maximal effective blockade at ₁-ARs in the prostate cannot be achieved at the maximum tolerated doses, compromising the therapeutic effect of nonselective antagonists.

A number of studies have shown that the _1a-AR subtype accounts for the majority of ₁-AR mRNAs and expressed protein in human prostatic smooth muscle and mediates contraction in this tissue (Marshall et al., 1992; Price et al., 1993; Faure et al., 1994; Forray et al., 1994; Lepor et al., 1995; Michel et al., 1996; Schwinn and Kwatra, 1998), whereas the ₁ subtypes primarily responsible for mediating vascular responses have not been established. Studies in the rat indicate that the _1d subtype is predominantly responsible for the contractile response of the aorta (Kenny et al., 1995), and several studies in dogs have indicated that selectivity for the _1a subtype correlates with in vivo uroselectivity (Kenny et al., 1994, 1996; Brune et al., 1996). A valuable pharmacological agent for the treatment of BPH symptoms would be one that would block ₁-ARs in the lower urinary tract without antagonizing the ₁-ARs responsible for maintaining vascular tone.

Tamsulosin (Flomax, Harnal) has been described as an _1a-AR subtype-selective antagonist, with a uroselective clinical profile in the delayed-release formulation (Yamada et al., 1994; Han et al., 1995; Rabasseda and Fitzpatrick, 1996). However, early trials with tamsulosin in an immediate-release formulation showed orthostatic effects in normal volunteers (Tsunoo et al., 1990).

We synthesized a series of 14 novel aryl piperazine compounds (X. Li, W. V. Murray, L. K. Jolliffe, and V. L. Pulito, unpublished data) and determined their binding to recombinant human ₁-AR subtypes. Four of the compounds, RWJ-38063 [N-(2-{4-[2-(methylethoxy)phenyl]piperazinyl}ethyl)-2-(2-oxopiperidyl)acetamide], RWJ-68141 [ethyl 1-{[N-(2-{4- [2-(methylethoxy)phenyl]piperazinyl}ethyl)carbomoyl]methyl}-5-oxopyrrolidine-2-carboxylate], RWJ-68157 [N-(2- {4-[2-(methylethoxy)phenyl]piperazinyl}ethyl)-2-(2-oxoazaperhydroepinyl)acetamide], and RWJ-69736 [N-(3-{4-[2- (methylethoxy)phenyl]piperazinyl}propyl)-2-(2-oxopiperidyl)acetamide], exhibited _1a-AR subtype selectivity in the binding assay. We describe here our investigation of the differences in ₁-AR receptor binding affinities, potencies in rat prostate and aorta tissue contraction assays, and uroselectivity in an in vivo canine model for these chemically related compounds. We compare their in vitro and in vivo properties with those of tamsulosin.

	Experimental Procedures

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DNA Cloning, COS Cell Transfection, and Membrane Preparation. The cDNA clones encoding the three human ₁-AR subtypes were obtained by reverse transcription-polymerase chain reaction amplification from human hippocampus and prostate poly(A)⁺ RNA libraries (Clontech, Palo Alto, CA). cDNA clones were verified by sequence analysis, and any deviation from published sequence was corrected by site-directed mutagenesis. cDNAs were subcloned into the pcDNA3 mammalian expression vector (Invitrogen Corp, Carlsbad, CA). COS-1 cells were transfected by the standard DEAE-dextran method with chloroquine shock (McCutchan and Pagano, 1968; Luthman and Magnusson, 1983). Each tissue culture dish was inoculated with 3.5 × 10⁶ cells and transfected with 10 µg of DNA. At 72 h post-transfection, the cells were scraped into TE buffer (50 mM Tris-HCl, 5 mM EDTA, pH 7.4). The cell suspension was disrupted with a Polytron homogenizer (Brinkmann Instruments, Westbury, NY) at setting 8 for 10 s. The disrupted cells were centrifuged at 1000g for 10 min at 4°C. Supernatants were centrifuged at 34,500g for 20 min at 4°C. The membrane pellets were suspended in TNE buffer (50 mM Tris-HCl, 150 mM NaCl, 5 mM EDTA, pH 7.4). The protein concentration was determined with the Bio-Rad DC Protein Assay kit (Hercules, CA) after membrane solubilization with Triton X-100.

Competitive Radioligand Binding Assays. Assays were conducted in 96-well plates with a final volume of 200 µl per well. Test compound concentrations for competition curves ranged from 0.1 pM to 10 µM in half-log increments. Then 0.1 µg of _1a- or _1b-AR-expressing membrane protein or 2.6 µg of _1d-AR-expressing membrane protein was added to TNE buffer, with a final concentration of 50 pM (±)--([¹²⁵I]iodo-4-hydroxyphenyl)-1-ethyl-aminoethyl-tetralone ([¹²⁵I]HEAT; 2200 Ci/mmol) and the appropriate concentration of test compound. After a 25°C incubation for 1 h, the plates were filtered onto GF/C filterplates (Packard Instruments Co., Meriden, CT) and washed with ice-cold saline and 0.05% Tween 20. Levels of radioactivity were determined using a Packard TopCount liquid scintillation counter. Competition curves were analyzed with the use of the curve-fitting capabilities of GraphPad Prism software (GraphPad Software, Inc., San Diego, CA). The concentration of antagonist needed to inhibit specific binding by 50% (IC₅₀) was used to calculate K_i values according to the relationship K_i = IC₅₀/(1 + [radioligand]/K_d), where K_d is the dissociation constant of the radioligand at the receptor (Cheng and Prusoff, 1973). The values are presented as the negative logarithm of the K_i, or pK_i .

Rat Isolated Prostate and Aorta Tissue Assays. Long-Evans male rats weighing 275 ± 25 g were sanitized, and the abdominal aorta and prostate gland were removed. Aortic strips 3 to 4 mm wide, with endothelium intact, were prepared and placed in 10-ml isolated tissue baths under a resting tension of 2 g. Prostate strips measuring 8 to 10 mm in length and 1 to 2 mm in width were placed under a resting tension of 2 g. Tissues were bathed in modified Krebs' solution of the following composition: 118 mM NaCl, 4.7 mM KCl, 1.18 mM KH₂PO₄, 25 mM NaHCO₃, 2.5 mM CaCl₂, 1.18 mM MgSO₄·7H₂O, and 5.55 mM (+)-glucose. Baths were maintained at 37°C and constantly bubbled with 95% oxygen, 5% CO₂, pH 7.4, with the solution being changed at frequent intervals throughout the 60-min equilibration period. Tissue strips were connected to isometric transducers connected to a strip-chart recorder. Before the concentration-response curves were started, tissues were exposed to (±)-norepinephrine (NE) at a concentration of 1.0 µM. A minimum response of 0.5 g of tension was required for the tissue to be used for concentration-response curves. After a 90-min wash period, a cumulative concentration-response curve was obtained to NE concentrations of 0.001 to 100 µM in half-log increments. After completion of the concentration-response curve, the tissue was washed for 90 min, and one of three concentrations of antagonist was added and incubated for 5 min before a second cumulative concentration-response curve was obtained. In a number of cases, Schild analysis could not be performed due to depression of the maximal response by high antagonist concentrations and the resulting nonparallel slopes of the concentration-response curves. Estimates of affinity were obtained by the receptor dissociation constant, K_B, from the concentration-response curves and represented as the negative logarithm, pK_B. Each NE concentration-response curve was analyzed using GraphPad Prism software to estimate the midpoint location (EC₅₀). EC₅₀ values were obtained in the presence and absence of antagonist and used to calculate the antagonist dissociation equilibrium constants according to the relationship K_B = [B]/(CR  1), where [B] is the antagonist concentration at which a concentration ratio could be accurately determined, and CR is the concentration ratio.

Anesthetized Dog Efficacy Testing. The in vivo investigation was in compliance with the National Institutes of Health Guide for the Care and Use of Laboratory Animals. The protocol was reviewed and approved by the Institutional Animal Care and Use Committee (IACUC). Male beagle dogs between 10 and 18 months of age were preanesthetized with thiopental sodium, and an endotracheal tube was inserted transorally. They were attached to a closed volume cycle respirator and maintained at a surgical plane of anesthesia with isoflurane inhalation. Intraurethral pressure (IUP) was monitored with a 7 to 8 French Fogarty venous thrombectomy balloon catheter positioned in the prostatic urethra with the balloon port of the catheter connected to a pressure transducer. Mean arterial pressure (MAP) was monitored via a 20- to 18-gauge catheter placed in the femoral artery and connected to a pressure transducer. Heart rate and ECG patterns were monitored through lead II of the ECG monitor. Compounds were administered via a 22-gauge catheter placed in the cephalic vein. To generate a control dose-response curve, test compound vehicle was administered i.v., followed 15 min later by 0.1- to 30- or 100-µg/kg i.v. doses of phenylephrine (PE) in ascending half-log increments. IUP and MAP responses were continuously monitored and allowed to return to baseline for approximately 2 min before administration of the next PE dose. An i.v. bolus dose of antagonist was given, followed 15 min later by the PE dose-response challenge (a maximal PE dose of 100 µg/kg was used in cases of strong antagonism). The doses of antagonist that were tested were 0.3, 3, 30, and 300 µg/kg for RWJ-38063; 3, 10, 30, and 100 µg/kg for RWJ-69736; and 0.3, 3, 10, and 30 µg/kg for tamsulosin. Antagonist doses were given in ascending concentrations at no less than 45-min intervals. The IUP and MAP are presented as the percentage of the maximal response after each PE challenge, with the maximal response as the IUP and MAP at the highest PE dose after the i.v. administration of vehicle only. Data from three experiments were used to calculate an average ± S.E. IUP or MAP response for each PE challenge. Dose-response curves were generated using GraphPad Prism software. Due to depression of the maximal response to PE by high antagonist concentrations, we observed nonparallel shifts in the dose-response curves for the effects of RWJ-38063, RWJ-69736, and tamsulosin on IUP. This precluded the determination of pseudo pA₂ values for the comparison of potency of action.

Materials. All tested ₁-AR antagonists were synthesized at the R. W. Johnson Pharmaceutical Research Institute (Raritan, NJ). The structures of the RWJ compounds are shown in Fig. 1. RWJ-38063 was synthesized as the citrate salt, whereas RWJ-68141, RWJ-68157, and RWJ-69736 were synthesized as the free bases. Tamsulosin was synthesized as the hydrochloride salt. Compounds were initially dissolved in DMSO before use in in vitro studies. For the in vivo studies, compounds were dissolved in saline vehicle, stored on ice, and used the same day. PE was obtained from Gensia (Irvine, CA) and diluted with saline vehicle for i.v. administration. (±)-NE was obtained from Sigma Chemical Co. (St. Louis, MO). [¹²⁵I]HEAT was obtained from NEN Life Science Products (Boston, MA).

View larger version (15K): [in this window] [in a new window]   Fig. 1.   Chemical structures of RWJ-38063, RWJ-68141, RWJ-68157, and RWJ-69736.

	Results

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Binding Studies with the Cloned Human ₁-ARs. The binding affinities of the tested compounds for the three cloned human ₁-AR subtypes are shown in Table 1. RWJ-68141 and RWJ-68157 displayed similar affinities for the human _1a-AR subtype, whereas RWJ-38063 had a slightly higher affinity than these compounds for this receptor subtype. RWJ-69736 had a 14- to 90-fold greater affinity for the _1a-AR than the other RWJ compounds tested. Tamsulosin had the highest affinity for the _1a subtype of all compounds tested, with a pK_i value nearly two orders of magnitude greater than that of RWJ-38063 and more than two orders higher than the pK_i values of RWJ-68141 and RWJ-68157. The binding affinities of each compound at the _1b- and _1d-AR subtypes were determined to assess the degree of receptor subtype selectivity. The pK_i values for the RWJ compounds at the _1b-AR were more than two orders of magnitude lower than the pK_i value of 8.71 ± 0.05 for tamsulosin at this receptor subtype. The pK_i values at the _1d-AR for the RWJ compounds were nearly three orders of magnitude lower, or more than the pK_i value of 9.67 ± 0.08 for tamsulosin. Receptor subtype selectivities are presented as ratios of average K_i values in Table 1. Of all of the tested compounds, RWJ-38063 displayed the highest degree of selectivity for the _1a subtype over the _1b, with a ratio of 953. RWJ-69736 had the highest degree of selectivity for the _1a subtype over the _1d subtype, with a selectivity ratio of 223. Among the RWJ compounds, RWJ-68157 was the least selective for the _1a versus the _1b subtype, with a ratio of 187; and RWJ-68141 was the least selective for the _1a versus the _1d subtype, with a ratio of 20. Tamsulosin was found to have the lowest level of selectivity of all compounds tested, with only a 15-fold higher affinity for the _1a over the _1b subtype and virtually no selectivity for the _1a over the _1d subtype.

View this table: [in this window] [in a new window]   TABLE 1 Affinity of 1-AR antagonists at the cloned human 1-AR subtypes Inhibition of [125I]HEAT binding to COS cell membranes expressing the cloned human 1-AR subtypes was determined as described in Experimental Procedures. Each pKi value is the mean ± S.E. of four to six determinations. Receptor subtype selectivity is the ratio of the average Ki values for the respective subtypes as noted.

Isolated Rat Prostate and Aorta Tissue Contractility Studies. The effects of the tested compounds on NE-induced contractions in isolated rat prostate and aorta tissue are shown in Table 2. All compounds suppressed tissue contractions, indicating that their actions at the receptors are those of antagonists. Increasing concentrations of RWJ-38063 and RWJ-68141 caused parallel rightward shifts in the NE concentration-response curves for both aorta and prostate. RWJ-68157 and RWJ-69736 also exhibited parallel rightward shifts in the concentration-response curves for effects on aortic contractions. However, nonparallel rightward shifts in the concentration-response curves due to depression of the maximal response were observed for RWJ-68157 and RWJ-69736 antagonism of NE-induced prostatic contractions and for tamsulosin antagonism of both aortic and prostatic contractions. RWJ-69736 and tamsulosin acted as equally potent inhibitors of NE-induced contractions of rat prostate tissue, with pK_B values of 9.26 ± 0.23 and 9.23 ± 0.31, respectively. RWJ-38063 was nearly 10-fold lower in potency, with a pK_B value of 8.24 ± 0.14 for inhibition of prostate contractility; RWJ-68141 and RWJ-68157 were the least potent of the compounds tested, with pK_B values of 7.35 ± 0.21 and 6.60 ± 0.29, respectively.

Effects on PE-Induced Increases in IUP and MAP in Anesthetized Dogs. RWJ-38063 and RWJ-69736 were chosen, based on their levels of selectivity and potency in the isolated tissue studies, for further examination of their uroselective properties in an in vivo canine model. Tamsulosin was also examined as a comparator. PE (0.1-30 or 100 µg/kg i.v.) produced dose-dependent increases in IUP and MAP, which were antagonized by the tested compounds (Fig. 2). Little effect on the PE-induced increases in IUP was seen for RWJ-38063 at the 0.3- and 3-µg/kg i.v. doses, but the 30- and 300-µg/kg doses caused dose-dependent rightward shifts in the dose-response curves. A far more limited rightward shift in the dose-response curves, even at the highest RWJ-38063 dose, was observed for the MAP response than for the IUP response. This indicates a lower potency in the antagonistic effects of the compound on PE-induced increases in MAP than IUP and the desired in vivo uroselectivity. RWJ-69736 also produced a dose-dependent rightward shift of the dose-response curves for the IUP response, with a potency that is slightly greater than that of RWJ-38063. The highest dose of RWJ-69736 tested, 100 µg/kg i.v., appeared to have a similar suppressive effect on the PE-induced increases in IUP as the 300-µg/kg i.v. dose of RWJ-38063. The suppressive effects of RWJ-69736 on the MAP response were also more potent than those of RWJ-38063, with the 100-µg/kg dose of RWJ-69736 resulting in a slightly greater inhibition of the MAP response than the 300-µg/kg dose of RWJ-38063. RWJ-69736 was also uroselective in its actions in that the inhibitory effects of increasing doses on the MAP response to PE were less than the effects on IUP, with a more limited rightward shift in the MAP dose-response curves. The tested dose range of RWJ-69736 was limited due to a sharp transient rise in heart rate of 1.5- to 2-fold over predrug levels after the 30- and 100-µg/kg doses.

View larger version (42K): [in this window] [in a new window]   Fig. 2.   Effects of increasing i.v. doses of RWJ-38063, RWJ-69736, and tamsulosin on PE-induced increases in the IUP and MAP in anesthetized dogs. A single bolus i.v. dose of test compound was administered, followed 15 min later by 0.1- to 30- or 100-µg/kg i.v. doses of PE in ascending log or half-log increments. IUP and MAP responses to the PE doses were monitored to produce dose-response curves. The control PE dose-response curves were generated after the i.v. administration of saline vehicle. The 100% maximal response is the response to 30 or 100 µg/kg i.v. PE after the administration of vehicle only. Each data point represents the mean ± S.E. of three separate experiments for each compound with the following exception: the 10-µg/kg dose of tamsulosin was tested in two experiments, and the 30-µg/kg dose was tested in one experiment.

	Discussion

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We compared the in vitro and in vivo uroselective properties of four novel arylpiperazine compounds with those of the ₁-AR antagonist tamsulosin, which is currently used in the treatment of BPH symptoms. The binding activities of RWJ-38063, RWJ-68141, RWJ-68157, RWJ-69736, and tamsulosin at each of the three cloned human ₁-AR subtypes were examined to determine their affinities and receptor subtype selectivities. All RWJ compounds had significantly higher binding affinities for the _1a-AR subtype than either the _1b or _1d subtype. Although tamsulosin had the highest affinity for the _1a subtype of all the compounds tested, it had the lowest level of selectivity for this subtype. The selectivity ratio of tamsulosin for the _1a versus the _1b subtype was more than 10-fold less than that of any of the RWJ compounds. Furthermore, tamsulosin had no selectivity for the _1a versus the _1d subtype. The pK_i values for tamsulosin at the three human ₁-AR subtypes reported here are within the range of values that have been reported for the human receptors as well as those of other species (Kenny et al., 1994; Foglar et al., 1995; Shibata et al., 1995; Testa et al., 1996; Martin et al., 1997; Leonardi et al., 1997). The K_d values for tamsulosin at the three cloned human ₁-AR subtypes have been determined and support the rank order of affinity of _1a = _1d > _1b for this compound (Richardson et al., 1997).

The abilities of these compounds to inhibit NE-induced contractions of isolated rat prostate and aorta tissue strips were examined to provide an indication of whether functional selectivity is present at the tissue level. Again, the RWJ compounds all displayed, to varying degrees, selective inhibition of NE-induced contractions of the prostate tissue over that of the aorta. Of the RWJ compounds, RWJ-38063 and RWJ-68141 were most selective for prostate tissue, with selectivity ratios of 319 and 341, respectively, followed by RWJ-69736, with a selectivity ratio of 100. RWJ-68157 was the least selective among the RWJ compounds, with only 7.3-fold greater potency in its effects on prostate tissue than aorta tissue. In contrast, tamsulosin displayed a 33-fold higher degree of potency in inhibiting contractions of rat aorta versus prostate tissue in these studies. Other reports of tamsulosin inhibitory activity in human isolated prostate and mesenteric artery assays (Testa et al., 1996) and in rabbit lower urinary tract and vascular tissues (Leonardi et al., 1997) indicate a lack of tissue selectivity as well. Overall, the pK_B values for the inhibition of NE-induced contractions of rat prostate for the tested compounds were comparable to their respective pK_i values for the human _1a-AR, indicating that the _1a subtype is responsible for mediating the adrenergic stimulation of prostate smooth muscle. However, the pK_B value for inhibition of NE-induced contractions in rat prostate for RWJ-68157 is 10-fold lower than its pK_i value at the human _1a subtype. An alternative ₁-AR subtype classification has been proposed that suggests that the primary receptor subtype responsible for the contractions of the lower urinary tract is the _1L and is distinguished from the _1a by its low affinity for prazosin (Muramatsu et al., 1990; Muramatsu, 1991). The discrepancy in the affinity of RWJ-68157 at the cloned _1a receptor and its inhibitory potency on prostate tissue contractions can be explained by the presence of a population of receptors, such as the _1L, which are distinct from the _1a, and responsible for prostate tissue contractility. However, this explanation is not definitive because the _1L receptor has not yet been cloned. There also is evidence that binding assay conditions such as temperature and cellular integrity may induce changes in the pharmacological state of the _1a receptor that allow it to display _1L properties and can result in a significant lowering in pK_i values for some antagonists (Ford et al., 1996; Williams et al., 1996). We also cannot rule out the possibility that species differences between ₁ receptors are responsible for the discrepancy seen between the human receptor binding activity and inhibition of NE-induced rat tissue contractility with RWJ-68157.

There have been a number of studies that have examined the effects of ₁-AR antagonists on IUP and MAP in anesthetized dogs (Shibasaki et al., 1992; Kenny et al., 1994; Testa et al., 1994). RWJ-69736 and RWJ-38063 were selected for further evaluation in an in vivo anesthetized canine model because they displayed high levels of specificity and potency in their actions on prostate tissue. RWJ-68141, although highly selective for prostate tissue, had a pK_B value that was 10- and 100-fold lower than that of RWJ-38063 and RWJ-69736, respectively, and was not examined further. RWJ-69736 demonstrated approximately one-half-log greater potency in its suppression of PE-induced IUP increases than RWJ-38063 in vivo. This correlates with the 14-fold higher pK_i value for _1a-AR binding and the 10-fold higher pK_B value in the prostate tissue assay for RWJ-69736 compared with RWJ-38063. RWJ-69736 also had a more potent inhibitory effect on PE-induced increases in MAP than RWJ-38063, which reflects the 34-fold higher pK_B value for RWJ-69736 than RWJ-38063 for inhibition of rat aortic tissue contractions. The 30- and 100-µg/kg doses of RWJ-69736 caused a 1.5- to 2-fold rise in heart rate. This effect is unlikely to be due to reflex tachycardia from low blood pressure because other compounds, which caused a similar suppression of MAP (results not shown), did not elicit an increase in heart rate. Either direct stimulation of cardiac -ARs, or antagonism of ₂-ARs in the central nervous system, which would result in increased sympathetic outflow, would be possible causes for the observed rise in heart rate. The binding of RWJ-69736 to human - and ₂-ARs was investigated (results not shown). This compound was found to have low binding affinity for the human -AR subtypes; however, binding to the -ARs of the dog was not determined and cannot be ruled out. RWJ-69736 was found to have moderate binding activity at the human _2A-AR; activity at the canine receptor is unknown. This rise in heart rate precluded testing of a higher dose of RWJ-69736 and of the further development of this compound as a potential therapeutic agent. RWJ-38063 proved to be selective in its inhibitory actions on IUP over MAP and caused no noticeable change in heart rate. Tamsulosin was a very potent inhibitor of both the IUP and MAP responses to PE. The 30-µg/kg i.v. dose caused virtually complete blockade of the IUP response and a significant suppression of the MAP response. This dose was not repeated in subsequent experiments due to the risk to the animals from tachycardia and hypotensive effects. The 0.3- to 10-µg/kg doses of tamsulosin had similar inhibitory effects on both the IUP and MAP responses, indicating poor uroselectivity in this study. Results from other studies of the effects of tamsulosin in an anesthetized dog model also report poor uroselectivity (Kenny et al., 1994, 1996; Blue et al., 1996).

In conclusion, we have shown that the RWJ compounds presented in this report are more selective than tamsulosin for the human _1a-AR subtype over the _1b and _1d subtypes and are more selective in their effects on isolated rat prostate tissue over vascular tissue. We have also demonstrated the in vivo uroselectivity of RWJ-38063. We propose that this compound has the potential to be an effective agent in the treatment of BPH symptoms with minimal effects on the vasculature and will present a more positive side effect profile than other ₁-AR antagonists currently available.