Faculty Bibliography

Alpha 1 adrenoceptor binding sites have been characterized in prostatic tissue homogenates using radioligand receptor binding studies. The objective of the present study was to characterize and localize prostatic alpha 1 adrenoceptor binding sites using slide-mounted tissue sections and the ligand 3H-prazosin. The present study demonstrated that preincubation is not required; the optimal incubation interval is 40 minutes; and a 1-minute wash (once or twice) maximizes the proportion of specific 3H-prazosin binding. Saturation studies were performed at 8 different concentrations of 3H-prazosin ranging between 0.0625 nM. to 8.0 nM. The binding of 3H-prazosin was consistently saturable and of high affinity. The mean Kd and Bmax determined from 6 saturation studies was 4.16 x 10(-10) M. and 1.30 fmol./mg. wet weight, respectively. The pharmacology of these 3H-prazosin binding sites was characterized using competitive displacement experiments. The mean IC50 corrected for prazosin, phentolamine and yohimbine was 7.8 x 10(-10) M., 6.0 x 10(-9) M. and 2.1 x 10(-6) M. The rank order of the IC50 corrected values indicates that alpha 1 binding sites were measured under the assay conditions. In the present study, the mean values for Kd, Bmax and IC50 corrected are similar to values previously reported using prostatic tissue homogenates. Prostatic tissue sections were apposed to x-ray film after being incubated with 3 nM. 3H-prazosin (total prazosin binding) and 3 nM. 3H-prazosin + 8 microM. prazosin (nonspecific prazosin binding). The autoradiograms were analyzed using a computerized analyzing system. The specific radioactive densities of 3H-prazosin in the stroma and glandular epithelium were 1099 +/- 48 pCi/mg. and 163 +/- 42 pCi/mg. The present study validates the technique of assaying alpha 1 adrenoceptor binding sites on slide-mounted prostatic tissue sections and provides further evidence that alpha 1 adrenoceptor binding sites are localized primarily to the stromal elements of the prostate

Endothelins mediate contractile responses in many types of vascular and nonvascular smooth muscle. The present study represents the first detailed characterization of endothelins in the human prostate. The objectives of this study were to determine the tissue levels and source of endogenous endothelin-1 (ET1) in the human prostate. The contractile effects of ET1 were also investigated using in vitro isometric tension studies. The mean tissue level of ET1 was 0.58 +/- 0.08 pg./mg. tissue wet weight. Endothelin-like activity was markedly prominent in the glandular epithelium of the human prostate, whereas minimal endothelin-like activity was observed in the prostatic stroma. Strips of human prostatic tissue were suspended in isolated tissue chambers and challenged to a concentration response of ET1. The mean EC50 and Emax for ET1 was 3.2 x 10(-8) M. and 0.12 +/- 0.02 gm. force per mm.2 cross-sectional area (CSA), respectively. Preincubation with indomethacin, terazosin, or nifedipine did not alter the concentration-dependent response to ET1. A calcium-free buffer abolished the contractile response to ET1. Thus, ET1 mediates a potent contraction of human prostatic smooth muscle that is not mediated via alpha 1 adrenergic or dihydropyridine sensitive calcium channels or prostaglandin synthesis. The presence of marked endothelin-like immunoreactivity strongly suggests a biological significance for endogenous endothelins in the human prostate

The objective of the present study was to determine the density and functional properties of alpha 1 adrenoceptors in different regions of the human prostate. Binding and functional studies were performed on eight different topographical regions of the prostate. The contractile response (gm. force/mm.2 cross-sectional area [CSA]) was determined at varying concentrations of phenylephrine, and saturation experiments were performed at seven different concentrations of 125I-Heat. The maximal response to phenylephrine (Emax) ranged from 0.067 to 0.272 gm. force/mm.2 The CSA and the EC50 ranged from 25 to 41 microM. The differences between EC50 and Emax were not significantly different among the eight prostatic regions. A 1.8-fold difference between the Emax for peripheral and central regions of the prostate was statistically significant (p = 0.04). The equilibrium dissociation constant (Kd) of 125I-Heat and the receptor density Bmax were determined from the Scatchard plots. The mean Kd and Bmax ranged from 0.15 to 0.26 nM. and 0.30 to 0.72 fmol. per mg. wet weight, respectively. There were no statistically significant differences between mean Kd and mean Bmax for the eight prostatic regions. The 1.7-fold difference between central and peripheral mean Bmax was not statistically significant (p = 0.07). A direct relationship was not observed between phenylephrine mean Emax and mean Bmax. The present study demonstrates regional differences of the binding and functional properties of prostatic alpha 1 adrenoceptors in the human prostate. These regional differences must be taken into account when investigating the pharmacologic and physiologic properties of the prostate

High affinity alpha 1 adrenoceptors have been characterized in the human prostate. The tension of prostatic smooth muscle is mediated by the alpha 1 adrenoceptor. The present study represents the first characterization of human alpha 1 adrenoceptor subtypes using radioligand receptor binding techniques. Binding studies were performed on tissue homogenates obtained from the human prostate. Competitive inhibition studies were performed in the presence of an 80 pM. 125I-Heat and 16 concentrations of unlabelled 5-methylurapidil (5 MU) or WB-4101 (10(-10) M. to 10(-5) M.). Saturation experiments were also performed with and without chloroethylclonidine (CEC, 10(-5) M.), a compound that selectively inactivates the alpha 1B subtype. The individual displacement plots for WB-4101 and 5-MU in the human prostate were consistently best fit by a 2 binding site model. WB-4101 and 5-MU exhibited a 594- and 186-fold higher affinity for the prostatic alpha 1A binding site relative to the alpha 1B binding site. The ratios of prostatic alpha 1A/alpha 1B binding sites discriminated by WB-4101 and 5-MU were 1.8 and 1.6, respectively. CEC inactivated 44% of the prostatic alpha 1 binding sites. The binding studies suggest that the dominant alpha 1 subtype in the human prostate is the alpha 1A. We are characterizing the functional properties of the alpha 1 subtypes in the human prostate

We have characterized the alpha 1 adrenoceptor subtypes in the human prostate using radioligand receptor binding studies. The objective of the present study was to determine the alpha 1 subtype mediating the tension of prostatic smooth muscle. Fresh human tissue was obtained from 9 males between 50 and 80 years of age undergoing prostatectomy for BPH. The incubation of prostatic tissue with the irreversible antagonist chlorethyclonidine (CEC) resulted in an 80% reduction of the maximal contractile response produced by phenylephrine. However, the alpha 1A-selective antagonists WB-4101 and 5-methylurapidil (5-MU) competitively inhibited the contractile response induced by phenylephrine, with KB = 2.64 and 4.46 nM, respectively, consistent with their affinity at the alpha 1A receptor subtype. The pharmacological profile of the alpha 1-receptor-mediated contractile response of prostate smooth muscle is inconsistent with their classification as either an alpha 1A or alpha 1B subtype. Alternatively, when compared with the properties of the cloned alpha 1 receptors, our results suggest that the alpha 1 receptors involved in the contraction of prostate smooth muscle have some pharmacological properties similar to those encoded by the gene of the bovine alpha 1C receptor subtype. The findings of the present study suggest that efforts should be made to confirm the identity of the alpha 1-receptor subtype expressed by prostate smooth muscle, in order to develop subtype-selective alpha 1 antagonists, and to evaluate their safety and efficacy in benign prostatic hyperplasia (BPH)