Alpha 1 Adrenoceptor Subtypes in the Human Prostate

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Abstract
High affinity α1 adrenoceptors have been characterized in the human prostate. The tension of prostatic smooth muscle is mediated by the α1 adrenoceptor. The present study represents the first characterization of human α1 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 α1B 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 α1Α binding site relative to the α1B binding site. The ratios of prostatic α1Α/α1Β binding sites discriminated by WB-4101 and 5-MU were 1.8 and 1.6, respectively. CEC inactivated 44% of the prostatic α1 binding sites. The binding studies suggest that the dominant α1 subtype in the human prostate is the α1Α. We are characterizing the functional properties of the α1 subtypes in the human prostate.