IDENTIFICATION OF ALPHA(1)-ADRENOCEPTOR SUBTYPES PRESENT IN THE HUMAN PROSTATE

alpha(1)-Adrenoceptors (ARs) play an important role in mediating human prostatic smooth muscle contraction. In the present study cDNA fragments covering different domains of 3 alpha(1)-AR subtypes (alpha(1b), alpha(1c) and alpha(1d)) were generated from human prostate by reverse transcription coupled to the polymerase chain reaction (RT-PCR). The reconstituted partial sequence (349 amino acids) of the human prostatic alpha(1c)-AR PCR products showed 94% identity at the amino acid level with that of the corresponding region of the cloned bovine brain alpha(1c)-AR. Using human alpha(1)-AR subtype selective cDNA probes in Northern blot analysis, the co-expression of mRNA transcripts corresponding to alpha(1b)-, alpha(1c)- and alpha(1d)-AR subtypes was detected in 4 different regions (apex, base, periurethra and lateral lobe) of the human prostate. Competitive inhibition experiments of [H-3]-prazosin binding to membrane preparations of human prostate revealed that the non-selective alpha(1)-subtype antagonist, alfuzosin, produced a monophasic inhibition curve, whereas oxymetazoline produced a 2-component inhibition curve with pK(i) values of 8.54 and 5.46. The high-affinity alpha(1)-AR component of the oxymetazoline inhibition curve was predominant (57%-66%) and showed an affinity for oxymetazoline comparable to that of the alpha(1c)-AR subtype. As such our results illustrate the expression of different alpha(1)-AR subtypes in human prostate and importantly that alpha(1c), represents the predominant alpha(1)-AR subtype present in this tissue.