Characterization of alpha-adrenoceptor subtypes in the corpus cavernosum of patients undergoing sex change surgery

Purpose: To characterize the subtypes of alpha(1)- and alpha(2)-adrenocepto rs in the human corpus cavernosum from patients undergoing sex change surge ry. Materials and Methods: Saturation and competition radioligand binding studi es were performed for characterization at the protein level. alpha(1)-Adren oceptors were labeled with [H-3]prazosin and [H-3]tamsulosin, while alpha(2 )-adrenoceptors were labeled with [H-3]RX 821002. alpha(1)-Adrenoceptor sub type mRNA mras additionally determined by reverse-transcriptase polymerase chain reaction and RNase protection assays. Results: Human corpus cavernosum expressed similar to 32 and similar to 22 fmol./mg. protein alpha(1)- and alpha(2)-adrenoceptors, respectively. Compe tition studies with the alpha(1A)-selective antagonists 5-methylurapidil an d (+)-niguldipine and the alpha(1D)-selective BMY 7378 revealed a mixed alp ha(1A)/alpha(1B)-adrenoceptor population with no evidence for alpha(1D)-adr enoceptor protein. In contrast alpha(1D)-adrenoceptors were readily detecte d at the mRNA level. Competition binding studies with the alpha(2A)-selecti ve oxymetazoline and the alpha(2B)-selective prazosin and ARC 239 revealed a homogeneous population of alpha(2A)-adrenoceptors. Conclusions: We conclude that human corpus cavernosum expresses predominant ly alpha(1A)-, alpha(1B)- and or alpha(2A)-adrenoceptor protein; additional ly the alpha(1D)-adrenoceptor is present at the mRNA level.