Materials and Methods: Saturation and competition radioligand binding studies were performed for characterization at the protein level. alpha(1)-Adrenoceptors were labeled with [H-3]prazosin and [H-3]tamsulosin, while alpha(2)-adrenoceptors were labeled with [H-3]RX 821002. alpha(1)-Adrenoceptor subtype 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. Competition studies with the alpha(1A)-selective antagonists 5-methylurapidil and (+)-niguldipine and the alpha(1D)-selective BMY 7378 revealed a mixed alpha(1A)/alpha(1B)-adrenoceptor population with no evidence for alpha(1D)-adrenoceptor protein. In contrast alpha(1D)-adrenoceptors were readily detected at the mRNA level. Competition binding studies with the alpha(2A)-selective 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 predominantly alpha(1A)-, alpha(1B)- and or alpha(2A)-adrenoceptor protein; additionally the alpha(1D)-adrenoceptor is present at the mRNA level.