α 1 - and α 2 -Adrenoceptors in BPH

The dynamic obstruction of the bladder outlet secondary to benign prostatic hyperplasia (BPH), and the contractile properties of the human prostate are mediated primarily by α1-adrenoceptors. There are now at least three subtypes (A, B, and D) of α1-adrenoceptors, and recent work revealed that α1A-adrenoceptor and α1B-adrenoceptor may have a prime role for prostatic obstruction, and contraction of artery, respectively. Very recently, the presence of a low affinity α1-adrenoceptor for prazosin, named α1L, in the human BPH tissue has been determined. Because the DNA sequence of α1L-adrenoceptor has not yet been cloned, the α1L-adrenoceptor may be another form of the α1A-adrenoceptor, or another pharmacologically distinct α1-adrenoceptor which mediates the norepinephrine-induced contraction of the prostatic smooth muscle. Furthermore, the contribution of α1-adrenoceptors in the prostate to symptoms (not only obstructive, but irritative symptoms) which are elicited by prostatic obstruction remains to be determined.