alpha1- and alpha2-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 alpha1-adrenoceptors. There are now at least three subtypes (A, B, and D) of alpha1-adrenoceptors, and recent work revealed that alpha1A-adrenoceptor and alpha1B-adrenoceptor may have a prime role for prostatic obstruction, and contraction of artery, respectively. Very recently, the presence of a low affinity alpha1-adrenoceptor for prazosin, named alpha1L, in the human BPH tissue has been determined. Because the DNA sequence of alpha1L-adrenoceptor has not yet been cloned, the alpha1L-adrenoceptor may be another form of the alpha1A-adrenoceptor, or another pharmacologically distinct alpha1-adrenoceptor which mediates the norepinephrine-induced contraction of the prostatic smooth muscle. Furthermore, the contribution of alpha1-adrenoceptors in the prostate to symptoms (not only obstructive, but irritative symptoms) which are elicited by prostatic obstruction remains to be determined.