Alpha‐1 adrenoceptor subtypes (high, low) in human benign prostatic hypertrophy tissue according to the affinities for prazosin

Abstract

BACKGROUND A novel classification of α-1 adrenoceptor subtypes (High, Low) was applied to human benign prostatic hypertrophy (BPH)tissue. METHODS Human BPH specimens were examined by a radioligand binding assay method using 3H-prazosin, and those data were compared with preoperative therapies. RESULTS (1) Scatchard analysis showed a high-affinity site (Kd:27.18 ± 6.41 pM; Bmax:9.29 ± 0.98 fM/mg protein; mean ± SE) as α1H, and a low-affinity site (Kd:4088.0 ± 744.34 pM; Bmax:140.81 ± 19.98 fM/mg protein; mean ± SE) as α1L subtype, for prazosin. (2) The Kd and Bmax were not different in the nontreated group (n = 5), α1 blocker group (n = 5), and antiandrogen group (n = 5), in either α1-high affinity or α1-low affinity subtype. (3) Phenoxbenzamine had different pKi value for the above two adrenoceptor subtypes. Scatchard analysis showed that α1-high affinity binding site disappeared in the presence of 1 μM of phenoxbenzamine, and the Kd and Bmax values in the prescence of 1 μM of phenoxybenzamine were almost identical to the α1-low affinity site of the two subtypes. CONCLUSIONS Human BPH tissue possesses both α1H-and α1L-adrenoceptor subtypes according to the affinities for prazosin, and only the α1H subtype can be completely inhibited by some concentration of phenoxybenzamine. Treatent by α1 blocker may not change the conditons of α1-adrenoceptors in prostatic tissue.Prostate 31:216–222, 1997. © 1997 Wiley-Liss, Inc.