Subtypes of alpha 1-adrenoceptors in urinary bladder and urethral smooth muscle and prostatic adenoma

Abstract

Two alpha 1-adrenoceptor subtypes (alpha 1A and alpha 1B) have been distinguished by competitive antagonists and alkylating agent chloroethylclonidine (CEC). The CEC-insensitive subtype (alpha 1A) had been suggested to selectively activate Ca2+ influx through Ca-channels in smooth muscle cell membrane. We examined the effects of WBC4101, CEC and verapamil on contractile responses to phenylephrine in rabbit aorta, urinary bladder and urethral smooth muscle and in human prostatic adenoma to examine the alpha 1-adrenoceptor subtypes in these tissue. Pretreatment with WB4101 caused a large shift to the right for phenylephrine-induced dose response curves and verapamil decreased the phenylephrine-induced contractions of rabbit aorta, urinary bladder and urethral smooth muscles and human prostatic adenomas. CEC inhibited only phenylephrine induced contractions of human prostatic adenomas. The pA2 value for WB4101 was significantly lower in human prostate than in rabbit aorta, urinary bladder and urethra. These results suggest that functional alpha 1-adrenoceptor subtypes involve alpha 1A and alpha 1B in human prostatic adenoma, while only alpha 1A in rabbit aorta, urinary bladder and urethral smooth muscles.