Relaxation of human detrusor muscle by selective beta-2 and beta-3 agonists and endogenous catecholamines.

OBJECTIVES

The goal of this study was to identify potent relaxant agents of the human detrusor muscle. Therefore, the relaxant effects of different selective beta (beta)-adrenoceptor agonists were examined. Also, the relaxant effects of the endogenous catecholamines were investigated to functionally characterize the beta-adrenoceptor subtype mainly responsible for adrenergic-mediated relaxation in the detrusor muscle of humans.

METHODS

Experiments were performed on muscle strips of human detrusor suspended in a tissue bath. The tissue originated from patients who had undergone total cystectomy. The selective beta3-agonists BRL 37344, ZD 7114, and CGP 12177, the selective beta2-agonists terbutaline and clenbuterol, and the nonselective beta-agonist isoprenaline were investigated. Concentration-relaxation curves of the catecholamines were performed to determine the rank order of potency.

RESULTS

The maximal relaxation induced by BRL 37344, ZD 7114, and CGP 12177 was 36%, 39%, and 37%, respectively. The corresponding pD2 values were 6.73, 4.82, and 6.09, respectively. Terbutaline and clenbuterol induced a maximal relaxation of 48% and 27%, and their pD2 value was 4.97 and 5.34, respectively. Isoprenaline, adrenaline, and noradrenaline induced a maximal relaxation of 72%, 58%, and 79%, respectively. The corresponding pD2 values were 6.18, 6.16, and 6.09, respectively. Because their differences were not significant, no rank order of potency was determined.

CONCLUSIONS

Beta-adrenergic agonists are potent relaxant agents of the human detrusor muscle in vitro. Both beta2 and beta3-adrenoceptors contribute to adrenergic-mediated relaxation. Our results point to a slightly greater role for the beta3-receptor in human detrusor muscle.