The role of alpha(1L)-adrenoceptor in rat urinary bladder: Comparison between young adult and aged rats

We examined the role of the alpha(1L)-adrenoceptors in the urinary bladder of young adult and aged rats in vitro. In the isolated body of the urinary bladder (corpus vesicae), phenylephrine-induced contractions were significa ntly facilitated in aged rats. Either prazosin, a non-selective alpha(1)-ad renoceptor antagonist, or JTH-601, an alpha(1L)-adrenoceptor antagonist, co mpetitively inhibited the phenylephrine-induced contraction of isolated bod y of the urinary bladder. The antagonistic effect of JTH-601 was almost equ ipotent between young adult and aged rats (pA(2) values were 9.61+/-0.12 an d 9.79+/-0.07, respectively), although a statistically significant differen ce was noted for that of prazosin (pA(2) values were 9.49+/-0.09 and 9.19+/ -0.06, respectively). In macroscopic autoradiographic studies, specific bin ding of [H-3]JTH-601 (5nM) was seen widely in the muscle layer of urinary b ladder, but no differences were noted between young adult and aged rats. In the present study, there was no evidence to suggest a role of the alpha(1L )-adrenoceptors in the body of rat urinary bladder. On the other hand, alph a(1A)-adrenoceptors may play an important role in an age-related increase o f alpha(1)-adrenoceptors response in this tissue. These results suggest tha t a facilitation of contractile response mediated by alpha(1A)-adrenoceptor s may be a cause of unstable bladder in aged persons.