The role of alpha 1L-adrenoceptor in rat urinary bladder: comparison between young adult and aged rats.

We examined the role of the alpha1L-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 significantly facilitated in aged rats. Either prazosin, a non-selective alpha1-adrenoceptor antagonist, or JTH-601, an alpha1L-adrenoceptor antagonist, competitively inhibited the phenylephrine-induced contraction of isolated body of the urinary bladder. The antagonistic effect of JTH-601 was almost equipotent between young adult and aged rats (pA2 values were 9.61+/-0.12 and 9.79+/-0.07, respectively), although a statistically significant difference was noted for that of prazosin (pA2 values were 9.49+/-0.09 and 9.19+/-0.06, respectively). In macroscopic autoradiographic studies, specific binding of [3H]JTH-601 (5nM) was seen widely in the muscle layer of urinary bladder, 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 alpha1L-adrenoceptors in the body of rat urinary bladder. On the other hand, alpha1A-adrenoceptors may play an important role in an age-related increase of alpha1-adrenoceptors response in this tissue. These results suggest that a facilitation of contractile response mediated by alpha1A-adrenoceptors may be a cause of unstable bladder in aged persons.