Effects of gender, age and hypertension on β-adrenergic receptor function in rat urinary bladder

beta-Adrenoceptors mediate urinary bladder relaxation, and gender, age and hypertension have been linked to bladder dysfunction. Therefore, we have studied whether any of these factors affects the ability of beta-adrenoceptor agonists to relax rat bladder detrusor muscle in vitro. For this purpose we have compared male and female Wistar rats, young and old male Wistar rats, and male normotensive and spontaneously hypertensive rats (SHR). Comparisons were done using KCl-precontracted bladder strips (length about 15-20 mm) and the endogenous agonist noradrenaline, the synthetic non-subtype-selective agonist isoprenaline, and the prototypical beta(3)-adrenoceptor agonists BRL 37,344 and CGP 12,177. While all agonists yielded numerically weaker relaxation in female as compared to male rats (for example for noradrenaline E-max 40 +/- 4% vs 53 +/- 6% relaxation, pEC(50) 5.41 +/- 0.13 vs 5.60 +/- 0.14), this difference reached statistical significance only for the weak partial agonist CGP 12,177. Responses to all agonists were attenuated in old as compared to young rats, largely due to a reduced maximum effect, although the difference did not reach statistical significance for isoprenaline. The maximum relaxation responses to noradrenaline and isoprenaline were significantly lower in SHR than in normotensive rats, but both strains exhibited similar responses to the partial agonist BRL 37,344. We conclude that factors associated with bladder dysfunction, such as gender, age and hypertension, can be associated with impaired beta-adrenoceptor-mediated bladder relaxation. However, these alterations are not always consistent across various agonists, and the extent of the differences can be small. Therefore, we propose that beta-adrenoceptor dysfunction may contribute to the pathophysiology of such conditions, but is unlikely to be the only or even the major factor in this regard. We speculate that beta-adrenoceptor agonists may be effective in the treatment of bladder dysfunction under all of these conditions.