Age-related change in alpha-adrenergic responsiveness of the urinary bladder of the rat is regionally specific.

The effects of age on the responsiveness of the body of the urinary bladder and base of the bladder to alpha-adrenergic agonists were studied. Regions of the bladder were isolated from Fischer 344 rats, ages 7, 16, and 27 months. Maximum isotonic contractions elicited by potassium chloride (KCl) in both regions of the bladder were unaffected by age. In the bladder body there was an age-related increase in the maximum contraction elicited by phenylephrine, norepinephrine and clonidine. No such alteration in responsiveness was observed in the base of the bladder with age. The ED50 values of all three agonists were unchanged with age in both regions of the bladder. The pA2 values of prazosin and yohimbine were approximately 8.5 and 6.0, respectively, in the body of the bladder, and these values were not altered by age. Thus, it is concluded that an age-related increase occurs in the responsiveness of the body of the bladder to alpha-adrenergic activation and that these changes are mediated by alpha 1-adrenoceptors.