The influence of age on isometric and isotonic rat detrusor contractions.

BACKGROUND Reductions in detrusor shortening velocity and detrusor contractility have been observed in association with aging. The reasons for these changes are unclear. METHODS We examined the isometric and isotonic responses of detrusor, taken from the bladder body, to adenosine 5'-triphosphate (ATP), noradrenaline (NA), serotonin, and acetylcholine (Ach) in vitro, using bladders from young (30 days) and old (365 days) Sprague-Dawley rats, to determine whether there were any significant age-related differences. RESULTS Isometric contractions with ATP at doses of 10(-3) to 10(-2) molar concentrations produced greater contractile forces in old rats when compared to young rats (p = .0136 at 10(-2) mole of ATP). Isotonic contractions at similar concentrations also produced significant differences between the young and the old rats, the latter being faster (p = .0225). Isometric contraction with noradrenaline produced significant differences between young and old rats, the latter being stronger. This became apparent at 10(-4) molar concentration of noradrenaline (p = .0043). Isometric contractions with serotonin also produced significantly greater contractions in the old rats when compared to young rats. The differences became apparent at 10(-4) molar concentration of serotonin (p = .045). There were no age-related differences in isotonic and isometric contractile responses to acetylcholine in the doses used in our experimental setup. CONCLUSIONS Age-related differences in isometric function were detected in response to ATP, NA, and serotonin. Differences in isotonic function were only found in response to ATP and Ach.