Age-related changes in the reactivity of postsynaptic adrenoceptors in the rat vas deferens: differences between the...

1. Age-related changes in the reactivity of postsynaptic alpha-adrenoceptors of isolated portions (epididymal and prostatic) and in whole vas deferens have been studied using 4, 12 and 20 month-old rats. 2. The pD2 values for adrenaline-induced contractions were reduced in the epididymal portion and whole vas deferens of middle-aged and old animals, but not in the prostatic portion. No age related change to phenylephrine or clonidine sensitivity was observed. 3. pA2 values of prazosin and yohimbine were not changed by aging in any preparation. Phentolamine pA2 values were reduced in the epididymal portion and in the whole vas deferens when adrenaline, but not when phenylephrine concentration-response curves were displaced by the antagonist. The mean pA2 value of yohimbine (6.78) indicates that this antagonist blocks alpha(1)-adrenoceptors in the rat vas deferens. 4. The data presented here suggest that age-related decreases in the sensitivity to adrenaline and phentolamine (when measured by displacing adrenaline concentration-effect curves) in the whole vas deferens are probably due to a variation in the proportion of alpha(1)-adrenoceptor subtypes in the epididymal portion of the rat vas deferens.