Further examination of the effects of ageing on the adrenoceptor responsiveness of the rat vas deferens.
Age-related changes in presynaptic alpha 2-adrenoceptors were investigated in prostatic and epididymal portions of vasa deferentia from young adult (2-3 months) and old (24-29 months) Sprague-Dawley rats, using the alpha 2-selective agonists xylazine and clonidine. In prostatic portions the inhibitory effects of clonidine against the isometric contractions to single pulse field stimulation were complicated by a postsynaptic action in old animals, but in epididymal portions in the presence of nifedipine both xylazine and clonidine were 3 times less potent in old rats. However, there were no significant differences between young and old in the potency of xylazine at inhibiting the overflow of tritium or the isometric contraction evoked by 5 Hz stimulation for 3 min in tissues pre-incubated with [3H]noradrenaline. It is suggested that there is reduced responsiveness of presynaptic alpha 2-adrenoceptors in the vas deferens of old rats, but that this can only be demonstrated using a sensitive measure of the presynaptic potency of agonists: the isometric contraction to a single stimulus.
D000375:Aging; D000818:Animals; D003000:Clonidine / Q000494:pharmacology; D004558:Electric Stimulation; D066298:In Vitro Techniques; D007537:Isometric Contraction; D008297:Male; D009130:Muscle, Smooth / Q000502:physiology; D009543:Nifedipine / Q000494:pharmacology; D051381:Rats; D011919:Rats, Inbred Strains; D011941:Receptors, Adrenergic / Q000187:drug effects*; D014649:Vas Deferens / Q000187:drug effects / Q000502:physiology*; D014991:Xylazine / Q000494:pharmacology
D011941:Receptors, Adrenergic; D014991:Xylazine; D009543:Nifedipine; D003000:Clonidine