title: The effect of age on the sensitivity of pre- and postsynaptic alpha-adrenoceptors to agonists and antagonists in the rat.
abstract: Age-related changes in presynaptic alpha-2 and postsynaptic alpha-1 adrenoceptors have been determined using the rat isolated vas deferens and the thoracic aorta, respectively. The IC50 values of clonidine, B-HT 933 and UK 14,304 for inhibition of the electrically evoked contractions of the vas deferens were significantly higher in 50 week old rats when compared with rats of 5 weeks. Similarly, EC50 values for the contraction of the thoracic aorta by noradrenaline, methoxamine and phenylephrine were significantly increased in 50 week old rats compared with 5 week old rats. No age-related changes in the potency of the selective alpha-2 adrenoceptor antagonists yohimbine and Wy 26392 were detected in the vas deferens. Similarly, there were no age-related changes in the alpha-1 adrenoceptor antagonist potency of indoramin or prazosin on the aorta. The results of the present study suggest that the potency of both alpha-1 and alpha-2 adrenoceptor agonists, as measured by their respective EC and IC50 values decreases with increasing age.
mesh_terms: D000316:Adrenergic alpha-Agonists / Q000494:pharmacology*; D000317:Adrenergic alpha-Antagonists / Q000494:pharmacology*; D000375:Aging; D000818:Animals; D001013:Aorta, Thoracic / Q000187:drug effects; D066298:In Vitro Techniques; D008297:Male; D009130:Muscle, Smooth / Q000187:drug effects*; D009131:Muscle, Smooth, Vascular / Q000187:drug effects*; D011189:Potassium Chloride / Q000494:pharmacology; D051381:Rats; D011919:Rats, Inbred Strains; D011942:Receptors, Adrenergic, alpha / Q000187:drug effects / Q000502:physiology*; D013569:Synapses / Q000187:drug effects*; D014649:Vas Deferens / Q000187:drug effects
chemical_list: D000316:Adrenergic alpha-Agonists; D000317:Adrenergic alpha-Antagonists; D011942:Receptors, Adrenergic, alpha; D011189:Potassium Chloride