title: The effect of aging on alpha-adrenoceptors and their responses in rabbits.
abstract: The effects of age on alpha-adrenoceptor responses, sensitivity and number were studied in rabbits aged from 1 to 36 months. Three types of investigation were carried out: conscious animal studies, isolated tissue studies and radioligand binding studies. Specific [3H]-prazosin binding decreased with age in both spleen and heart suggesting that the number of alpha 1-receptors declined at least in the tissues studied. The specific binding of [3H]-clonidine to spleen membranes and [3H]-yohimbine to platelets was not affected by age. In vitro responsiveness to alpha-adrenoceptor agonists decreased with age in abdominal aorta and renal artery, while the affinity of adrenoceptors for prazosin (pA2) was not altered. The decrease may be non-specific as responses to potassium were also altered. No change in alpha 2-adrenoceptor mediated platelet aggregation was observed. No change in pressor or depressor responses to full adrenoceptor agonists or to antagonists was observed in vivo. However, responses to clonidine, which is a partial agonist at alpha 1-adrenoceptors, were decreased. While aging influenced alpha-adrenoceptor subtypes differently, there was no direct relation between functional changes and number of receptors.
mesh_terms: D000375:Aging; D000818:Animals; D001012:Aorta, Abdominal / Q000187:drug effects / Q000254:growth & development*; D001794:Blood Pressure; D004837:Epinephrine / Q000097:blood; D006339:Heart Rate; D008297:Male; D009638:Norepinephrine / Q000097:blood / Q000494:pharmacology*; D010656:Phenylephrine / Q000494:pharmacology*; D010974:Platelet Aggregation; D011311:Pressoreceptors / Q000187:drug effects / Q000502:physiology; D011817:Rabbits; D011942:Receptors, Adrenergic, alpha / Q000187:drug effects / Q000502:physiology*; D012077:Renal Artery / Q000187:drug effects / Q000254:growth & development*
chemical_list: D011942:Receptors, Adrenergic, alpha; D010656:Phenylephrine; D009638:Norepinephrine; D004837:Epinephrine