title: The effects of ageing on vascular alpha-adrenoceptors in pithed rat and rat aorta.
abstract: In the pithed rat preparation in the absence of captopril, the pressor potency of the alpha 2-adrenoceptor agonist xylazine was significantly reduced in 24 month old rats. This difference between young (3-6 month) and old rats in xylazine potency was eliminated by captopril (5 mg kg-1), which caused a greater shift in xylazine potency in young than in old rats. In the rat isolated aorta, the contractile potency both of the alpha 1-adrenoceptor agonist phenylephrine and of 5-hydroxytryptamine were significantly reduced in 24 month old rats. Hence, both in pithed rats and in the rat isolated aorta, the contractile potency of alpha-adrenoceptor agonists is reduced in aged rats, but the altered responsiveness is not at the level of the alpha-adrenoceptor. In the pithed rat, alpha 2-adrenoceptor responsiveness is reduced with ageing probably due to decreased levels of angiotensin II, and in the rat aorta alpha 1-adrenoceptor responsiveness is reduced with ageing, but since responsiveness to 5-HT is also reduced, this may be a post-receptor change in responsiveness.
mesh_terms: D000316:Adrenergic alpha-Agonists / Q000494:pharmacology; D000375:Aging / Q000502:physiology*; D000818:Animals; D001011:Aorta / Q000187:drug effects / Q000502:physiology; D001794:Blood Pressure / Q000187:drug effects; D003655:Decerebrate State; D004983:Ethanolamines / Q000494:pharmacology; D007537:Isometric Contraction / Q000187:drug effects; D008297:Male; D009119:Muscle Contraction / Q000187:drug effects; D009131:Muscle, Smooth, Vascular / Q000187:drug effects / Q000502:physiology*; D051381:Rats; D011919:Rats, Inbred Strains; D011942:Receptors, Adrenergic, alpha / Q000502:physiology*; D014991:Xylazine / Q000494:pharmacology
chemical_list: D000316:Adrenergic alpha-Agonists; D004983:Ethanolamines; D011942:Receptors, Adrenergic, alpha; D014991:Xylazine; C016980:amidephrine