AJP - Heart and Circulatory Physiology, Vol 253, Issue 6 1566-H1572, Copyright © 1987 by American Physiological Society

ARTICLES

Age-related changes in adrenergic vasoconstrictor responses of the rat hindlimb

R. K. Handa and S. P. Duckles
Department of Pharmacology, College of Medicine, University of California, Irvine 92717.

Vascular adrenergic responses were examined in the hindlimb perfused with blood at constant flow using pentobarbital-anesthetized male Fischer 344 rats aged 6, 12, 20, and 24 mo. The increase in hindlimb perfusion pressure to lumbar sympathetic nerve stimulation was significantly smaller in 20- and 24-mo-old rats than in younger animals, whereas vasoconstrictor responses to intraarterial administration of norepinephrine, L-phenylephrine, and methoxamine were reduced only in the 24-mo-old animals. Thus neurogenic vasoconstriction in the hindlimb is reduced at 20 mo of age, whereas there is a more generalized postjunctional loss of adrenergic responsiveness at 24 mo. In the presence of the beta-adrenoceptor antagonist, propranolol, vasoconstrictor responses to exogenous norepinephrine did not differ when 12- and 20-mo-old animals were compared. Furthermore, in the presence of propranolol the nerve-mediated rise in hindlimb perfusion pressure also did not differ in 12- and 20-mo-old rats. Blockade of neuronal norepinephrine uptake with cocaine produced a greater potentiation of vasoconstrictor responses to both nerve stimulation and exogenous norepinephrine in the older rats. Therefore, the reduced nerve-mediated vasoconstriction in 20-mo-old rats may be due to neuronal activation of beta-adrenoceptors as well as enhanced neuronal norepinephrine reuptake.

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