Senescent beagle coronary arteries in response to catecholamines and adrenergic nerve stimulation

With advancing age from 2 to 12 years, relaxations induced by norepinephrine and epinephrine were suppressed or reversed to contractions in large and medium-size coronary arteries isolated from beagles. Norepinephrine-induced contractions in the senescent beagle arteries treated with propranolol were greater than those in the young beagle arteries and were inhibited by prazosin but not by yohimbine. Relaxant responses to isoproterenol were less in the arteries from old beagles than in the young beagle arteries. The magnitude of relaxations induced by norepinephrine and epinephrine was greatest in small arteries from old beagles, followed by medium and large arteries, in that order. Transmural electrical stimulation tended to produce a contraction in the old beagle arteries and a relaxation in the strips from young beagles. It appears that alpha 1 adrenoceptor function increases with advancing age in beagle coronary arteries of large and medium sizes, and beta receptor function declines. Vasoconstriction mediated by alpha 1 receptors is postulated to be related inversely to the distance from the coronary orifice in senescent beagles, and vice versa with vasodilatation mediated by beta receptors.