Abstract
In helically cut stripes of monkey coronary arteries of different sizes, contracted with prostaglandin F2 alpha or K+, responses to norepinephrine, epinephrine, isoproterenol, and transmural electrical stimulation were compared. In response to norepinephrine, only contractions were induced in large arteries, contractions at low concentrations and relaxations at high concentrations in medium-size arteries, and only relaxations in small arteries. Epinephrine produced a greater contraction than norepinephrine in the arteries. Relaxant effects of isoproterenol were greater in small and medium-size arteries than in large arteries. Transmural electrical stimulation applied at frequencies of 2,5, and 20 Hz to strips of medium-size arteries produced a frequency-dependent contraction that was reversed to a relaxation following treatment with phentolamine. Propranolol abolished the relaxation. In strips of dog coronary arteries of medium size, transmural stimulation elicited only a relaxation which was suppressed or reversed to a contraction by propranolol. Dog arteries of this size responded to norepinephrine and epinephrine with only a relaxation. It may be concluded that the quantity or the susceptibility of alpha-adrenoceptors is in the order of large greater than or equal to medium greater than small-size arteries from monkeys, whereas that of beta-adrenoceptors is in the order of medium = small greater than large arteries. Monkey coronary arteries appear to respond to endogenous and exogenous norepinephrine with a contraction more consistently than dog coronary arteries.
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