Analysis of Ouabain-Induced Contractions in Isolated Coronary Arteries

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Abstract
Contractile responses to ouabain in helical strips of dog and monkey coronary arteries were investigated. Ouabain (5 .times. 10-8 to 5 .times. 10-6 M) caused a dose-related contraction in dog and monkey arteries; the response of monkey coronary arteries was significantly greater. In dog coronary arteries, contractile responses to high concentrations of ouabin were potentiated by treatment with propranolol. In the arteries contracted with ouabain, the addition of phentolamine caused a relaxation. Contractile responses of dog coronary arteries to ouabain were markedly suppressed by exposure to Ca2+-free media or by treatment with verapamil. Reduction of external concentration of K+ or lowering the temperature of bathing media did not selectively influence the ouabin-induced contraction. These results suggest that ouabain-induced contractions of dog coronary arteries are associated mainly with an increase in the Ca2+-influx, which does not result from an inhibition of the Na+, K+-activated ATPase nor from an activation of .alpha. adrenoceptors by noradrenaline released from adrenergic nerves. Ouabain in high concentrations seems to liberate noradrenaline from adrenergic nerves, which preferentially activates .beta. adrenoceptors in dog coronary artery.