Effect of norepinephrine on isolated coronary artery of normal and myocardial infarcted pigs.

The effect of norepinephrine, the adrenergic neurotransmitter, on isolated coronary arterial strips of normal and myocardial infarcted pigs was investigated with the view to characterize the nature of adrenoceptors in this tissue. In small, as well as large, isolated coronary arterial strips of normal pigs norepinephrine produced relaxation which was found to be mediated through activation of beta 1-adrenoceptors. While alpha adrenoceptors were also found to be present in large coronary arteries, they were absent in the small coronary arteries. In isolated coronary arterial strips dissected out from pigs in which myocardial infarction was induced, norepinephrine produced contraction, its alpha-adrenergic effect. This could be due to arterial hypoxia and/or sensitization of alpha-receptors present in the coronary artery.