Comparison of Adrenergic Mechanisms in an Elastic and a Muscular Artery of the Rabbit

Abstract

Elastic and muscular arteries are known to differ in function and in the magnitude of their response to vasoconstrictor influences. With the isolated thoracic aorta and ear artery of the rabbit as representative arteries, the morphological, physiological, and pharmacological correlates of these differences have been sought among their presynaptic adrenergic mechanisms. The adrenergic nerve plexus in the ear artery is wider and the nodes are denser than they are in the aorta. There is some evidence consistent with the hypothesis that the thicker the plexus, the greater the reuptake of released transmitter, the smaller the transmitter overflow, and the lower the efficiency of uptake of exogenous norepinephrine. Measurements of fractional release of tritiated norepinephrine suggest that qualitative differences in the adrenergic transmitter storage and release mechanisms may exist between the two vessels. Thus the considerable functional difference between the two vessels is in part, at any rate, a consequence of adrenergic mechanisms which differ both quantitatively and qualitatively from each other.