Abstract
Summary
Metarterioles are not currently thought by most investigators to either (i) be able to narrow their vascular walls to the point of occlusion in response to circulating vasoactive substances; or (ii) contract in a dose-dependent manner to vasoactive agents. In vivo experiments, using the rat mesentery and a high magnification (up to 6500X) image-splitting television microscope recording system, were designed to test these tenets. The results clearly and quantitatively demonstrate that metarterioles, at least in rat mesentery, not only contract to complete lumen occulsion in a graded, dose-dependent manner to catecholamines and neurohypophyseal hormone peptides but respond to extremely low (physiologic ?) doses of these substances.
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