MODULATION BY ACETYLCHOLINE OF ADRENERGIC TRANSMISSION IN THE RABBIT EAR ARTERY

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Abstract
Low concentrations of acetylcholine (4 × 10−11 and 1 × 10−10 M) increase the vasoconstrictor response of the isolated ear artery of the rabbit to stimulation of the periarterial sympathetic nerves. Higher concentrations (4 × 10−8 M and greater) decrease the response. Low concentrations of acetylcholine (1 × 10−11 and 1 × 10−10 M) increase the stimulation‐induced efflux of radioactivity from artery segments previously incubated with [3H]‐noradrenaline. Higher concentrations (3 × 10−8 M and greater) decrease the efflux. Neither atropine nor hexamethonium affects the facilitatory action of low concentrations of acetylcholine on adrenergic transmission in the rabbit ear artery. Atropine antagonizes the inhibitory effect of higher concentrations of acetylcholine on adrenergic transmission.