Sympathetic vasodilatation in the rabbit ear.

Changes in the blood content of a 1 cm(2) portion of the intact rabbit's ear were studied with transillumination and a photocell. Stimulation of the post-ganglionic sympathetic nerves produced a decrease in blood content, attributable to vasoconstriction, followed by an increased blood content, attributable to vasodilatation. The vasodilatation was enhanced by eserine and decreased by atropine. Guanethidine abolished the vasoconstriction but not the vasodilatation. After the ganglion had been decentralized by degeneration of the pre-ganglionic sympathetic nerves the vessels had an increased sensitivity to acetylcholine and the vasodilatation in response to sympathetic stimulation was enhanced. It is concluded that sympathetic stimulation results in the liberation of acetylcholine which causes vasodilatation.