SYMPATHETIC VASODILATATION IN THE DOG'S PAW

¹ Department of Pharmacology, University of Minnesota, Minneapolis, Minnesota

Experiments were performed in the dog's paw and gracilis muscle perfused at constant blood flow. Sympathetic stimulation (20 cps) of the lumbar chain after bretylium caused vasodilatation in the paw equivalent to maximal va. sodilatation produced by methacholine injected intraarterially in the paw. In the muscle, however, under similar conditions, sympathetic vasodilatation was significantly less than the maximal vasodilator effect. Atropine administered intravenously reduced the vasodilator response obtained for short-duration stimulation (5-10 sec) but not for long-duration stimulation (30-60 sec) in the paw, yet it blocked almost completely vasodilatation produced by methacholine. Antihistamines administered intravenously also appeared to reduce the response to short-duration stimulation, but with considerable variation between experiments. The combination of atropine and antihistamine administration resulted in the significant reduction of the response to both the short- and long-duration stimulations, which suggested that acetylcholine and histamine might be involved in sympathetic vasodilatation in the cutaneous vascular bed. Activation of the release of bradykinin by sympathetic stimulation in the paw did not appear to occur.