ACTIVE REFLEX VASODILATATION INDUCED BY VERATRINE AND DOPAMINE

¹ Department of Pharmacology, University of Michigan Medical Center, Ann Arbor, Michigan

The nature of the reflex dilatation elicited by veratrine and dopamine has been studied in the innervated hindquarter preparation of the dog perfused at constant blood flow with a Sigmamotor pump. Intravenous injection of either drug evokes a large reflex vascular dilatation which can be aboiished by hindquarter sympathectomy. The magnitude of the reflex dilatation exceeds the loss in vascular tone produced by interruption of the sympathetic pathways to the hindquarters. A large proportion of the reflex can be antagonized by the administration of antihistamines. From these and closely related studies, it is concluded that the reflex is partially active in character and is mediated by the neurogenic release of histamine from nerve fibers distributed to the periphery over the lumbar sympathetic outflow.