DISTRIBUTION OF HISTAMINE IN THE CANINE AUTONOMIC NERVOUS SYSTEM

¹ Department of Pharmacology, College of Medicine, University of Iowa, Iowa City, Iowa

To study further the role of histamine as a sympathetic neurotransmitter released during active reflex vasodilatation, uptake of histamine-H³ into autonomic nerves and distribution of endogenous histamine in autonomic nerves were examimied. One hour after administration, histamine-H³ was found in highest concentration in postganglionic sympathetic nerves and in lower concentration in parasympathetic and motor nerves. The relative distribution of norepinephrine-H³, studied in an identical fashion, was similar to that of histamine-H³. Endogenous histamine concentration was also highest in postganglionic sympathetic nerves with values ranging from 10.1 to 17.3 µg/g. Lower amounts of histamine were found in parasympathetic and motor nerves. Pretreatment with the catecholamine depletor reserpine or the histamine depletor compound 48/80 failed to reduce histamine concentration in autonomic nerves. On the basis of pharmacologic evidence, neurogenic stores of histamine appeared to be nonmast cell in nature, and the integrity of these stores appears to be unrelated to the presence of norepinephrine. If the nerve trunk is assumed to represent a model for the nerve terminal, then these data on the distribution of histamine provide supportive evidence for the postulate that histamine is liberated from sympathetic histaminergic fibers during reflex vasodilatation.