Abstract

Further support for the role of histamine as the neurotransmitter released during active reflex vasodilatation was sought by determining the effect of chronic denervation on histamine levels in skeletal muscle and the presence of histamine in vascular smooth muscle. Chronic denervation of dog gracilis muscle resulted in a slight increase in histamine concentration in denervated muscle when compared to sham-operated muscle, one, two and three weeks after denervation. In all but one of the seven arteries and veins (splenic, brachial, gracilis, femoral, renal, mesenteric, tibial) studied, highest average histamine concentrations were found in veins. In general, removal of adventitia from arteries and veins failed to lower histamine concentration suggesting that histamine is not concentrated in the adventitial layer. The presence of histamine in arterial walls is consistent with the proposed release of histamine during active reflex vasodilatation. However, the failure of histamine levels to fall after chronic denervation suggests one or more of the following: 1) loss of neurogenic histamine is masked by increased non-neurogenic histamine; 2) neurogenic histamine contributes only a small fraction of the total histamine pool; or 3) histamine may be contained in a postsynaptic storage site postulated to be controlled by activity of adrenergic nerves.