Indirect adrenergic effect of histamine in cat right atrium

Superfused cat atrial fragments preincubated with [3H]noradrenaline showed an increased tritium release under the action of 10(-4) M histamine. Reserpine pretreatment of the animals, external calcium removal or the presence of 10(-6) M cocaine, 10(-6) M diphenhydramine or 10(-3) M colchicine in the superfusion medium significantly reduced this effect of histamine (10(-4) M). Diphenhydramine (10(-5) M) also decreased the release of tritium brought about by 10(-6) M tyramine. These results suggest that histamine may release neurotransmitter from cardiac sympathetic nerve endings by means of an exocytotic process and needs to enter the nerve terminals through the amine uptake system.