Indirect adrenergic effect of histamine in cat cerebral arteries

Histamine (10(-4) M) induced an increase in the tritium outflow from cat cerebral arteries preloaded with 3H-noradrenaline. Pretreatment with reserpine (3 mg/kg, i.p., total dose) or removal of both superior cervical ganglia two weeks before the experiment abolished that increase. The presence of cocaine or diphenhydramine also prevented the rise in tritium efflux induced by histamine. Histamine (10(-8 M to 10(-3) M) elicited dose-dependent contractions in the isolated posterior communicating artery of the cat which were reduced in the presence of diphenhydramine at all doses except the highest three. The addition of phentolamine to the bath decreased the contractile responses at the doses lower than 10(-6) M. Pretreatment with reserpine or removal of both superior cervical ganglia also diminished the responses at doses of histamine below 10(-6) M and 10(-5) M, respectively. When cocaine was added to the bath there was a decrease in the contraction elicited at all doses except the last one. These results suggest the existence of an indirect adrenergic mechanism in the contractile response to histamine in cat cerebral arteries.