Histamine, histamine antagonists and regional blood flow.

The effects of mepyramine, a selective histamine H1-receptor antagonist, and metiamide, a selective histamine H2-receptor antagonist, have been determined on the cardiovascular response to intravenous infusions of a large dose of histamine, 1 X 10(-7) mol/kg/min. Pretreatment with either mepyramine, 2.5 X 10(-6) mol/kg, or metiamide, 2 X 10(-6) mol/kg/min, had no significant effect on the fall in blood pressure or fall in total peripheral resistance during histamine infusion. Pretreatment with mepyramine, 2.5 X 10(-6) mol/kg, and metiamide, 2 X 10(-6) mol/kg/min, abolished the fall in blood pressure and total peripheral resistance during infusion of histamine. Histamine-induced vasodilatation in the stomach was unaltered by pretreatment with mepyramine but abolished by pretreatment with metiamide. Histamine-induced coronary vasodilation was reduced slightly by pretreatment with mepyramine and substantially by pretreatment with metiamide. Coronary vasodilatation was abolished by treatment with mepyramine and metiamide.