The cardiovascular response to dimaprit, a selective histamine H2-receptor agonist

1 The cardiovascular responses to dimaprit (S-(3-dimethylaminopropyl) isothiourea) a selective histamine H2-receptor agonist have been studied in anaesthetized cats, dogs, rats and rabbits. 2 Dimaprit lowered systemic arterial blood pressure in all species whether given by intravenous injection or by continous infusion. Intra-arterial injections or infusions caused vasodilatation in the femoral vascular bed. 3 In the cat, continuous intravenous infusions of dimaprit lowered blood pressure without any significant change in heart rate or cardiac output. The fall in blood pressure was thus due to a decrease in peripheral vascular resistance. 4 Dimaprit, given intravenously, increased coronary and gastric blood flows and there were associated marked reductions in vascular resistance. Small reductions in vascular resistance occurred in skeletal muscle, in the intestine and the kidneys. 5 The histamine H2-receptor antagonists, metiamide and cimetidine, antagonized the depressor and vasodilator responses to dimaprit.