Abstract
Injections and infusions of histamine (0.5 to 5.0 μg/kg/min) increased blood flow (heat clearance technique) in the muscle of the left ventricle of the closed-chest chimpanzee, monkey and baboon. With the smallest doses used this increase occurred without changes in mean systemic blood pressure or in heart rate and is attributed, at least in part, to a vasodilator effect of histamine on the myocardial microcirculation. The responses to larger doses were modified by propranolol, a pressor effect of histamine being demonstrated. It is concluded that with these larger doses the increase in myocardial blood flow observed is the result of a direct effect of histamine on the myocardial vessels and on the myocardium, together with effects of released catecholamines. Histamine-induced increases in myocardial metabolic heat production were antagonised by propranolol.
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