Action of histamine and H, and H, blockers on the cardiopulmonary circulation

WOODS, JAMES R., JR., C. R. BRINKMAN, III, A. DANDAVINO, K. MURAYAMA, AND N. S. ASSALI. Action of histamine and H, and H, blockers on the cardiopulmonary circulation. Am. J. Physiol. 232(l): H73-H78, 1977 or Am. J. Physiol.: Heart Circ. Physiol. l(1): H73-H78, 1977. -Systemic and pulmonary hemodynamic responses to histamine were investigated in chronically instrumented unanesthetized nonpregnant ewes. Histamine was administered intravenously and into the pulmonary artery. The effects of the same doses of histamine were assessed following H1 and HZ receptor blockade and after ganglionic blockade. The effects of pentobarbital anesthesia on the histamine-induced pulmonary vascular changes were also monitored. Results indicate that intravenous histamine produces tachycardia, systemic hypotension, pulmonary hypertension, and reduced cardiac output. The pulmonary response could be modified significantly by pentobarbital anesthesia. When injected directly into the pulmonary artery histamine failed to elicit any circulatory response. Blockade of H, and HZ receptors, as well as autonomic ganglia, resulted in a comparable attenuation of the histamine circulatory response. It is concluded that a) central hemodynamic responses do not seem to be mediated through specific H, and HZ receptors; b) histamine-induced pulmonary vasoconstriction can be reversed by pentobarbital anesthesia, and c) the absence of circulatory response to intrapulmonary histamine administration suggests that whatever receptors that may exist in the pulmonary vascular bed are not necessary for the central hemodynamic effects.