Effect of histamine on the pulmonary circulation in dogs.

Histamine was administered to dogs by the intravenous route near the right atrium in doses of 9.6 to 19 y/Kg. body weight. It produced a severe drop in systemic blood pressure, negligible changes in heart rate and respiration, usually a fall in cardiac output and no change in left atrial or pulmonary artery wedge pressure. The pulmonary artery pressure showed an initial rise and then a fall following the drop in systemic blood pressure. Pulmonary arteriolar resistance followed the changes in cardiac output. There appeared to be no consistent evidence of pulmonary vascular constriction following the injection of histamine in the doses used in this study.