Influence of Angiotensin II on the Systemic and Pulmonary Circulations of Intact Anesthetized Dogs

Abstract

Initial hemodynamic studies of angiotensin I1 were primarily concerned with the influence on arterial blood pressure (1-5). Our interest in the venous system and recognition of its importance in regulation of the circulation prompted these studies to define more clearly the effects of angiotensin I1 on the veins (6, 7). It was found that in proper doses angiotensin I1 can constrict systemic precapillary (resistance) vessels without affecting equally postcapillary (capacitance) vessels. Although some studies of the effects of angiotensin I1 on the pulmonary circulation have been reported (8, 9), the effect on small pulmonary veins of intact dogs has not been previously studied. I n these experiments simultaneous pressures and volume flow measurements in many sites of the pulmonary and systemic circulations were olbtained in intact dogs during an intravenous infusion of angiotensin I1 to learn whethler or not the hemodynamic effects of angiotensin I1 on the pulmonary and systemic venous circulations differ.Material and Methods. Fifteen mongrel dogs weighing 15.0-18.2 kg were lightly anesthetized with urethane (1.5 g/kg) and loosely taped supine to a fluoroscopic table. After the trachea was intubated, 100% oxygen was administered into the lendotracheal tube via a plastic catheter at a rate of 2-2.5 1itersJmin in order to assure that the animals were not hypoxic.Catheters were placed in the left atrium and a small pulmonary vein of the lower lobe 1 Supported by grants HE-06769 from the National Heart Institutes of the US. Public Health Service; the Rudolph Matas Memorial Fund for the Kate Prewitt Hess Laboratory; and the Rowell A. Billups Fund for Research in Heart Disease.of the left lung by the transseptal technique ( l o ) . The pulmonary vein catheter had an internal diameter of 0.5 mm and an external diameter of 0.91 mm.Previous studies showed that this catheter did not significantly alter the pressure in the pulmonary vein ( 11 ) . Catheters were also placed in the main pulmonary artery, right femoral artery, right atrium, and a small vein of the left leg. Stathani strain gauge transducers (P23Db) were used to monitor pressures which were recorded with an Electronics for Medicine research recorder. A catheter for infusion of angiotensin I1 was placed in the right femoral vein.After control pressure tracings were recorded, cardiac output and pulmonary blood volume were determined by the indicator dilution technique using indocyanine green (Cardio-Green) ( 12). The stroke volume and pulmonary and systemic vascular resistances were calculated by methods previously described (13). The pulmonary venous resistance was calculated by the formula: Pulmonary venous resistance = PVS -PLA/CO, where PVS is pressure in small pulmonary vein, PLA is left atrial pressure and CO is cardiac output. Lead I1 of the electrocardiogram, heart rate and respiratory rate were also monitored.After a "steady state" was reached for 10-15 min, as indicated by relatively constant cardiac output and pressures, angiotensin I1 ( 5 pg/min) was i...