HEMODYNAMIC-RESPONSES TO ANGIOTENSIN-II IN THE NEWBORN LAMB

Angiotensin II is known to increase both pulmonary and systemic arteri olar tone in adult animals. Its influence on these vascular beds short ly after birth is less well understood. Therefore, we studied the effe cts of infusions of angiotensin II (0.1-mu-g/kg/min) on pulmonary and systemic hemodynamics in 13 anesthetized newborn lambs. Systemic vascu lar resistance increased significantly from a mean of 0.079 +/- 0.03 t o 0.094 +/- 0.04 mm Hg/ml/min during angiotensin II infusion while the mean pulmonary vascular resistance was unchanged at 0.024 +/- 0.01 mm Hg/ml/min. Interestingly, cardiac output increased significantly by 1 8.9% during angiotensin II infusion. During hypoxemia produced by vent ilating with 10-12% oxygen, the responses to angiotensin II infusion w ere similar to those obtained during normoxia. The absence of an effec t on pulmonary vascular resistance and the increase in cardiac output were not predicted based on results reported for older animals. The me chanisms responsible for these age-related differences are unknown. Ou r findings have implications regarding the potential clinical use of a ngiotensin II as a modulator of blood pressure in the hypotensive newb orn.