Saturated phosphatidylcholine secretion and the effect of natural surfactant on premature and term lambs ventilated for 2 days.

Lambs prematurely delivered by cesarean section and term lambs were supported on ventilators and studied over a period of 2 days. Sequential measurements of ventilatory requirements, lung compliance, and arterial pH, pO2, and pCO2 values documented the course of the lung disease. In five premature lambs the pCO2 increased to 77 +/- 5 mm Hg (mean +/- SE) by 40.5 +/- 3.1 hr of age, at which time treatment with 50 mg natural sheep surfactant lipid/kg body weight by tracheal instillation resulted in improvements in pH, pO2, and pCO2 measurements. Radiolabeled palmitic acid was injected systemically after birth to detect the appearance of endogenously synthesized and secreted saturated phosphatidylcholine in sequential airway samples. Radiolabeled saturated phosphatidylcholine specific activity increased in a relatively linear fashion for about 30 hr in lambs treated with natural surfactant, in untreated premature lambs, and in term lambs. The study demonstrates that surfactant therapy can improve the ventilatory status of premature lambs despite many hours of ventilation for pulmonary immaturity. The overall kinetics of secretion of saturated phosphatidylcholine is similar in lambs with and without pulmonary immaturity.