Combined effects of corticosteroid, thyroid hormones, and beta-agonist on surfactant, pulmonary mechanics, and beta-receptor binding in fetal lamb lung.

We studied the interactions of corticosteroids, thyroid hormones, and beta-agonist on surfactant phospholipids, pulmonary mechanics, and beta-receptor binding in fetal lambs. We infused cortisol (450 micrograms/h for 48 h), thyrotropin-releasing hormone (TRH) (25 micrograms/h for 48 h), and ritodrine (1.3 micrograms/kg/min for 24 h) independently, and in double (cortisol plus beta-agonist, cortisol plus TRH), and in triple (cortisol plus TRH plus beta-agonist) combinations into chronically catheterized fetal lambs between 0.88 and 0.90 gestation. Infusion of the triple combination of cortisol plus TRH plus beta-agonist resulted in a 20.9-fold increase in the saturated phosphatidylcholine content of fetal lung lavage, in a 5.8-fold increase in the saturated phosphatidylcholine content of whole fetal lung, and in a 13.3-fold increase in the saturated phosphatidylcholine content of fetal tracheal fluid. In addition, lung stability to inflation increased 3-fold, and lung stability to deflation increased 8-fold. The increases in the saturated phosphatidylcholine content of fetal lung lavage and tracheal fluid were greater than the effects of each hormone acting independently, or in the double combinations. The beta-receptor maximal binding capacity was increased 30% by the combined infusion of cortisol and TRH. In addition, the maximal binding capacity after cortisol plus TRH plus beta-agonist infusion was 54% greater than the maximal binding capacity after beta-agonist infusion.(ABSTRACT TRUNCATED AT 250 WORDS)