Synergistic Effect of Triiodothyronine and Dexamethasone on Male and Female Fetal Rat Lung Surfactant Synthesis

It has previously been reported that morphologic and functional indices of fetal lung maturation are delayed in male rabbit fetuses, and these differences cannot be overcome by glucocorticoid treatment. Since thyroid hormone also stimulates surfactant production we have studied the effects of triiodothyronine (T3) and dexamethasone on saturated phosphatidylcholine (SPC) synthesis by day 20 male and female rat lung. Control male lung slices incorporated significantly less 3H-choline into SPC than females; surgery on day 17 markedly stimulated 3H-choline incorporation into SPC by both sexes, but the sex difference persisted. The optimal dose of T3 inhibited SPC synthesis by both sexes while dexamethasone was stimulatory. When T3 and dexamethasone were given together they had a greater effect than that of dexamethasone or T3 alone. Based on these results we conclude that the male deficit in pulmonary surfactant production may be overcome by the synergistic effects of T3 and dexamethasone.