PRENATAL GLUCOCORTICOID AND T-4 EFFECTS ON LUNG MORPHOLOGY IN PRETERMLAMBS

Prenatal glucocorticoid plus T-4 treatment of fetal sheep results in i mprovements in oxygenation, gas exchange, lung mechanics, and lung vol umes after preterm delivery. We have evaluated the morphometric change s in the lungs of lambs exposed to betamethasone and T-4 48 h before p reterm delivery at 121 and 135 d gestation and related those changes t o the physiologic improvements in lung function. The lungs used for th e morphometric studies were from lambs with postnatal physiologic resp onses similar to those of the entire group of lambs reported previousl y (16). At both 121 and 135 d gestation, lung gas volumes and fixed ti ssue volumes increased, the percent of collapsed (nonaerated) parenchy ma decreased, and the percent of perilobular connective tissue decreas ed with both gestational age and prenatal hormone exposure. Alveolar s ize, as estimated by mean linear intercept length, did not change with gestation or hormone exposure, but there was a decrease in alveolar w all thickness with advancing gestation and at each gestation with horm one exposure. The major anatomic effect of prenatal hormone exposure w as a decrease in alveolar wall thickness and an increase in aerated pa renchyma, effects that were consistent with the physiologic improvemen ts in postnatal lung function.