Impaired surfactant production in cretin lambs

Midgestation ovine fetal thyroidectomy resulted in profound congenital hypothyroidism and severe respiratory distress at term. Amniotic fluid obtained at delivery revealed low lecithin: sphingomyelin (L:S) ratios in all animals with a predominantly acidic phosphatide pulmonary phospholipid profile. Surfactant was diminished in the lung effluent of cretins at birth as compared with normal lambs. The acidic phosphatides and low L:S ratios persisted in the pharyngeal aspirates of the cretin lambs following attempted air breathing and the onset of severe respiratory distress. Conversely, normal lambs released considerable surfactant at birth that contained nonacidic phosphatides dominated by dipalmitoyl lecithin and yielding strongly positive L:S ratios. Comparative histologic studies revealed poor alveolar differentiation in certain lambs and persistence of the midgestation canalicular stage of lung development.