Ultrastructural and biochemical evidence of glycogen in the developing lung of the chick embryo: possible contribution to surfactant.

1. Glycogen was identified ultrastructurally in undifferentiated type-II cells of the lung of the day 16 chick embryo. 2. By 4 days after hatching, glycogen in type-II cells could not be observed, although lungs were actively secreting surfactant. 3. Biochemical measurements of pulmonary glycogen revealed a depletion during days 14-20 of incubation, corroborating ultrastructural data. 4. Using lung slices, 14C-glucose was incorporated in vitro into pulmonary surfactant phospholipids at a high rate in day 14 embryos, and a significantly lower rate on day 19. 5. Hypophysectomy resulted in sub-normal initial accumulation of pulmonary glycogen on day 14 of development, but did not alter the depletion pattern after day 16. 6. Thus, glycogen stores may contribute to avian embryonic pulmonary surfactant, and accumulation of early stores may be under hormonal control.