The ontogeny of pulmonary surfactant secretion in the embryonic green sea turtle (Chelonia mydas)

Pulmonary surfactant, consisting predominantly of phosphatidylcholine (PC), is secreted from Type II cells into the lungs of all air-breathing vertebr ates, where it functions to reduce surface tension. In mammals, glucocortic oids and thyroid hormones contribute to the maturation of the surfactant sy stem. It is possible that phylogeny, lung structure, and the environment ma y influence the development of the surfactant system. Here, we investigate the ontogeny of PC secretion from cocultured Type II cells and fibroblasts in the sea turtle, Chelonia mydas, following 58, 62, and 73 d of incubation and after hatching. The influence of glucocorticoids and thyroid hormones on PC secretion was also examined. Basal PC secretion was lowest at day 58 (3%) and reached a maximal secretion rate of 10% posthatch. Dexamethasone ( Dex) alone stimulated PC secretion only at day 58. Triiodothyronine (T-3) s timulated PC secretion in cells isolated from days 58 and 73 embryos and fr om hatchling turtles. A combination of Dex and T-3 stimulated PC secretion at all time points.