Endogenous corticoids and lung development in the fetal rabbit.

TLDR: In the rabbit, increases in plasma cortisol and nuclear receptor-cortisol complex are not temporally associated with the major events of lung development as in other species.

Abstract: Corticosteroid treatment of the fetus, which accelerates lung maturation, may mimic a modulating role of endogenous corticoids in normal development. To investigate this question, we determined the developmental pattern of plasma corticoids and their binding proteins in the rabbit, a commonly used species for studies of lung differentiation. The concentration of cortisol, the most potent glucocorticoid in the rabbit, was maximal at 23 days gestation (1.89 μg/dl), declining to 0.54 μg/dl at term (31 days). Levels of plasma corticosterone were always lower than those of cortisol. The adrenal content of corticoids, expressed per adrenal DNA or g BW, decreased during late gestation. Corticosteroid-binding globulin in fetal plasma decreased strikingly between day 23 (36 fig cortisol bound/dl) and day 31 (4.4 μg/dl; P < 0.001), whereas maternal levels increased about 10-fold during this time. Free cortisol in the fetus increased between 21 and 23 days (0.041 μg/dl) and then decreased somewhat until after day 29...