Endogenous corticoids and lung development in the fetal XXXX .

@entity2819 @entity95 @entity701
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 @entity95 , a commonly used species for studies of lung differentiation. The concentration of @entity701 , the most potent glucocorticoid in the @entity95 , was maximal at 23 days gestation (1.89 micrograms/dl), declining to 0.54 micrograms/dl at term (31 days). Levels of plasma @entity2819 were always lower than those of @entity701 . 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 micrograms @entity701 bound/dl) and day 31 (4.4 micrograms/dl; P less than 0.001), whereas maternal levels increased about 10-fold during this time. Free @entity701 in the fetus increased between 21 and 23 days (0.041 micrograms/dl) and then decreased somewhat until after day 29 when there was an increase. To examine more directly the influence of endogenous glucocorticoids in the fetal lung, we assayed @entity701 in extracts of purified lung nuclei as a reflection of receptor- @entity701 complexes. The nuclear content of @entity701 was constant between 23 and 30 days at levels (0.056-0.074 ng/mg DNA) comparable to those predicted from data for plasma free @entity701 . Thus, in the @entity95 , increases in plasma @entity701 and nuclear receptor- @entity701 complex are not temporally associated with the major events of lung development as in other species. We speculate that endogenous glucocorticoids may have a permissive or delayed influence on the lung during normal development in the @entity95 .
