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Cortisol and cortisone were measured in maternal and cord plasma, as well as in newborn plasma, by a double isotope dilution derivative assay. An assessment of the reproducibility, precision and sensitivity of the method is presented. It was found that cortisone concentration in cord plasma is greater than in maternal plasma, that following birth the plasma level of cortisone is maintained during at least the first week of life, and that both cortisol and cortisone concentration increased following the administration of ACTH. (J Clin Endocr 25: 243,1965)

Fetal lung cells from 28 day gestation rabbits cultured in the presence of cortisol (5.5 times 10 - minus 6M) or dexamethasone (5.5 times 10- minus 8M) incorporated [3-H] choline into lecithin to a significantly greater extent than did control cultures. 11-Deoxycortisol, 21-deoxycortisol and 11beta-hydroxyprogesterone, at a concentration of 5.5 times 10- minus 5 M, had no effect on lecithin synthesis. However, when lung cells were simultaneously exposed to these steroids and to cortisol at the concentrations quoted, [3-H] choline incorporation was reduced to control values. Cortisone (5.5 times 10- minus M) also enhanced lecithin synthesis, the activity of the steroid likely being related to the capacity of the lung cells to convert cortisone to cortisol. This hypothesis was supported by the observations that 11-ketoprogesterone (1.3 times 10- minus 5M), which totally inhibited the conversion of cortisone to cortisol and which had no effect of its own on [3-H] choline incorporation, inhibited the effect of cortisone on lecithin synthesis but not that of cortisol. These data support the view that glucocorticoids affect lung cell maturation in a manner comparable to the interaction of other steroid hormones with their target tissues. The capacity of the fetal lung to convert cortisone to cortisol may be physiologically significant in light of the high concentration of 11-oxo-steroids in the fetal circulation throughout pregnancy.

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Cortisol affects the growth of serially propogated, fibroblast cell cultures derived from the rabbit fetal lung in a manner which is dependent upon the gestational age of the material used: early in gestation (20 days), the hormone (10(-7)-10(-5) M) stimulates [6-3H]thymidine incorporation into DNA, while in late gestation (28 days), cortisol (10(-7) and 10(-6) M) inhibits this process. Cultures derived from the rabbit fetal skin are inhibited by cortisol (10(-5) M) at both gestational ages. Fibroblasts derived from lung, but not from skin, efficiently convert cortisone to cortisol and this activity increases with advancing gestation. Cortisol does not affect the incorporation of [3H]choline into lecithin by confluent cultures of any of the fibroblast types studied.