Abstract
Endogenous glucocorticoids are known to influence pulmonary development. We studied factors affecting the availability of cortisol (F) and corticosterone (B) to lung tissue of fetal rabbits during the last week of gestation. The adrenal content of F+B was 3.33 ± 0.7, 6.34 ± 1.2 and 8.74 ±0.5 ng/adrenal at 23, 27 and 30 d, respectively, with an F:B ratio of 0.5:1. Plasma F+B was maximal (2.32 ± 0.11 μg/dl) at 23 d, and decreased progressively to 0.72 ± 0.05 at 28-30 d; the F:B ratio was 3.7:1 between 21 and 28 d and 1.5:1 at 29-31 d. Corticosteroid binding globulin (CBG) capacity decreased from 36.0 μg F bound/dl at 23 d to 2.1 g/dl in the newborn, whereas maternal levels increased from 6.2 ± 0.6 to 40.8 ± 0.8 μg/dl. Fetal levels of albumin, a low affinity binder, increased from 1.13 to 2.29 g/dl. Plasma free F (by charcoal absorption) was 0.04 μg/dl at 23 d and 0.02 at 31 d. The dissociation constant (KD) of F and B for nuclear binding in cultured explants of lung was 7.3 ± 0.1 and 70.6 ± 9.2 nM, respectively, and binding was decreased in the presence of either albumin or serum. Receptor concentration assayed both in vitro and in culture increased 48% from 23-30 d.
We conclude that F is the physiologically important corticosteroid in the fetal rabbit, but unlike other species, there is no developmental increase in the free circulating concentration. We suggest that factors other than adrenal production and serum binding determine whether there is an increase in F within the lung during development.
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Huemmelink, R., Ballard, P. ENDOGENOUS CORTICOSTEROIDS AND LUNG MATURATION IN THE FETAL RABBIT. Pediatr Res 18 (Suppl 4), 139 (1984). https://doi.org/10.1203/00006450-198404001-00279
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DOI: https://doi.org/10.1203/00006450-198404001-00279