Cortisol production and inactivation by the human lung during gestation and infancy

The enzyme which interconverts the active hormone cortisol (F) and its biologically inactive analog cortisone (E), viz. 11 beta-hydroxysteroid dehydrogenase, is known to be present in many tissues. In this study, its possible role as a regulator of cortisol concentration in the human lung was investigated. Small amounts of minced tissue were incubated for 2 h at 37 C in the presence of tracer F or E. After extraction, the steroids were chromatographed using Sephadex LH-20 column chromatography. From 11-21 weeks of gestation, inactivation of F to E occurred (54.7 +/- 8.0%), while in 11 premature infants there was no conversion in either direction and in 9 infants (4 months to 2 yr of age) there was slight conversion of E to F (7.0 +/- 3.4%). Activity in children was negligible. Lung tissue from 4 anencephalics (35-40 + weeks) retained the ability to inactivate F to E (21.3 +/- 4.3%), though to a lesser extent (P less than 0.01) than fetuses up to 21 weeks. The validity of these in vitro studies was borne out by assays of the endogenous steroids in lung tissue and serum. These results suggest that there is an alteration from rapid inactivation of F to E in early fetal life to slight F production in infancy and that this change is advanced by pituitary or other factors which are decreased in anencephaly. This decreasing inactivation by the lung during late gestation results in higher intracellular F levels which probably act to promote lung maturation in preparation for birth.