Cortisol-Cortisone Interrelationship in the Late Gestation Rhesus Monkey Fetus in Utero*

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Abstract
The metabolic interrelationship between cortisol (F) and cortisone (E) was studied in four long term catheterized rhesus monkey fetuses in utero during the last third of gestation. The MCR of E (50.8 ± 5.4 liters/day) was greater than that of F (22.4 ± 2.1, P < 0.005) as was the plasma concentration (187.9 ± 5.0 us. 86.1 ± 2.5 ng/ml, P < 0.001). The production rate of E (9.6 ± 1.4 mg/day) was several-fold greater than for F (1.9 ± 0.2, P < 0.005). Of all fetal F, 79.5 ± 7.0% was metabolized to E, and 43.4 ± 3.9% originated from E within the fetal circulation. A significant mass of F was infused in these experiments because of the low specific activity of [14C]F. Nevertheless, the fetus was able to maintain F concentrations in the normal range. The MCR of F was similar to that which we previously found using trace amounts of [3H]F. This indicates that the fetus regulates the amount of F in the fetal compartment, probably by decreasing fetal adrenal secretion rate. We conclude that F in the primate fetus is extensively oxidized to E. We conclude also that E is produced and metabolized much more extensively than is F. Reduction of E back to F could be an important source of fetal F, and increasing activity of this pathway, if present, could contribute to the increase in fetal F levels observed in late gestation in the primate.