Diurnal Steroid Patterns During Gestation in the Rhesus Macaque: Onset, Daily Variation, and the Effects of Dexamethasone Treatment

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Abstract
Serum samples for cortisol, estradiol-17β (E2), and progesterone analysis were obtained twice daily or more frequently to determine the onset of diurnal steroid patterns in the maternal circulation of pregnant rhesus monkeys. The expected a.m./p.m. fluctuations in serum cortisol (31.6/22.9µ g/dl) were evident from Day 25, whereas nocturnal elevations in progesterone (9.62/16.31 ng/ml) were demonstrable on Day 30, and diurnal increments in E2 (283/138 pg/ml), coincident with those of cortisol, appeared about Day 40. Microscopic examination of fetal adrenals from rhesus embryos (ages 30 to 50 days) indicated that the gland differentiates and undergoes extensive development when diurnal E2 release first appears.