The concentrations of androstenedione, testosterone and cortisol have been measured in the maternal peripheral plasma of normal pregnant rhesus monkeys (Macaca mulatto), and in rhesus monkeys treated daily with dexamethasone during late pregnancy. During the last 30 days of pregnancy, the mean plasma concentrations of androstenedione, testosterone and cortisol were about 1400–2000 pg/ml, 375–425 pg/ml and 300–400 ng/ml, respectively. None of these steroids increased significantly before parturition. As there was no rise in maternal androgens in late pregnancy when plasma estrogens increase sharply, it is suggested that this elevation of plasma estrogens is related to an increase of fetal precursors. Dexamethasone treatment resulted in a 90% suppression of plasma cortisol, and a 40–60% suppression of androstenedione and testosterone. As the suppression of maternal androgens was of lesser magnitude than the decline of plasma estrogens, and as the androgens did not continue to fall with continuing dexamethasone treatment as did the estrogens, these findings also suggest that the decline in plasma estrogens is related in large part to suppression and atrophy of the fetal adrenals.
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