Circulating steroids and the relationship between ovarian and placental secretion during early and mid pregnancy in the baboon

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Abstract
Ovarian and placental steroid secretion was examined at intervals during early and mid-pregnancy in the olive baboon, Papio anubis. Progesterone, androstenedione, testosterone, estrone, and estradiol-17β were measured after celite chromatography in samples from peripheral circulation and from utero-ovarian veins draining ovaries with and without corpora lutea at the following stages of pregnancy: days 8–9 (unconfirmed pregnant), 10–19, 34–40, 60–66, and 104–106 after ovulation. The pattern of hormone levels in peripheral and utero-ovarian vein samples indicated the following: 1) The corpus luteum was the principal source of progesterone until at least day 19. Placental secretion was well advanced by days 34–40 and provided the major contribution to circulating progesterone levels by day 60.2) There was a significant elevation in peripheral concentrations of androstenedione and testosterone on days 10–19 and 34–40 of pregnancy; androgen levels in peripheral and utero-ovarian vein samples declined to baseline values by day 60. 3) Estrogens were secreted by the corpus luteum on days 10–19 but not on days 34–40. Placental secretion of estradiol-17β increased markedly after days 60–66, whereas little, if any, placental secretion of estrone was apparent at this time. These results provide circumstantial evidence that progesterone secretion by the corpus luteum of early pregnancy extends beyond the time when estrogen secretion has declined and that the timing of the luteo-placental shift in the baboon is intermediate between that in rhesus monkeys and that in marmosets and humans. Increased secretion of androgens during the first 6 weeks of gestation may be useful in early pregnancy diagnosis in the baboon, although the physiological significance of this event is not clear.