Influence of the fetus and estrogen on serum concentrations and placental formation of insulin-like growth factor I during baboon pregnancy.

In the present study, we used an in vivo approach to determine whether the fetus and estrogen have direct effects on placental production and serum concentrations of insulin-like growth factor I (IGF-I) in baboons. On day 100 of gestation, fetuses were removed and placentas left in situ (fetectomy). On days 100-155 of gestation after fetectomy, baboons received 50 mg androstenedione pellets sc in increasing numbers (1-3 every 10 days, n = 8), were injected sc with estradiol (E2) benzoate (0.50-2.5 mg/day, n = 8), or were not further treated (n = 6). Placentas were obtained on day 160, and cells were dispersed in 0.1% collagenase, isolated on 50% Percoll, then incubated for 24 h at 37 C in medium 199. Mean (+/- SE) peripheral serum E2 (nanograms per ml) in untreated baboons (n = 5) was 1.33 +/- 0.06 on days 101-160. Fetectomy decreased (P less than 0.001) E2 to 0.28 +/- 0.04, and androstenedione and E2 after fetectomy increased serum E2 to 0.75 +/- 0.08 and 2.51 +/- 0.23, respectively. Serum IGF-I (nanograms per ml) determined by RIA was 182 +/- 6 on days 101-160 in controls. Serum IGF-I increased (P less than 0.001) rapidly after fetectomy to 403 +/- 22 on days 101-160 and fell precipitously to 185 +/- 8 after placental delivery. Androstenedione and E2 treatment after fetectomy decreased IGF-I to 291 +/- 16 and 239 +/- 6, respectively, values similar to those before fetectomy. Uterine vein concentrations of IGF-I were similar to those in peripheral maternal serum, and the same relative treatment effects were observed. IGF-I secretion (picograms per ml/24 h) by placental trophoblasts of fetectomized baboons (80.1 +/- 9.8) was 242% greater (P less than 0.001) than controls (23.4 +/- 4.7) and decreased after fetectomy by androstenedione (56.7 +/- 15.1) and E2 (62.3 +/- 12.8). Thus, removal of the fetus decreased serum E2 and markedly elevated placental production and maternal serum levels of IGF-I, and these effects were largely reversed by androstenedione or E2. We suggest that the fetus, via secretion of estrogen precursors, regulates placental IGF-I production and consequently maternal serum concentrations of IGF-I during primate pregnancy.