Pituitary-Placental Interaction: Hypophysectomy Modulates the Secretion of Mouse Placental Lactogen-I*

To determine whether the pituitary gland influences the concentration of mouse placental lactogen-I (mPL-I) in maternal serum, pregnant Swiss Webster mice were hypophysectomized or sham-operated on day 9 of gestation. Blood was collected on days 10-13 and 18, and the mPL-I concentration of the serum was measured by RIA. The serum mPL-I concentration of hypophysectomized mice was significantly higher than that of sham-operated and intact mice on days 10-13. There was no difference in mPL-I concentration on day 18 of pregnancy among the groups. Similar elevations in serum mPL-I concentration were observed when hypophysectomy was performed on day 10 of pregnancy. Steady state levels of placental mPL-I messenger RNA (mRNA) were analyzed by Northern hybridization. No differences were observed in the amount of mPL-I mRNA among hypophysectomized, sham-operated, and intact mice. These results demonstrate that the pituitary gland exerts inhibitory control over the maternal serum mPL-I concentration. This control does not appear to be affected at the level of steady state amounts of mPL-I mRNA.