INTERLEUKIN-6 INHIBITS MOUSE PLACENTAL LACTOGEN-II BUT NOT MOUSE PLACENTAL LACTOGEN-I SECRETION IN-VITRO

The mouse placenta produces several polypeptides belonging to the prol actin-growth hormone gene family, including mouse placental lactogen ( mPL) I and mPL-II. The present study was undertaken to determine wheth er the secretion of mPL-I and mPL-II is regulated by interleukin 6 (IL -6), which is present in the placenta and has previously been reported to stimulate the secretion of pituitary members of this gene family. Effects of human and mouse IL-6 on mPL-I and mPL-II secretion were exa mined in primary cultures of placental cells from days 7, 9, and 12 of pregnancy. IL-6 caused a dose-dependent reduction in the mPL-II conce ntration in the medium of cells from days 9 and 12 of pregnancy but di d not affect the mPL-II concentration in the medium of cells from day 7 of pregnancy or the mPL-I concentration in the medium of cells from days 7 or 9 of pregnancy. The lowest concentration of human IL-6 that significantly inhibited mPL-II secretion was 250 pM. The effect of IL- 6 on the mPL-II concentration in the medium was due primarily to inhib ition of mPL-II synthesis, which resulted at least partly from a decre ase in the steady-state level of mPL-II mRNA. These data raise the pos sibility that IL-6 may regulate mPL-II production after midpregnancy i n vivo.