Synthesis of two lactogenic proteins by the mouse placenta in vitro

The culture medium of mouse placental tissues was analyzed on acrylamide gel electrophoresis to localize lactogenic substances. Placental explants from 12- or 14-day-pregnant BALB/cHe mice were organ-cultured for 6 days in leucine-free Way-mouth's medium supplemented with 3H-leucine (10 mu/Ci/ml) and insulin (0.12I.U./ml). The medium was collected every other day and subjected to acrylamide gel electrophoresis. The electrophoretic pattern of radioactive leucine incorporated into proteins was examined on stained 7% gels. Five protein bands were associated with high radioactivity. The location of lactogenic activity on acrylamide gel was when investigated by the technique of organ culture of mouse mammary tissues. Placental explants from 12- to 14-day-pregnant BALB/cHe mice were organ-cultured in Waymouth's medium supplemented with insulin for 2 days. After electrophoresis, proteins were eluted by keeping the segment of acrylamide gel in phosphate buffer, dialyzed and dissolved in tissue culture medium 199 supplemented with insulin and cortisol. Mammary tissues from 8-day-pregnant KA2 mice were cultured for 3 days in the medium containing each eluate. Mammary glands always responded to eluted proteins from two positions of 7% gel, as judged in histological sections. The data suggest the presence of two lactogenic substances in the mouse placenta.