Promotion by estriol of the development of grafted fetal livers in mice.

Mouse fetal livers of 12 days gestation were transplanted beneath the kidney capsule of syngeneic castrated male hosts. Recipients received a single intraperitoneal injection of 5 mg estriol (E3) immediately after transplantation and were sacrificed 4, 7 and 14 days later. Control mice received injections of solvent only. The fetal liver grafts of the E3 groups showed remarkable growth compared with the control grafts at each corresponding time. In the grafted fetal livers of the E3 groups, many more basophilic hepatocytes appeared for much longer periods, and the early formation of wide sinusoids was noted. Although hemopoietic activity had almost ceased a short time after transplantation in the control grafts, many prominent extrasinusoidal erythroid, granulocytic and megakaryocytic hemopoietic foci developed and persisted to the end of the experiments in the grafted fetal livers of the E3 groups. In the next experiment, the recipients received three injections of 0.5-5 mg E3 at 5-day intervals, and were sacrificed 21 days after transplantation. Control animals received solvent only in the same manner. The fetal liver grafts of the E3 groups also showed remarkable, dose dependent growth. The growth was particularly striking at doses of 3-5 mg E3. In the grafts of these groups, basophilic hepatocytes were predominant, and hepatic cords and sinusoids were well formed. Moreover, sinusoidal erythropoiesis was intense. These results provide evidence for the possible role of E3, secreted from the placenta into the fetal circulation, in the development of the fetal liver.