Enhancement by human placental lactogen of mammary hyperplastic nodules in ovariectomized mice.

The effect of human placenta! lactogen on the mainte nance and growth of precancerous mammary hyperplastic nodules was studied in ovariectomized, multiparous C3H/He female mice. In mice receiving injections of 0.5 mg of human placenta! lactogen twice daily for 19 days and on the morning of the 20th day, beginning the morning following bilateral ovariectomy, the number of nodules per mouse was similar to that in the intact controls. The ovariectomized controls had significantly fewer nodules than the intact controls and the ovariectomized, placenta! lactogen-treated mice. The average size of nodules was significantly larger in the ovariectomized, placenta! lacto gen-treated mice and was smaller in the ovariectomized controls than in the intact controls. The number of very large nodules was extremely high in the ovariectomized, placental lactogen-treated mice. These results suggest that placenta! lactogen plays an important role in the mainte nance and growth of precancerous mammary hyperplastic nodules in mice.