Mammary Gland Growth during Pseudopregnancy and Pregnancy in the Rat ∗

Abstract

Summary

Growth of the mammary gland of the rat during normal pseudopregnancy was only 18% of the growth found at day 18 of normal pregnancy as measured by DNA. This suggests that the corpora lutea of pseudopregnancy function at approximately one-fifth the level of those in pregnancy. Hysterectomy, which resulted in a 6-day extension of pseudopregnancy, was without effect in the enhancement of mammary gland growth over normal pseudopregnancy. However, the ratio of RNA to DNA in the mammary glands of these animals was raised significantly. The production of deciduomata concomitant with pseudopregnancy resulted in a 9-day extension of pseudopregnancy and a slight increase in mammary gland growth over that of normal pseudopregnancy. It was only 30% of that at day 18 of pregnancy and 76% of that at day 12 of pregnancy when DNA was standardized to body weight.