Influence of the Uterus on Ovary and Mammary Gland

Abstract

While Caesarian section normally initiates lactation in the rat, it has been found that milk secretion does not occur if the uterus is filled with paraffin immediately after the foetuses have been removed. 1 Furthermore, no oestrus is usually observed in such rats for several weeks after the operation; while in the controls, the uteri of which have not been distended, normal cycles set in 3 days after the interruption of pregnancy. We have recently repeated these experiments, and it is the object of this paper to describe the morphological changes observed in the ovary, pituitary and mammary gland.

In 10 pregnant rats, the uteri were emptied through a small incision during the second half of gestation; then each horn of the uterus was injected separately with melted paraffin (melting point 42°C.) after tying the lower end with silk. When the uterus was well distended, the upper end, through which the injection was made, was also tied.

During the 6 weeks following the operation, only 2 of these animals came into oestrus—one had 2 cycles, the other, 4. At autopsy it was found that the ovaries were greatly enlarged (75–110 mg. as compared with 40–45 mg. in the normal controls), and contained many large corpora lutea similar in appearance to those observed during gestation (Fig. 1).

In a control series where the foetuses were removed, but the uterus was not filled with paraffin, the corpora lutea of gestation shrank rapidly after the operation, and were as small as the corpus luteum of a normal cycle within 6 days after operation.

Histologically, the corpora lutea of the experimental animals consisted of cells rich in cytoplasm with a large vesicular nucleus; they showed no signs of round cell infiltration or of invasion by connective tissue, and resembled closely the corpora lutea of gestation. Sections stained with Sudan III showed, however, that besides the small lipoid granules characteristic of the active corpus luteum of gestation, larger fat globules appear in many of the cells. In none of these ovaries did we find mature follicles.