A Histological Study of the Reproductive Tract of the Lactating Mouse

Abstract

The histology of the reproductive tract of the lactating mouse is described.During the first 11 days post partum, the largest vesicular follicles are 350\g=m\ in diameter, the corpora lutea of pregnancy are larger than the corpora lutea of lactation, and the vagina has a two-layered epithelium. Significant changes occur after 12 days post partum: the size of the follicles in most animals increases to 400-450\g=m\, the corpora lutea of lactation are larger than the old set, and the vagina becomes mucified. This suggests that lactation in the mouse is divided into two periods: the first in which progesterone and negligible amounts of oestrogen are present lasts until the 11th day. This is followed by a period of increasing levels of oestrogen and a gradual subsidence in that of progesterone.A hypothesis is proposed to account for the morphological changes that occur during lactation.

Oestrus and Ovarian Histology in the Lactating Vole (Microtus Agrestis)

“…In rabbits, receptivity declines markedly during the first 10 days of lactation after which anoestrus sets in (Hammond, 1925). In the field vole, M. agrestis, on the other hand, no spontaneous ovulation occurred post partum and the cl of pregnancy degenerated at a faster rate than those of mice (Greenwald, 1958). Graafian follicles were present throughout the lactation period although they appeared slightly reduced in size at mid-lactation; no increase in inter¬ stitial tissue was detected.…”

A Comparison of 35s Methionine Incorporation by the Blastocysts of Normal and Delayed Implanting Mice

“…During lactation in the mouse, negligible amounts of oestrogen are present until the 11th day and thereafter the levels increase (Greenwald, 1958) ; presumably, this would also be true of delayed implanting animals. Since oestrogen is responsible for the incorporation of 35S methionine by the uterine epithelium (Greenwald & Everett, 1959) Delayed implantation offers an excellent opportunity to analyse events which are of short temporal duration in normal pregnancy.…”

Effect of Local Application of Ovarian Hormones on the Delay in Implantation in Lactating Rats

“…There is ample evidence that little oestrogen is secreted during lactation in small rodents (Selye, Collip & Thomson, 1935;Greenwald, 1958). It there¬ fore seems likely that in natural circumstances oestrogen lack is responsible for the delay, intervening as a limiting factor.…”