Cell proliferation in the mammary gland during late pregnancy and lactation

Abstract

Nulliparous, CFW mice were injected with 25pc of tritiated thymidine on day 19 of pregnancy, and days 1, 2, 3, 5, 7, 10, 15 and 20 of lactation. The animals were killed one hour after injection. The inguinal manimary glands were removed and processed for paraffin sectioning. Radioautographs were prepared, using the dipping technique.Quantitation of mammary epithelial cell proliferation for the intra-and interlobular (ducts) epithelium was performed by determining the percent of labeled epithelial cells in a large sample of cells (labeling index). It was concluded that epithelial cell sample sizes of 1,000-2,000 cells were adequate to measure mammary epithelial proliferation. A wave of epithelial proliferation was observed during early lactation.hi the intralobular epithelium, a peak labeling index of 11.1% was attained on day two of lactation whereas a peak labeling index of 7.9% was observed on day three of lactation in the interlobular epithelium. Cells of the connective tissue and vascular bed proliferated in response to the growth of the mammary epithelium. Myoepithelial cells were frequently labeled on days two and three of lactation.

Development of the mammary gland

“…The mouse has a cell population doubling time of 6 days; in the rat it is somewhat longer. Our own results and those of Traurig (1967a) for the mouse and Grahame & Bertalanffy (1972) for the rat indicate that the proportion of dividing cells declines during the second half of pregnancy; thus in order to maintain exponential growth the time taken for each cell to divide must decrease, as is known to occur under the influence of ovarian steroids (Bresciani, 1971).…”

Expression of dominant-negative ErbB2 in the mammary gland of transgenic mice reveals a role in lobuloalveolar development and lactation

“…This lack of phenotype during the second and most pronounced stage of mammary epithelial proliferation (Traurig, 1967b) suggests that ErbB2 signaling is also dispensable during this period of mammary epithelial proliferation. The ®nding that EGF injected i.p.…”

“…Condensed lobuloalveoli with cuboidal epithelium predominated in mammary glands from multiparous transgenic females at 1 day post-partum ( Figure 4f). At 3 days post-partum the alveolar epithelia of both transgenic and control mice are rounded as they enter the ®rst phase of post-partum proliferation (Traurig, 1967a) (Figure 4g and h). Despite the apparent recovery of epithelial cell function, lobuloalveoli of ErbB2DIC expressing mice at 3 days post-partum remained much smaller than those of non-transgenic controls.…”

Breast-feeding after breast cancer: if you wish, madam

“…Progesterone acts as the main inhibitor of milk production and when this hormone decreases after birth, stage II lactogenesis begins, governed as well by high prolactin levels. As suckling starts, there is an additional increase in the expression of genes involved in milk secretion with further expansion of the alveolar epithelium [13] (Fig. 1).…”