GROWTH OF THE MAMMARY DUCT SYSTEM IN INTACT AND OVARIECTOMIZED MICE OF THE CHI STRAIN

Abstract

SUMMARY The changes in the rate of growth in area and in arborescence of the duct system of intact and ovariectomized female mice of the CHI strain have been measured by objective means. The duct system of intact mice grows in area at a rate isometric with (body weight)⅔ until the mice are about 24 days old, when the rate of growth becomes positively allometric. The number of junctions in the duct system is almost constant before the phase of rapid growth in area begins, but increases rapidly for a time, then more slowly until the mice are between 56 and 84 days old when little further increase is seen. These changes do not occur in ovariectomized mice less than 84 days old, but by 1 year such mice showed evidence of stimulation of the mammary glands (mammae) and uteri, the source of the stimulating factor being presumably hyperplastic tissue in the adrenal cortices. The duct system of ovariectomized mice 42 days old, given 0·055 μg oestrone daily in 0·1 ml. arachis oil, did not differ significantly from that of intact controls, either in area or arborescence, and increasing the dose of oestrone to 0·1 μg daily caused no further change in area or arborescence. Ovariectomized mice given 0·01 μg oestrone daily showed duct systems which were double the area of those of ovariectomized controls, but considerably smaller than those of intact controls. Weaning at 15 instead of the normal 21 days did not affect either normal or oestrone-induced growth of the mammae. The mammae of intact, suckling mice between 10 and 15 days old did not respond to oestrone or progesterone, but showed a slight growth in response to unfractionated anterior-pituitary suspension and a greater response when this suspension and oestrone (0·01 μg daily) were given together. A combination of anterior-pituitary suspension and progesterone caused a great increase in duct branching, but little if any increase in area of the duct systems. There was no response in area or branching when these mice were given oestrone and progesterone together, but a slight thickening of the ducts was observed, although this was less than in mice given unfractionated anterior-pituitary extract.