A QUANTITATIVE ANALYSIS OF THE ROLE OF OESTROGEN IN MAMMARY DEVELOPMENT IN THE RAT

Abstract

SUMMARY A quantitative analysis of mammary development in the gonadectomized Hooded Norway rat treated with various levels of oestradiol dipropionate (Oe. DP.) from the 20th to 80th day of life was carried out. The relative rate of mammary growth in the oestrogen-treated animals was compared with that found in intact and gonadectomized control rats. Over the dose range 0·05–1·0 μg Oe. DP./2 days a positively allometric mammary-growth phase was induced, but the equilibrium constants obtained for all groups, except the males receiving 1·0 μg Oe. DP., were significantly lower than the value of 3·40±0·17 for the intact female. In the majority of oestrogen-treated groups no statistically significant differences between the values of α were found, although the approximate time of onset of the artificially-induced allometric phase of growth appeared to be related to the dose of hormone given. When a dose of Oe. DP. increasing proportionately with the body weight was employed, the resultant rate of mammary growth relative to body growth (α=3·70±0·13) was similar to that found in the intact female. An analysis of the number of ducts and side-buds present in the thoracic glands after various treatments at the end of the 60-day experimental period was made in the female groups. While duct development at all levels of oestrogen treatment was similar to that found in the intact female, the degree of side-bud proliferation appeared to be dependent on the dose of Oe. DP. administered.