EFFECTS OF OESTROGEN AND/OR PITUITARY GRAFTS ON NUCLEIC ACID SYNTHESIS IN THE MAMMARY GLANDS OF LACTATING MICE

Abstract

The mammary gland synthesizes little DNA during lactation in mice. The effects of daily injections of oestradiol benzoate (OB) between days 9 and 11 of lactation, and/or grafting with three isologous anterior pituitary glands on day 1, on the growth of the litter and the development and function of mammary glands were studied on day 12 of lactation in C3H/He mice. The level of prolactin in the plasma of mice with pituitary grafts was raised, but mammary gland function was not affected. The synthesis and content of mammary gland RNA was depressed after injection of 0·5 μg OB/day; at a dose of 10 μg/day, OB also depressed litter growth and mammary DNA content, but increased the synthesis of DNA and the level of prolactin in the plasma. Pituitary grafting enhanced the effect of 10 μg OB/day on DNA synthesis. These findings suggest that one of the causes of the low level of DNA synthesis in the mammary gland during lactation in mice is a low level of oestrogen in the circulation.