[The behavior of 7, 12-dimethylbenz(a)anthracene (DMBA)-induced mammary tumors in rats during pregnancy and lactation and hormone levels in the pituitary and plasma (author's transl)].

In order to keep a long-term lactation in primiparous SD strain rats with DMBA-induced mammary tumors, 5 pups aged 5 to 10 days were exchanged every 10 days. FSH, LH and prolactin (PRL) in pituitary tissues and FSH, LH, PRL, estradiol (E2) and progesterone (PRG) in plasma were determined during pregnancy (1,2 and 3-week), at paturition (0 to 12 hours after parturition) and during lactation (1,2,3,4,5 and 6-week). Experimental rats were divided into 6 groups according to the lactating period (non-lactating 3,6,8,12 and 17-week). Blood samples were collected by cardiac puncture 1 hour after an intraperitoneal injection of urethane (150 mg/100 g body weight), and the pituitary gland was removed simultaneously. During pregnancy, plasma PRL was low in the first and second week. PRL, E2 and PRG were high in the third week, during which DMBA-induced mammary tumors began to proliferate. PRG in plasma in the third week was lower than that of the second week. After paturition, the tumors regressed and did not develop for three weeks of lactation, during which plasma PRL was high whereas E2 and PRG were low. The tumors began to proliferate again from the fifth week of lactation, during which E2 was high and the estrous cycle reappeared. The behavior of DMBA-induced mammary tumors in rats during pregnancy and lactation seems to be closely related to plasma estrogen levels.