The effects of bilateral
adrenalectomy or
estradiol benzoate treatment were observed on growth of 7,12-dimethylbenz(a)-anthracene-induced mammary
tumors during postpartum lactation. In the control and
estradiol benzoate-treated postpartum lactating rats, the mammary
tumors decreased approximately 40% in size by Day 5 postpartum and continued to regress to 50% of their average original diameter by Day 25 postpartum.
Adrenalectomy on Day 3 postpartum prevented mammary
tumor regression and resulted in renewed mammary
tumor growth. By Day 10 postpartum, average mammary
tumor size in the adrenalectomized rats reached prepartum diameter and continued to increase in size until Day 25. Although serum
prolactin concentrations were significantly higher in the lactating rats with mammary
tumors than in the nonlactating rats with mammary
tumors, there were no significant differences in serum
corticosterone values.
Adrenalectomy resulted in a significant increase in serum
prolactin levels and in a marked fall in serum
corticosterone levels. It is concluded that in rats adrenocortical activity is primarily responsible for reduced mammary
tumor growth during postpartum lactation.