[Mechanism of mammary cancer regression in lactating rats]

Dependence of the incidence of regression of the transplantable carcinoma of the mammary gland RMK-1 in albino rats on lactation conditions was studied. The tumour was subject to regression in 47% of the animals nursing 8 +/- 1 ratlings. Following ovariectomy and cortisone and oxytocine administration which produced mediated inhibitory effect of FSH secretion of the hypophysis the frequency of the tumour regression in rats nursing the same number of ratlings rose to 71--81%. In rats with prolonged lactation nursing 8 +/- 1 ratlings for 2--2.5 months and in rats with intensive lactation nursing 13 +/- 2 ratlings the tumour regression practically failed to occur. The data obtained confirmed the suggestion that along with high LTH of the hypophysis secretion of importance for regression of mammary carcinoma in the course of lactation was reduction of the secretion of FSH of the hypophysis.