Hypophyseal tumors induced by estrogenic hormone.

The effects of estradiol benzoate (EB) injection on sexual development and the pituitary gland were studied in 240 immature rats after 16 weeks of treatment. Treatment resulted in eunuchoid dwarfing. Males showed enlargement of the pituitary after 4 months, while in females it remained normal. After continued treatment for 8 months, enormous hypophyseal tumors were observed in 29 of 35 rats of both sexes; 1 animal died as a result of these tumors. No tumor developed in less than 7 months, which suggests that the duration of treatment, rather than the dose, is of primary importance in tumorigenesis. The amount of gonadotropic hormones in the enlarged pituitaries and tumors was the same as in normal pituitaries of control animals, which indicates that it is the utilization, rather than the production, of gonadotropic hormones that is inhibited by EB-induced eunuchoid dwarfs.