Induction of mammotropic pituitary tumors by x-rays in rats and mice: the role of mammotropes in development of mammary tumors.

Irradiation of the head and neck with 800 r induced pituitary tumors in twenty of 27 female W/Fu rats (74 per cent). Three of these primary tumors were transplanted. The anatomic findings in the tumor-bearing rats indicated that these were mammosomatotropic. In addition, three mammary tumors, one osteogenic sarcoma, and one sebaceous gland carcinoma occurred in the irradiated area and none elsewhere. Mammotropic honnone(s) greatly enhanced the induction of mammary tumors by ionizing radiation. Two mammary tumors occurred in 22 rats given, whole-body, 200 or 400 r x-rays alone (9 per cent) and thirteen in seventeen irradiated rats (76 per cent) that also received a mammotropic tumor graft 2 weeks earlier. In the former group the two tumors were benign; in the latter, benign and malignant tumors occurred in about equal number. Mammotropic graft alone failed to produce tumors in nine rats (and earlier in much larger series). In mice, doses larger than 550 r administered over head and neck failed to increase the induction rate of pituitary tumors, whereas oophorectomy with adrenalectomy markedly reduced and estrogen treatment appeared to enhance the pituitary tumor formation. Head and neck x-radiation produced thyrotropic pituitary and thyroid tumors in female LA mice in larger numbers than hitherto observed in normal and total-body x-rayed mice of this strain. Radiation-induced pituitary tumors caused mammo-somatotropic effects similar to those observed in animals bearing estrogen-induced or spontaneous pituitary tu mors. Attention is called to the puzzling phenomenon that in animals bearing such tumors (MtT)1 both thymus and adrenals are enlarged and data (of others) suggest that these tumor cells may also secrete some corticotropin (AtH).