Gamma irradiation effects on human ACTH-producing pituitary tumors in organ culture.

Morphology (studied by light and electron microscopy) and hormone secretion were followed in organ cultures of adrenocorticotropic hormone (ACTH)-secreting hormones after in vitro irradiation with a single dose of 70 Gy. The increase is ACTH secretion immediately after exposure was interpreted as an irradiation-induced direct effect on cell membrane permeability. The low secretional capacity for 120 h after irradiation is probably caused by an impairment of cell metabolism. Cell morphology slightly deteriorated 24-48 h after exposure. Later, cell morphology was restored and specimens investigated 5 days after irradiation showed normal morphology. It is concluded, that the fluctuations in serum ACTH in patients with Cushing's disease treated by stereotactic radiosurgery are caused by changes in the tumor cells proper rather than being due to hypothalamic influence.