Effect of adrenalectomy on the latency of radiation myelopathy in rats.

The effect of adrenalectomy on the development of radiation myelopathy was studied. A 1-cm section of cervical cord of adrenalectomized and intact animals was exposed to graded doses (18 to 30 Gy) of gamma rays. The radiation tolerance, the latent period from exposure to paralysis, plasma corticosterone levels at the time of paralysis, and histopathology of the cord were evaluated. Adrenalectomy essentially eliminated endogenous production of corticosterone and significantly shortened the mean latent period between irradiation (24 to 30 Gy) and paralysis by more than 10 weeks. This reduced latent period was not reversed by the administration of the exogenous glucocorticoid, dexamethasone, and corticosterone, although prolonged administration of dexamethasone resulted in the development of Cushingoid features, indicating hypercorticoidism. Histopathological examinations indicated that adrenalectomized paretic animals had multiple hemorrhages in both the gray and the white matter, but less white matter necrosis than normally observed in intact paretic animals irradiated similarly. Possible mechanisms for the shortened latent period in adrenalectomized animals are discussed.