Abstract
Under pentobarbital anesthesia, adult male dogs were irradiated with 1, 000 R of X-rays to their heads, and the adrenocortical response to histamine was investigated. The secretory activity was determined by estimating 17-hydroxycorticosteroids (17-OHCS) in adrenal venous blood. One day after irradiation, an intravenous injection of histamine (0.5 mg/ kg body weight) to irradiated animals increased considerably the secretion of 17-OHCS from the adrenal, but the response was significantly less than that in non-irradiated animals. Thirty days after exposure, irradiated animals responded to the injection of histamine and secreted an appreciably large amount of 17-OHCS. However, the responsiveness was still lower than normal. It appears from these results that the corticotrophic effect of 0.5 mg histamine/kg can be dimi-nished considerably by pretreatment with head X-irradiation of 1, 000 R, possibly due to a disturbed activity of the hypothalamic-pituitary axis.
