Plasma and adrenal corticosterone levels in male rats following x-irradiation at different times of day.

Adrenal and plasma corticosterone levels were investigated in male rats irradiated at 3-h intervals during the 24-h period (light : dark - 12 h : 12h). Adrenal and plasma corticosterone levels were markedly increased in animals exposed to a single whole-body X-irradiation with a lethal dose of 387 X 10(-3) C/kg (1 500R) and a 24-h fasting, compared to the sham-irradiated fasting controls, even during the lowest values of the intact group (08.00 h); the difference between the mean values of the irradiated and control group was not significant. The basal diurnal rhythm of corticosterone was retained even after irradiation. In comparison with the control, sham-irradiated group, the animals exposed to irradiation with a non-lethal dose of 64.5 X 10(-3) C/kg (250R) and a 48-h fasting showed adrenal corticosterone levels insignificantly higher in the light phase and lower in the dark phase. In comparison with the intact controls, both irradiated and sham-irradiated groups showed considerably shifted fluctuations during the 24-h period: the lowest levels in the middle of the dark phase and the highest in the middle of the light phase. Plasma levels of corticosterone were lower in irradiated animals than in the controls throughout the 24-h period. There were more irregular fluctuations and the diurnal rhythm was disturbed.