Circadian phenomena and irradiation. Modifications of enzyme activity in the small intestine after sublethal exposure

Irradiation effects after a 3 Gy dose administered at four different times of a 24 h light/darkness cycle were studied: the modifications in the brush border enzyme activity of epithelial cells of the small intestine were determined. In controls the activity of these enzymes showed circadian oscillations with the maximum during the dark period and the minimum during the light period. The trend after irradiation in the various groups was very similar but some differences were present specially at the initial intervals when the effect appeared to be different depending on the enzyme level at the time of exposure. Lactase activity in animals irradiated at 0.00 and 18.00 o'clock returned to control levels later than in the other groups.