Ornithine decarboxylase in organs of rat following chronic gamma-irradiation at low dose-rates.

Purpose: To investigate the consequence of continuous low dose-rate exposure to gamma-rays on ornithine decarboxylase (ODC EC 4.1.1.17) activity in organs of rat.

Materials And Methods: Young male Wistar rats were irradiated at 1.1, 2.1 and 12.9 cGy/day in the dose ranges of 9-165, 17-315 and 100-2000 cGy, respectively, in a specially designed chamber. ODC activity was determined in 20000 g supernatant fluid of thymus, spleen and lung by measuring the release of 14CO2 from L-[1-14C]ornithine.

Results: Chronic y-irradiation modulated ODC activity. It decreased at low cumulated doses (after 8 and 15 days of exposure). At longer periods after chronic irradiation (after 45 and 90 days), ODC activity was restored up to control levels despite increasing values of cumulated doses. On day 150 a similar increase in ODC activity in spleen 2.1 cGy/day and in lung at 12.9 cGy/day was observed.

Conclusions: These studies showed a non-monotonic pattern of the 'dose-response' curve. The results were interpreted in terms of the triggering of a homeostatic system.