Ornithine decarboxylase activity in rat organs and tissues under artificial hypobiosis.

The influence of hypothermia-hypoxia-hypercapnia on ornithine decarboxylase (ODC, EC 4.1.1.17) activities in rat organs and tissues and also on the thymocyte distribution throughout the cell cycle stages was studied. The state of artificial hypobiosis in rats on decrease in the body temperature to 14.4-18.0°C during 3.0-3.5 h was accompanied by drops in the ODC activities in the neocortex and liver by 50-60% and in rapidly proliferating tissues (thymus, spleen, and small intestine mucosa) by 80% of the control value. In kidneys the ODC activity raised to 200% of the control level. Twenty-four hours after termination of the cooling and replacing the rats under the standard conditions, the ODC activities in the neocortex, liver, kidneys, spleen, and intestinal mucosa returned to the control values, but remained decreased in the thymus. Forty-eight hours later the ODC activities in the thymus and spleen exceeded the normal level. The distribution of thymocytes throughout the cell cycle stages did not change in rats in the state of hypothermia (hypobiosis); 24 and 48 h after termination of the cooling the fraction of thymocytes in the S stage was decreased and the fraction of the cells in the G(0)+G(1) stage was increased. The normal distribution of thymocytes throughout the cell cycle stages recovered in 72 h. Thus, in the thymus the diminution of the ODC activity preceded the suppression of the cell proliferation rate. The tissue-specific changes in the ODC activity are suggested to reflect adaptive changes in the functional and proliferative activities of organs and tissues during the development of hypobiosis under conditions of hypothermia-hypoxia-hypercapnia.

Nuclear and chromatin lipids: metabolism in normal and gamma-irradiated rats.

The data on nuclear and chromatin lipid metabolism are reviewed. The amount of neutral lipids and phospholipids in nuclei of rat thymus, liver and neocortex neuron as well as the amount of lipids in rat thymus and liver chromatin are described. The metabolic responses of nuclear and chromatin lipids from thymus to different doses and dose rates of gamma-irradiation of rats are discussed. In most cases, the nuclear and chromatin lipid responses are distinct. Changes in nuclear and chromatin lipid metabolism in response to gamma-irradiation are suggested to connect with the signal transduction pathway and the regulation of the transcriptional and replicative chromatin activity. The influence of beta-carotene and picrotoxin on rat liver nuclear lipids and neocortex neuronal nuclear lipids, respectively, was analyzed. The possible involvement of the lipid traffic in the chromatin lipid responses to gamma-irradiation and other agents is suggested.

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.

Nonmonotonous Changes in Metabolic Parameters of Tissues and Cells under Action of Ionizing Radiation on Animal.

A nonmonotonous relationship between changes of metabolic parameters of tissues and cells of animal and radiation dose were discussed. Under acute irradiation of animals the nonmonotonous dose-response curve for metabolic parameters of tissues and cells were found. The nonmonotonous dose-response curves of metabolic and functional tissues and cells parameters were also revealed upon chronic irradiation of animals at a low dose-rate. The nonmonotonous shape of dose-response curves may be explained on the basis of nonmonotonous kind of the time-course of metabolic response after irradiation. Living cells were supposed to possess a fundamental property in response to action of different stress agents by nonmonotonous changes of cell metabolism. This response was damping in time oscillation of the value of metabolic parameters around the normal level. Amplitudes and periods of oscillations in these changes of metabolic parameters could be observed. In case of chronic irradiation at a low dose-rate the metabolic and functional parameters showed some modified oscillation during irradiation. The nonmonotonous type of changes in metabolic and functional parameters of tissue and cell by chronic low dose-rate irradiation threw some new light on the peculiarities of biological effects of chronic irradiation.

On the mechanism of a radiation-induced change in enzymic differentiation during development.

In experiments on glucose-6-phosphatase and tyrosine aminotransferase it was shown that radiation induces changes in enzymic differentiation in perinatal rat liver. A study was made of the probable reasons for the observed changes. It was shown that the macromolecular system of the protein enzyme synthesis was not damaged by the radiation doses used. The observed decrease in glucose-6-phosphatase activity during late embryogenesis, after pre-irradiation at early organogenesis, is eliminated by administration of exogenous thyroxine. A radiation-induced rise in the tyrosine aminotransferase activity during the perinatal period correlated with the cyclic AMP system status. It is proposed that modification of enzymic differentiation after irradiation results from the change in the amount of inductors.