The effect of y-irradiation in a dose of 1.5 Gy at a dose intensity of 3 sGy/day on the rat thymocyte nuclear lipids and of I~-carotene diet on the metabolism of thymocyte nuclear lipids is studied in intact and -/-irradiated rats. The irradiation activated the incorporation of 2-~'C-acetate in the total lipid fraction and in cholesterol and suppressed the label incorporation in sphyngomyelin. The I~-carotene diet decreased the content of cholesterol and monoglycerides in the thymocyte nuclei of intact and irradiated rats. In irradiated rats 13-carotene increased the label incorporation in the total phosphatidylserine+phosphatidylinositol fraction.Key Words: chronic -/-irradiation; thymocyte; nuclei; lipids; p-carotene A single or prolonged exposure to low-dose ionizing radiation impairs the immunity in mammals [7]. The molecular mechanisms of the effects of low-dose and low-dose intensity ionizing radiation on cellular metabolism in the thymus, the central organ of the immune system, are little known. At present, the attention of scientists is focused on lipid metabolism in cell nuclei and their role in the function of cellular genetic system [1]. Studies of the effects of immunostimulants involved in natural regulation of lipid metabolism, specifically, carotenoids, on the metabolic effects of low-dose radiation, are particularly interesting.Carotenoids We examined the effect of prolonged (the whole life) -/-irradiation of low intensity not affecting the life span and negligibly modifying the hemopoiesis [6] on the metabolism of thymocyte nuclear lipids and the effect of BC-containing diet on nuclear lipid metabolism in rats exposed to y-radiation.
MATERIALS AND METHODSFour groups of male Wistar rats weighing 80-90 g were used: 1) intact controls, 2) control+BC, 3) irradiation, and 4) irradiation+BC. Chronic irradiation in a dose of 1.5 Gy at a dose intensity of 3 sGy/day was carded out in a special ,/-chamber with 137Cs as the source of radiation. Animals of groups 2 and 4 were fed synthetic BC with curds for 50 days, groupa 1 and 3 were fed curds. In a daily dose of 3 mg/kg BC produces an antitumor effect [12]. After a total dose of 1.5 Gy had been attained, the animals were decapitated, the thymuses were removed, and a thymocyte suspension was prepared. The cells were incubated with 2-~4C-acetate. The conditions for preparation of thymocytes, their 000%4888/98/0009-0918520.00 9Kluwer Academic/Plenum Publishers
The reactivity of polyenes (b-carotene, canthaxanthin, lycopene and some retinyl polyenes as related compounds) in the solid state towards molecular oxygen at various temperatures and oxygen pressures was studied. The specimens were thin (ca 0.1 mm) amorphous films prepared by evaporation of one or two drops of appropriate solution on quickly rotating supports. The autoxidation was monitored by recording the changes in the electronic and infrared spectra of oxidizing films and was demonstrated to be a chain free-radical process with extremely high chaininitiation rates (10 À5 -10 À6 mol l À1 s À1 ). For various polyenes the kinetic parameters of the initiation reaction were measured. In the films of several polyenes (retinyl acetate, retinal, methyl retinoate, b-carotene), the formation of free radicals proceeds in the absence of oxygen and the mechanism of the process was suggested. The observed ratios of the propagation and termination rate constants depend on the oxygen pressure, indicating the involvement of polyenyl radicals in the chain termination process. The observed trends are explained using the concepts of the stabilization energy of radicals, the reversibility of oxygen addition to polyenyls and morphological features of polyene films.
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