Protective efficacy of combined administration of lipopolysaccharide of E. coli and chemical radioprotectors under conditions of prolonged irradiation

We investigated the protective effectiveness of the lipopolysaccharide of E. coli (LPS) in a combination with a mixture of chemical radioprotectors in female mice of the strain H at various radiation dose rates. LPS in a dose of 0.08 mg per kg of body mass was administered 1,3, or 24 hours prior to irradiation, the radioprotective mixture (cystamine 90 mgxkg-1+5-methoxytryptamine 15 mgxkg-1) was administered 10 minutes before irradiation. Dose rates of 612 mGyxmin-1 (irradiation time 10 to 15 minutes), 38 mGyxmin-1 (3 to 4 hours), and 8.2 mGyxmin-1 (27 to 29 hours) were used. The results showed that isolated administrations of LPS or of the radioprotective mixture increased the resistance of the mice against prolonged irradiation; the combined administration even enhanced the efficacy of the radioprotective action. However, this efficacy depended on the magnitude of the dose rate. At dose rates higher than 38 mGyxmin-1 the effectiveness of the chemical protection prevailed, whereas at lower dose rates the biological and especially the combined protection became effective. We demonstrate a slight pyrogenic effect of LPS by measuring oxygen consumption and changes in some parameters of the hematopoiesis. (orig.)