[Chemical protective agents against ionizing radiation].
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The SH-groups of alpha-mercapto-propionylglycine (MEPRIN) are remarkably stable in diluted solution either at room temperature or at 50 degrees C, even if storing takes place under air-bubbling. The SH-activity was measured by polarographic method and amperometric titration. Neutralization of the carboxyl group decreases the stability of the sulfhydryl groupings. Evaporation of neutralized solution leads to a 30--50 per cent decrease of SH-activity. Lyophilization reduces this loss by 10--15 per cent. Neutralization is best carried out in the absence of oxygen; in this case, 94 per cent of the sulfhydryl activity will persists, irrespective of the pH. The dissociation constant of MEPRIN-SH is pK' = 8.47. The SH-stability of the product is satisfactory when neutralized in nitrogen atmosphere to pH 3--5; a loss of only 5 per cent can be expected after storing in an oxygen-free 10(-3) molar solution for 144 hours. Between pH 6 and 8 this value is 31 per cent on the average, while at pH 9 it is more favorable again.
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The work reported was done as part of an intensive investigation on toxic and radioprotective properties of three substances, ATP, AET and serotonin, administered singly or in combination to mice, with a view to identifying optimal dose ratios for cocktails. Male C57BL mice were exposed to 850 R X-rays (LD100/11) following pretreatment with drug pairs at various dose ratios. Thirty-day survival was scored. For ATP-AET, protection increased with the amount of ATP in the combination; this pair was found to be most effective at an ATP-to-AET ratio of 11:1. A similar trend was observed with ATP-Serotonin, though only up to a certain ATP level beyond which no further increase in protective effect were produced; the most favorable ratio was of 24:1. A maximum synergistic action was displayed by the AET-Serotonin pair as compared to the other two pairs; its best ratio was of 4:1. Using probit analysis, a number of PD50 (protectant dose affording 50% survival in lethal irradiation) values were estimated for the three pairs of protective agents.
The effect of metanabol given to rats before irradiation (600 R) on exploring motility and cataleptic action of nitrazepam was investigated. The level of nitrazepam in the blood plasma and urine was determine. Most evident radioprotective effect of metanabol was found on 3rd day after irradiation. The drug inhibited the inhibited the increased response of the rats to the anticonvulsive action of nitrazepam and prevented the pharmacokinetic disturbances appearing in the course of radiation disease.
The effect of metanabol (1 mg per kg) applicated to rats during 10 days before irradiation (600 R) on pharmacodynamics and some indices of thioridazine kinetics was investigated. It was found that the increased cataleptic action of thioridazine (20 mg per kg), during radiation disease was inhibited ater metanabol premedication. The protective effect of metanabol was found to be due to shortening of the half-life time of thioridazine (from 5.5 h in irradiated to 2.38 h in irradiated premedicated animals) as well as to lowering of thioridazine content in the brain tissue.
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It was shown in experiments on mice, rats and rabbits that resistance of animals in the state of acute radiation sickness to severe intoxication by aminoglycoside antibiotics, such as streptomycin, dihydrostreptomycin and monomycin did not significantly change. The exception was kanamycin the toxicity of which during the period of the acute state of radiation sickness increased by 30 per cent. The use of cystamine and merkamine before irradiation or their administration to non-irradiated animals resulted in lowering of the antibiotic tolerance by 1.5--2 times. The above aftereffects of the radioprotectors was observed within 3--12 days after their use and was most pronounced for the combination of cystamine and streptomycin. The acute toxicity of tetracyclines did not significantly differ at various stages of radiation disease and at the background of cystamine use. No significant cumulation of the toxicity of aminoglycoside antibiotics and tetracyclines or signs of adaptation in the healthy and irradiated animals was observed on prolong treatment with therapeutic doses. Cystamine had no effect on the tolerance of the antibiotics on their prolonged use.
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