Endogenous biochemical factors affecting the efficiency of some radioprotective or radiosensitizing drugs: sulfhydryl groups and lipid peroxides.

The changes in the amounts of blood and tissular sulfhydryl groups and lipid peroxides were investigated in lethally gamma-irradiated rats treated with cystamine, AET (radioprotectors) or alpha-methyl-dopa (a radiosensitizer). The results of experiments revealed the following findings: 1. The ionizing radiation generally causes increases in the levels of tissular sulfhydryl groups and lipid peroxides (excepting the hepatic levels of these compounds). 2. AET and, especially, cystamine are able to reverse the radiation-induced changes in the tissular amounts of sulfhydryl groups and lipid peroxides; there are close relationships between this effect (including its intensity and extension) and the radioprotective action of these drugs. 3. In spite of its radiosensitizing action, alpha-methyl-dopa induces approximately similar changes in the tissular amounts of sulfhydryl groups and lipid peroxides, suggesting that biochemical processes other than an excessive yield of free radicals are also involved in radiosensitivity.