Protection of Mouse Thymus against Cobalt-60 Radiation by 2-Mercaptopropionylglycine (MPG)

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Normal adult male Swiss albino mice, weighing 25 g on the average, were exposed to 500 R gamma rays from a Cobalt-60 source in the presence and absence of the chemical MPG or 2-mercaptopropionylglycine and histological studies of thymus were conducted at various postirradiation intervals. It was found that MPG, when given 30 minutes before irradiation, protected the thymus tissue and caused an early regeneration of the organ as indicated by the presence of dividing cells in different stages of mitosis in both cortex and medulla as early as 72 hours postirradiation. The normal structure was regained by the end of two weeks in this group in contrast to the unprotected controls where recovery was not complete even at the end of four weeks after exposure. MPG when given 30 minutes after exposure is not so effective, even though protection is afforded in this case also. The mechanism of action of this drug is not known. The high radiosensitivity of the mammalian thymus was recognized as early as the beginning of this century. Kallman and Kohn, judging from the organ weight changes, reported the thymus to be even more sensitive than the spleen. Thymus weight reduction after irradiation has been reported by several workers. Other radiation-induced changes observed in the thymus include depletion of lymphocytes, pyknosis, karyorrhexis and karyolysis.
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