Cold-stress induces thymocyte apoptosis in the rat

Although various stresses have been known to induce atrophy of the thymus, its pathogenesis remains to be clarified. To elucidate the mechanism of stress-induced atrophy of the thymus, possible involvement of thymocyte apoptosis was studied using rats which were exposed to cold environment. Exposure to cold temperature (5°C) for 4 h induced the fragmentation of thymocyte DNA in fasted rats but not in fed animals. Glucose levels in the blood and the body temperature of both fasted and fed rats markedly decreased during the exposure to cold temperature. Cold-stress significantly increased the plasma levels of corticosterone in fasted rats by some mechanism which was suppressed by feeding. The cold-stress-induced apoptosis was inhibited by either adrenalectomy or administration of RU486, a glucocorticoid receptor antagonist. Administration of glucose (7.5 g/kg body weight) also prevented the stress-induced apoptosis of thymocytes. These results suggested that cold-stress might enhance the secretion of glucocorticoid from the adrenal gland and induce apoptosis of thymocytes by some glucose-inhibitable mechanism.