Changes in lymphocyte subpopulations in Otsuka Long-Evans Tokushima fatty rats

The changes in the thymus, spleen and adrenal glands associated with age from 5 weeks to 12 weeks old and lymphocyte subpopulations in the thymus and spleen were examined in the new strain of diabetic rats, Otsuka Long-Evans Tokushima Fatty (OLETF). Effects of restraint stress were also compared with those in the control strain, Long-Evans Tokushima (LETO) rats. The body weight, and weights of spleen and adrenal glands significantly increased with age in both strains, while the weight of the thymus in OLETF rats decreased although it increased in LETO rats. The percentage of CD4(+)CD8(-) increased and CD4(+)CD8(+) decreased in the thymus with age in both strains, and these changes were significantly enhanced in OLETF rats. The numbers of cells positive for nick end-labeling in the thymus were greater in OLETF than in LETO rats as shown by histological examination, although no significant difference was observed in the spleen or adrenal gland. The changes in lymphocyte subpopulations in the spleen, and the plasma corticosterone levels associated with age were comparable for both strains. The responses of these factors to restraint stress were not significantly different between the two strains. It has been suggested that the changes in T cell subpopulations in the thymus of OLETF rats may be simply induced by the enhanced apoptosis associated with age.