ALTERATION OF ENERGY SUBSTRATES UTILIZED BY SMALL AND LARGE THYMOCYTES IN RESTING AND STIMULATING STATE

Glucose and glutamine are well known as a major energy source for prol iferating rat thymocytes. Nevertheless, it is still unclear whether th ere is a difference in utilization of energy substrates between the ma ture and immature thymocytes. in the present study, we prepared small and large thymocytes from male Wistar rats by Percoll density-gradient centrifugation to answer these questions. The average diameter of the large thymocytes was approximately 1.6 times that of the small thymoc ytes. By now cytometry analysis, the most of small thymocytes was imma ture T cells (CD4(+)8(+) cells) and about 20% of the large thymocytes was CD4(+)8(+) T cells. After phytohemagglutinin (PHA) and concanavali n A (ConA) stimulations in vitro, large thymocytes showed significantl y higher incorporation of [H-3]thymidine. In contrast, small thymocyte s did not exhibit a proliferative response at all. After 48 hours cult ure of large or small thymocytes with or without ConA stimulation, the alterations in the medium concentrations of glucose, pyruvate, lactat e, ketone bodies, free fatty acids (FFA), and amino acids were analyze d. The resting large thymocytes showed significantly higher consumptio n of glucose and production of lactate, which were further elevated in response to ConA. in contrast, the resting small thymocytes showed sl ight consumption of glutamine and production of glucose. When small th ymocytes were stimulated with ConA, a change to glucose consumption an d lactate production was observed without an increase in either total substrate consumption or proliferative response. These results suggest that the substrates utilized by thymocytes vary from immature to matu re cells and that these changes of energy substrates utilized by thymo cytes are closely related to the maturation and function of thymic T l ymphocytes.