Effects of age and sex on certain metabolic functions and mitogenic activity in rat thymocytes

In female and male Sprague-Dawley CD rats, both total mass and thymocyte content of thymus gland peaked during the second month of life and then declined with age. Values of both 2-deoxyglucose (2-DG) uptake and thymidine incorporation in thymocytes were higher in cells from females than from males in all age groups studied, these differences being significant only at 3 months of age and onward. In cells from both sexes, thymocyte 2-DG uptake and thymidine incorporation were at maximum at the first and second months of age, respectively. Thereafter, in cells from males, 2-DG uptake and thymidine incorporation declined rapidly with advancing age; whereas in cells from females, these functions started to decline only after 6 months. In both freshly isolated and cultured cells, the concanavalin A (Con A)-induced increase in thymidine incorporation was also affected by age, peaking at about 3 months. The proportionate effect of Con A on thymidine incorporation was similar in cells of both sexes, but because of differences in basal values, the absolute increase in thymidine incorporation produced by Con A was higher in cells from females than from males. Since thymocytes are the progenitors of T-cells, these changes in the number and function of thymocytes may be the forerunner of similar functional abnormalities that are seen in circulating T-cells, but at a later age.