The effects of cortisol upon glycerol-3-phosphate dehydrogenase in the thymus of the immature mouse

Thymuses of sexually immature female DDS strain mice contain the enzyme glycerol-3-phosphate dehydrogenase(SN-glycerol-3-phosphate: NAD oxidoreductase, EC 1.1.1.8). The activity of this enzyme (GPDH) varied in a circadian fashion with a maximum about 12:00 noon. When determined at 8:00 a.m., total GPDH activity was about 0.49 units/thymus or about 0.05 units/mg protein. Based upon kinetic, Chromatographic, and thermostability properties, it is concluded that the thymus contains predominantly the “adult” form of GPDH. The “fetal” form of the enzyme could not be detected. Total GPDH activity increased in the thymus of the cortisol-treated mouse. Twenty-four h after a single injection of 2 mg Cortisol, total GPDH activity was doubled (0.96 units/thymus). Total GPDH increased to 1.29 units/thymus by 48 h after cortisol injection. During this period thymic weight decreased by about 75% such that the specific activity of GPDH increased about 10 fold (0.53 units/mg protein). GPDH has been extracted and partially characterized from cortisol-treated thymuses. The kinetic, Chromatographic, and thermstability properties of the enzyme from cortisol-treated thymuses resembled that from control thymuses. Cortisol had no detectable effect on hepatic GPDH. Thymuses were disaggregated by mechanical and enzymatic techniques and lymphoid cells were resolved from thymic stroma. Depending upon the technique employed, 10–80% of the activity was recovered in the stroma while 1–30% of the activity was recovered with thymocytes. In all cases, GPDH activity was higher in stromal elements. Enzymatic activity in both stroma and isolated thymocytes increased under the influence of cortisol, but the cortisol-mediated increase in total thymic GPDH undoubtedly results from changes in stromal enzyme activity.