Glucose disappearance rate in rhesus monkeys: Some technical considerations

The intravenous glucose tolerance test (IVGTT) has been widely used as a tool to assist in the diagnosis of diabetes mellitus. Glucose disappearance rate (K_G) is calculated as an indicator of relative glucose tolerance; however, a standardized dose, consistent sampling times, and a consistent formula for the calculation of K_G have not yet been established for rhesus monkeys. Interpretation of results reported by different laboratories has, therefore, been rendered difficult. In the present study, 48 IVGTTs obtained from 33 male rhesus monkeys ranging widely in glucose tolerance have been analyzed. Various formulas for calculating K_G values have been tested in all experiments including a range of different pairs of time points, as well as the t_1/2. Regression analysis revealed that the log_e transformation of the plasma glucose levels obtained after an intravenous glucose load were best fitted with a straight line during the period between five and 20 minutes (R² = 0.97 ± 0.005). The use of time points prior to the five-minute value tended to produce spuriously larger K_G values, while sampling points that were later than 30 min occasionally produced an invalid K_G because in some monkeys the plasma glucose levels had already returned to basal levels. The advantages of using the five- and 20-minute glucose levels in calculating the K_G include (1) the optimal reflection of tissue uptake of glucose; (2) the relatively short sampling time required to obtain an accurate, consistent, and meaningful value for K_G; and (3) the relative ease in the calculation of K_G.