Method of insulin administration has no effect on insulin sensitivity estimates from the insulin-modified minimal model protocol

The effect of the method of insulin administration on insulin sensitivity estimates from the insulin modified minimal model (MINMOD) protocol was evaluated using the tolbutamide-boosted protocol as a reference, The study included 21 nondiabetic men ages 40 +/- 2 years (mean +/- SE) with a BMI of 26.6 +/- 1.1 kg/m(2). Each subject underwent four frequently sampled intravenous glucose tolerance tests (FSIGTT), one with tolbutamide and three with the same insulin dosage (0.03 U/kg) given as a bolus or infusion over 5 or 10 min, The insulin sensitivity index (S-I) of each subject was calculated from each FSIGTT with MINMOD. Insulin sensitivity indexes from the four FSIGTTs were highly correlated (r > 0.85, P < 0.001), S-I(insulin) from the bolus and the 5- and 10-min infusion protocols were similar, but were 21 +/- 5, 29 +/- 5, and 23 +/- 4% lower than S-I(tolbutamide), respectively. S-G(tolbutamide) and S-G(insulin) were not different among the four protocols and were significantly correlated (r > 0.55, P < 0.01), Thus the tolbutamide and insulin protocols must not be used interchangeably in any single cross-sectional or longitudinal study, When the same insulin dosage is used, the method of its administration has no bearing on insulin sensitivity estimates from the insulin-modified FSIGTT. The same method of insulin administration should be used, however, in any single study for purpose of standardization.