Mechanisms of glucose intolerance during triglyceride infusion.

Lipid infusions may affect glucose tolerance by effects on glucose production or utilization. We performed double-labeled oral glucose tolerance tests with and without a lipid infusion in eight normal subjects. During the lipid infusion, plasma glucose and insulin levels were higher, showing some insulin resistance. The increased glucose level was due to a higher total glucose appearance rate, partly reproducible by a control infusion of glycerol [saline 1,181 +/- 71 mg . kg-1 . 330 min-1 vs. lipid 1,388 +/- 100 (P < 0.05) vs. glycerol 1,276 +/- 126 (NS)]. The tracer-determined appearance rate of exogenous glucose was higher with lipid infusion but was probably overestimated because of higher 13C recycling into glucose. Residual systemic glucose production was increased but was reproducible by the glycerol infusion. Total glucose disposal was increased. This was observed despite a lower stimulation of total glucose oxidation as measured by indirect calorimetry, whereas oxidation of exogenous glucose was normal after correction for the lipid-induced modification of excretion rate of 13CO2. Accordingly, glucose nonoxidative disposal was increased. These moderate modifications of glucose metabolism (increased appearance, increased nonoxidative disposal, and lower total oxidation) have been reported in starvation-induced or spontaneously impaired glucose tolerance. Further impairment, especially decreased nonoxidative glucose disposal, seems to be required to produce non-insulin-dependent diabetes mellitus.