Adaptation of Insulin Clearance to Metabolic Demand Is a Key Determinant of Glucose Tolerance.

Abstract

With the development of insulin resistance (IR), there is a compensatory increase in the plasma insulin response to offset the defect in insulin action to maintain normal glucose tolerance. The insulin response is the result of two factors: insulin secretion and metabolic clearance rate of insulin (MCR_I). Subjects (104 with normal glucose tolerance [NGT], 57 with impaired glucose tolerance [IGT], and 207 with type 2 diabetes mellitus [T2DM]), divided in nonobese and obese groups, received a euglycemic insulin-clamp (40 mU/m² ⋅ min) and an oral glucose tolerance test (OGTT) (75 g) on separate days. MCR_I was calculated during the insulin-clamp performed with [3-³H]glucose and the OGTT and related to IR: peripheral (glucose uptake during the insulin clamp), hepatic (basal endogenous glucose production × fasting plasma insulin [FPI]), and adipocyte (fasting free fatty acid × FPI). MCR_I during the insulin clamp was reduced in obese versus nonobese NGT (0.60 ± 0.03 vs. 0.73 ± 0.02 L/min ⋅ m², <i>P</i> < 0.001), in nonobese IGT (0.62 ± 0.02, <i>P</i> < 0.004), and in nonobese T2DM (0.68 ± 0.02, <i>P</i> < 0.03). The MCR_I during the insulin clamp was strongly and inversely correlated with IR (<i>r</i> = -0.52, <i>P</i> < 0.0001). During the OGTT, the MCR_I was suppressed within 15-30 min in NGT and IGT subjects and remained suppressed. In contrast, suppression was minimal in T2DM. In conclusion, the development of IR in obese subjects is associated with a decline in MCR_I that represents a compensatory response to maintain normal glucose tolerance but is impaired in individuals with T2DM.