Effect of insulin infusion on spillover of meal-derived fatty acids.

CONTEXT: Spillover of chylomicron triglyceride fatty acids directly into the circulation as free fatty acids (FFAs) during lipoprotein lipase hydrolysis may contribute to the elevated total FFAs seen in insulin-resistant states.
OBJECTIVE: The objective of the study was to determine whether spillover is regulated by rates of intracellular lipolysis, we studied overweight and obese nondiabetic subjects (n = 7) on two occasions, during infusion of saline and insulin.
DESIGN: During insulin infusion (20 mU · m(-2) · min(-1)), plasma glucose was clamped at the concentration achieved during saline infusion. On both study days, subjects sipped 1-2 oz of a liquid mixed meal every 15 min for 6.5 h to achieve steady-state chylomicron and FFA concentrations. Spillover was measured with infusions of [(3)H]triolein and [U-(13)C] oleate.
RESULTS: Glucose concentrations were similar during saline compared with insulin (113 ± 2 vs. 113 ± 1 mg/dl, P = NS). Insulin levels during saline and insulin infusion were 18 ± 3 and 44 ± 5 μU/ml, respectively. Glucose infusion rate during insulin infusion was 5.5 ± 1.0 mg · kg fat-free mass(-1) · min(-1). Plasma FFA concentrations were lower during insulin compared with saline (75 ± 8 vs. 124 ± 13 μmol/liter, P = 0.002). Oleate rate of appearance was lower during insulin vs. saline (27 ± 3 vs. 36 ± 5 μmol/min, P = 0.004). Spillover was similar during saline and insulin (26 ± 2 vs. 25 ± 2%, P = 0.60).
CONCLUSIONS: These results indicate that suppression of intracellular lipolysis with insulin does not reduce lipoprotein lipase-mediated spillover in humans during meal absorption. It is possible that spillover did not decrease because of an impaired or absent antilipolytic effect of increased insulin concentrations in visceral fat.