Abstract
Insulin signaling in the central nervous system (CNS) is required for the inhibitory effect of insulin on glucose production. Our aim was to determine whether the CNS is also involved in the stimulatory effect of circulating insulin on the tissue-specific retention of fatty acid (FA) from plasma. In wild-type mice, hyperinsulinemic-euglycemic clamp conditions stimulated the retention of both plasma triglyceride-derived FA and plasma albumin-bound FA in the various white adipose tissues (WAT) but not in other tissues, including brown adipose tissue (BAT). Intracerebroventricular (ICV) administration of insulin induced a similar pattern of tissue-specific FA partitioning. This effect of ICV insulin administration was not associated with activation of the insulin signaling pathway in adipose tissue. ICV administration of tolbutamide, a K(ATP) channel blocker, considerably reduced (during hyperinsulinemic-euglycemic clamp conditions) and even completely blocked (during ICV administration of insulin) WAT-specific retention of FA from plasma. This central effect of insulin was absent in CD36-deficient mice, indicating that CD36 is the predominant FA transporter in insulin-stimulated FA retention by WAT. In diet-induced insulin-resistant mice, these stimulating effects of insulin (circulating or ICV administered) on FA retention in WAT were lost. In conclusion, in insulin-sensitive mice, circulating insulin stimulates tissue-specific partitioning of plasma-derived FA in WAT in part through activation of K(ATP) channels in the CNS. Apparently, circulating insulin stimulates fatty acid uptake in WAT but not in BAT, directly and indirectly through the CNS.
Highlights
Insulin signaling in the central nervous system (CNS) is required for the inhibitory effect of insulin on glucose production
To establish to what extent tissue-specific fatty acid (FA) uptake from plasma is stimulated by circulating insulin, we compared in various organs the retention of FA derived from both glycerol tri[3H]oleate-labeled VLDL-like emulsion particles and albumin-bound [14C]oleic acid between mice during hyperinsulinemic-euglycemic clamp conditions and mice in basal conditions infused with vehicle (Fig. 1)
This study addressed the effects of circulating insulin on tissue-specific TG-derived FA and albumin-bound FA retention, and the role of central insulin action in these effects
Summary
Insulin signaling in the central nervous system (CNS) is required for the inhibitory effect of insulin on glucose production. ICV administration of tolbutamide, a KATP channel blocker, considerably reduced (during hyperinsulinemic-euglycemic clamp conditions) and even completely blocked (during ICV administration of insulin) WAT-specific retention of FA from plasma. This central effect of insulin was absent in CD36-deficient mice, indicating that CD36 is the predominant FA transporter in insulin-stimulated FA retention by WAT. In insulinsensitive mice, circulating insulin stimulates tissue-specific partitioning of plasma-derived FA in WAT in part through activation of KATP channels in the CNS. P.C.N. Rensen is an Established Investigator of the Netherlands Heart Foundation (2009T038).
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