Abstract
Background:
Insulin suppresses lipolysis through direct effects on adipocytes and indirectly through its neuronal receptors by reducing sympathetic outflow to adipose tissue.
Results:
Three-day voluntary overfeeding impairs the ability of brain insulin to suppress lipolysis
in vivo
.
Conclusion:
Unrestrained lipolysis that is commonly seen in obesity and diabetes can be caused by impaired brain insulin action.
Significance:
Enhancing brain insulin action potentially restores lipolytic control.
Insulin controls fatty acid (FA) release from white adipose tissue (WAT) through direct effects on adipocytes and indirectly through hypothalamic signaling by reducing sympathetic nervous system outflow to WAT. Uncontrolled FA release from WAT promotes lipotoxicity, which is characterized by inflammation and insulin resistance that leads to and worsens type 2 diabetes. Here we tested whether early diet-induced insulin resistance impairs the ability of hypothalamic insulin to regulate WAT lipolysis and thus contributes to adipose tissue dysfunction. To this end we fed male Sprague-Dawley rats a 10% lard diet (high fat diet (HFD)) for 3 consecutive days, which is known to induce systemic insulin resistance. Rats were studied by euglycemic pancreatic clamps and concomitant infusion of either insulin or vehicle into the mediobasal hypothalamus. Short term HFD feeding led to a 37% increase in caloric intake and elevated base-line free FAs and insulin levels compared with rats fed regular chow. Overfeeding did not impair insulin signaling in WAT, but it abolished the ability of mediobasal hypothalamus insulin to suppress WAT lipolysis and hepatic glucose production as assessed by glycerol and glucose flux. HFD feeding also increased hypothalamic levels of the endocannabinoid 2-arachidonoylglycerol after only 3 days. In summary, overfeeding impairs hypothalamic insulin action, which may contribute to unrestrained lipolysis seen in human obesity and type 2 diabetes.