Insulin decreases AMPK phosphorylation in cardiac muscle in vivo

Increasing evidence has shown that the AMPK signaling pathway and the insulin signaling pathway may interact with each other in regulating in vivo protein and energy metabolism. The aim of the present study was to determine if insulin regulates AMPK phosphorylation in vivo in cardiac muscle of mice. If so, we further asked whether insulin‐mediated alterations in AMPK phosphorylation are dose dependent and whether they are mediated by mTOR. To accomplish these goals, two‐month‐old cardiac specific kinase dead mTOR transgenic mice (αMHC‐mTORkd) and nontransgenic littermates were fasted overnight, followed by a single intraperitoneal injection of insulin (1.5 IU or 100 IU/kg BW). Sixty minutes later, the animals were sacrificed and AMPK phosphorylation on Thr172 in cardiac muscle was determined by Western blotting. Our results showed that insulin inhibited fasting‐induced AMPK phosphorylation in cardiac muscle in a dose dependent manner. A supraphysiological dose (1.5 IU/kg) and pharmacological dose (100 IU/kg) of insulin decreased AMPK phosphorylation by 30% and 60%, respectively. A similar inhibition was also seen in the heart of αMHC‐mTORkd mice. We conclude that in vivo AMPK signals are down regulated in a dose‐dependent manner by insulin via an mTOR‐independent pathway. This provides a molecular explanation of the beneficial roles of insulin infusion in post‐ischemic heart recovery.