AMPK stimulation increases LCFA but not glucose clearance in cardiac muscle in vivo

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Abstract
AMP-activated protein kinase (AMPK) independently increases glucose and long-chain fatty acid (LCFA) utilization in isolated cardiac muscle preparations. Recent studies indicate this may be due to AMPK-induced phosphorylation and activation of nitric oxide synthase (NOS). Given this, the aim of the present study was to assess the effects of AMPK stimulation by 5-aminoimidazole-4-carboxamide-1-β-d-ribofuranoside (AICAR; 10 mg·kg−1·min−1) on glucose and LCFA utilization in cardiac muscle and to determine the NOS dependence of any observed effects. Catheters were chronically implanted in a carotid artery and jugular vein of Sprague-Dawley rats. After 4 days of recovery, conscious, unrestrained rats were given either water or water containing 1 mg/ml nitro-l-arginine methyl ester (l-NAME) for 2.5 days. After an overnight fast, rats underwent one of four protocols: saline, AICAR, AICAR + l-NAME, or AICAR + Intralipid (20%, 0.02 ml·kg−1·min−1). Glucose was clamped at ∼6.5 mM in all groups, and an intravenous bolus of 2-deoxy-[3H]glucose and [125I]-15-( p-iodophenyl)-3- R, S-methylpentadecanoic acid was administered to obtain indexes of glucose and LCFA uptake and clearance. Despite AMPK activation, as evidenced by acetyl-CoA carboxylase (Ser221) and AMPK phosphorylation (Thr172), AICAR increased cardiac LCFA but not glucose clearance. l-NAME + AICAR established that this effect was not due to NOS activation, and AICAR + Intralipid showed that increased cardiac LCFA clearance was not LCFA-concentration dependent. These results demonstrate that, in vivo, AMPK stimulation increases LCFA but not glucose clearance by a NOS-independent mechanism.

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