Regulation of Adipocyte Lipolysis Catecholamines Epinephrine & Norepinephrine Beta Adrenergic Receptors Stimulate Alpha Adrenergic Receptors Inhibit Insulin Inhibitory

Catecholamines Stimulatory Inhibitory B-Adrenergic Receptors Activates Stimulatory G-Protein Activates Adenylate Cyclase Generates cAMP Activates cAMP-dependent protein kinase Phosphorylates HSL & Perilipins Break down triglycerides Inhibitory A-Adrenergic Receptors Activates Inhibitory G-protein Inhibits Adenylate Cyclase

Catecholamines stimulate HSL to break down triglycerides to fatty acids and glycerol Fatty acids and glycerol are released into the blood and circulated to other body tissues

ATGL Adipose Triglyceride Lipase Enzyme that may be responsible for catalyzing the initial steps of triglyceride hydrolysis. Zimmermann et al. (2004) HSL knock-out mice showed an accumulation of diglycerides, suggesting that additional lipases may be present that can hydrolyze the first ester bond of triglycerides Still controversial

Lipoprotein Lipase (LPL) Phosphatidylinositol 3-Kinase (PI3K) Insulin Lipoprotein Lipase (LPL) Phosphatidylinositol 3-Kinase (PI3K) Hydrolyzes Phosphorylates Plasma Triglycerides Phosphodiesterase-3 Degrades Into cAMP FFA

Insulin & LPL

PI3K Insulin Phosphorylates LPL Hydrolyzes triglycerides in the blood to increase FFA levels PI3K Inhibits lipolysis in adipose cells Mediates insulin-stimulated glucose uptake Phosphodiestesterase-3 Degrades