Epinephrine binds to a beta-adrenergic receptor in the cell membrane of the adipocyte, which causes cAMP to be generated inside the cell.
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The cAMP activates a protein kinase, which phosphorylates and thus, in turn, activates a hormone-sensitive lipase in the fat cell.
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This lipase cleaves free fatty acids from their attachment to glycerol in the fat stored in the fat droplet of the adipocyte.
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The free fatty acids and glycerol are then released into the blood.
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The activity of hormone sensitive lipase is regulated by the circulation hormones insulin, glucagon, norepinephrine, and epinephrine.
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#LIPOLYSIS_Concept !
Under physiological conditions when metabolic fuels are low and/or energy demand is high, such as fasting, exercise, and cold exposure, adipocytes mobilize their TAG stores via the catabolic process of lipolysis to supply fuel to peripheral tissues.
Lipolysis is a highly regulated biochemical process that generates glycerol and FFAs from the enzymatic cleavage of TAGs by lipases and can occur in all tissues, although it is most prevalent in AT where the bulk of TAG is stored.
TAGs are broken down into diacylglycerols (DAGs) and monoacylglycerols (MAGs) by the sequential action of adipocyte triglyceride lipase (ATGL), hormone sensitive lipase (HSL), and monoacylglycerol lipase (MGL).
At each step a single FFA is released, and in the final step MGL releases the glycerol backbone from the last FFA.
These breakdown products can be re-esterified within the adipocyte or released into circulation to be used by other tissues, including by the liver for gluconeogenesis (glycerol) and for oxidative phosphorylation by muscle or other oxidative tissues.