Lipolys

Lipolys, commonly referred to as lipolysis, is the enzymatic breakdown of lipids, primarily triacylglycerols, into glycerol and free fatty acids. The process provides energy during fasting or increased demand and supplies fatty acids to other tissues as needed. It occurs mainly in adipose tissue but also in muscle, liver, mammary glands, and the digestive tract.

In adipose tissue, lipolysis proceeds through a sequential action of three major lipases. Adipose triglyceride lipase (ATGL) initiates the process by converting triglycerides to diacylglycerols. Hormone-sensitive lipase (HSL) then hydrolyzes diacylglycerols to monoacylglycerols, and monoacylglycerol lipase (MGL) completes the reaction by producing glycerol and free fatty acids. The released fatty acids enter the bloodstream bound to albumin, while glycerol travels to the liver for energy or gluconeogenesis. Lipid droplets in adipocytes are regulated by proteins such as perilipin and CGI-58 to control lipase access.

In the digestive system, lipolysis refers to the hydrolysis of dietary triglycerides by pancreatic triglyceride lipase, with colipase and bile salts facilitating the process. This yields two free fatty acids and a monoacylglycerol, which are absorbed by enterocytes and reassembled into triglycerides for chylomicrons.

Regulation is tightly controlled by hormonal signals. Catecholamines stimulate lipolysis via β-adrenergic receptors and increased cAMP, while insulin inhibits it. Physiologically, lipolysis supports energy homeostasis during fasting, cold exposure, and lactation; dysregulation is associated with metabolic disorders such as obesity and insulin resistance.