lipolízist

Lipolysis is a metabolic process that hydrolyzes stored triglycerides into glycerol and non-esterified fatty acids (NEFAs), primarily in adipose tissue but also in muscle and liver. In adipocytes, lipolysis mobilizes energy reserves to supply substrates for energy production during fasting or increased activity.

The hydrolysis of triglycerides occurs in a stepwise sequence catalyzed by lipases: adipose triglyceride lipase (ATGL) initiates the reaction converting triglycerides to diglycerides; hormone-sensitive lipase (HSL) further converts diglycerides to monoglycerides; monoglyceride lipase (MGL) completes the process yielding glycerol and free fatty acids. The activity is regulated by hormonal signals: catecholamines activate via beta-adrenergic receptors increasing cyclic AMP and protein kinase A, which stimulates ATGL and HSL; insulin inhibits lipolysis by reducing cAMP. Cortisol and growth hormone can promote lipolysis; energy demand and tissue needs modulate the balance.

Physiological roles include providing substrates for beta-oxidation and gluconeogenesis during fasting or exercise; glycerol can be converted to glucose in the liver, while fatty acids serve as a primary energy source for peripheral tissues and, in brown adipose tissue, for thermogenesis. Lipolysis occurs mainly in adipose tissue but also at other sites, including the liver.

Clinical relevance encompasses the regulation of lipolysis in health and disease. In obesity, chronically elevated free fatty acids can contribute to insulin resistance and metabolic syndrome; in cachexia or certain cancers, excessive lipolysis drives weight loss. Measuring plasma glycerol and free fatty acids can assess lipolytic rate, and pharmacological approaches may target lipolytic pathways in metabolic disorders.