Localization and function of myocardial lipolysis.

Mobilization of triacylglycerol stored in heart cells is accomplished by the combined action of lysosomal (acid) lipase and microsomal monoacylglycerol lipase or carboxylesterase. Non(heparin)-releasable neutral or alkaline lipase is similar to non(readily)-releasable lipoprotein lipase (LPL). The enzyme is mainly localized extracellularly. Non(readily)-releasable LPL probably represents LPL in caveola or vacuolae of vascular endothelium and/or LPL on myocardial interstitium. It contributes to the uptake of lipoprotein constituents in heart cells. Glycerol, an endproduct of lipolysis, is not a reliable marker for the net mobilization of lipid stored in heart cells. It is formed both intra- and extracellularly, and does not reflect the rate of oxidation of part of free fatty acids formed.