Studies on the involvement of lipolytic enzymes in endogenous lipolysis of the isolated rat heart

Short-term incubation of cardiac myocytes with isoprenaline has no effect on heparin-releasable or cellular lipoprotein lipase activity

“…Palmer et al [26] have reported that LPL-like activity in heart homogenates was increased by perfusion with adrenaline, phosphodiesterase inhibitors or dibutyryl cyclic AMP, but other investigators have shown that perfusion of hearts with noradrenaline or glucagon produced either no change [27] or a decline [28,29] in residual LPL activity in postnuclear fractions from heparin-perfused hearts, depending on the time of perfusion. There is a clearer consensus, however, that a chronic increase in cyclic AMP produced by the administration of cholera toxin to intact rats does increase heart LPL activity in both heparin-releasable and residual fractions [30,31].…”

Involvement of lysosome-like particles in the metabolism of endogenous myocardial triglycerides during ischemia/reperfusion. Uptake and degradation of triglycerides by lysosomes isolated from rat heart

“…The engulfment of lipid-droplcts by lysosomal membranes was demonstrated earlier (39). The lysosomal origin of such a pool of metabolically active triglycerides has been proposed by us previously (34). In addition the maintenance of lipolysis in cycloheximide-pretreated rat hearts, with a virtually absent neutral lipase activity and a normal acid lipase activity, and the large decrease in the relative specific distribution of triglycerides in the lysosomal fraction after hormonal stimulation (34), support the involvement of lysosomes in endogenous myocardial lipolysis.…”

“…Sevcral lipases have been demonstrated in heart tissue but the lipase responsible for basal and glucagonstimulated endogenous lipolysis is still a matter of dispute, although the inhibition of lipolysis in isolated perfused rat hearts in the presence of methylamine (11,12,22) and other lysosomotropic agents (8) favors a distinctive role of the acid lysosomal lipase in the lipolysis of endogenous triglycerides. The existence of several, distinct pools of triglycerides has been proposed previously (20,34). About one-half of the myocardial endogenous triglycerides present however, appears to be metabolically available (20,36).…”

“…About one-half of the myocardial endogenous triglycerides present however, appears to be metabolically available (20,36). Based on the decrease in the relative specific distribution and the large decrease in the specific triglyceride content of myocardial lysosomes during perfusion we proposed that these organelles, or related lysosomal-like particles, form at least a part of the metabolically active pool of triglycerides in the heart (34,38). The present study was undertaken to elucidate further the existence and origin of the metabolically active pool of myocardial triglycerides and to investigate whether lysosomes or lysosomal-like particles are involved in the process of endogenous lipolysis in the isolated rat heart.…”

“…The intracellular triglycerides are present as cytosolic lipid droplets (35) and membrane-bound particles (3), probably of lysosomal origin (5,8,9,38,39). Cell fractionation studies have revealed the presence of a lysosomal fraction enriched in triglycerides (1,19,34). Sevcral lipases have been demonstrated in heart tissue but the lipase responsible for basal and glucagonstimulated endogenous lipolysis is still a matter of dispute, although the inhibition of lipolysis in isolated perfused rat hearts in the presence of methylamine (11,12,22) and other lysosomotropic agents (8) favors a distinctive role of the acid lysosomal lipase in the lipolysis of endogenous triglycerides.…”