Marked Reutilization of Free Fatty Acids during Activated Lipolysis in Human Skeletal Muscle

Release of glycerol and free fatty acids (FFA)was investigated in human skeletal muscle strips. In the basal state, glycerol and FFAwere released at almost equimolar rates (0.3 nmol/ng tissue90 min). A nonselective -adrenoceptor agonist, iso-prenaline, caused a concentration-dependent stimulation of glycerol release, whereas FFA release was unaffected. Basal and isoprenaline-induced glycerol release correlated posi-tivelywith theageof thedonors (r 0.5,P< 0.005) butnotwith their bodymass index (P> 0.4). Biochemical experimentswith hormone-sensitive lipase (HSL) showed that most enzyme ac-tivity was both in the cytosol and mitochondrial fraction and that it constituted the common long and active form of the protein. Electron microscopy studies in rat skeletal muscle using labeled highly specific HSL antibodies verified the cy-tosolic location of HSL and, furthermore, indicated an accu