title: Marked reutilization of free fatty acids during activated lipolysis in human skeletal muscle.
abstract: Release of glycerol and free fatty acids (FFA) was investigated in human skeletal muscle strips. In the basal state, glycerol and FFA were released at almost equimolar rates (0.3 nmol/ng tissue.90 min). A nonselective beta-adrenoceptor agonist, isoprenaline, caused a concentration-dependent stimulation of glycerol release, whereas FFA release was unaffected. Basal and isoprenaline-induced glycerol release correlated positively with the age of the donors (r = 0.5, P < 0.005) but not with their body mass index (P > or = 0.4). Biochemical experiments with hormone-sensitive lipase (HSL) showed that most enzyme activity 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 cytosolic location of HSL and, furthermore, indicated an accumulation of HSL-adjoining mitochondria. These results suggest that FFA produced in myocytes during catecholamine-induced lipolysis are retained by the muscle and, therefore by inference, reused. It is conceivable that efficient hydrolysis of acylglycerol by HSL located in the cytosol as well as near the mitochondria may facilitate mitochondrial FFA oxidation. In addition, muscle lipolysis activity increases during aging and may be independent of total body fat.
authors.affiliation: Department of Vascular Surgery, Karolinska University Hospital Huddinge, S-141 86 Stockholm, Sweden. staffan.enoksson@cfss.ki.se
authors.forename: Staffan
authors.initials: S
authors.lastname: Enoksson
authors.forename: Eva
authors.initials: E
authors.lastname: Hagström-Toft
authors.forename: Joakim
authors.initials: J
authors.lastname: Nordahl
authors.forename: Kjell
authors.initials: K
authors.lastname: Hultenby
authors.forename: Nils
authors.initials: N
authors.lastname: Pettersson
authors.forename: Bengt
authors.initials: B
authors.lastname: Isaksson
authors.forename: Johan
authors.initials: J
authors.lastname: Permert
authors.forename: Rolf
authors.initials: R
authors.lastname: Wibom
authors.forename: Cecilia
authors.initials: C
authors.lastname: Holm
authors.forename: Jan
authors.initials: J
authors.lastname: Bolinder
authors.forename: Peter
authors.initials: P
authors.lastname: Arner
mesh_terms: D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D000818:Animals; D005230:Fatty Acids, Nonesterified / Q000378:metabolism*; D005260:Female; D005990:Glycerol / Q000378:metabolism; D006801:Humans; D007545:Isoproterenol / Q000494:pharmacology; D008066:Lipolysis / Q000502:physiology*; D008297:Male; D008875:Middle Aged; D018482:Muscle, Skeletal / Q000187:drug effects / Q000378:metabolism* / Q000648:ultrastructure; D051381:Rats; D017207:Rats, Sprague-Dawley
chemical_list: D005230:Fatty Acids, Nonesterified; D007545:Isoproterenol; D005990:Glycerol