Marked Heterogeneity of Human Skeletal Muscle Lipolysis at Rest
In this study, variations in lipolysis among different muscle groups were examined by measuring local net glycerol release in vivo in healthy, normal-weight subjects (n = 11) during rested, postabsorptive conditions. Microdialysis of the gastrocnemius, deltoid, and vastus lateralis muscle regions revealed that extracellular glycerol concentrations of these three muscle regions were 84.7 ± 6.7, 59.7 + 7.3, and 56.4 ± 7.5 μmol/l, respectively, and the arterial plasma glycerol concentration was 44.8 ± 2.3 μmol/l (P = 0.0003–0.006, gastrocnemius vs. others). Local tissue blood flow, as measured by Xe clearance, did not differ among the regions. Net glycerol release was significantly higher in gastrocnemius muscle than in the two other regions. There were no regional differences in glycerol uptake when studied during glycerol infusion. Gastrocnemius muscle showed a dominance of type 1 fibers (70%), whereas the vastus lateralis muscle had equal distribution of fiber types (P = 0.02). No differences in intramuscular triaclyceride content, perimuscular fat, or the adipocyte-specific protein perilipin were observed among the muscle regions. Triglyceride turnover in the gastrocnemius muscle was 3.3 + 1.4% over 24 h, which is about 10 times more rapid than the turnover rate in subcutaneous adipose tissue (P < 0.01). Thus there were marked differences in lipolytic activity among skeletal muscle groups at rest, possibly reflecting variations in fiber type.
Address correspondence and reprint requests to Dr. Eva Hagström-Toft, Center of Metabolism and Endocrinology, M63, Huddinge University Hospital, SE-141 86 Stockholm, Sweden. E-mail:.
Received for publication 24 August 2001 and accepted in revised form 26 August 2002.
FFA, free fatty acid; H-E, hematoxylin-eosin; HSL, hormone-sensitive lipase; IA, interstitial-arterial; LPL, lipoprotein lipase; PS value, permeability surface product area; TBF, tissue blood flow; TG, triglyceride.