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Adipose Tissue Free Fatty Acid Storage in vivo – Effects of Insulin versus Niacin as a Control for Suppression of Lipolysis


Ali, A., Mundi, M., Koutsari, C., Bernlohr, D., and Jensen, M.



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Endocrine Research Unit, Mayo Clinic, Rochester, MN,; King Abdulla International Medical Research Center, National Guard Health Affairs, Riyadh, Saudi Arabia,; Biochemistry, Molecular Biology & Biophysics, University of Minnesota, Minneapolis, MN, USA.



Insulin stimulates the translocation FATP1 to plasma membrane, and thus greater FFA uptake, in adipocyte cell models. Whether insulin stimulates greater FFA clearance into adipose tissue in vivo is unknown. We tested this hypothesis by comparing direct FFA storage in subcutaneous adipose tissue during insulin vs. niacin-medicated suppression of lipolysis. We measured direct FFA storage in abdominal and femoral subcutaneous fat in 10 and 11 adults, respectively, during euglycemic hyperinsulinemia or after oral niacin to suppress FFA compared with 11 saline control experiments. Direct palmitate storage was assessed using a [U-13C]palmitate infusion to measure palmitate kinetics and an IV palmitate radiotracer bolus/timed biopsy. Plasma palmitate concentrations and flux were suppressed to 23 ± 3 and 26 ± 5 µmol•L-1 (P = 0.91) and 44 ± 4 and 39 ± 5 µmol•min-1 (P = 0.41) in the insulin and niacin groups, respectively; much less (P < 0.001) than the saline control group (102 ± 8 µmol•L-1 and 104 ± 12 µmol•min-1, respectively). Abdominal palmitate storage rates were 0.25 ± 0.05 vs. 0.25 ± 0.07 vs. 0.32 ± 0.05 µmol•kg adipose lipid-1•min-1, respectively (P=NS) in the insulin, niacin and saline groups and 0.19 ± 0.06 vs. 0.20 ± 0.05 vs. 0.31 ± 0.05 µmol•kg adipose lipid-1•min-1, respectively (P=NS) in the femoral adipose depot. In conclusion, insulin does not increase FFA storage in adipose tissue compared with niacin, which suppresses lipolysis via a different pathway.