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Lactate and Glycerol Release from Adipose Tissue in Lean, Obese, and Diabetic Women from South Africa¹

Carbohydrate and Lipid Metabolism Research Group (M.-T.v.d.M., B.I.J.), Departments of Chemical Pathology (N.J.C., I.P.G.), Radiology (G.P.S.), and Nuclear Medicine (I.H.B.), Johannesburg Hospital and University of the Witwatersrand Medical School, Johannesburg 2193, South Africa; and Department of Internal Medicine, University of Goteborg, Sahlgren’s Hospital (P.N.L.), S-41345 Goteborg, Sweden

Address all correspondence and requests for reprints to: Dr. M.-T. van der Merwe, Department of Medicine, University of the Witwatersrand Medical School, 7 York Road, Parktown 2193, South Africa. E-mail: 014jhp{at}chiron.wits.ac.za

Abstract

Abnormalities observed in intermediary metabolism may be related to the pathogenesis of obesity-related diseases such as type 2 diabetes. Glycerol and lactate production was estimated in the sc adipose tissue of two anatomical regions of 10 lean (LW), 10 obese (OW), and 10 matched diabetic (DW) black urban women. This was done with the sc microdialysis technique and combined with adipose tissue blood flow (ATBF) rates calculated from ¹³³Xe clearance. Biochemical measurements were made in the postabsorptive and postprandial state. Bioimpedance and computed tomography scans were used to define body composition. DW present with more visceral fat (DW, 138 ± 5.0; OW, 66.6 ± 5.0 cm; P < 0.01). This was associated with elevated free testosterone levels (DW, 1.21 ± 0.1; OW, 0.75 ± 0.1 nmol/L; P < 0.05). The fasting FFA, glycerol, and lactate levels increased across the three groups (LW < OW < DW). During the oral glucose tolerance test, glucose levels were elevated in DW, with higher insulin levels [0 h: DW, 207 ± 8.6; OW, 100 ± 7.2 pmol/L (P < 0.01); 1 h: DW, 410 ± 15.2; OW, 320 ± 10.9 pmol/L (P < 0.05)], but with a flat Cpeptide response (1 h: DW, 932 ± 40; OW, 1764 ± 40 pmol/L; P < 0.05). Plasma lactate levels increased significantly in LW and OW at 1 h (P < 0.001), but remained lower in LW vs. OW for all time points. ATBF was highest in LW [abdominal, 0 h: DW, 4.5 ± 0.2; OW, 1.7 mL/100 g·min (P < 0.01); femoral, 0 h: DW, 3.4 ± 0.2; OW, 1.8 ± 0.3 mL/100 g·min (P < 0.01)]. ATBF did not increase in DW during the oral glucose tolerance test. Glycerol release (GR) was used to assess the lipolytic rate and was highest in LW in the abdominal area [0 h: LW, 1.7 ± 0.2; OW, 1.1 ± 0.2 µmol/kg·min (P < 0.05); DW, 0.78 ± 0.05 µmol/kg·min (P < 0.05 vs. OW)]. By contrast, GR was higher in the femoral area of OW (0 h: OW, 1.6 ± 0.2; LW, 1.15 ± 0.1 µmol/kg·min; P < 0.05). Regional differences were observed for GR in both OW and DW (femoral > abdominal). Lactate release (LR) was low in DW [abdominal, 0 h: DW, 3.5 ± 0.4; OW, 7.8 ± 1.0 µmol/kg·min (P < 0.001); femoral, 0 h: DW, 3.1 ± 0.3; OW, 9.0 ± 0.9 µmol/kg·min (P < 0.001)]. LR was appropriately low for body fat mass in LW, with a brisk increase between 0 and 1.5 h. A negative correlation exists between GR (abdominal area) and insulin levels in the postabsorptive state (P < 0.0001). In conclusion, 1) the fasting lipolytic rate is associated with insulin levels; 2) OW and DW have more adipose tissue insulin resistance than LW; 3) OW and DW have a brisker lipolysis in the femoral area; and 4) in DW, higher visceral mass is associated with elevated free testosterone and FFA concentrations. Obesity in the black population is therefore characterized by a marked degree of adipose tissue lipolysis. This degree of resistance together with increasing body fat mass may predispose the obese women to developing type 2 diabetes. Once this disease is established, the onset of adipose tissue vascular insulin resistance will sustain ongoing insulin resistance, even in the presence of relative insulinopenia.

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