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In Situ Lipolytic Responses to Isoproterenol and Physiological Stressors Are Similar in Obese Pima Indians and Caucasians

Clinical Diabetes and Nutrition Section (S.S., O.E.O., M.B.M.,. E.R.), National Institute of Diabetes and Digestive and Kidney Diseases, National Institutes of Health, Phoenix, Arizona 85016; the Laboratory of Human Behavior and Metabolism, Rockefeller University (J.H., M.B.), New York, New York 10021; and Northwestern University Medical School (J.B.Y.), Chicago, Illinois 60611

Address all correspondence to: Søren Snitker, M.D., Ph.D., Clinical Diabetes and Nutrition Section, National Institute of Diabetes and Digestive and Kidney Diseases, National Institutes of Health, 4212 North 16th Street, Room 5–41, Phoenix, Arizona 85016. E-mail: ssnitker{at}phx.niddk.nih.gov

Evidence suggests that impaired lipolysis may contribute to fat accumulation. To test whether the lipolytic response to adrenergic stimulation is lower in Pima Indians, a population prone to obesity and type 2 diabetes mellitus, than in Caucasians, 48 healthy, nondiabetic subjects were studied: 27 Pima Indians (12 males and 15 females, 30 ± 7 yr, 85 ± 18 kg, 36 ± 10% body fat; mean ± SD) and 21 Caucasians (11 males and 10 females, 34 ± 7 yr, 105 ± 26 kg, 39 ± 11% body fat). Lipolysis in the abdominal sc adipose tissue was assessed in situ by glycerol concentration in microdialysis samples at baseline and during local infusion of the nonselective ß-adrenergic agonist isoproterenol (10^-6 mol/L), mental stress, and submaximal exercise. The baseline dialysate glycerol concentrations were similar in Pima Indians and Caucasians. Lipolytic response (relative increment in dialysate glycerol concentration, percentage above the baseline) was similar in Pima Indians and Caucasians in response to local isoproterenol infusion (77 ± 36% and 76 ± 40%) and exercise (38 ± 38% and 41 ± 41%). During mental stress, the dialysate concentration did not change significantly from baseline in either group. Changes in local blood flow, determined by ethanol dilution, did not differ between the two groups. In conclusion, the high propensity for obesity in Pima Indians does not seem to be due to an impaired lipolytic response to stimuli.