IN-SITU LIPOLYTIC RESPONSES TO ISOPROTERENOL AND PHYSIOLOGICAL STRESSORS ARE SIMILAR IN OBESE PIMA-INDIANS AND CAUCASIANS

Evidence suggests that impaired lipolysis may contribute to fat accumu lation. To test whether the lipolytic response to adrenergic stimulati on is lower in Pima Indians, a population prone to obesity and type 2 diabetes mellitus, than in Caucasians, 48 healthy, nondiabetic subject s were studied: 27 Pima Indians (12 males and 15 females, 30 +/- 7 yr, 85 +/- 18 kg, 36 +/- 10% body fat; mean If: so) 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 b y glycerol concentration in microdialysis samples at baseline and duri ng local infusion of the nonselective beta-adrenergic agonist isoprote renol (10(-6) mol/L), mental stress, and submaximal exercise. The base line dialysate glycerol concentrations were similar in Pima Indians an d Caucasians. Lipolytic response (relative increment in dialysate glyc erol concentration, percentage above the baseline) was similar in Pima Indians and Caucasians in response to local isoproterenol infusion (7 7 +/- 36% and 76 +/- 40%) and exercise (38 +/- 38% and 41 +/- 41%). Du ring mental stress, the dialysate concentration did not change signifi cantly from baseline in either group. Changes in local blood flow, det ermined by ethanol dilution, did not differ between the hive groups. I n conclusion, the high propensity for obesity in Pima Indians does not seem to be due to an impaired lipolytic response to stimuli.