African-American women (AAW) are twice as likely to be obese as Caucasian women (CW); however, previous in-vitro studies have shown that AAW have higher densities of beta-adrenergic receptors (B-AR) in the subcutaneous (SC) adipose tissue and an increased lipolytic response to B-AR stimulation when compared to CW. There are no in-vivo studies to help resolve this apparent contradiction between in-vitro lipolytic response and the incidence of obesity. The purpose of this study is therefore to determine if AAW, as compared to CW, have a larger lipolytic response to pharmacological (isoproterenol) and physiological (exercise) stimulation. Methods: 33 obese women (16 AAW; 17 CW) participated in the microdialysis (MD) study. MD consisted of two probes placed in SC abdominal adipose tissue and perfused with either isoproterenol (ISO) or a control solution. Dialysate glycerol (index of lipolysis) was measured from probes at rest and, from the control probe, during exercise. Results: Dialysate glycerol increased 384.9% in AAW and 191.2% in CW in response to ISO (p=0.046 AAW vs CW). Dialysate glycerol increased 66 [mu]mol/L in AAW and 84 [mu]mol/L in CW in response to exercise (p=0.94 AAW vs CW). Conclusion: AAW have a higher lipolytic response to pharmacological B-AR stimulation, but have a similar lipolytic response to exercise, as compared to CW. These findings suggest that lipolytic response to B-AR stimulation and exercise are likely not contributing factors to the higher incidence of obesity in AAW as compared to CW.M.S
