Acute modulation of adipose tissue lipolysis by intravenous Estrogens

Objective: The aim of this study was to determine whether intravenous (IV) conjugated estrogens (EST) acutely enhance the suppression of whole-body or regional subcutaneous adipose tissue (SAT) lipolysis by insulin in postmenopausal women. Research Methods and Procedures: We assessed wholebody lipolysis by [H-2(5.)]glycerol rate of appearance (Glyc(RA)) and abdominal and femoral SAT lipolysis (interstitial glycerol; Glyc(IS)) by Subcutaneous microdialysis. Postmemopausal women (n = 12) were studied on two occasions, with IV EST or saline control (CON), under basal conditions and during a 3-stage (4, 8, and 40 rnU/m(2)/min) hyperinsulinemic, euglycemic clamp. Ethanol outflow/inflow ratio and recovery of [C-13] glycerol during microdialysis were used to assess blood flow changes and interstitial glycerol concentrations, respectively. Results: Compared with CON, EST did not affect systemic basal or insulin-mediated suppression of lipolysis (Glyc,,) or SAT nutritive blood flow. Basal Glyc(IS) in SAT was reduced on the EST day. How-ever, insulin-i-nediated suppression of lipolysis in SAT was not significantly influenced by EST. Discussion: These findings suggest that estrogens acutely reduce basal lipolysis in SAT through an unknown mechanisin but do not alter whole-body or SAT Suppression of lipolysis by insulin.