Regional difference in lipolysis caused by a beta-adrenergic agonist as determined by the microdialysis technique

We have investigated the difference in lipolysis caused by a beta-adrenergic agent between visceral and abdominal subcutaneous adipose tissues in vivo. Glycerol levels (lipolysis index) were continuously monitored in mesenteric and abdominal subcutaneous adipose tissues of anaesthetized Wistar rats using the microdialysis technique. During microdialysis, increasing concentrations of the lipolytic agent, isoproterenol (10(-8), 10(-7), 10(-6), 10(-5) mol L-1), were added to the perfusion. Glycerol concentrations in dialysate at each isoproterenol concentration, blood glucose concentrations during the experiment, and plasma insulin concentrations before and immediately after the experiment were measured. The effect of isoproterenol on local blood flow was investigated using the ethanol technique. The clearance rate of ethanol from the perfusion medium was used as the index of local blood flow. There was no significant change in blood glucose or plasma insulin concentrations during the study. Glycerol levels in dialysate were significantly higher in mesenteric than in abdominal subcutaneous adipose tissues at all isoproterenol concentrations. The percentage change of baseline ethanol ratio was not altered by increasing isoproterenol concentrations in both mesenteric and subcutaneous adipose tissues. There was also no significant difference in percentage change of the baseline ethanol ratio between mesenteric and abdominal subcutaneous adipose tissues. These results suggest that mesenteric adipose tissue is characterized by an even higher beta-adrenergic agonist-induced lipolysis than abdominal subcutaneous adipose tissue.