IN-VIVO INCREASE IN BETA-ADRENERGIC LIPOLYTIC RESPONSE IN SUBCUTANEOUS ADIPOSE-TISSUE OF OBESE SUBJECTS SUBMITTED TO A HYPOCALORIC DIET

The effects of 28 days of a very low calorie diet (382 Cal/day)) on th e beta-adrenergic lipolytic response and nutritive blood flow in sc ad ipose tissue were investigated in vivo using the microdialysis techniq ue in 24 obese subjects. The diet did not modify the extracellular gly cerol concentrations, but increased the local nutritive blood flow (me asured by the ethanol escape method). The lipolytic response and the v asodilating effect of increasing concentrations of isoprenaline (from 0.001-10 mu mol/L) added to the perfusate were enhanced after 28 days of diet. Before the diet, equimolar concentrations (100 mu mol/L) of d obutamine [selective beta(1)-adrenoceptor (beta(1)-AR) agonist], terbu taline (selective beta(2)-AR agonist), and CGP 12,177 (selective beta( 3)-AR agonist) increased glycerol concentration in adipose tissue. The lipolytic effect of terbutaline was the greatest, and the effect of C GP 12,177 was the least marked. After 28 days of the diet, the effects of terbutaline and CGP 12,177 were not modified, whereas the effect o f dobutamine was increased and reached the effect of terbutaline. The three agonists increased nutritive blood flow; this effect was not mod ified during the diet. In summary, this study demonstrates an increase in the in vivo lipolytic responses to isoprenaline and dobutamine dur ing the hypocaloric diet. Furthermore, functional beta(3)-AR are prese nt in the sc adipose tissue of obese patients; however, their activati on is only weakly involved in the lipolytic process in this population and is not modified by the hypocaloric diet.