NORADRENALINE-INDUCED LIPOLYSIS IN ISOLATED MESENTERIC, OMENTAL AND SUBCUTANEOUS ADIPOCYTES FROM OBESE SUBJECTS

OBJECTIVE: The action of noradrenaline on human mesenteric, omental an d subcutaneous adipocytes was compared. We also determined whether reg ional differences in the noradrenaline-effect were linked to variation s in adrenoceptor subtype function. DESIGN: The lipolytic effects of d ifferent concentrations of noradrenaline (beta 1-, beta 2-, beta 3- an d alpha 2-adrenoceptor agonist), isoprenaline (beta 1-, beta 2- and be ta 3-adrenoceptor agonist) and selective beta 1-, beta 2- and beta 3-a drenoceptor agonists (dobutamine, terbutaline and CGP 12177, respectiv ely) were studied in adipocytes isolated from the three adipose tissue regions in the same subject. In addition, the effect of the alpha 2-a drenoceptor antagonist, yohimbine, was studied on noradrenaline-induce d glycerol release. SUBJECTS: Thirteen otherwise healthy obese subject s (nine females, four males). RESULTS: The noradrenaline-induced lipol ytic response did not differ between omental and mesenteric adipocytes but was 50% higher than in subcutaneous adipocytes (P < 0.05). Furthe rmore, noradrenaline sensitivity and intrinsic activity (in relation t o isoprenaline) were higher in the two visceral fat cells than in the subcutaneous fat cells. The intrinsic activity of noradrenaline increa sed close to that of isoprenaline when yohimbine was added to the incu bation system. Isoprenaline sensitivity was five times higher in the t wo visceral fat cells than in the subcutaneous fat cells. For CGP 1217 7, sensitivity and intrinsic activity did not differ between mesenteri c and omental adipocytes, but was higher in these two regions when com pared to subcutaneous adipocytes. For dobutamine and terbutaline no si gnificant regional differences were found. CONCLUSION: beta 3-adrenoce ptor action is enhanced and alpha 2-adrenoceptor action is decreased i n both mesenteric and omental adipocytes as compared to subcutaneous a dipocytes. However, the two visceral fat depots show no difference in adrenoceptor function. The difference in beta 3- and alpha 2-adrenocep tor function might explain why noradrenaline induced lipolysis is incr eased in the two visceral fat depots, as compared to the subcutaneous fat depot.