INSITU STUDIES OF CATECHOLAMINE-INDUCED LIPOLYSIS IN HUMAN ADIPOSE-TISSUE USING MICRODIALYSIS

Abstract

The effect of catecholamines on lipolysis in situ were investigated in humans. Subcutaneous adipose tissue was microdialyzed with solvents containing adrenergic agents. Norepinephrine caused a rapid increase in the glycerol level in adipose tissue (lipolysis index) that was further increased by the alpha adrenoreceptor blocker phentolamine. At 10-11 mol/l of norepinephrine caused a 100% stimulation of lipolysis (P<.025). In the presence of phenlolamine the lipolytic effect of catecholamines at 10-12 mol/l was isoproterenol > epinephrine > norepinephrine. All these three lipolytic catecholamines caused a transient increase in the adipose tissue dialysate glycerol level, which peaked after 20 to 30 min of catecholamine exposure and then declined. The apparent tachyphylaxia could not be overcome by a gradual increase of the catecholamine concentration from 10-12 to 10-8 mol/l. However, the selective alpha-2 adrenoreceptor agonist clonidine caused a continuous and dose-dependent decrease in the dialyate glycerol level; the minimum effective concentration was 10-9 mol/l. In conclusion, catecholamines have a lipolytic effect in situ at much lower concentrations than those in the circulation. This effect is transient and is related to beta adrenoreceptors. In addition, catecholamines have alpha adrenoreceptor-mediated effects on lipolysis in situ.