In situ studies of catecholamine-induced lipolysis in human adipose tissue using microdialysis

The effects 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 less than .025). In the presence of phentolamine the lipolytic effects of catecholamines at 10(-12) mol/l was isoproterenol greater than epinephrine greater than 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 dialysate 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 additio, catecholamines have alpha adrenoreceptor-mediated effects on lipolysis in situ.