Adrenergic receptor stimulation attenuates insulin-stimulated glucose uptake in 3T3-L1 adipocytes by inhibiting GLUT4 translocation

Abstract

Activation of the sympathetic nervous system inhibits insulin-stimulated glucose uptake. However, the underlying mechanisms are incompletely understood. Therefore, we studied the effects of catecholamines on insulin-stimulated glucose uptake and insulin-stimulated translocation of GLUT4 to the plasma membrane in 3T3-L1 adipocytes. We found that epinephrine (1 μM) nearly halved insulin-stimulated 2-deoxyglucose uptake. The β-adrenoceptor antagonist propranolol (0.3 μM) completely antagonized the inhibitory effect of epinephrine on insulin-stimulated glucose uptake, whereas the α-adrenoceptor antagonist phentolamine (10 μM) had no effect. When norepinephrine was used instead of epinephrine, the results were identical. None of the individual selective β-adrenoceptor antagonists (1 μM, β1: metoprolol, β2: ICI-118551, β3: SR-59230A) could counteract the inhibitory effect of epinephrine. Combination of ICI-118551 and SR-59230A, as well as combination of all three selective β-adrenoceptor antagonists, abolished the effect of epinephrine on insulin-stimulated glucose uptake. After differential centrifugation, we measured the amount of GLUT1 and GLUT4 in the plasma membrane and in intracellular vesicles by means of Western blotting. Both epinephrine and norepinephrine reduced insulin-stimulated GLUT4 translocation to the plasma membrane. These results show that β-adrenergic (but not α-adrenergic) stimulation inhibits insulin-induced glucose uptake in 3T3-L1 adipocytes, most likely via the β2- and β3-adrenoceptor by interfering with GLUT4 translocation from intracellular vesicles to the plasma membrane.