CHRONIC NOREPINEPHRINE INFUSION STIMULATES GLUCOSE-UPTAKE IN WHITE AND BROWN ADIPOSE TISSUES

Cold exposure activates the sympathetic nervous system and markedly stimulates glucose uptake in rat peripheral tissues [A. L. Vallerand, F. Perusse, and L. J. Bukowiecki. Ant. J. Physiol 259 (Regulatory Integrative Comp. Physiol. 28): R1043-R1049, 1990]. To test whether norepinephrine (NE) mimics the effects of cold exposure, we estimated the effects of chronic NE treatment on tissue glucose uptake by determining the glucose metabolic index using the 2-[1,2-H-3(N)]deoxy-D-glucose method. NE was administered in conscious rats at various doses (ranging from 1.9 to 25.1 nmol.kg(-1).min(-1)) during 4 days via minipumps implanted subcutaneously. At doses > 10 nmol.kg(-1).min(-1), NE maximally stimulated glucose uptake in interscapular brown adipose tissue (similar to 50 times above controls) and epididymal white adipose tissue (similar to 3 times above controls). NE infusion (18.8 nmol.kg(-1).min(-1)) increased the circulating levels of NE from 1.1 +/- 0.1 to 19.2 +/- 0.4 nM (P < 0.001), which is in the range of concentrations for the stimulatory effects of NE on glucose uptake in isolated brown adipocytes. At all concentrations tested, NE infusion did not stimulate glucose uptake in the heart and skeletal muscles. NE treatment did not significantly alter plasma insulin or glucose levels but increased the concentration of circulating free fatty acids. The capacity of brown adipose tissue for NE stimulation of glucose uptake (expressed per g of tissue) was much higher than that of white adipose tissue (100 times), various types of white or red skeletal muscles (10-80 times), or the heart (3-4 times). Nevertheless, the skeletal muscles, because of their large mass, still represent a major site of glucose uptake under adrenergic stimulation. It is concluded that chronic NE infusion mimics the stimulatory effects of cold exposure on glucose uptake in brown and white adipose tissues but not in heart and skeletal muscles (possibly because of a retroinhibition of glucose uptake by fatty acids). These in vivo results also confirm recent in vitro studies showing that NE increases glucose uptake in isolated brown adipocytes in the presence or absence of insulin.