Palmitate Metabolism and Norepinephrine Sensitivity in Brown Adipose, Liver, and White Adipose Tissues of Zucker Rats

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Abstract
Interscapular brown adipose tissue (BAT) in vitro utilization of palmitate (0.5 mM) and glucose (5.0 mM) were examined at 0, 0.1, 1.0 and 10.0 .mu.g norepinephrine-bitartrate (NE)/ml. With increasing NE concentrations, in vitro palmitate oxidation was stimulated and glucose oxidation was inhibited in BAT of nonobese rats. This characterization of BAT metabolism provided the constraints for an analysis of fatty acid utilization and norepinephrine sensitivity at submaximal response concentrations in BAT of lean and obese Zucker rats. Liver and inguinal white adipose were used for tissue comparisons. In comparison to its lean littermates, it was demonstrated that the obese rat had heavier interscapular BAT pads; oxidized a similar amount of palmitate to CO2 per 100 mg of BAT; oxidized more palmitate in response to NE stimulation of BAT; and had slower rates of hepatic ketogenesis and palmitate oxidation. Altered palmitate oxidation or NE sensitivity in BAT was not contributing to the obesity of the fatty Zucker rat at 5 wk of age. [Defective non-shivering thermogenesis was postulated as the cause of greater energetic inefficiency in obese mice and some obese humans.].

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