Regulation of sympathetic activity in lean and obese Zucker (fa/fa) rats.

Norepinephrine concentration and turnover (measured by the time-dependent loss of tissue [3H]norepinephrine specific activity) were reduced in the brown adipose tissue (BAT) of obese Zucker rats but were normal in the heart. After acclimation to a 4 degrees C environment for 7 days, BAT norepinephrine turnover was increased to similar levels in lean and obese rats. After overfeeding with sucrose BAT norepinephrine turnover increased in lean rats but was unaffected in obese rats. Propranolol prevented the normalization of BAT mitochondrial GDP binding that followed adrenalectomy of obese rats. Adrenalectomy of obese rats restored BAT norepinephrine turnover to levels observed in lean rats. However, the increase in BAT GDP binding associated with sucrose overfeeding of adrenalectomized lean and obese rats was neither prevented by propranolol nor associated with a stimulation of norepinephrine turnover. The results suggest that the pituitary-adrenal endocrine axis may influence diet-related BAT thermogenesis and that this influence is only partially mediated by the sympathetic nervous system.