Altered norepinephrine turnover in the brown fat of rats with chronic renal failure.

Disturbances of the sympathetic nervous system (SNS) have been described in chronic renal failure, but their role in the metabolic derangements of uremia has not been well established. In these studies, SNS activity has been measured in the ventromedial hypothalamic (VMH) nuclei and in the intercostal brown adipose tissue (IBAT) of Sprague Dawley 5/6 nephrectomized or sham-operated rats. SNS activity was determined by calculating the norepinephrine (NE) turnover rate (in picograms per milligram per hour) 3, 6, and 12 h after the inhibition of NE synthesis with L-methyltyrosine. The endogenous NE concentration was significantly (P < 0.01) higher in the VMH (14,567 +/- 1,130 pg/mg wet wt) and IBAT (17,902 +/- 2,308 pg/mg wet wt) of uremic than control rats (9,600 +/- 1,110 and 5,752 +/- 320 pg/mg wet wt, respectively). The turnover rates of NE in the VMH (582 +/- 146 pg/mg per hour) and in the IBAT (1,432 +/- 179 pg/mg/hr) of uremic rats were significantly faster (P < 0.01) than in control rats (192 +/- 96 and 173 +/- 58 pg/mg per hour, respectively). These studies demonstrate a significant increase in NE turnover in the VMH nuclei and IBAT of uremic rats. It is suggested that increased efferent sympathetic nerve discharge from the VMH to the IBAT may play a role in the pathogenesis of malnutrition in uremia.