Altered norepinephrine turnover in the brain of rats with chronic renal failure

Disturbances of the sympathetic nervous system have been described in chronic renal failure, but their role in the genesis and maintenance of hypertension frequently associated with this condition has not been established. The neuroadrenergic activity in brain nuclei involved in the regulation of blood pressure in uremic animals has also not been previously evaluated. In these studies, the neuroadrenergic activity was measured in the anterior, lateral, and posterior hypothalamic nuclei, in the locus coeruleus, and in the nucleus tractus solitarius of Sprague Dawley rats 5/6 nephrectomized or sham operated 4 wk before the experiments. Neuroadrenergic activity was determined by calculating norepinephrine (NE) turnover rate (in picograms per milligram per hour), 3, 6 and 12 h after inhibition of NE synthesis with L-methyltyrosine. The endogenous NE concentration was significantly greater in the posterior hypothalamic nuclei (21,501 +/- 1,777 pg/mg wet wt) and in the locus coeruleus (16,152 +/- 1,114 pg/mg wet tissue) of uremic compared with control rats (12,213 +/- 1,404 and 7,991 +/- 622 pg/mg wet wt, respectively). On the other hand, the endogenous NE content of the nucleus tractus solitarius and the anterior hypothalamic nuclei did not differ between uremic and control rats. The turnover rate of NE in the posterior hypothalamic nuclei of uremic rats (2150 +/- 430 pg/mg per hour) was significantly faster (P < 0.05) than in control rats (977 +/- 244 pg/mg per hour). The turnover rate of NE in the locus coeruleus of uremic rats (2,584 +/- 323 pg/mg per hour) was also significantly faster than in control animals (400 +/- 140 pg/mg per hour; P < 0.01).