RENAL AFFERENT IMPULSES, THE POSTERIOR HYPOTHALAMUS, AND HYPERTENSIONIN RATS WITH CHRONIC-RENAL-FAILURE

Hypertension in 5/6 nephrectomized (CRF) rats is partly related to inc reased activity of the sympathetic nervous system. We have previously shown a greater norepinephrine turnover rate in the posterior hypothal amic nuclei and lotus coeruleus of CRF than control rats. Dorsal rhizo tomy prevented the rise in blood pressure and the increase in NE turno ver rate in the posterior hypothalamus and the locus coeruleus. The st udies suggest that afferent impulses from the kidney to central integr ative structures in the brain may be responsible for hypertension in C RF rats. To further evaluate the role of renal afferent nerves in the regulation of blood pressure, and whether renal afferent pathways inte grate with the posterior hypothalamus, we studied the effects of an in trarenal injection of 50 mu l of 10% phenol on blood pressure and NE s ecretion from the posterior hypothalamus of Sprague-Dawley rats. Mean arterial pressure increased from 89 +/- 4.0 to 114 +/- 4.3 mm Hg in ra ts which received intrarenal injection of phenol, but it did not chang e in rats that received vehicle (95 +/- 4.3 and 89 +/- 3.6 mm Hg, resp ectively). Renal denervation totally prevented the increase in blood p ressure caused by intrarenal injection of phenol. The secretion of NE from the posterior hypothalamus increased from 139 +/- 4.5 to 250 +/- 9.9 pg/ml (P < 0.01) in rats that received intrarenal phenol, but it d id not change in rats which received vehicle or in those with renal de nervation. In CRF rats NE secretion from the posterior hypothalamus wa s greater than in control and CRF rats subjected to dorsal rhizotomy. These studies show that afferent impulses from an injured kidney incre ase NE secretion from the posterior hypothalamus and raise blood press ure. NE secretion is higher in the posterior hypothalamus of CRF than control rats. The posterior hypothalamus appears to be an important in tegrative structure of the sympathetic regulation of blood pressure.