HIGH SODIUM INTAKE - EFFECTS ON AFFERENT RENAL NERVE ACTIVITY

Abstract

Objective: Previous work of ours suggests that the sensitivity of renal afferent neurons is decreased under pathological conditions. Here we tested the hypothesis that pathologically decreased sensitivity of renal afferent neurons due to high salt diet is normalized after renal denervation. Design and method: Six male Sprague Dawley (SD) rats were put on high salt diet (HS; 8% NaCl) for 10 days. In another group of 18 rats on high salt diet (HS) left kidneys were denervated (DNX) 7 days prior to examination. 17 rats on standard diet with and without DNX were used as controls. Dorsal root ganglion neurons with renal afferents were investigated in primary neuronal cell culture using current clamp mode to assess action potential generation during current injection. Neurons were characterized as tonic highly active (less than 5 action potentials, AP) and phasic less active neurons (more than 5 AP upon stimulation). Results: In renal neurons from rats on HS the relation of tonic to phasic neurons shifted towards less active phasic units (62% tonic neurons in control vs. 42% on HS, p < 0.05, z-test). Denervation (DNX) of the left kidney in rats on high salt diet (HS-DNX) led to a recovery of afferent renal DRG neurons remaining vital after denervation. They regained their electrophysiological property of mainly tonic firing (42% tonic neurons in HS vs. 71% HS-DNX, p < 0.05, z-test). Conclusions: In rats on high salt diet the proportion of highly active tonic neurons with renal afferents decreased at the expense of less active phasic neurons. This HS effect could be abolished by DNX. Hence the input of afferent renal pathways to the central nervous system was normalized form the first neuron onward to the brain.