Stress and salt intake: Experimental data on Dahl salt-resistant and salt-sensitive rats

The objective of the study was to evaluate the susceptibility of genetically predisposed to salt sensitivity Dahl rats to psychological stress and the effect of sodium ion on stress development. After weaning, Dahl salt-resistant (DR) and two groups of salt-sensitive (DS) rats were fed low-Na (0.5 per cent NaCI) and high-Na (8 per cent NaCI) diets for 2 months. A constellation of sensorimotor and behavioural tests were employed. The psychological stress was produced using a new model of acoustic startle device. DS weanling rats showed significantly increased sensorimotor reactivity, increased emotionality and increased sensitivity to acoustic stress, as compared to DR weanling rats. All the above parameters were exaggerated after 2-month Na loading: there was a significant decrease in the latency of the stressful response and increased magnitude of the hypertensive response to auditory stress. Blood pressure of Na-loaded DS rats increased by 43 per cent after auditory stress, as compared to 18 per cent increase in the Na-restricted rats. The effect of Na ion was mediated by an increased activity of the sympathetic nervous system (SNS). The chronic effect of Na restriction showed reduced SNS responsiveness and diminished neurohumoral reserve to maintain cardiovascular homeostasis. Risks of both Na loading and Na depletion in sodium sensitivity were discussed. (C) 1998 John Wiley & Sons, Ltd.