Dietary salt intake alters cardiovascular responses evoked from the rostral ventrolateral medulla

The present experiments examined whether in rats consuming diets with eithe r high NaCl content (8%) or low Na+ content (0.01%) for 2 wk excitatory inp uts to the rostral ventrolateral medulla (RVLM) would be altered. In chlora lose-anesthetized rats, injection of glutamate into the RVLM elicited a pre sser response that, compared with rats fed a control diet, was 50% larger i n rats fed a diet containing 8% NaCl and was 25% smaller in rats fed a diet containing 0.01% Na+. Presser responses produced by electrical stimulation of sciatic nerve afferents, as well as by microinjections into the RVLM of L-dihydroxyphenylalanine or carbachol, were all potentiated by high dietar y salt intake and reduced by low dietary salt intake. Dietary salt intake h ad no effect on presser responses produced by intravenous injection of phen ylephrine, indicating that salt-related alterations in cardiovascular respo nses produced by central activation could not be accounted for by changes i n peripheral vascular reactivity. The decrease in arterial pressure produce d by injection of glutamate into the nucleus of the solitary tract was also potentiated by the high salt diet, suggesting that the sensitivity of cent ral baroreceptor reflex pathways may be altered by dietary NaCl. These resu lts indicate that the amount of NaCl consumed in the diet can change the se nsitivity of RVLM sympathoexcitatory neurons, and this change in sensitivit y is not restricted to any particular class of cell surface receptors.