Effect of chronic sodium depletion on cerebrospinal fluid and plasma catecholamines

To test the role of central neurogenic factors in sodium-depleted states, cerebrospinal fluid (CSF) norepinephrine, epinephrine, and dopamine were measured in mongrel dogs first on a normal sodium intake (65 mEq sodium/day) and then on a 21-day regime of low sodium diet (4 mEq/day combined with diuretics). Plasma catecholamines were measured in the same group of dogs. Three weeks of sodium depletion supplemented with diuretics caused a 24-fold increase in plasma renin activity, hemoconcentration, and elevated serum protein concentration. Both plasma and CSF sodium decreased significantly. After sodium depletion, plasma norepinephrine rose 76% but epinephrine and dopamine did not change. The same pattern was observed whether samples were obtained in conscious or anesthetized animals. In CSF, norepinephrine rose 44% during sodium depletion, while epinephrine and dopamine remained unchanged. The CSF norepinephrine was related inversely to the CSF sodium concentration and directly to plasma renin activity. These observations support the view that the combined procedure of restricted dietary sodium intake and diuretic therapy causes alterations in CSF norepinephrine in a direction compatible with possible overactivity of central noradrenergic neurons.