ELECTROLYTE EXCRETION AND SODIUM-INTAKE

Established essential hypertension is characterized by normal equilibr ium between the intake and renal excretion of sodium. Urinary sodium e xcretion is interrelated with that of other ions, such as potassium an d calcium, and that the response of blood pressure to salt ingestion c an be conditioned by the simultaneous intake of varying levels of thos e ions. The authors address three aspects: the correlations between ur inary excretion of sodium and calcium and sodium and potassium in a po pulation of untreated essential hypertensive persons, the response of blood pressure during the escape induced by exogenous mineralocorticoi d administration in mild essential hypertension, and the effect of int ravenous calcium gluconate infusion on sodium excretion and renal func tion. The first part shows that sodium excretion is closely correlated with that of other ions in essential hypertension, and the second par t shows that, to escape from the sodium-retaining effect of a mineralo corticoid, mild hypertensive subjects must have increased blood pressu re within or near the cutoff point that defines salt sensitivity. Of i nterest, the elevation in blood pressure takes place while sympathetic nervous activity is blunted. The third part provides evidence to expl ain one of the mechanisms by which calcium influences renal function a nd enhances renal sodium excretion. The intrarenal effects of low dose s of calcium are dependent on the renal production of prostaglandins.