Nocturnal urinary electrolyte excretion and its relationship to the renin system and sympathetic activity in normal and hypertensive man.

The categorization of patients with essential hypertension into low, normal, and high renin subgroups may be of some value as a research tool. We compared two different methods of renin-sodium indexing, relying on both 24 hr and 10 hr night urine specimens, to a renin suppression-stimulation method involving sodium loading with 2 L of intravenous saline and sodium depletion with 120 mg of oral furosemide plus a 10 mEq sodium diet. Age and race were considered in the analysis. The results from renin-sodium indices failed to consistently correspond with those obtained by the provocative maneuvers. Nocturnal UNaV exhibited a high degree of inverse correlation with renin in normals and all subgroups of hypertensives, whereas aldosterone was not correlated with nocturnal UNaV in patients with nonstimulable or nonsuppressible renin levels. UNeV and PNe were correlated inversely with UNaV and directly with UkV in normal subjects. Similar results were found in hypertensives. We conclude that renin-sodium indices and renin suppression-stimulation maneuvers do not necessarily identify the same hypertensive subgroups, particularly those with nonsuppressible renin. Aldosterone release is dependent on modulators other than sodium balance in patients at either end of the renin spectrum. Sodium intake influences sympathetic activity in normals and hypertensives. The relationship between potassium homeostasis and sympathetic activity warrants further study.