Do hypertensive patients have a different diurnal pattern of electrolyte excretion?

Studies generally indicate that excretion of sodium, potassium, and water is greater during the day than during the night. To determine whether hypertensive patients exhibit this same pattern of excretion, diurnal variations in excretion of sodium, potassium, creatinine, and water were examined in 107 hypertensive men and women from a clinical trial on control of hypertension by nonpharmacological means--the Hypertension Control Program. Each participant provided two carefully timed 24-hour urine collections divided into daytime and overnight specimens. The median ratios of 24-hour to 8-hour overnight excretion were 2.84, 3.95, 2.99, and 2.77 for sodium, potassium, creatinine, and water, respectively. Thus, more than half of this hypertensive group exhibited a greater rate of sodium and water excretion during sleep than during daytime hours, a reversal of the usual pattern. When the group was subdivided based on age, sex, race, trial randomization group, use of diuretics, and hypertension severity, women had significantly lower ratios of 24-hour to overnight excretion for sodium and water than men and blacks had significantly lower 24-hour to overnight ratios for water and potassium than whites. When the 24-hour to overnight ratios for these hypertensive patients were compared with those for a group of 30 men and women with high-normal blood pressure, those with high-normal blood pressure had significantly larger ratios for sodium and water excretion than the hypertensive group. The results of this study suggest that hypertensive patients may have a different diurnal pattern of sodium and water excretion than normotensive subjects and that further research is needed to clarify this issue.