Diurnal Cycle of Renal Hemodynamics and Excretion of Chloride and Potassium in Hypertensive Subjects *

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Abstract
Inulin and p-aminohippurate were employed to measure glomerular filtration rate (GFR) and effective renal plasma flow (RPF) by continuous intravenous infusion for about 36 hours with 3-hour urine collection periods. Of 12 patients, 7 showed a nocturnal depression of the GFR and of Cl and K excretion with RPF changing nearly pari passu with GFR in most of them. A diurnal rhythm in filtration fraction was usually present. The phase and amplitude of these cycles did not differ significantly from those in normotensives. GFR changes were significantly correlated with chloride excretion changes. Five patients exhibited a reversal of the Cl cycle with peak rate of Cl excretion occurring at night. GFR cycle in these patients was flattened, and its phase may have been slightly retarded, but it was clearly out of phase with the chloride cycle. Changes in GFR were not significantly correlated with chloride excretion. The RPF cycle closely paralleled the GRF cycle. No correlation was noted between phase shift and degree of impairment of renal function. The K cycle exhibited the normotensive pattern with maximal excretion in the daytime in all subjects.