Circadian variations in urine excretion in chronic renal failure.

The pattern of urine excretion over 24 hours has been studied in nineteen patients with stable chronic renal failure of varying severity and due to a variety of renal disorders. The patterns were compared with those in eighteen health control subjects of similar age. The 24 hour urine volume was not significantly greater in the patients (1608 +/- 112 compared with 1710 ml +/- 169). A lower urine concentration (341 +/- 79 mOsm compared with 430 +/- 160 mOsm/kg) was associated with a lower total 24 hour solute excretion (596 +/- 224 compared with 699 +/- 169 mOsm/24 hours). Frequency of micturition, expressed in relation to periods of 24 hours, was similar (6.8 +/- 0.6 compared with (6.4 +/- 0.5). There was an alteration in the normal pattern of urine flow, with more urine at night and less in the day. Nocturia, a consistent feature of the patients with renal failure is due to reversal of the normal pattern and not to an increased volume of urine or increased frequency of micturition. The time of onset of decreased urine excretion during the day was associated with the change from recumbency to activity. The morning antidiuresis, and the nocturnal diuresis, are associated with, and probably the result of, changes in sodium and total solute excretion. The circadian rhythm of potassium excretion remained normal in chronic renal failure, except in very severe renal failure when it was reversed. Alterations in sodium, total solute and water excretion were associated with changes in creatinine excretion and were observed even in mild renal failure. In some patients, studied just before commencing regular dialysis, renal function would have been adequate for reasonable health had the rates of excretion observed at night persisted throughout the 24 hours. Nocturia, in nineteen patients with chronic renal failure, was due to a change in the circadian pattern of urine flow; it is suggested that this results, at least in part, from an inability to respond normally to changes from recumbency to activity.