Diurnal variations of renal function in man.

A diurnal rhythm in water and electrolyte excretion in man has been described by several investigators. Kleitman (1) reported decreased urine flow and chloride excretion during sleep as compared to "waking" hours, and suggested decreased blood pressure during sleep as the cause. Simpson (2, 3) confirmed these observations in young healthy adults who ingested the same amount of water at hourly intervals throughout 24 hours and suggested the acidosis of sleep, with the resultant intracellular shift of chloride and water, as a possible mechanism for the positive balance of these substances during sleep. Manchester (4) studied the 24 hour variations of water and mineral balance in two epileptic children on graded activity. He found that the maximum excretion of water, sodium, potassium and chloride occurred from 6:00 A.M. to 12:00 midnight, the minimum excretion from 12 midnight to 6:00 A.M. He concluded that the diurnal variation of water and mineral excretion is related to sleep rather than to changes in physical activity. Simpson (5) was unable to affect the cycle by means of dehydration, fasting, changes in posture or short periods of sleep during the day. Norn (6) reported a reversal of the cycle with respect to time in a night watchman who obtained his normal complement of sleep, during the day. Brod (7) showed that normal subjects have depressed endogenous "creatinine" clearances at night associated with diminished urine flow. It has been adequately demonstrated that the diurnal rhythm in water and electrolyte excretion may be absent or reversed in pathologic states. Fishberg (8) states that the nocturia of nephritis is due to a lack of concentrating ability and that this symptom in hypertension may be due to this