Renal electrolyte circadian rhythms: independence from feeding and activity patterns.

The interrelationships between urinary electrolyte circadian rhythms and rhythms of feeding, drinking and activity were studied in six conscious chair-acclimatized squirrel monkeys (Saimiri sciureus) kept in temperature-controlled isolation chambers on a light-dark (LD) 12:12 h cycle. With lights on (600 lx) from 0800 to 2000 h and off (less than 1 lx) from 2000 to 0800 h, renal potassium excretion in monkeys fed ad libitum fell to a daily minimum of 64 +/- 6 mueq/h at 0500 h and rose to a maximum of 274 +/- 13 mueq/h at 1700 h. Sodium excretion fell to a minimum of 13 +/- 2 mueq/h at 1000 h and rose to a maximum of 43 +/- 6 mueq/h at 2100 h, while water excretion fell to a minimum of 869 +/- 63 mul/h at 0500 h and rose to a maximum of 2,307 +/- 222 mul/h at 1700 h. Feeding, drinking, and activity occurred only during the lights-on period. Independence of the urinary rhythms from diurnal variations in feeding, drinking, and activity was established a) by depriving monkeys of food, b) by depriving monkeys of water, and c) by training monkeys to perform a 2-hourly schedule of feeding, drinking, and activity throughout day and night. None of these three regimens resulted in major reductions of the amplitude, or changes in the phase of the circadian rhythms of urinary electrolyte or water excretion. These findings indicate that the circadian rhythms of urinary potassium, sodium, and water excretion are controlled by mechanisms that are not passively dependent on the behavioral patterns of feeding, drinking, and activity.