Rhythmic changes in renal function in the rat

¹ New England Medical Center Hospitals and Department of Medicine, Tufts University School of Medicine, Boston, Massachusetts

Cold exposure causes rats to increase their urine output. This increase in urine output was found to occur in 5- to 8-day cycles with peak urine volumes three or more times the volumes prior to exposure to the cold. Cycles in urine volume occurred on a constant electrolyte intake and in animals receiving exogenous Pitressin. The peaks in urine volume were accompanied by a threefold increase in the variability of sodium excretion but not potassium excretion. The increase in urine volume which occurred at the same time in all rats in a group began at night and continued through the following day. These data have been discussed in the light of a possible mechanism controlling sodium intake with water intake and electrolyte excretion.

Key Words: biological rhythms • cyclic renal function • electrolyte excretion • urine concentration • Pitressin

Submitted on March 15, 1965