CIRCADIAN-RHYTHMS AND TIME-COURSE OF ADAPTIVE SODIUM AND POTASSIUM EXCRETION IN RATS AFTER UNINEPHRECTOMY

The relationship between renal circadian cyclic excretion and renal co mpensatory adaptation after uninephrectomy for K, Na, and water was st udied. Rats in a 12:12-h light-dark environment were given a liquid di et, and urine was collected for 16 days with consecutive 90-min period s. Days 1-4 were control, 5-10 followed a sham operation, and 11-16 fo llowed uninephrectomy. The major findings were 1) the circadian cycles in excretion were virtually unchanged after sham and uninephrectomy; 2) an adaptive increase in excretion of Na, K, and water by the remain ing kidney occurred within 90 min after uninephrectomy; 3) after unine phrectomy the distribution of the 24-h increment in excretion for the remaining kidney closely followed the preexisting pattern of circadian excretion for Na but was evenly distributed between light and dark ph ases for K; and 4) after uninephrectomy the ratio of excretion to inta ke was unchanged. This is the first study to document the time course of adaptation to uninephrectomy using consecutive brief collections ov er several days in unanesthetized and undisturbed rats. Adaptation aft er uninephrectomy occurred essentially immediately; was maintained unc hanged; and preserved Na, K, and water homeostasis. Uninephrectomy did not alter the circadian control of excretion.