Decrease in the time-dependent difference in urinary excretion of furosemide with age.

The influence of age on the time-dependent difference in urinary excretion of furosemide, a loop diuretic agent, was examined in this longitudinal study. Male Wistar rats were maintained under conditions of light from 07:00 to 19:00 h and dark from 19:00 to 07:00 h. Furosemide (30 mg/kg) was given orally at 12:00 h (day trial) or 00:00 h (night trial) to rats at 3 months of age, and urine was collected for 8 h after dosage. Thereafter, the identical protocol was repeated using the same animals at 6, 9, 12, 15, 18, and 21 months of age. The urinary excretion of furosemide was significantly greater in the day than in the night trial at 3 months of age. Such a time-dependent difference was observed for up to 15 months, but disappeared at 18 and 21 months of age. The time-dependent difference in urinary excretion of furosemide (day trial - night trial) decreased gradually throughout the observation period of the study. These results suggest that the time-dependent difference in the urinary excretion of furosemide diminishes during the aging process and disappears by 18 months of age in male Wistar rats.