Refinement of the urine concentration test in rats.

Abstract

The urine concentration test is a potentially stressful procedure used to assess renal function. Historically, animals have been deprived of water for 24 h or longer during this test, creating the potential for distress. Refinement of the technique to lessen distress may involve decreasing the water-deprivation period. To determine the feasibility of reduced water-deprivation time, 10 male and 10 female rats were food- and water-deprived for 22 h. Clinical condition and body weights were recorded, and urine was collected every 2 h, beginning 16 h after the onset of food and water deprivation. All rats lost weight (P < 0.001). All rats were clinically normal after 16 h, but 90% of the males and 30% of the females appeared clinically dehydrated after 22 h. After 16 h, mean urine specific gravities were 1.040 and 1.054 for males and females, respectively, and mean urine osmolalities were 1,362 and 2,080 mOsm/kg, respectively, indicating the rats were adequately concentrating urine. The rats in this study tolerated water deprivation relatively well for 16 h but showed clinical signs of dehydration after 22 h. Based on this study, it was concluded that the urine concentration test can be refined such that rats are not deprived of water for more than 16 h without jeopardizing test results.