Establishing Standards for Studying Renal Function in Mice through Measurements of Body Size-Adjusted Creatinine and Urea Levels
Influence of freezing on the quantification of plasma and urinary urea. Blood and urine were obtained from C57BL/6 mice and urea concentration was determined. Urine was obtained from mice maintained in metabolic cages for a period of 24 h. After urine collection, the blood was collected from the ophthalmic plexus. Both types of samples were centrifuged at 1831 ×g for 10 min and supernatants were divided into different aliquots. An initial evaluation of the samples was made at room temperature, before freezing, and further aliquots were frozen at −20°C or −70°C for 4 or 90 days, followed by quantification of the respective blood or urinary urea. In (a), we evaluated the concentrations of plasma urea by the colorimetric method (ultraviolet), following the time and temperature variations described above. In (b), we evaluated the concentrations of urinary urea at 24 h, using the same colorimetric method (ultraviolet) as for the plasma. Values are expressed in mg/dL. No significant differences at were observed.