Aims: Polyuria is a symptom that appears in association with diabetes mellitus. Because sustained polyuria causes serious dehydration, it is believed that the body has a compensating mechanism to alleviate dehydration. In the present study, the role of renal aquaporin 2 (AQP2) in the compensating mechanism was investigated in KKAy mice, a type 2 diabetes model.
Main methods: The renal AQP2 expression levels in KKAy mice aged between 5 and 24 weeks were determined using Western blotting. The hypothalamic vasopressin mRNA expression levels also were measured by real-time RT-PCR. Insulin was subcutaneously administered to 11-week-old KKAy mice twice a day for 7 days. After insulin treatment, the renal AQP2 protein expression and the hypothalamic vasopressin mRNA expression were measured.
Key findings: The urinary volumes of 5- and 12-week-old KKAy mice were 1.5 ± 0.3 mL and 9.5 ± 1.2 mL, respectively. The inner medullary AQP2 protein expression of 12-week-old KKAy mice was approximately 2.5-fold higher than that of 5-week-old KKAy mice. The hypothalamic vasopressin mRNA expression of 12-week-old KKAy mice was approximately twice that of 5-week-old KKAy mice. Insulin treatment in KKAy mice resulted in a significant reduction in the plasma glucose level, urinary volume, and inner medullary AQP2 protein and hypothalamic vasopressin mRNA expression.
Significance: The present study demonstrated that AQP2 is a renal functional molecule of vasopressin that controls urinary volume and that AQP2 in the kidney increases to alleviate dehydration due to type 2 diabetes with polyuria.
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