Altered Regulation of Water Channels and Sodium Transporters in Fasting-induced Polyuria in Rat Kidney / 대한신장학회잡지

ABSTRACT

PURPOSE: Starvation causes impairment in the urinary concentration ability. However, the molecular basis for the impaired urinary concentration and polyuria remains undefined. We examined the effects of food deprivation on the water handling by the kidney and it's regulatory mechanism. METHODS: Sprague-Dawley rats were used. They were placed in metabolic cages and deprived of food but had free access to water for 24 hours. Control rats had free access to both water and food. Protein expression of aquaporin-2 (AQP2) and Na+-K+-2Cl- cotransporter (NKCC2) was determined in the kidney by Western blot analysis. Protein expression of type VI adenylyl cyclase and prostaglandin E2 synthase (PGES) was determined. Urinary PGE2 excretion was also determined by radioimmunoassay. RESULTS: Food deprivation (FD) resulted in impaired urinary concentration associated with decreased tubular water reabsorption and increased urine output. The expression of AQP2 proteins was significantly decreased in the inner stripe of the outer medulla (ISOM). The expression of NKCC2 was not affected in ISOM. The adenylyl cyclase VI expression was increased in ISOM in FD rats. The protein expression of PGES was decreased in the cortex/OSOM and ISOM. The 24 hr urinary excretion of PGE2 was significantly decreased in FD rats compared with controls. CONCLUSION: These findings indicate that FD-induced urinary concentration defect may related to a reduced abundance of AQP2 in the kidney. It is also suggested that the primary impairment in the pathway to the activation of AQP2 in food deprivation is independent of vasopressin/cAMP or prostaglandin activity.