Aquaporin-2 urinary excretion in cirrhosis: relationship to vasopressin and nitric oxide

The aquaporin (AQP) water channel plays an important role in the regulation of water. AQP2 is expressed in the collection duct of the kidney, serving as the final channel that helps to regulate water excretion in the kidneys and affecting the regulation of water and hyponatremia in cirrhotic patients. So far, research on aquaporin expression in cirrhosis has had various results. The purpose of this study is to investigate the factors that affect the regulation of expression of AQP in patients with cirrhosis. The study comprised 81 cirrhosis patients and 18 control subjects. In each group, 24-h urine was collected and nitric oxide and vasopressin levels were measured in the blood. The amount of urinary AQP was measured by Western blot. In this study, the positivity rate and amount of expression of AQP was higher in the cirrhotic group than that of the control group. AQP expression in urine was also compared between the groups with use of diuretics and the groups with no use of diuretics. A 57.4% positivity was observed with the former, whereas a 51.5% was seen in the latter. No significance was found between the groups (P = 0.581). Expression of AQP in compensated cirrhotic patients is significantly higher than decompensated cirrhotic patients and is especially higher in cirrhotic patients with ascites than with no ascites. There is no relationship between the concentration of vasopressin and expression of AQP. Concentration of serum NOx is higher in cirrhotic patients than the control group and there is a positive association between the concentration of serum nitric oxide and AQP in urine. In conclusion, expression of AQP is increased in cirrhotic patients and is significantly higher in patients with ascites. There is a positive association between the expression of AQP and concentration of serum nitric oxide.