Perioperative urinary excretion of aquaporin-2 dependent upon vasopressin in cardiac surgery

Aquaporin-2 is found in the apical cell membranes of the principal cells of the collecting duct of the kidney. Plasma arginine vasopressin has been reported to be markedly elevated during cardiac surgery. However fluctuations in urine aquaporin-2 levels have never been reported. We aimed to determine the responses of urine aquaporin-2 and evaluated the relationship between urine aquaporin-2 and plasma arginine vasopressin levels during perioperative periods in cardiac surgical patients. Eight patients undergoing elective isolated aortic valve replacement in normothermia were enrolled prospectively. Blood and urine samples were collected preoperatively and on postoperative days 1, 4, and 7. Patients received furosemide and spironolactone, as needed, during the clinical course; tolvaptan was not needed. Median plasma arginine vasopressin levels [with interquartile range] significantly increased to 1.5 [1.3-2.0], 15.3 [11.4-22.2]*, 2.2 [2.1-2.3], 1.7 [1.5-1.9] pg/mL preoperatively, on postoperative days 1, 4, and 7, respectively (*: p = 0.0001). Similarly, levels of urine aquaporin-2 markedly increased in 3.4 [1.9-5.6], 25.8 [18.4-33.5]**, 9.3 [5.9-14.0], 5.4 [5.3-6.1] (ng/mL), respectively (**p = 0.0004). A significant correlation between plasma arginine vasopressin and urine aquaporin-2 was observed during the entire investigation (R-2 = 0.616, p < 0.0001). Plasma arginine vasopressin and urine aquaporin-2 levels were significantly elevated on postoperative day 1 in patients who underwent aortic valve replacement with cardiopulmonary bypass. A significant correlation between plasma arginine vasopressin and urine aquaporin-2 was observed. Urine aquaporin-2 should be further investigated as a potential biomarker for postoperative cardiac dysfunction.