1998 Global Conference Proceeding
March 02 - 04, 1998
| Conference: | 1998 Global Conference |
|---|---|
| Title: | Urinary Aquaporin-2 in Diagnosis of Disorders of Water Metabolism |
| Author: | Ishikawa, San-e |
| Institution: | Jichi Medical School |
Aquaporin-2 (AQP-2) is vasopressin(AVP)-regulated water channel in renal collecting duct cells. AQP-2 is, in part, excreted into the urine. We examined whether urinary excretion of AQP-2 (UAQP-2) is of value to diagnose the pathological states of water metabolism. UAQP-2 had a positive correlation with plasma AVP levels in normal subjects. UAQP-2 in the patients with central diabetes insipidus (CDI) was one-eighth less, and in the patients with water retention was 2.8-fold greater, than that in the normal subjects. Hypertonic saline test made a marked difference in UAQP-2 between the CDI patients and normal subjects. After the 5% NaCl-infusion, UAQP-2 increased by 12-fold in the normal subjects, but remained low in the CDI and NDI patients. An acute oral water load test (20 ml/kg) was carried out in the patients with water retention and hyponatremia. After the water load, the nadir of UAQP-2, obtained in 60 - 90 min., was 76 fmol/mg creatinine in the normal subjects. However, it was reduced only to 284 fmol/mg creatinine in patients with water retention. These results indicate that UAQP-2 is a potent marker to diagnose the disorders of water metabolism, dependent upon AVP.
Aquaporin-2 (AQP-2), located in the kidneys' collecting duct cells and regulated by the antidiuretic hormone (AVP) is, in part, excreted into the urine. Ishikawa, et. al., tested to see if urinary AQP-2 (UAQP-2) could serve as an indicator in diagnosing disorders of water metabolism dependent on AVP, such as water retention and nephrogenic and central diabetes insipidus (NDI and CDI). Patients with CDI showed one-eighth less UAQP-2 in their urine than the control group. While patients with water retention showed 2.8 times more AQP-2 in their urine than the control group. After receiving an injection of a 5% sodium chloride solution, AQP-2 increased 12-fold in the control group, but remained low in patients with CDI and NDI. UAQP-2 remained high in patients with water retention after an acute water intake compared to the control group. These findings show that UAQP-2 is a potent indicator for AVP dependent disorders of water metabolism.