Aquaporin-2 as a biomarker of distal renal tubular function using lithium as an experimental model

Aquaporin-2 protein levels can be detected in the urine of normal of subjec ts if measured after fluid deprivation. By contrast, in patients with nephr ogenic diabetes insipidus caused by mutations in the aquaporin-2 gene, urin e aquaporin-2 protein excretion cannot be detected. We propose that properl y standardized measurements of urinary aquaporin-2 protein may provide a us eful biomarker of distal tubular function in a variety of acquired conditio ns that impair concentrating ability inducting some nephrotoxic agents.