AQP2 and Polydipsia: 2008b; Walker 1993). In this regard, ~70% of patients that receive lithium therapy develop nephrogenic diabetes insipidus (NDI) characterized by polyuria, polydipsia, and reduced urine osmolality due to impaired urine concentrating capability (Bedford et al. 2003; Timmer and Sands 1999). Although diverse mechanisms might be involved, the downregulation of renal AQP2 is considered to play a major role in the pathogenesis of NDI (Kwon et al. 2000; Marples et al. 1995).