AQP2 and nephrogenic diabetes insipidus: Although measurement of urinary AQPs was beyond the scope of our study, a recent study by Luo and colleagues [39] reported in a mouse model of lithium-induced nephrogenic diabetes insipidus (a water balance disorder) that daily administration of the H2S donor, GYY4137, for 7 days upregulated the expression of renal AQP2 in the principal cells of the collecting duct, and thereby improving urinary concentrating ability.