Lack of vasopressin-independent upregulation of AQP-2 gene expression in homozygous Brattleboro rats.

Arginine vasopressin (AVP) plays an important role in the expression of aquaporin (AQP-2) in the collecting duct. The present study was undertaken to determine whether there is an AVP-independent regulation of AQP-2 gene expression in homozygous Brattleboro rats in which endogenous AVP is absent. Exogenous administration of 1-deamino-8-D-AVP produced an antidiuresis and expressed AQP-2 mRNA and AQP-2 protein in the renal medulla of the homozygous Brattleboro rats. Twelve hours of water deprivation produced severe dehydration in the homozygous Brattleboro rats, such that urinary osmolality increased from 200 to 649 mosmol/kgH(2)O. However, no increase in AQP-2 mRNA expression was observed after this dehydration, and the medullary tissue content and urinary excretion of AQP-2 also remained unchanged. Increases in AQP-2 mRNA expression and AQP-2 protein were evident in Long-Evans rats after 64 h of water deprivation, with a severity of dehydration almost equal to the 12-h dehydrated, homozygous Brattleboro rats. These results indicate the lack of an AVP-independent mechanism for upregulating AQP-2 mRNA expression in renal collecting duct cells.