For decades, the Brattleboro rat has been a useful model in kidney physiology. These animals manifest
central diabetes insipidus (lack of circulating
vasopressin) due to a mutation in the
vasopressin-
neurophysin gene.
V2 receptor-mediated
vasopressin actions in the kidney can be assessed in these animals by infusing the V2-selective
vasopressin analog 1-desamino-8-D-arginine
vasopressin (
dDAVP). However, the major commercial supplier in the United States has ceased production, creating the need for another reliable experimental model of
V2 receptor-mediated
vasopressin action in rodents. We designed an in vivo protocol to investigate
vasopressin responses in the rat kidney using osmotic minipumps loaded with
tolvaptan, a nonpeptide competitive inhibitor of the
vasopressin V2 receptor.
Tolvaptan-infused rats had a mean urinary osmolality of <300 vs. >2,000 mosmol/kgH₂O in vehicle-infused rats. The
tolvaptan infusion produced large decreases in the renal abundance of
aquaporin-2 (AQP2), aquaporin-3 (AQP3), the β-subunit of the
epithelial sodium channel (β-ENaC), and γ-ENaC that were comparable to the differences seen in vehicle-infused vs.
vasopressin-infused Brattleboro rats. Thus we conclude that
tolvaptan infusion in rats provides an additional model (besides
dDAVP-infusion in the Brattleboro rat) for the assessment of
V2 receptor-mediated
vasopressin actions in the kidney. We also provide ancillary in vitro data in rat inner-medullary-collecting-duct
suspensions showing that
tolvaptan can block
vasopressin's effects on phosphorylation of the
water channel AQP2 in vitro. Specifically,
tolvaptan almost completely inhibited the ability of
vasopressin to increase AQP2 phosphorylation at Ser256, Ser264, and Ser269, while strongly inhibiting a
vasopressin-induced decrease in AQP2 phosphorylation at Ser261.