Administration of oxytocin affects vasopressin V2 receptor and aquaporin-2gene expression in the rat

Oxytocin (OT) binds to the vasopressin V2 receptor (V2R) because of its str uctural similarity to arginine vasopressin (AVP). Though the affinity of OT for V2R is low, it is known that OT causes antidiuresis. To clarify the ef fect of OT as an agonist of V2R, we investigated the influence of acute ele vation of plasma OT levels on the rat mRNA expression of V2R and aquaporin- 2 (AQP2), the water channel regulated by V2R. The plasma Of level increased from 11.1+/-1.6 pg/ml to 331.0+/-67.9 pg/ml by 1 h after subcutaneousinjec tion of 20 mu g OT. V2R mRNA expression decreased to 68.3+/-4.1% of the con trol at 3 h, and AQP2 mRNA expression increased to 239.3+/-26.8% of the con trol at 6 h. The plasma AW level did not change significantly during the ex periment. The influence of a subcutaneous injection of 20 mu g OT on V2R an d AQP2 mRNA expression is comparable to that of 10 mu g AVP that we documen ted in the previous study. In conclusion, Of can downregulate V2R mRNA expr ession and upregulate AQP2 mRNA expression in the collecting duct as an ago nist of the V2R like AVP.