Influence of acute elevation of plasma AVP level on rat vasopressin V2 receptor and aquaporin-2 mRNA expression.

It is known that vasopressin V2 receptor (V2R) mRNA is downregulated by elevated plasma arginine vasopressin (AVP) following chronic osmotic stimulation. To elucidate the response in V2R mRNA expression to acute elevation of the plasma AVP level, we investigated the time-course change of rat V2R mRNA expression after subcutaneous injection of AVP (10 microg/body). Plasma AVP levels increased from 1.4+/-0.3 pg/ml to 56.8+/-10.7 pg/ml by an hour after injection,and returned to the control level at 6 h. By Northern blotanalysis, V2R mRNA expression decreased to 52.7+/-3.7% of the control level at 2 h, and then returned to the control level by 6 h. Furthermore we investigated the time-course change of aquaporin-2 (AQP2) mRNA expression. AQP2 mRNA expression increased gradually after injection and reached 240.3+/-7.5% of the control level at 6 h. Then it returned to the control level. This study showed that the downregulation of V2R mRNA occurred rapidly after acute elevation of the plasma AVP level, and AQP2 mRNA expression was upregulated despite the downregulation of V2R mRNA.