INFLUENCE OF ACUTE ELEVATION OF PLASMA AVP LEVEL ON RAT VASOPRESSIN V2 RECEPTOR AND AQUAPORIN-2 MESSENGER-RNA EXPRESSION

It is known that vasopressin V2 receptor (V2R) mRNA is downregulated b y elevated plasma arginine vasopressin (AVP) following chronic osmotic stimulation. To elucidate the response in V2R mRNA expression to acut e elevation of the plasma AVP level, we investigated the time-course c hange of rat V2R mRNA expression after subcutaneous injection of AVP ( 10 mu g/body). Plasma AVP levels increased from 1.4 +/- 0.3 pg/ml to 5 6.8 +/- 10.7 pg/ml by an hour after injection,and returned to the cont rol level at 6 h. By Northern blotanalysis, V2R mRNA expression decrea sed 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 in creased gradually after injection and reached 240.3 +/- 7.5% of the co ntrol level at 6 h. Then it returned to the control level. This study showed that the downregulation of V2R mRNA occurred rapidly after acut e elevation of the plasma AVP level, and AQP2 mRNA expression was upre gulated despite the downregulation of V2R mRNA.