Renal escape from vasopressin: role of pressure diuresis

This study was designed to examine the role of increased renal artery pressure (RAP) in mediating escape from the antidiuretic action of vasopressin (AVP). In six conscious dogs in which RAP was permitted to increase, AVP infusion, at a rate (0.2 mU X kg-1 X mm-1 iv) that was acutely subpressor, gradually raised mean arterial pressure (MAP) from 97 +/- 2 to 126 +/- 4 mmHg after 5 days while decreasing urine volume and increasing urine osmolality. However, after 4-5 days of AVP infusion, urine volume and osmolality returned to control, and the hypertensive effect of AVP waned so that after 9 days of AVP, MAP averaged only 113 +/- 5 mmHg. In contrast, when RAP was prevented from increasing in seven dogs with a servo-controlled aortic occluder, AVP caused sustained decreases in urine volume and elevated urine osmolality from 609 +/- 27 to 1,160-1,711 mosmol/kg H2O throughout 8 days of infusion. The hypertensive effect of AVP did not wane when RAP was servo-controlled, and after 8 days of AVP infusion, MAP averaged 152 +/- 7 mmHg, compared with a control of 96 +/- 2 mmHg. Servo-controlling RAP also prevented the marked sodium and chloride losses seen with chronic AVP infusion in normal dogs. These findings indicate that escape from the antidiuretic action of AVP is mediated by increased RAP, which causes diuresis and natriuresis, thereby diminishing the hypertensive effect of AVP. However, when pressure diuresis and natriuresis are prevented, AVP causes severe chronic hypertensive, suggesting that AVP could be an important hypertensive mechanism when renal function is impaired.