Chronic effects of vasopressin on plasma renin activity in sodium-restricted dogs

The effects of chronic (4 days) arginine vasopressin (AVP) infusion were studied in two separate groups of animals: normal Na-restricted dogs with intact renal nerves (n = 8) and renal-denervated Na-restricted dogs (n = 5). Volume expansion during AVP infusion was prevented in these studies with a sensitive servo-controlled cage-scale system. With intravenous AVP infusion (0.36 ng X kg-1 X min-1), plasma AVP levels increased from nearly 3 to 15 pg/ml, whereas total body weight remained unchanged from the control level. In renal-innervated dogs, plasma renin activity (PRA) decreased significantly (P less than 0.05) from control levels of 5.50 +/- 0.61 to an average level of 3.45 +/- 0.76 ng angiotensin I (ANG I) X ml-1 X h-1 on days 1 and 2 of AVP infusion. Thereafter, PRA tended to remain decreased on days 3 and 4, averaging 3.82 +/- 1.02 ng ANG I X ml-1 X h-1, but this was not statistically significant. Urinary Na excretion and balance, however, were not significantly altered during the 4-day AVP infusion period. In renal-denervated dogs, the rise of PRA with Na restriction was 50% that seen in normal dogs. In this group, a transient suppression of PRA was observed on day 1 of AVP infusion from 2.84 +/- 0.75 to 1.46 +/- 0.47 ng ANG I X ml-1 X h-1. Urinary Na excretion increased transiently with a small net Na loss of 4.9 +/- 1.3 meq on day 2 of AVP infusion. No significant changes occurred in average 24-h mean arterial pressure (MAP) in response to AVP in either group of dogs. Thus, in contrast to our previous observations in Na-replete dogs, elevations of plasma AVP within the physiological range result in suppression of PRA, but for periods of no longer than 1-2 days in Na-restricted dogs. This decrease of PRA occurred in the absence of measurable changes in MAP, total body weight, or plasma catecholamines. In addition, this transient AVP-induced suppression of PRA was only partially blunted by prior renal denervation. Finally, in the Na-restricted dog, AVP appears to have minimal or no long-term effects on urinary Na excretion.