Effect of vasopressin antagonist on water excretion in inferior vena cava constriction

Elevated levels of plasma arginine vasopressin (AVP) have been suggested to impair water excretion in congestive heart failure. In the present study, to determine a role for AVP in the impaired water excretion in rats with the inferior vena cava constriction (IVC), two AVP antagonists were used in the IVC rats at the proximal portion of the hepatic vein under the diaphragm and in sham-operated (control) rats. After surgery, 48 hrs were allowed before the experiments were started. A mean cardiac index of 260.0 +/- 12.3 ml/min/kg in the IVC rats was significantly lower than that in the control rats, 323.6 +/- 13.2 ml/min/kg (P less than 0.01). The rats were given an antidiuretic antagonist, [1-(beta-mercapto-beta, beta-cyclopentamethylenepropionic acid), 2-(O-ethyl)-D-tyrosine, 4-valine] AVP (30 micrograms/kg) or the antagonist vehicle, i.p., and 20 min later they were administered 30 ml/kg of water orally. Minimal urinary osmolality (Uosm) in the IVC rats receiving the vehicle was significantly greater than the control rats (292.7 +/- 53.1 vs. 97.8 +/- 10.6 mOsm/kg H2O, P less than 0.01). The administration of the antidiuretic antagonist in the IVC rats decreased minimal Uosm to 90.0 +/- 3.6 mOsm/kg H2O. This value was significantly lower than the vehicle rats (P less than 0.01), and was a comparable level to minimal Uosm of 82.1 +/- 3.7 mOsm/kg H2O in the control rats receiving the antidiuretic antagonist. The IVC rats excreted 51.4 +/- 5.9% of the water load in three hr, a value significantly less than that excreted by the control rats, 95.1 +/- 6.0% (P less than 0.01).(ABSTRACT TRUNCATED AT 250 WORDS)