Effects of tolvaptan on systemic and renal hemodynamic function in dogs with congestive heart failure.

PURPOSE: We investigated the effects of tolvaptan, a vasopressin V(2)-receptor antagonist, on diuretic response and systemic and renal hemodynamic characteristics in conscious dogs with congestive heart failure (CHF). We also compared these effects with those of furosemide, a loop diuretic. METHODS: CHF was induced by rapid right-ventricular pacing at 260 beats/min for at least 3 weeks, and maintained with a pacing rate of 220-240 beats/min. CHF dogs were orally given tolvaptan (10 mg/kg), furosemide (10 mg/kg) and vehicle in random order during the stable CHF state. Urine excretion, systemic and renal hemodynamic parameters, and plasma hormone levels were measured over 6-hour periods after drug administration. RESULTS: Tolvaptan induced aquaresis with an increase in free water clearance, resulting in a significant increase in serum sodium concentrations and a decrease in cumulative water balance. Tolvaptan also decreased pulmonary capillary wedge pressure without affecting systemic vascular resistance, glomerular filtration rate or renal blood flow. Tolvaptan tended to increase plasma arginine vasopressin concentrations but did not affect plasma renin activity. In contrast, furosemide induced clear saluresis with increased electrolyte excretion, resulting in decreased pulmonary capillary wedge pressure. However, furosemide also decreased serum potassium concentration and increased plasma arginine vasopressin concentrations and plasma renin activity. CONCLUSION: Tolvaptan elicited a potent aquaretic response and reduced the cardiac preload without unfavorable effects on systemic or renal hemodynamics, the renin-angiotensin-aldosterone system, or the sympathetic nervous system in CHF dogs. Thus, tolvaptan may offer a novel approach to remove excess water congestion from patients with CHF.

Therapeutic effects of tolvaptan, a potent, selective nonpeptide vasopressin V2 receptor antagonist, in rats with acute and chronic severe hyponatremia.

The therapeutic efficacy of tolvaptan (OPC-41061), a potent, selective nonpeptide vasopressin V(2) receptor antagonist, on acute and chronic severe hyponatremia was assessed in rats. Experiments were designed to demonstrate the efficacy of tolvaptan reducing mortality in an acute model, and controlling the extent of serum sodium elevation without causing abnormal animal behavior suggesting neurological symptoms in a chronic model. In the acute model, rats developed rapidly progressive, severe hyponatremia by continuous sc infusion of [deamino-Cys(1), D-Arg(8)]-vasopressin (10 ng/h) and forced water-loading (additional 10% initial body weight per day). By d 6, untreated rats had a 47% mortality rate. However, rats treated with repeated oral administrations of tolvaptan (1, 3, and 10 mg/kg) produced dose-dependent aquaresis (i.e. urine volume increased and urine osmolality decreased) that resulted in a gradual increase in plasma sodium concentration. Consequently, tolvaptan treatment reduced mortality and, at higher doses, resulted in no observed deaths. In the gradual model, rats receiving a continuous sc infusion of [deamino-Cys(1), D-Arg(8)]-vasopressin (1 ng/h) combined with a liquid diet were induced to stable, severe hyponatremia (approximately 110 mEq/liter), which lead to increased organ weight and water content. Rats receiving dose titrations of tolvaptan (0.25, 0.5, 1, 2, 4, and 8 mg/kg) increased plasma sodium to healthy levels without causing abnormal animal behavior suggesting neurological symptoms or death, improved hyponatremia-driven increases in wet weight and water content in the organs. Thus, in animal models, analogous to the hyponatremia forms seen in humans, tolvaptan presents exciting therapeutic implications in the management of patients with severe hyponatremia.

Antidiuretic effects of a novel nonpeptide vasopressin V(2)-receptor agonist, OPC-51803, administered orally to dogs.

We elucidated the pharmacological properties of a novel nonpeptide vasopressin V(2)-receptor agonist, OPC-51803 ((5R)-2-[1-(2-chloro-4-(1-pyrrolidinyl)benzoyl-2,3,4,5-tetrahydro-1H-1-benzazepine-5-yl]-N-isopropylacetamide), via both in vitro binding experiments incorporating canine kidney and platelet membrane fractions and in vivo experiments that would determine the compound's antidiuretic effects after oral administration to water-loaded dogs. OPC-51803 displaced [(3)H]arginine vasopressin (AVP) binding to canine V(2) and V(1a) receptors, as determined by resulting K(i) values of 15.2 +/- 0.6 nM (n = 4) and 653 +/- 146 nM (n = 4), respectively. These data indicate that OPC-51803 was about 43 times more selective for V(2) receptors than for V(1a) receptors. Antidiuretic studies showed that orally administered doses of OPC-51803 (0.03 to 0.3 mg x kg(-1)) decreased urine volume and increased urinary osmolality in a dose-dependent manner in water-loaded dogs. Intravenous OPC-51803 infusions (0.3 and 3 microg x kg(-1) x min(-1)) did not affect renal or systemic hemodynamics in anesthetized dogs. Since these results confirm that OPC-51803 shows antidiuretic action in dogs, the compound may be useful for treating AVP-deficient pathophysiological states.