The effect of vasopressin V1- and V2-receptor antagonists on hemodynamics in early and late phase after myocardial infarction in rats

Effect of the vasopressin receptor antagonist conivaptan in rats with heart failure following myocardial infarction

Myocardial infarction often induces congestive heart failure accompanied by a significant increase in plasma vasopressin concentration. To delineate the role of vasopressin in the pathogenesis of congestive heart failure, the acute hemodynamic and aquaretic effects of conivaptan (YM087, 4'-(2-methyl-1,4,5,6-tetrahydroimidazo[4,5-d][1]benzoazepine-6-carbonyl)-2-phenylbenzanilide monohydrochloride), a combined vasopressin V(1A) and V(2) receptor antagonist, were assessed in rats with heart failure induced by myocardial infarction. Left coronary artery ligation resulted in decreased left ventricular systolic pressure and first derivatives of left ventricular developed pressure, as well as increased left ventricular end-diastolic pressure, lung and right ventricular weight. Single oral administration of conivaptan (0.3 to 3.0 mg/kg) dose-dependently increased urine volume and decreased urine osmolality in heart failure rats. Furthermore, conivaptan (3.0 mg/kg) attenuated the changes in left ventricular end-diastolic pressure, lung and right ventricular weight induced by heart failure while reducing blood pressure. These results show that vasopressin plays a significant role in elevating vascular tone through vasopressin V(1A) receptors and plays a major role in retaining free water through vasopressin V(2) receptors in this model of congestive heart failure. Additionally, conivaptan, with its dual vasopressin V(1A) and V(2) receptor-inhibiting properties, could exert a beneficial effect on cardiac function in the congestive heart failure rat model.

Vasopressin inhibits sarcolemmal ATP-sensitive K+ channels via V1 receptors activation in the guinea pig heart

To examine the effect of vasopressin on the sarcolemmal ATP-sensitive K (K(ATP)) channel, cell-attached, insideout and open-cell-attached methods of patch clamp techniques were used in isolated guinea pig ventricular myocytes. Suppressing both glycolytic and oxidative ATP production attained K(ATP) channel activation. In the cell-attached mode, vasopressin inhibited KATP channels in a concentration-dependent manner with an IC50 of 15.1+/-1.8 nmol/L. In the inside-out configuration, vasopressin failed to block K(ATP) channels. In the cell-attached mode, manning compound (1 micromol/L), a V1 receptor-selective antagonist, blocked the inhibitory action of vasopressin, although OPC-31260 (1 micromol/L), a V2 receptor-selective antagonist could not affect the action of vasopressin. In addition, vasopressin lost its inhibitory action on K(ATP) channels when the channel was activated by pinacidil, a K channel opener and in the open-cell-attached mode effected by streptolysin-O. Thus, the inhibitory action of vasopressin K(ATP) channels may occur via V1 receptor related mechanism.