Inhibitory effect of 1,4-dimorpholino-7-phenylpyrido[3,4-d]-pyridazine (DS-511) and its 4'-hydroxy derivative on antidiuretic action of vasopressin in rats.

The water-diuretic features of 1,4-dimorpholino-7-phenylpyridol[3,4-d]-pyridazine (DS-511) and its water-soluble 4'-OH derivative [DS-511(4'-OH)] were investigated. In saline-infused rats the minimum i.v. diuretic dose of DS-511(4'-OH) was 1.0 micrograms/kg/min, while in water-diuretic rats the minimum dose was 50 micrograms/kg/min. Intravenous infusion of DS-511 or DS-511(4'-OH) at rates of 1 to 10 micrograms/kg/min caused a dose-dependent inhibition of the ADH-induced antidiuresis in water-diuretic rats, and a decrease in urinary osmolality. However, hydrochlorothiazide even at 500 micrograms/kg/min did not alter the antidiuresis, but increased the osmolality. Furosemide at a rate of 10 micrograms/kg/min increased urinary excretion of water and sodium in both saline-infused and water-diuretic rats, but the same dose did not inhibit the ADH-induced antidiuresis. These findings indicate that the specific anti-ADH action at relatively low doses of DS-511 and DS-511(4'-OH) is partly involved in the diuretic mechanism of these agents.