In the previous report, we reported the results of absorption, protein binding, and pharmacokinetics of the dopamine-2 agonists (D2-agonists) 4-(2-di-n-propylaminoethyl)-7-hydroxy-2-(3H)-indolone, N-(2'-hydroxy-5'-[N,N-di-n-propylaminoethylphenyl])methanesulfonamide, and 4-(di-n-propylaminoethyl)-2-(3H)-indolone. Both phenolic compounds, 1 and 2, were subject to more rapid metabolism than the nonphenol 3. In the present study, we investigated the metabolic basis of the differences in the pharmacokinetics of these compounds. In both rats and dogs, the principal urinary metabolite of 1 and 2 was the corresponding glucuronide. In contrast, 3 was first converted to 1 which then was converted to a glucuronide. On the basis of the urinary excretion of 1 and its glucuronide after intravenous administration of 1 and 3, approximately 78% of the dose of 3 in rats and 58% in dogs was converted to 1. The depropyl analogue of 3 was identified as a minor urinary metabolite. 4-(2-Di-n-propylaminoethyl)-7-hydroxy-2-(3H)-indolone was found in the plasma of rats, dogs, and cynomolgus monkeys treated with 3. The concentration of 1 declined in parallel with that of 3 in dogs and monkeys, indicating that the true half-life of 1 is shorter than or equal to that of 3. On the basis of plasma concentrations of 1 in dogs, the apparent conversion of 3 to 1 was 9%.(ABSTRACT TRUNCATED AT 250 WORDS)