IN-VIVO AND IN-VITRO FORMATION OF MORPHINONE FROM MORPHINE IN RAT

1. Morphinone, a toxic metabolite, and its glutathione adduct (MO-GSH) were identified in the bile of rat after subcutaneous injection of mo rphine (25 mg/kg) by hplc procedures. The amounts of morphinone and MO -GSH excreted in the 12-h bile were 0.8 +/- 0.3 and 8.4 +/- 4.3% respe ctively. 2. The 9000 g supernatants of rat, guinea pig, rabbit, mouse, hamster and bovine livers produced morphinone from morphine in the pr esence of either NAD(+) or NADP(+). NAD(+) was a more efficient cofact or than NADP(+) except in the guinea pig which equally utilized both c ofactors. With NAD(+) as cofactor, the amounts of morphinone formed in rat and guinea pig were 5.70 and 5.82 mu mol/g liver/30 min respectiv ely and were three-to-four times those in other species. 3. The enzyme activity responsible for formation of morphinone from morphine in the rat was almost exclusively distributed in the microsomal fraction, wh ereas guinea pig, hamster and bovine expressed the enzyme activity mai nly in the cytosolic fraction. Rabbit and mouse gave higher activity i n the cytosolic and microsomal fractions respectively, but other fract ions of both species contained considerable activity. 4. The enzyme ac tivities in male and female rat microsomes were characterized with res pect to developmental pattern, kinetic parameters, pH dependency and s usceptibility to inhibitors. 5. In conclusion the metabolism of morphi ne to morphinone in rat was confirmed by in vivo and in vitro experime nts. It is also suggested that this pathway is a common route in morph ine metabolism in several mammalian species.