Development of the hepatic mixed function oxidase system in a marsupial, the quokka (Setonix brachyurus).

The development of the mixed function oxidase system has been studied in pouched and young-at-heel joey quokkas. Cytochrome P-450 was first detectable at 35 days, rose sharply to one-third of the adult level by 53 days, and reached levels in the adult range between 155 and 255 days. NADPH-Cytochrome c reductase was approximately one-fifth the adult level at 45 days and , by 80–105 days of life, had reached values within the range for adult animals. Benzpyrene hydroxylase activity was barely detectable at 35 days; its development lagged behind that of the components of the cytochrome P-450 system and adult levels were not seen until 200 days. Electron microscopy showed that hepatocytes in 20- and 35-day joeys contained some short chains of rough endoplasmic reticulum. Areas of smooth endoplasmic reticulum were first evident at 45 days and at subsequent stages (80, 100, and 150 days and adult) increasing concentrations of both smooth and rough endoplasmic reticulum were present. Development of the mixed function oxidase system in the quokka liver is slow and resembles more closely the pattern of development in human fetal liver than that in many common laboratory animals.