The behaviour of microsomal mono-electron carriers in adult and fetal liver and in placenta throughout pregnancy.

The activities and contents of microsomal mono-electron carriers (NADPH-cytochrome c reductase, NADH-cytochrome b5 reductase, cytochrome P-450 and cytochrome b5) in the liver of 160 pregnant rabbits and their response to phenobarbital (PB) administration were found to be different to that of non pregnant animals and to vary depending on the period of gestation. In fetal liver and in placenta the activities and contents of mixed function oxidase system enzymes are very low and increase from the mid-gestation up to the term of pregnancy. PB has either effect or decreases the enzyme levels. The variations of enzyme content and activity in maternal liver and the different response to PB are related to the hormonal modifications of pregnancy. The behaviour of mono-electron carriers in fetal liver can be related to the process of maturation of this organ. The effect of PB can be due to the interference of the drug with steroid metabolism. The behaviour of mixed function oxidase system enzymes in placenta can be related to the processes of maturation and ageing of organ.