Effects of pregnancy and protein-energy malnutrition on monooxygenase O-dealkylation activity in rat liver microsomes

Xenobiotic metabolism is influenced by a variety of physiological and environmental factors including pregnancy and nutritional status of the individual. Pregnancy has generally been reported to cause a depression of hepatic monooxygenase activities. Low-protein diets and protein-energy malnutrition have also been associated with a reduced activity of monooxygenases in nonpregnant animals. We investigated the combined effects of pregnancy and protein-energy malnutrition on liver monooxygenase O-dealkylation activity. On pregnancy day 0 rats were assigned at random to a group fed adlibitum (well-nourished, WN) or to a malnourished group (MN) which received half of the WN food intake (12 g/day). WN and MN rats were killed on days 0 (nonpregnant), 11 or 20 of pregnancy and ethoxy(EROD), methoxy- (MROD) and penthoxy- (PROD) resorufin O-dealkylation activities were measured in liver microsomes. Only minor changes in enzyme activities were observed on pregnancy day 11, but a clear-cut reduction of monooxygenase activities (pmol resorufin min(-1) mg protein(-1)) was noted near term (day 0 vs 20, means +/- SD, Student t-test, P<0.05) in WN (EROD: 78.9 +/- 15.1 vs 54.6 +/- 10.2; MROD: 67.8 +/- 10.0 vs 40.9 +/- 7.2; PROD: 6.6 +/- 0.9 vs 4.3 +/- 0.8) and in MN (EROD: 89.2 +/- 23.9 vs 46.9 +/- 15.0; MROD: 66.8 +/- 13.8 vs 27.9 +/- 4.4; PROD: 6.3 +/- 1.0 vs 4.1 +/- 0.6) dams. On pregnancy day 20 MROD was lower in MN than in WN darns. Malnutrition did not increase the pregnancy-induced reduction of EROD and PROD activities. Thus, the present results suggest that the activities of liver monooxygenases are reduced in near-term pregnancy and that protein-energy malnutrition does not alter EROD or PROD in pregnant rats.