Time course reversibility of liver and blood changes induced in weanling rats after polychlorinated biphenyl exposure during lactation.

Phenoclor DP5 (DP5), a mixture of polychlorinated biphenyls (PCBs), was administered to lactating rat dams, every two days from postnatal days 2 to 20, at 50 mg/kg of body weight. Resulting effects on tissue concentrations of PCBs and on liver lipids, nucleic acids (DNA and RNA), proteins and blood lipids of offspring, at different times after weaning, until postnatal day 100, were studied. On postnatal day 21, DP5 contents found in liver, brain and fat of young rats indicated that a great part of the dam's body stores of PCBs was eliminated into the milk. These accumulations were related to an increase of relative liver weight, a decrease in DNA concentration and a rise in liver RNA, protein and phospholipid levels, indicating an inducing effect of DP5 in weanling rat. Changes in lipid metabolism were associated with increases of liver triacylglycerol and cholesterol and decrease of blood triacylglycerol. Both sexes exhibited an identical responsiveness to PCBs. The biochemical alterations observed in liver and blood at weaning, disappeared with time and were no longer detectable after postnatal day 40 in both sexes. Relative liver weight increase persisted until postnatal day 60 in males and postnatal day 100 in females. Residual aspects of alterations induced before weaning, by exposure via milk, could persist until postnatal day 100. Permanent effects of PCBs, after perinatal exposure could be assessed in later life of rats, when PCBs were almost completely cleared from body tissues.