The effect of pregnancy and lactation on the disposition of [2,4,2',4'-14C]tetrachlorobiphenyl in the mouse.

The disposition of 150 mg/kg 2,4,2',4'-tetrachlorobiphenyl (4-CB) administered intraperitoneally as a function of nonpregnant body weight was studied in virgin, late pregnant, and early postpartum mice and their offspring. Highest concentrations of the polychlorinated biphenyl (PCB) were observed in adipose tissue and mammary gland regardless of reproductive state. Concentrations of 4-CB equivalents in the tissues examined, however, differed among the three groups, possibly due to the alterations in lipid deposition/mobilization associated with pregnancy and lactation. Approximately 20% of 14C activity was eliminated from carcasses of virgin mice at 4 days after 4-CB administration. No significant decrease in carcass 14C content was observed during this 4-day interval in late pregnant animals. Minimal transplacental transfer of 14C activity occurred (approximately 1% of total maternal body burden) but 4-CB was rapidly eliminated in breast milk to nursing offspring. Ninety percent of total carcass 14C activity was eliminated from lactating mice over a 4-day period, approximately 75% of which could be accounted for in neonatal carcasses. This indicates milk to be the preferred route of elimination for this PCB congener in postpartum animals. Virtually all radioactivity recovered from milk comigrated with parent compound following thin-layer chromatographic analysis. A comparison between hepatic microsomal ethoxycoumarin-O-deethylase activity (ECOD) and liver concentrations of 14C activity showed that pregnant animals were less responsive to the inducing effects of 4-CB than virgin or postpartum mice. This diminution in response may be, in part, responsible for the lack of elimination of 4-CB equivalents from the late pregnant animal during the 4-day experimental period.