Placental transfer and tissue distribution of dextro-amphetamine in the mouse

3H-d-amphetamine (5 mg/kg, free base) was injected i.p. to male and non-pregnant female mice and to pregnant female mice on day 16 of gestation. The tissue levels of amphetamine were examined as a function of time. Peak concentrations in matured tissues occurred at 15 min, those in placenta, whole fetus, fetal brain and liver at 1 hr. No notable differences were detected in tissue levels of amphetamine in males and non-pregnant females. Disappearance of amphetamine from tissues of pregnant animals was slower than those of other groups. At 15 min, the fetal brain and liver accumulated 1/6 amounts of amphetamine compared to corresponding maternal tissues. Pregnant animals excreted significantly lower amount of total radioactivity compared to non-pregnant females. It is concluded that amphetamine was transported across the placenta and that the lower concentrations in fetal tissues compared to maternal tissues appear to be due to several physico-chemical factors that regulate the transplacental transfer of a foreign chemical compound.