Transfer and accumulation of cadmium,and the level of metallothionein in perfused human placentae

The purpose of the present study was to investigate the effect of perfusion with a medium containing 12 or 24 g Cadmium (as CdCl₂) per ml on this metal's accumulation, transfer rate and metallothionein (MT) level. The experiments were performed with an isolated lobule of a dually-perfused human term placenta. Placental cell integrity and viability were characterised by their morphology and metabolic function, manifested in the tissue's electron microscopic structure and glucose and oxygen (O²) consumption, respectively. Perfusion with 24 g Cd/ml medium for 5 h resulted in significant elevation in MT. The transfer rate of Cd to the fetal side of the placenta was very slow, and not until 40 min after the addition of Cd into the maternal side was a significant increase in the metal's level observed in the fetal perfusate. Thereafter, the level of the metal increased gradually and reached a steady state about 1 h later, at a level which was less than 1/20th of its concentration in the maternal perfusate. There was a 60-fold increase in Cd level in the cytosolic fraction obtained from the Cd-treated samples. At 12 g Cd/ml no significant changes were noted in morphology, metabolic function and MT content. None of the Cd levels caused a signicant change in O² and glucose consumption, in spite of the fact that with the higher Cd dose the microstructure of the tissue showed some pathological changes. The observed elevation in MT may provide the fetus some protection against the harmful effects of the metal.