Transport kinetics of chromium in perfused human placental lobule in late gestation: in vitro study.

OBJECTIVE: Reports relating to maternal-fetal transport kinetics of chromium, an essential trace element in the human pregnancies are scanty. Hence, we thought it interesting to investigate the transport kinetics of this trace element in the human placenta in late gestation in vitro.

METHODS: Human placentae were collected immediately after delivery from normal uncomplicated pregnancies. Chromium chloride solution (GFS Chem Inc, Ohio, USA) at 10 times the physiological concentrations and antipyrine (Sigma Chem Co., St. Louis, USA) as internal reference marker was injected as a single bolus (100 µl) into the maternal arterial circulation of perfused placental lobules and perfusate samples were collected from maternal and fetal circulations over a study period of 5 minutes. National culture and Tissue collection medium, diluted with Earle's buffered salt solution was used as the perfusate. Serial perfusate samples were collected from fetal venous perfusate for a period of 30 minutes. Chromium concentration in perfusate samples was determined using atomic absorption spectrophotometry and the concentration of reference marker, antipyrine was measured by spectrophotometry. Transport kinetics and transport parameters of study and reference markers were assessed using well-established parameters.

RESULTS: Differential transport rates of chromium and antipyrine in 10 perfusions differed significantly for 10 and 50% efflux fractions (ANOVA test, p < .05) while those of 25, 75, and 90% efflux fractions were not significantly different between the study and reference substances. Chromium transport fraction (TF) averaged 54.9% of bolus dose in 10 perfusions while that of antipyrine averaged 89% of bolus dose, representing 61.80% of reference marker TF. The difference observed in TF values of chromium and antipyrine was statistically significant (Student's t-test, p < .05). Pharmacokinetic parameters such as area under the curve, clearance, absorption rate, elimination rate of chromium compared to reference marker was significantly different (ANOVA test, p < .05) between the study and reference substances.

CONCLUSIONS: Our studies report for the first time maternal-fetal transport kinetics of chromium in human placenta in vitro. Considering the restricted transfer of this essential trace element from maternal to fetal circulation despite its small molecular weight, we hypothesize an active transport of chromium across the human placental membrane. Further studies relating to placental transport kinetics of this trace element in various pregnancy-related disease states are in progress.