Cocaine and cocaethylene binding to human placenta in vitro

The aim of the study was to determine the binding profiles of cocaine and its ethyl homolog, cocaethylene, in human placenta.

Pooled whole human placental homogenates supplemented with either nonlabeled cocaine or cocaethylene over the concentration range 10 to 5000 x 10(-7) mol/L were submitted for equilibrium dialysis. Drug concentrations were measured by high-pressure liquid chromatography. Scatchard analysis of the data was performed.

A high-affinity, low-capacity binder was identified for cocaine (equilibrium constant of association, 3.68 x 10(5) L/mol; concentration of binding sites, 4.36 x 10(-6) mol/L) and for cocaethylene (equilibrium constant of association, 2.42 x 10(4) L/mol; concentration of binding sites, 2.65 x 10(-5) mol/L). Also, a low-affinity, high-capacity binder was noted for cocaine (equilibrium constant of association, 1.93 x 10(3) L/mol; concentration of binding sites, 5.28 x 10(-4) mol/L) and for cocaethylene (equilibrium constant of association, 2.15 x 10(2) L/mol; concentration of binding sites, 2.65 x 10(-3) mol/L). The concentration of binding sites expressed as moles per gram of placenta was as follows: high-affinity binder (cocaine, 4.36 x 10(-8); cocaethylene, 2.65 x 10(-7) and low-affinity binder (cocaine, 5.28 x 10(-6); cocaethylene, 2.65 x 10(-5). Up to 59% of cocaine and up to 42% of cocaethylene was bound.

Human placenta may serve as a depot for cocaine and cocaethylene.