COCAINE AND COCAETHYLENE BINDING TO HUMAN PLACENTA IN-VITRO

OBJECTIVE: The aim of the study was to determine the binding profiles of cocaine and its ethyl homolog, cocaethylene, in human placenta. STU DY DESIGN: 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. Dr ug concentrations were measured by high-pressure liquid chromatography . Scatchard analysis of the data was performed. RESULTS: A high-affini ty, tow-capacity binder was identified for cocaine (equilibrium consta nt 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 as sociation, 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 fo r cocaine (equilibrium constant of association, 1.93 x 10(3) L/mol; co ncentration of binding sites, 5.28 x 10(-4) mol/L) and for cocaethylen e (equilibrium constant of association, 2.15 x 10(2) L/mol; concentrat ion of binding sites, 2.65 x 10(-3) mol/L). The concentration of bindi ng 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. CONCLUSION: Human placenta may serve as a depot for cocaine and cocae thylene.