Determination of rhodamine 123 by sequential injection technique for pharmacokinetic studies in the rat placenta

The sequential injection (SIA) technique was applied in pharmacokinetic studies of the transporter-mediated passage of a model substrate, rhodamine 123 (Rho123), through the dually perfused rat term placenta. The method described was used for real-time monitoring of Rho123 concentrations in both the maternal and fetal compartments. Determination was processed by fluorescence detection (λex=480 nm, λem⩾580 nm); calibration curve was linear over the range 0.01–50 μmol l−1 (r=0.99965), detection limit was 10 nmol l−1 (3σ) and RSD⩽2% (10 readings). Transport of Rho123 was scanned under various conditions (ATP-synthesis inhibition) and several inhibitors of P-glycoprotein transporter were tested (e.g. quinidine). The advantages of the modern SIA method—an automated analytical tool providing both fast and precise analysis—were successfully demonstrated for examination of transport profiles to investigate the effect of P-glycoprotein on the placental transfer of Rho123.