Purpose: To develop an isolated perfused rat liver model to study the hepatic disposition of cyclosporine A (CyA) in both sexes.
Methods: Livers were isolated from male (n = 6) and female (n = 7) rats and perfused with a physiological buffer in a single-pass manner. A bolus 1-mg dose of CyA was injected into the inlet catheter and periodical samples (0-15 min) were collected from the outlet perfusate. The concentrations of CyA in the outlet perfusate, collected bile (0-15 min), and liver tissue (at the end of perfusion) were quantitated by HPLC and subjected to statistical moment analysis.
Results: The dilution curves of CyA in the outlet perfusate exhibited unusually long terminal phases due to large volume of distribution of the drug (approximately 100 mL/g) and its slow release from binding sites in the liver (net release rate constant of approximately 0.020 min(-1)). This was in contrast to the rapid uptake of the drug, indicated by significant amounts of the intact drug (>40%) taken up during one single pass through the liver. Consequently, the liver tissue:perfusate distribution ratio of CyA was very high (approximately 220). No significant differences were found between the male and female livers in any of the estimated parameters.
Conclusions: The tissue binding of cyclosporine A is substantial, slowly reversible, and gender-independent in isolated perfused rat livers.