Effects of low-density lipoprotein and ethinyl estradiol on cyclosporine metabolism in isolated rat liver perfusions.

The effects of low-density lipoprotein (LDL) on cyclosporine (CyA) metabolism were studied in the isolated perfused rat liver, in a recirculating mode, using Krebs-Ringer buffer in the absence (control perfusion) or presence of LDL (1 microM) (LDL perfusion). In the LDL perfusions, CyA concentrations at all sampling times were about 2-fold higher, whereas the biliary excretion of CyA and measured metabolites (AM1, AM9, AM1c, and AM4N) were all lower than those obtained with the control perfusions. At the end of the perfusion (3 hr), the percentage of total CyA remaining (liver, bile, and perfusate) was significantly higher (76 +/- 1.2% to 85 +/- 2.4%) and the percentage of dose metabolized to AM9 was lower (4.8 +/- 1.2% to 2.4 +/- 0.6%) in the LDL perfusions (N = 4). These results further suggest the inhibitory effects of LDL on CyA uptake, and, thereby, its metabolism as we observed previously in isolated rat hepatocyte studies. Because ethinyl estradiol (EE) is known to increase LDL receptors in rats, we investigated the possible involvement of LDL receptors in transporting CyA into liver cells using rats pretreated with EE (5 mg/kg/day sc for 5 days). The effects of LDL in maintaining CyA perfusate concentrations, and in decreasing biliary excretion of CyA and its metabolites in the EE-treated animals, were in the same direction as those noted in animals without EE, but the differences due to LDL were not statistically significant.(ABSTRACT TRUNCATED AT 250 WORDS)