Effect of albumin on the absorption of phenol red, bromphenol blue and bromosulphonphthalein as model drugs from the liver surface membrane in rats.

The effect of bovine serum albumin (BSA) on drug absorption from the liver surface in rats was examined by using three organic anions (phenol red, bromphenol blue and bromosulphonphthalein) as model drugs which have a high affinity for albumin. The binding ratio of the model drugs (3 mg/ml in phosphate buffer) to BSA varied widely at a BSA concentration of 0.1--10% (w/v). The model drugs (3 mg/ml x 0.1 ml) with or without BSA were applied to the rat liver surface in vivo employing a cylindrical glass cell (i.d. 9 mm, area 0.64 cm2). The absorption ratios of the model drugs from the rat liver surface at 6h, calculated from the amount recovered from the glass cell, decreased with an increase in BSA concentration. A similar trend was observed with biliary recovery of the model drugs. A marked reduction in the absorption ratio was seen with bromosulphonphthalein, which has the highest binding activity to BSA among the three organic anions. Accordingly, protein binding appears to be a significant factor with respect to the drug absorption from the liver surface.