Dialyzable serum cofactor(s) required for the protein-mediated transport of DL-propranolol into rat brain

To elucidate the characteristics of promotion factor(s) in rat serum required for the protein-mediated transport of drugs into the brain, we examined the brain uptake of DL-propranolol as a model drug using the in vivo brain uptake index (BUI) method in rats. The protein-mediated transport was not observed in rats injected with the buffer solution containing either various concentrations of purified rat alpha 1-acid glycoprotein (alpha 1-AGP) or rat albumin. When the filtrate from rat serum was used as an injection vehicle to which a physiological concentration of purified rat serum protein(s) was added, the protein-mediated transport of DL-propranolol was observed in the rat brain. Moreover, the ability of protein-mediated transport of DL-propranolol was reduced in rats injected with the dialyzed serum compared with the undialyzed serum. These results suggest that the dialyzable promotion factor in serum is required for the protein-mediated transport of DL-propranolol into the brain.