Accumulation of peptides by choroid plexus in vitro: Tyr-d-Ala-Gly as a model

Accumulation of Tyr-d-Ala-Gly (TAG) in rat choroid plexus was studied in vitro. Choroid plexus of the lateral ventricles and the fourth ventricle accumulated TAG against a concentration gradient. This accumulation was inhibited by some metabolic inhibitors and some peptides, but not by amino acids. The charge and stereo-configuration of peptides had great influence on the accumulation. Metenkephalin was one of the strongest inhibitors. Absence of sodium ions in the medium did not affect the accumulation, but increase or decrease of potassium ions reduced it. Injection of reserpine for chemical denervation of sympathetic nerves or bilateral removal of the superior cervical ganglion had no effect. These results indicate that choroid plexus has different transport systems for amino acids and peptides, which are not affected by denervation of the sympathetic nerves that innervate choroid plexus.