The role of the blood-brain barrier transporter PTS-1 in regulating concentrations of methionine enkephalin in blood and brain

Previous studies have suggested that peptide transport system (PTS)-1, a saturable efflux system from brain to blood, regulates the concentration in the brain of methionine enkephalin (Met-Enk), an opiate peptide related to the drinking of ethanol in mice. We determined the relationship of PTS-1 to concentrations of immunoreactive Met-Enk in plasma and whole brain in eight randomly selected strains of mice. An active PTS-1 system could be demonstrated in five of the eight strains. In those five strains, faster efflux rates due to PTS-1 correlated with higher concentrations of Met-Enk in brain and plasma. These concentrations of Met-Enk in brain and plasma were positively correlated in the five strains in which PTS-1 was demonstrable and were inversely correlated in the three strains in which PTS-1 was not demonstrable. The results are consistent with previous observations indicating that the chronic level of brain Met-Enk can set the level of activity of PTS-1 and that, once set, PTS-I can play a major role in determining the concentrations of Met-Enk in brain and blood. (C) 1997 Elsevier Science Inc.