Evidence that [125I]N-Tyr-delta sleep-inducing peptide crosses the blood-brain barrier by a non-competitive mechanism.

Delta sleep-inducing peptide (DSIP), a nonapeptide, has previously been shown to cross the blood-brain barrier (BBB) in rats and the blood-CSF barrier in dogs. New experiments were conducted to determine if this crossing was competitive. Neither DSIP nor several analogs, including non-radioactive [127I]N-Tyr-DSIP, injected by the jugular vein or carotid artery, inhibited passage of radioactive [125I]N-Tyr-DSIP across the rat BBB. Column chromatography of brain samples confirmed that the radioactivity in the brain represented intact [125I]N-Tyr-DSIP and that the non-radioactive competing materials did not interfere with the degradation or binding of [125I]N-Tyr-DSIP. In addition, N-Tyr-DSIP was unable to inhibit the appearance of radioactive [125I]N-Tyr-DSIP in the CSF of dogs. In conclusion, the evidence from these experiments suggests that [125I]N-Tyr-DSIP crosses the rat BBB and dog blood-CSF barrier by a non-competitive mechanism.