An enzymatically stable peptide with activity in the central nervous system: its penetration through the blood-CSF barrier.

Vasopressin, other neurohpophyseal peptides and certain of their fragments can affect central nervous system function. Cyclo(Leu-Gly), formally derived from the C-terminal dipeptide of oxytocin, is also active in memory processes. This molecule, radioactively labeled for this study, was found to be resistant to enzymatic degradation both in vivo and in vitro. Furthermore, after its intravenous application in cat, it easily penetrated into cerebrospinal fluid. This indicates that cyclo(Leu-Gly) can readily pass from blood into the central nervous system to exert it's central pharmacological actions. Thus, labeled cyclo(Leu-Gly) is a valuable model for studying the distribution and localization of peptides which have activity in the central nervous system.