Neuropeptide K is present in human cerebrospinal fluid.

Neurokinin A-like immunoreactivity (NKA-LI) in human cerebrospinal fluid (CSF) was determined by radioimmuno assay (RIA) combined with high performance liquid chromatography (HPLC). The major immunoreactive component did not coelute with NKA, but coeluted with neuropeptide K (NPK), which contains the NKA sequence in its C-terminus. Trypsin treatment of this component from human CSF and of synthetic NPK, produced a substance which coeluted with NKA in the HPLC system. When the NKA-LI was oxidized with hydrogen peroxide and rechromatographed, the immunoreactivity coeluted with NPK sulfoxide. The results indicate that the main part of the NKA-LI in CSF is identical with NPK. The mean concentration of NPK measured in CSF from 6 healthy subjects by HPLC-RIA was 23 +/- 11 (SD) pmol/L.