Neuropeptide FF-like immunoreactivity in human plasma

In order to examine whether neuropeptide FF (NPFF), an octapeptide with pain-modulating and blood pressure-raising properties in the rat, is present in circulating human blood, a radioimmunoassay (RIA) was established. Using this highly specific and sensitive RIA, the mean concentration of NPFF in human plasma was 2.9 pg/ml +/- 1.1 (n = 111). The concentration did not correlate with age or sex. Reversed-phase high pressure liquid chromatography (HPLC) followed by RIA using two different antisera for NPFF showed that plasma NPFF eluted in a position identical to that of synthetic NPFF. In view of published Kd values (0.06 mM) for NPFF receptor, the concentrations detected of NPFF in human plasma may be too low for systemic actions. Thus, plasma NPFF may represent leakage of the peptide from nervous tissue.