Neuropeptide FF analog RF9 is not an antagonist of NPFF receptor and decreases food intake in mice after its central and peripheral administration
2013
Maletínská, Lenka | Tichá, Anežka | Nagelová, Veronika | Špolcová, Andrea | Blechová, Miroslava | Elbert, Tomáš | Železná, Blanka
Neuropeptide FF (NPFF) belongs to the RF-amide family of peptides bearing the identical C-terminal amino acid sequence (R-F-NH₂). In addition to NPFF, prolactin-releasing peptide (PrRP), another RF-amide, binds to NPFF receptors with high affinity. A selective antagonist of PrRP has not yet been identified, but a selective antagonist of NPFF, 1-adamantanecarbonyl-RF-NH₂ (RF9), was recently reported to antagonize the hyperalgesic effect of NPFF after central administration to mice. In the present study, RF9 competed with NPFF analog D-Y-L-(N-Me)-F-Q-P-Q-R-F-NH₂ (1DMe) in binding to CHO-K1 cell membranes transfected with the human NPFF2 receptor. In rat pituitary RC-4B/C cells, where the expression of the NPFF2 receptor was proved by immunodetection, RF9 did not reverse the phosphorylation of MAPK/ERK1/2 induced by [Tyr¹]NPFF. In vivo experiments with fasted mice confirmed that centrally injected [Tyr¹]NPFF significantly lowered food intake. However, RF9, a putative NPFF₂ antagonist, did not reverse the anorectic effect of [Tyr¹]NPFF. Paradoxically, RF9 itself exhibited an anorectic effect in fasted mice not only after intracerebroventricular but also after subcutaneous administration. This finding casts doubt on claims that RF9 is an NPFF antagonist.
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