The 26-amino acid RF-amide peptide, P518 functions as a high-affinity ligand of GPR103. Both GPR103 and P518 precursor mRNA exhibited highest expression in brain.[6] The 43-amino acid QRFP peptide, a longer form of the P518 peptide is necessary to exhibit full agonistic activity with GPR103. Intravenous administration QRFP caused release of aldosterone, suggesting that QRFP and GPR103 regulate adrenal function.[7]
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Thuau R, Guilhaudis L, Ségalas-Milazzo I, et al. (2005). "Structural studies on 26RFa, a novel human RFamide-related peptide with orexigenic activity". Peptides. 26 (5): 779–89. doi:10.1016/j.peptides.2005.01.006. PMID15808908. S2CID24088690.