STRUCTURE-ACTIVITY STUDY OF NEUROPEPTIDE FF - CONTRIBUTION OF N-TERMINAL REGIONS TO AFFINITY AND ACTIVITY

Twenty neuropeptide FF (NPFF) analogs having various lengths were synt hesized by solid-phase peptide synthesis to gain more information on t he role of N-terminal residues for the NPFF receptor affinity. The aff inities were evaluated in the rat spinal cord membrane preparations, a nd the biological activities were measured on morphine analgesia in th e mouse tail-flick test. Shortening of the NPFF sequence from the N-te rminus produced only a moderate decrease in affinity until NPFF(4-8) w as reached. In the same way, NPFF(3-8) significantly decreased morphin e analgesia, while NPFF(4-8) had no significant effect at a dose of 22 nmol. The introduction in the N-terminal part of NPFF of a D-enantiom er at positions 2 and 1 or the presence of an N-methyl group on positi on 3 did not modify affinity and activity. Substitution of proline(5) by the D-isomer decreased the affinity of NPFF analogs whatever their length, and [Tyr(1),D-Pro(5)]NPFF(1-8) was 2.5-fold less potent than [ Tyr(1)]NPFF(1-8) in reversing morphine-induced analgesia. In contrast, the presence of a glycine residue in position 5 did not influence the affinity toward NPFF receptors. Data provide evidence that the N-term inal segment of neuropeptide FF is responsible for high-affinity bindi ng.