NPFF, a FMRF-NH2-like peptide, blocks opiate effects on ileum contractions.

We studied the ability of NPFF, a FMRFamide-like peptide with certain antiopiate properties, to affect the inhibitory effect of morphine on the electrically induced contraction of guinea pig ileum. Neuropeptide FF had no effect when administered alone but reduced morphine inhibition in a noncompetitive manner. Neuropeptide FF also altered the inhibitory effect of opioid peptides as released by an intense electrical stimulation at 10 Hz. These results suggest that NPFF receptors exist in guinea pig ileum in association with opiate receptors, and that endogenous NPFF may play a role in the diarrhea observed in the morphine withdrawal syndrome.