The effects of a range of FMRFamide-related peptides (FaRPs) on
isometric
contractility were tested using isolated muscle
strips from the liver fluke, F. hepatica. The neuropeptides tested
were
the molluscan FaRPs, FMRFamide and
FLRFamide, the turbellarian FaRPs, RYIRFamide and GYIRFamide, the cestode
peptides, NPF and GNFFRFamide,
and the nematode FaRPs, AF-1 (KNEFIRFamide), AF-2 (KHEYLRFamide), AF-8
(KSAYMRFamide), and PF-4
(KPNFIRFamide). Dose-response experiments were undertaken at a concentration
range of 5 nM–5 μM for all of the
neuropeptides tested. FMRFamide and AF-8 caused statistically significant
increases in the amplitude and frequency of
contractions at concentrations of 0·5 μM and 5 μM.
FLRFamide and AF-2 also caused significant increases in contraction
frequency at concentrations of 0·5 μM and 5 μM,
although a significant increase in amplitude of contraction was observed
only at a concentration of 5 μM. GYIRFamide increased both
amplitude
and frequency significantly at concentrations of
50 nM, 0·5 μM and 5 μM. RYIRFamide
significantly increased frequency of contractions at concentrations of
0·5 μM and
5 μM, but failed to have a significant effect on contraction
amplitude. AF-1 at a concentration of 5 μM increased contraction
amplitude, but failed to have an effect on frequency at any of the concentrations
used. PF-4 caused a statistically significant
increase in both the amplitude and frequency of contractions at a concentration
of 5 μM. NPF and GNFFRFamide had
no effect on the in vitro motility of F. hepatica over
the
range of concentrations tested. The results are discussed in the
light of possible structure–activity relationships in the FaRPs tested.