Nematode neuropeptide modulation of the vagina vera of Ascaris suum: in vitro effects of PF1, PF2, PF4, AF3 and AF4

Ascaris suum possesses a large number of FMRFamide-related peptides (FaRPs) of which KNEFIRFamide (AF1), KHEYLRFamide (AF2) and KSAYMRFamide (AF8/PF3) have been shown to modulate the intrinsic, rhythmic activity of the vagina vera of A. suum in vitro. In the present study, the effects of the nematod e FaRPs, SDPNFLRFamide (PF1), SADPNFLREamide (PF2) and KPNFIRFamide (PF4) ( from Panagrellus redivivus) and AVPGVLRFamide (AF3) and GDVPGVLRFamide (AF4 ) (from A. suum) on the in vitro activity of the vagina vera were examined. The effects of each of the peptides were qualitatively and quantitatively distinct. All 3 FaRPs from P. redivivus were inhibitory, causing a cessatio n of contractions. PF2 was 3 times more potent than PF1, with a threshold o f 1 nM. Although PF4 was the least potent (threshold, 10 nM), its effects a t greater than or equal to 10 nM were quantitatively the greatest. Both AF3 and AF4 (1 mu M) induced complex, multiphasic responses consisting of an i nitial contraction and spastic paralysis followed by a return of contractil e activity of increased amplitude. AF3 was 3 times more potent than AF4. Th e effects of these peptides had some similarities to those observed on A. s uum somatic body wall muscle in vitro, with PF1, PF2 and PF4 being inhibito ry and AF3 and AF4 being excitatory.