Ascaris suum contains a large number of FMRFamide-related peptides (FaRPs) of which KNEFIRFamide (AF1), KHEYLRFamide (AF2) and KSAYMRFamide (AF8, also called PF3) have been extensively studied and are known to exert actions on somatic muscle strips of the worm. In the present study, the effects of AF1, AF2 and AF8 on the activity of the vagina vera of female A. suum have been examined in vitro. The vagina vera is a muscular tube connecting the uterus and vagina uteri to the gonopore and is probably involved in regulating egg output. The tissue exhibited spontaneous, rhythmic contractions in vitro, which were modulated by each of the FaRPs tested. The effects of each of the peptides were qualitatively and quantitatively different, and in each case were reversible. AF1 (1 microM) caused a biphasic response in the form of a transient lengthening of the preparation, followed by a shortening; contractions were initially inhibited but resumed 5 min post-addition of the peptide. Lower concentrations (< or = 0.1 microM) induced a less marked effect, with rhythmic contractions returning 5 min post-addition. AF2 and AF8 reduced contraction frequency at concentrations > or = 0.1 microM. Both peptides also caused the tissue to shorten, although the effects of AF8 on baseline tension were inconsistent. The apparent potencies of AF1 and AF8 on contraction frequency of the vagina vera were 10-fold greater than AF2 and, unlike their actions on A. suum somatic body wall muscles, the actions of AF1 and AF2 were qualitatively different. Indeed, the effects of each of these FaRPs on the vagina vera were markedly different from those observed on the somatic muscle.

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 nematode 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 cessation of contractions. PF2 was 3 times more potent than PF1, with a threshold of 1 nM. Although PF4 was the least potent (threshold, 10 nM), its effects at > or = 10 nM were quantitatively the greatest. Both AF3 and AF4 (1 microM) induced complex, multiphasic responses consisting of an initial contraction and spastic paralysis followed by a return of contractile activity of increased amplitude. AF3 was 3 times more potent than AF4. The effects of these peptides had some similarities to those observed on A. suum somatic body wall muscle in vitro, with PF1, PF2 and PF4 being inhibitory and AF3 and AF4 being excitatory.

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Ascaris suum possesses a well-developed nervous system which is regulated by a number of classical neurotransmitters including acetylcholine (ACh), γ-aminobutyric acid (GABA), glutamate and serotonin. The vagina vera, the distal part of the ovijector, displays intrinsic, rhythmic activity which has been shown to be modulated by FMRFamide-related peptides (FaRPs) in vitro. Confocal scanning laser microscopy coupled with immunocytochemistry, and histochemical studies, revealed that the nerve plexus of the ovijector contains GABAergic and glutamatergic innervation. Although no distinctive cholinergic or serotoninergic innervation was apparent, cholinesterase activity was localized to discrete areas of the musculature of the vagina vera. The effects of classical transmitters on the activity of the vagina vera in vitro were examined. ACh was excitatory, stimulating a brief but powerful contraction of the vagina vera with a threshold for activity of 1 μM. Both GABA and glutamate were inhibitory, causing a cessation of contractile activity at high concentrations (> 10 μM). Although less potent than glutamate, GABA had more profound effects and induced longer-lasting paralysis of the tissue. The threshold concentrations for activity were 5 μM for glutamate and 10 μM for GABA. Serotonin had no consistent effect on the vagina vera. This study demonstrates that classical transmitters modulate the activity of the ovijector of A. suum.