[Fasciolinip-1: experimental fasciolicidal activity in sheep]

The aim of the present study was to evaluate the flukicide efficacy of the 2-amino-5(6)-chloro-1-methoxycarbonylbenzimidazole (II), named Fasciolinip-1, against eight and twelve-week old flukes in sheep. In a first experiment 35 young sheep were infected each with 300 metacercariae of Fasciola hepatica. Eight weeks postinfection five groups of seven animals each were treated as follows: Groups 1, 2 and 3 were given 2.5, 5 and 10 mg/kg of Fasciolinip-1. Groups 4 and 5 remained as non-treated and vehicle controls, respectively. In a second study, 32 sheep were infected each with 150 metacercariae. Twelve weeks postinfection, the animals were divided into 4 groups of 8 sheep each. Groups 1, 2 and 3 were treated orally with 5, 10 and 15 mg/kg of Fasciolinip-1, respectively. Group 4 remained as non-treated control. Fifteen days after treatment, all sheep from both experiments were killed to collect the flukes present in liver. Results indicated efficacies of 19.1%, 49.6% and 65.2% for groups 1, 2 and 3 of the first study and 48.3%, 64.8 and 90.6% for sheep of the second experiment, respectively. It was concluded that Fasciolinip-1 removed 8-week old flukes in limited numbers and 12-week old flukes in 90.6% when used at 15 mg/kg body weight.

The effect of triclabendazole ("Fasinex") on protein synthesis by the liver fluke, Fasciola hepatica

The effect of the active sulphoxide metabolite of the anthelmintic triclabendazole (TCBZ-SX, 15-50 micrograms ml-1) on the incorporation of radioactively labelled [14C] leucine by adult Fasciola hepatica tissue slices was measured by liquid scintillation counting. In addition, the ability of the microfilament-disrupting drug, cytochalasin B, and the microtubule-disrupting drug, tubulozole-C, to inhibit protein synthesis, was assessed by similar methods and compared with TCBZ-SX. The established protein synthesis inhibitors, cycloheximide and actinomycin D were used as positive controls. All the drugs showed a significant inhibition of protein synthesis, albeit to different extents; however, TCBZ-SX was the most potent, with no significant difference between its effect and that of cycloheximide or actinomycin D. Moreover, the concentration of TCBZ-SX, above 15 micrograms ml-1, had little further influence on incorporation of [14C] leucine. This investigation demonstrates the inhibitory effect of TCBZ-SX, cytochalasin B and tubulozole-C on protein synthesis in F. hepatica and confirms the qualitative observations made in several previous ultrastructural studies.

Fasciola hepatica: ultrastructural changes to the tegument of juvenile flukes following incubation in vitro with the deacetylated (amine) metabolite of diamphenethide

Ultrastructural changes to the tegument of 5-week-old, 3-week-old and freshly-excysted Fasciola hepatica following in vitro incubation with the deacetylated (amine) metabolite of diamphenethide (DAMD, 10 microgramsml-1) were examined by transmission electron microscopy. A similar sequence of tegumental changes occurred in all three age groups of fluke, although, with increasing fluke age, the time before onset increased and the damage became more extensive. The 5-week-old flukes showed an initial stress response after 3 h, typified by blebbing of the apical plasma membrane, formation of microvilli and an accumulation and accelerated release of secretory bodies at the tegumental apex, as well as swelling of the basal infolds. The swelling increased in extent with progressively longer periods of incubation in DAMD, leading to extreme edema and sloughing of the tegument after 9 h. The 3-week-old flukes showed a stress response and swelling of the basal infolds after only 1.5 h, although sloughing of the tegument did not occur until after 9 h. In the freshly-excysted metacercaria, a stress response and some sloughing of the tegument were evident after only 0.5 h. At all stages of development, the ventral tegument was more severely affected than the dorsal. Changes also occurred to the tegumental cells which were indicative of a disruption in the synthesis and release of tegumental secretory bodies: the amount of GER became reduced, the cisternae became swollen and their ribosomal covering decreased, the Golgi complexes disappeared from the cells and the numbers of secretory bodies in the cells also decreased. The heterochromatin content of the nuclei increased and eventually the tegumental cells began to break down. Again, the changes became apparent more rapidly at the earlier stages of development. The ultrastructural changes to the tegument are linked to a possible mode of action for diamphenethide as an inhibitor of protein synthesis. In turn, the results may help to explain the drug's high efficacy against juvenile stages of F. hepatica.

Glutathione S-transferases as markers of salicylanilide resistance in isolates of Fasciola hepatica

A possible link between the level of glutathione S-transferase (GST, E.C. 2.5.1.18) activity and the development of salicylanilide resistance in Fasciola hepatica was investigated. Various isolates of F. hepatica with varying susceptibilities to salicylanilides were isolated and maintained in the laboratory. Individual flukes of these isolates were surveyed for their level of GST activity and a correlation between the level of GST activity and drug efficacy was found. In contrast to most other studies, a decrease in GST activity was associated with an increase in drug resistance. Evidence was collected to show that this may be a selective process since flukes which had survived exposure to rafoxanide and closantel in vivo (in sheep) had lower activity levels of GST than flukes from untreated sheep. Treatment with other flukicides (oxyclozanide, luxabendazole and triclabendazole) did not have this effect. Furthermore, in vivo treatment with closantel induced selection of particular isoenzymes in different isolates of F. hepatica having different degrees of susceptibility to closantel. However, no single isoenzyme or isoenzyme profile was associated with resistance and, in total, up to 8 different isoenzymes could be present in a single isolate. Thus, GST has some potential as a marker enzyme for salicylanilide resistance in F. hepatica. However, the precise role of GST in resistance is unclear and the extensive inter- and intra-isolate variation in activity levels and isoenzyme characteristics of this enzyme indicate the need for considerably more study before application in field situations.

The effect of the sulphoxide metabolite of triclabendazole ('Fasinex') on the tegument of mature and immature stages of the liver fluke, Fasciola hepatica

The effects of the novel benzimidazole, triclabendazole (TCBZ) ('Fasinex', Ciba-Geigy), in its active sulphoxide metabolite form (TCBZ-SX), on the tegumental ultrastructure of Fasciola hepatica were determined in vitro by transmission electron microscopy (TEM), using both intact flukes and tissue-slice material. At a concentration of 15 micrograms/ml, the tegument of the whole adult fluke showed ultrastructural changes only after prolonged time-periods, with vacuolation at the base of the syncytium and accumulation of T2 secretory bodies in the tegumental cells. At a concentration of 50 micrograms/ml, with both whole flukes and tissue-slices, the tegument appeared extremely abnormal with accumulation of secretory bodies towards the base of the syncytium. With longer incubation times, the tegument was completely sloughed away and the tegumental cells became synthetically inactive. The tegument of the 3-week-old juvenile became progressively convoluted at the apex, while in the basal regions there was severe vacuolation. In the tegumental cells, there were accumulations of T1 secretory bodies. These results confirm TCBZ as a potent fasciolicide, being very effective in disrupting the fluke tegument. They may go some way to explain the mode of action of this important fasciolicide.

Effects of luxabendazole on the tegument of Fasciola hepatica

The effects in vivo of 5, 10, and 20 mg/kg of luxabendazole (LBZ) on the tegument of Fasciola hepatica have been examined 48 h, 7 days and 14 days post-treatment of experimentally-infected rats. As early as 48 h post-treatment, the drug is shown to provoke significant damage to the tegument. The pathological phenomena characterizing LBZ damage are blebbing of the apical plasmalemma, formation of microvillus-like projections over the free surface, swelling of the basal infolds and stimulation of autophagy. The spines are often fractured; the tegument in the vicinity of spines seems more strongly altered than that in other foci. The basal layer is often changed, from increase of electron density to lack of integrity with the apical cytoplasm. The progress of the ultrastructural damage with time is not expressed. However, cytochemical data show that a longer post-treatment intervals the surface-coat structure becomes irregular and patches of ruthenium red positive material of variable thickness are focally accumulated. Only a slight dose-effect is noted 48 h after LBZ application when the alterations provoked by 5 mg/kg are less evident than those by 10 and 20 mg/kg.

The effect of diamphenethide on protein synthesis by the liver fluke, Fasciola hepatica

The effect of the deacetylated (amine) metabolite of diamphenethide (DAMD, 10 micrograms ml-1) on the uptake and incorporation by adult Fasciola hepatica of radioactively labelled precursors of DNA, RNA and protein synthesis ([3H]thymidine, [3H]uridine and [3H]leucine, respectively) was measured by liquid scintillation counting. Comparison was made between the effects of DAMD and those of specific inhibitors of DNA, RNA and protein synthesis, namely, 5-fluorouracil, cordycepin and cycloheximide, respectively. DAMD caused a significant decrease in the overall uptake and incorporation of [3H]uridine by F. hepatica, decreased the incorporation of [3H]leucine and also caused a significant decrease in the overall protein content of the flukes. The effect of DAMD was similar to that of cycloheximide (1 x 10(-3) M), a potent inhibitor of protein synthesis, which also caused a significant decrease in the incorporation of [3H]leucine by the fluke and a decrease in the overall protein content of the fluke. Cordycepin (100 micrograms ml-1) caused a significant decrease in the protein content of the fluke, but had no effect on the uptake or incorporation of [3H]uridine. 5-Fluorouracil (1 x 10(-4) M) did not affect the uptake or incorporation of [3H]thymidine, nor did it decrease the protein content of the fluke. The results indicate that DAMD inhibits protein synthesis by F. hepatica, possibly by inhibiting RNA synthesis. The results are also consistent with previous morphological investigations involving DAMD.

Fasciola hepatica: the effect of the microtubule inhibitors colchicine and tubulozole-C on the ultrastructure of the adult fluke

The effect of the microtubule inhibitors colchicine (1 x 10(-3) M) and tubulozole-C(1 x 10(-6) M) on the ultrastructure of adult Fasciola hepatica has been determined in vitro by transmission electron microscopy (TEM), using both intact flukes and tissue-slice material. With colchicine treatment, the apical membrane of the tegument became increasingly convoluted and blebbed, while accumulations of T1 secretory bodies occurred in the basal region of the syncytium, leading to progressively fewer secretory bodies in the syncytium. In the tegumental cells there were distinct accumulations of T1 secretory bodies around the Golgi complexes, which remained active for up to 12 h incubation. Tubulozole-treated flukes showed more severe effects, with initial accumulations of secretory bodies, both at the tegumental apex and base. This was followed in the later time-periods by the sloughing of the tegumental syncytium. In the underlying tegumental cells, the granular endoplasmic reticulum (GER) cisternae were swollen and disrupted, becoming concentrated around the nucleus. The Golgi complexes were dispersed to the periphery of the cells and gradually disappeared from the cytoplasm. After treatment with both drugs, the cell population in the vitelline follicles was altered, with an abnormally large proportion of stem cells and relatively few intermediate type 1 cells. The nurse cell cytoplasm became fragmented and was no longer in contact with the vitelline cells, while the shell globule clusters within the intermediate type 2 and mature cells were loosely packed. In the mature vitelline cells, 'yolk' globules and glycogen deposits became fewer than normal and lipid droplets were observed. The results are discussed in relation to the different modes of action of the two drugs and potential significance of this to anthelmintic (benzimidazole) therapy.

Effect of early treatment with rafoxanide on antipyrine clearance in sheep infected with Fasciola hepatica

1. The effect of the salicylanilide compound rafoxanide against immature stages of Fasciola hepatica was investigated in sheep using a series of antipyrine clearance tests and measuring glutamate dehydrogenase and gamma-glutamyl transferase activities in plasma. 2. Three animal groups were used. In two groups, sheep were infected with 200 metacercariae each. Four weeks after infection one of the two groups was treated with rafoxanide and the other was left untreated. The third group was unparasitized and also received rafoxanide. 3. Infection was confirmed by post-mortem examination of the livers of infected sheep. Infection did not alter the plasma disposition of rafoxanide. 4. The efficacy of rafoxanide, as assessed by the reduction in the number of adult flukes in treated animals compared with controls, was 85%. 5. Glutamate dehydrogenase activity fell dramatically 2 weeks after treatment but increased again at 12 weeks post-infection in the infected rafoxanide-treated group. 6. Antipyrine clearance decreased between 8 and 14 weeks post-infection in untreated sheep. In the infected rafoxanide-treated group plasma clearance of antipyrine remained unchanged until 10 weeks after rafoxanide administration when it decreased from the preinfection value of 5.09 to 3.90 ml.kg/min. Rafoxanide did not affect antipyrine disposition in uninfected sheep. 7. It was concluded that rafoxanide had an incomplete anthelmintic effect against immature stages of Fasciola hepatica, and that surviving parasites caused delayed liver damage which was reflected in an elevation in glutamate dehydrogenase activity and decreased plasma clearance of antipyrine.

Fasciola hepatica: tegumental surface changes in adult and juvenile flukes following treatment in vitro with the sulphoxide metabolite of triclabendazole (Fasinex)

The effects of the novel benzimidazole, triclabendazole (Fasinex, Ciba-Geigy), in its active sulphoxide metabolite form (TCBZ-SX), on the tegumental surface of Fasciola hepatica has been examined in vitro. The tegument of adult flukes incubated in TCBZ-SX (50 micrograms/ml) appeared swollen and blebbed after only 6 h. In addition, progressive spine loss at the oral cone was evident following 12 h treatment. After 24 h, the tegumental syncytium and spines had completely sloughed away, leaving an exposed basal lamina and empty spine sockets. Juvenile flukes (3 weeks old) also demonstrated tegumental alterations after treatment with TCBZ-SX (20 micrograms/ml). The syncytium became extremely roughened and corrugated on both dorsal and ventral surfaces after only 3 h. Following 6- and 9-h incubations, there were many deep furrows, which were especially pronounced on the ventral surface, and by 18 h, the juvenile tegument was severely disrupted, especially on the ventral surface. In all cases, the effects were more marked than in the previous incubation periods. The results confirm the potent activity of triclabendazole against F. hepatica and suggest that the tegument of adult and juvenile flukes may be a target organ for this important fasciolicide.

Experiments on anthelmintic control of Fasciola hepatica in Brazil

Two separate field trials involving naturally infected cattle were carried out on two farms known to have a history of Fasciola hepatica infection. On the first farm, 15 animals per group were allocated as follows: G1, triclabendazole (TCBZ) four times a year; G2, TCBZ twice a year (May and September); G3, untreated control. All groups grazed together and after 3.5 years the animals were slaughtered and their livers examined by federal meat inspectors who condemned 100% of livers in G3 and 8.3% in G2 owing to the presence of lesions of fasciolosis. In G1 no livers were condemned. Significant differences in weight gains were not detected and fluke counts remained at low levels in the treated groups. Also, in the control group, egg counts started to decrease when animals were 2 years old. On the second farm, groups of 20 animals were treated as follows: G1, TCBZ three times a year (May, September and December); G2, TCBZ twice a year (May and September); G3, nitroxynil twice a year (May and September); G4, rafoxanide twice a year (May and September); G5, untreated controls. All animals were weighed and faecal samples examined at approximately 28-day intervals. During the period of the study, larger weight gains were detected in the TCBZ treated groups than in the others. TCBZ treatment kept F. hepatica egg counts at a lower level for longer periods than the other drugs and significant differences in weight gains were only obtained between the group receiving TCBZ three times a year and the control group.

Fasciola hepatica: disruption of spermatogenesis by the microfilament inhibitor cytochalasin B

The distribution of actin filaments in the spermatogenic cells of Fasciola hepatica was determined using a fluorescent derivative of phalloidin. Actin was localised primarily in the region of separation of a secondary spermatogonium from a primary spermatogonium, in the inner faces at the centre of four-cell clusters of tertiary spermatogonia and in the cytophore region of spermatocyte and spermatid rosettes. The effect of the microfilament inhibitor cytochalasin B (100 micrograms/ml) on the ultrastructure of the spermatogenic cells was determined in vitro by transmission electron microscopy using tissue-slice material. Cytochalasin B treatment led to the formation of bi- and multinucleate cells, whose frequency increased with progressively longer incubation periods. Few typical rosettes of spermatocyte and spermatid cells were evident from 6 h onwards, being replaced by syncytial masses of cells. Spermatozoon formation became abnormal in the longer treatment periods, the spermatozoa containing variable numbers of axonemes and an altered distribution of cortical microtubules. Multiple axonemes were observed in the cytoplasm of spermatid cells. The results are discussed in relation to the established role of actin in the cytokinesis phase of cell division and to the effects of cytochalasin B on other tissues and organ systems within the fluke.

Fasciola hepatica: the effect of the microfilament inhibitor cytochalasin B on the ultrastructure of the adult fluke

The effect of the microfilament inhibitor cytochalasin B (10 and 100 micrograms/ml) on the ultrastructure of adult Fasciola hepatica was determined in vitro by scanning and transmission electron microscopy (SEM, TEM) using both intact flukes and tissue-slice material. SEM revealed that initial swelling of the tegument led to surface blebbing and limited areas of sloughing after 24 h treatment at 100 micrograms/ml. In the tegumental syncytium, basal accumulations of secretory bodies (especially T2s) were evident in the earlier time periods but declined with longer incubations, until few secretory bodies remained in the syncytium overall. Blebbing of the apical plasma membrane and occasional areas of breakdown and sloughing of the tegument were observed over longer periods of treatment at 100 micrograms/ml. In the tegumental cell bodies, the Golgi complexes gradually decreased in size and activity, and few secretory bodies were produced. In the later time periods, the cells assumed abnormal shapes, the cytoplasm shrinking in towards the nucleus. In the vitelline follicles, a random dispersion of shell protein globules was evident within the intermediate-type cells, rather than their being organized into distinct shell globule clusters. Disruption of this process was more severe at the higher concentration of 100 micrograms/ml and again was more evident in tissue-slice material. In the latter, after prolonged (12 h) exposure to cytochalasin B, the intermediate and mature vitelline cells were filled with loosely packed and expanded shell globule clusters, containing few shell protein globules. The mature vitelline cells continued to lay down "yolk" globules and glycogen deposits. Disruption of the network of processes from the nurse cells was evident at the higher concentration of cytochalasin. Spaces began to appear between the vitelline cells and grew larger with progressively longer incubation periods, and the cells themselves assumed abnormal shapes. A number of binucleate stem cells were observed in tissue-slice material at the longest incubation period (12 h).

Efficacy of clorsulon for the treatment of experimentally induced infections of Fasciola hepatica in goats

A dose titration study was undertaken to determine the efficacy of clorsulon against the adult stage of Fasciola hepatica in goats. Thirty-nine goats were experimentally infected with metacercariae of F hepatica. At 14 weeks after infection, each goat was assigned randomly to 1 of 5 groups. Goats in groups 1 to 4 received a single oral administration of clorsulon at dosages of 3.5, 7, 11, and 15 mg/kg of body weight, respectively. The fifth group of goats (control group) was infected with F hepatica, but were not treated with clorsulon. Postmortem examination of goats at 3 weeks after treatment revealed mean reductions in numbers of flukes of 83, 98, 99, and 100% for groups 1 to 4, respectively. Mean percentage of reduction in eggs following treatment of groups was 82, 98, 100, and 100%, respectively. The clinical effects of clorsulon in 24 goats that were not infected with F hepatica were studied. Goats in groups 1 to 3 received a single oral administration of clorsulon at dosages of 7, 21, and 35 mg/kg, respectively, every other day for a total of 3 doses/goat. Group-4 goats (control group) received a vehicle placebo. Goats in group 3 were subject to postmortem examination at 14 days after dosing. Abnormal signs or lesions that could be attributed to clorsulon were not found in any goat.

A study of a restricted programme of strategic dosing against Fasciola hepatica with triclabendazole

A restricted programme of strategic dosing with triclabendazole was used to treat a sheep flock with severe clinical fascioliasis. After five years the percentage of ewes passing fluke eggs was reduced from 49 per cent to less than 1 per cent, without the reappearance of clinical fascioliasis. It is suggested that this programme offers an efficient and practical means of controlling fascioliasis.

Comparative efficacy of closantel and triclabendazole against Fasciola hepatica in experimentally infected sheep

The effect of closantel (10 mg/kg orally) and triclabendazole (10 mg/kg orally) on the reappearance of a patent infection of Fasciola hepatica was studied in experimentally infected sheep. The treatments resulted in the interruption of faecal egg output for 11 weeks with triclabendazole and 13 weeks with closantel. Necropsy of untreated control animals revealed a mean burden of 360 flukes with a mean (+/- se) surface area of 171 +/- 64.3 mm2, whereas the fluke burdens in the closantel and triclabendazole-treated animals 14 weeks after treatment were 61 (83 per cent reduction) and 21 (94 per cent reduction), respectively. The surface areas of the flukes in the triclabendazole-group were comparable with the untreated controls (141 +/- 51.8 mm2), but the flukes in the closantel group were markedly smaller (43.1 +/- 26.9 mm2). It is concluded that closantel has, in epidemiological terms, a potency comparable with that of triclabendazole, despite its slightly lower efficacy against the very immature stages.

The effect of the hydrogen ionophore closantel upon the pharmacology and ultrastructure of the adult liver fluke Fasciola hepatica

The present study describes the effects of the H+ ionophore and anthelmintic closantel upon the in vitro motility and in vivo ultrastructure of the liver fluke, Fasciola hepatica. At a concentration of 50 micrograms/ml, closantel caused an initial stimulation, then suppression of activity, which was accompanied by an increase in muscle tone and led to a spastic paralysis within 2 h. The pattern of response was similar at lower concentrations, although the initial stimulation was not always evident, but the onset of paralysis could be reached more quickly. Scanning electron microscopy revealed gross surface damage from 24 h onwards in vivo, in the form of erosion of the anterior and posterior extremities of the fluke and large-scale sloughing of the tegument on both dorsal and ventral surfaces. Tegumental changes prior to sloughing included some swelling of the basal infolds and an apical accumulation of T1 secretory bodies. In the underlying tegumental cells there was reduced secretory activity and the mitochondria were consistently swollen and deformed. Reduced secretory activity was a feature of the gastrodermal cells as well; these cells were characterized by swollen, electron-lucent mitochondria, vesiculated GER cisternae and apical blebbing of packets of cytoplasm. The vitelline follicles became severely disrupted as a result of the breakdown of the nurse cell cytoplasm. The stem and intermediate type 1 (It1) cells rounded up and showed nuclear abnormalities. There did not appear to be a severe disruption of shell protein production in the intermediate vitelline cells, but there was a noticeable absence of glycogen in the mature vitelline cells. The effects of closantel are discussed in relation to its proposed mode of action as an uncoupler of oxidative phosphorylation.

The efficacy of triclabendazole (Fasinex) against immature and adult Fasciola hepatica in experimentally infected cattle

Eighteen Chinese cattle were experimentally infected with metacercariae of Fasciola hepatica and randomly assigned to 6 groups. Five groups of cattle were treated with a single oral dose of triclabendazole at a dose rate of 12 mg kg-1. At necropsy, the reduction in fluke burden compared with the untreated group was 85, 99.6, 99.8, 100 and 100% for cattle treated 2, 6, 8, 12 and 16 weeks after infection, respectively. Data are also presented on body weight changes during the experimental period and on serum gamma-GT activity in cattle from selected groups. Triclabendazole is considered to be safer and more efficacious than currently available fasciolicides in China.

Thiol proteases released in vitro by Fasciola hepatica

Immature Fasciola hepatica release 11 distinct proteases when cultured in vitro for 16 h as revealed by gelatin-substrate sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE). Six of these proteases are active in the pH range 4.5 to 8.0. Five are acid proteases, being most active in the pH range 3.0 to 4.5. The majority of proteases released in vitro by immature flukes are also released by mature flukes; however, a 40-kDa protease released by immature flukes is a very minor protease released by mature flukes. The activity of all proteases is inhibited by leupeptin, L-trans-epoxysuccinyl-leucylamido(4-guanidino)butane, phenylmethylsulfonyl fluoride and iodoacetamide and enhanced or stabilized by the reducing agents cysteine and dithiothreitol. Therefore, all F. hepatica in vitro-released proteases identified by gelatin-substrate SDS-PAGE are thiol proteases.

In vivo regulation of phosphorylation level and activity of phosphofructokinase by serotonin in Fasciola hepatica

The level of phosphorylation and activation of phosphofructokinase by serotonin (5-hydroxytryptamine) was studied in intact liver flukes Fasciola hepatica. The enzyme was immunoprecipitated with antiserum prepared against pure enzyme from the liver flukes. The resuspended immunoprecipitated enzyme retained most of its original activity and its kinetic properties. The level of phosphorylation was determined by a "back phosphorylation" technique. According to this technique, the immunoprecipitated phosphofructokinase was phosphorylated with the catalytic subunit of pure cAMP-dependent protein kinase. Incubation of intact liver flukes with serotonin caused an increase in the level of enzyme phosphorylation which was concomitant with an increase in enzyme activity. The level of phosphorylation was increased by 0.08 mol per protomer as a result of maximal activation by serotonin. It is proposed that phosphorylation plays, at least in part, a functional role in the regulation of phosphofructokinase from the liver fluke F. hepatica under in vivo conditions.

Gastrointestinal hormones: environmental cues for Fasciola hepatica?

The effects of pharmacological concentrations of several gastrointestinal hormones on the rate of sucker activity and the frequency and the amplitude of spontaneous longitudinal muscle contractions have been examined in adult Fasciola hepatica. Caerulein and serum decrease the rate of oral sucker activity; motilin decreases and CCK-PZ increases ventral sucker activity when compared to controls. Caerulein, serum and motilin significantly inhibit the frequency of contractions while bile, caerulein and motilin decrease the amplitude of contractions. These results suggest that F. hepatica can recognize and respond to certain gastrointestinal hormones and there may be adaptive value in these behavioural responses.

Effect of closantel on intrategumental pH in Schistosoma mansoni and Fasciola hepatica

It has been proposed that the anthelmintic activity of the flukicide, closantel, is due to the drug's ability to interfere with the proton gradient in the parasite's mitochondria that in turn inhibits the generation of ATP by the parasite. Recent results using 31P-NMR suggest that this is not the primary target of the drug. We measured the effects of closantel on fluke intrategumental pH and observed a significant decrease (6.8 to 6.5). This decrease occurred within 10 min and at concentrations that were lower than those that produced significant changes in parasite ATP concentration. We also noted that this drug-induced change in intrategumental pH was associated with a marked reduction in fluke motility. Our results, when coupled to previous reports, would suggest that closantel is a membrane-active molecule that is capable of affecting a number of helminth biochemical and physiological processes.