D.F. Mettrick

Ecological and Physiological Aspects of Helminth-Host Interactions in the Mammalian Gastrointestinal Canal

Publisher Summary This chapter discusses interaction of helminths and their hosts within the alimentary canal and, especially the stomach and intestines. Many such parasites live in the gastro-intestinal canal while others penetrate into the wall of the canal and a few invade organs, such as the liver and pancreas. The dynamic relationship between parasite and host is clearly shown and a good example set for future researchers. First, there is a study of the parasite–host interface, including the various kinds of organs of attachment, the varied nature of the lumen and the mucosa of the gastrointestinal canal, the nature of adhesion, and absorptive surfaces of the helminth and the host. The chapter describes the ecology of helminth site selection by trematodes, cestodes, and nematodes and matters concerning concurrent infections, transplantation, and migration. The chemical and physical characteristics of the intestinal lumen ionic and osmotic characters, microbial ecology, enzymes, bile acids and dietary fats, nutritive gradients, and matters of luminal homeostasis are discussed. The functional gradients in the gastrointestinal tract, bearing on the absorption of electrolytes and nonelectrolytes, water absorption, and malabsorption are also discussed.

Parasite Behaviour: Understanding Platyhelminth Responses

Publisher Summary This chapter discusses parasite behavior in understanding platyhelminth responses. Parasitic organisms are similar to free-living organisms in that they respond to changes in their environment. These responses can take the form of measurable behavioral changes, underlying which there obviously has to be mechanisms involving the biochemistry and physiology of the parasitic organism. This chapter focuses on the importance of behavioral analyses to elucidate the mechanisms of orientation. In the free-living stages of parasitic platyhelminths, the ability to orient to specific cues is crucial. The host-finding behavior of the free-living miracidia involves at least three sequential steps where, at a minimum, the parasites must be able to respond directionally to cues that characterize the host habitat and the specific host. The long-term goal is to explain the reciprocal inhibition between the behavior of the pharynx (used in feeding) and the behavior of the ventral sucker (used in attachment and locomotion). The study of platyhelminth neurobiology can only advance through an approach that integrates behavioral analyses with neurobiology.

Hymenolepis diminuta: behavioral effects of 5-hydroxytryptamine, acetylcholine, histamine and somatostatin.

Consistent in vitro behavioral patterns were found in the scolex and strobila of adult Hymenolepis diminuta. These patterns were measured with a force transducer and the behavior analyzed with a slow motion closed circuit T.V. Varying concentrations of serotonin (5-HT), acetylcholine (Ach), histamine and somatostatin, in the range of 10(-3) to 10(-9) M, were tested for their influence on the rhythmic patterns of behavior. High concentrations of 5-HT and of Ach decreased scolex motility. While 5-HT significantly increased motility in the anterior-, mid- and posterior regions of the strobila at 10(-3) M, Ach inhibited motility in all 3 regions of the strobila at the same concentrations. At high concentrations, somatostatin had a smaller stimulatory effect on worm motility in the anterior and mid-regions; histamine only significantly affected worm motility in the posterior region of the strobila. Depending on concentration, the action of 5-HT, Ach and histamine can be reversed, particularly in the anterior and posterior regions of the strobila. The in vivo assay for worm migrational responses suggests that the action of the neuromuscular stimulators and inhibitors on worm migration is indirect.

Hymenolepis diminuta: pH changes in rat intestinal contents and worm migration.

Abstract Rats, each inoculated with 10 cysticercoids of the tapeworm, Hymenolepis diminuta , were starved for 18 hr prior to being fed 2 g glucose in 2.5 ml water given via stomach tube while the rats were anesthetized. At hourly intervals following feeding, the entire rat small intestine was removed, divided into eight equal regions, and the position of each scolex, the distribution of worm biomass by weight, and the pH of the intestinal contents were recorded. The changes in intestinal pH in rats with 13 and 23-day-old infections were compared with those in uninfected rats following a 2 g glucose meal in 2.5 ml water. In the uninfected rats, the entire small intestine, with the exception of the lower ileum, remained slightly acid over the 8-hr experimental period. The efflux of acid chyme from the stomach caused a statistically significant reduction in the pH of the duodenum and jejunum for up to 4 hr after feeding. In the infected rats the intestinal pH was significantly lower than in the uninfected animals. This appears to be a physicochemical effect of parasitism upon the host that has not previously been recorded. There were also pH gradients in the intestine of the infected rats, both down the length of the gut at any one time, and in the same region of the intestine at different times after feeding. These changing gradients were related to the migrational movements of H. diminuta within the intestine following feeding of the hosts. The changes in the intestinal pH following feeding of infected rats are greater than can be attributed to either acid chyme entering the duodenum, or changes in the distribution of worm biomass, and must, therefore, involve acid excretions from the worms themselves. The variation in the pH of the anterior half of the intestine of infected rats was 5.17 to 6.95 with a mean of 6.29. This mean value appears to be a far more appropriate pH to use in future in vitro studies involving H. diminuta than the range of alkaline hydrogen ion concentrations previously used.

THE BEHAVIOR OF JUVENILE FASCIOLA HEPATICA

The behavioral repertoire of the infective stage of Fasciola hepatica was qualitatively characterized. During activation, a primary activity was the emptying of the ceca by peristaltic-like contractions. Emergence behavior comprised coordinated patterns of body movement and sucker activity specifically directed at disruption of the ventral plug. The stimulus specificity of the emergence response for glycine-conjugated cholic acid and the log dose-effect relationship of this response with glycocholic acid suggested a receptor-mediated sensory recognition. Extracts from the duodenum (departure organ) and the liver (arrival site) significantly affected the rate of locomotion and the orientation of the migratory stage. The evidence for orientation in the migrating stages is unequivocal, but the mechanisms by which they orient are unclear.

Hymenolepis diminuta: Determination of unidirectional uptake rates for nonelectrolytes across the surface “epithelial” membrane

Abstract Methods used to determine unidirectional uptake rates of a variety of nonelectrolytes by Hymenolepis diminuta in vitro were examined for sources of error originating both from natural variability and from the various techniques used. The validity of the uptake rates were confirmed by computing the propagated variance due to methodological errors. A transport value for a single worm determination was significant only if it exceeded 13.8 μmol/g wet wt/hr. If the error due to the incomplete extraction of radiolabeled absorbate with ethanol is considered methodological, then the minimum transport value was 18.7 μmol/g wet wt/hr. Tissue wet or dry weight was found to be a valid measure for normalization procedures. Uptake rates determined with worms maintained for 2 hr in a cestode culture medium or 1 hr in a balanced electrolyte solution were similar to controls preincubated for only 10 min. Uptake rates using worms maintained for similar periods of time after removal from the host in a Tris-maleate-buffered solution were much lower than the controls or those obtained with worms in the culture medium or balanced electrolyte solution. Uptake rates were independent of the medium volume between 2 and 5 ml using either single or five-worm incubations in 1 and 5 mM glucose, although five-worm incubations required a larger correction factor for the adherent mucosal fluid. Ths most significant source of artifact in uptake rates occurred if results were not corrected for extracellular absorbate in the unstirred layer. This error accounted for an overestimation of uptake rates of up to 90% for some absorbates but was negligible for others. For those absorbates rate-limited primarily by the unstirred layer, correction for the unstirred layer was insignificant at low medium concentrations but became significant as the medium concentration approached and exceeded maximum influx for the transport system. Correction for the unstirred layer effect also varied from experiment to experiment due to differences in postincubation procedures. Using a combination of markers to determine the volume of the unstirred layer, glucose uptake was shown to be linear over a 5-min incubation period. The use of markers to determine the intracellular concentration of absorbates is also demonstrated and the method discussed with reference to the assumptions upon which it is based.

EFFECTS OF CHOLINERGIC DRUGS ON LONGITUDINAL MUSCLE CONTRACTIONS OF FASCIOLA HEPATICA

Acetylcholine, cholinergic agonists and acetylcholinesterase inhibitors significantly decrease the amplitude and frequency of spontaneous longitudinal muscle contractions in Fasciola hepatica. In order of their effects on the inhibition of muscle contractions, the cholinergic agonists can be ranked as nicotine greater than carbachol greater than acetylcholine. High calcium ion concentration also causes a significant inhibition of contractions. Atropine, a cholinergic antagonist that acts on muscarinic receptors, significantly increases the amplitude and frequency of spontaneous contractions and completely reverses the effects of cholinomimetic drugs, including nicotine. In adult F. hepatica, the levels of acetylcholine and its precursor choline are 3.14 +/- 0.55 and 13.75 +/- 3.72 pmol/mg wet weight, respectively. The activities of choline acetyltransferase, specific acetylcholinesterase and the nonspecific cholinesterase are 1.25 +/- 0.19, 238.0 +/- 13.0, and 83.0 +/- 33.0 nmol/hr/mg protein, respectively.

Effect of gastrointestinal hormones and amines on intestinal motility and the migration of Hymenolepis diminuta in the rat small intestine

Abstract Mettrick D. F. and Podesta R. B. 1982. Effect of gastrointestinal hormones and amines on intestinal motility and the migration of Hymenolepis diminuta in the rat small intestine. International Journal for Parasitology 12: 151–154. The effect of oral and/or intravenous administration of the gastrointestinal hormones gastrin, secretin and cholecystokinin-pancreozymin, the amine serotonin, histamine and glucose on intestinal transit and the distribution of the tapeworm Hymenolepis diminuta in the rat intestine, were examined at 30-min intervals for up to 4 h. Oral and/or intravenous administration of the GI hormones, serotonin, histamine and glucose accelerated intestinal transit of the marker but, except for the smaller histamine-stimulated increase in the parasitised animals, no significant differences were evident between infected and uninfected intestines. Concomitant administration of Mg 2+ with serotonin inhibited the serotonin-induced increase in intestinal marker transit. With the exception of gastrin, administration of the hormones and of serotonin induced a proximal redistribution of parasites. Histamine resulted in a strong distal movement of the parasites. The serotonin induced a proximal migration and was inhibited by Mg 2+ The results suggest that parasite relocation in the intestine is not a response to any single luminal parameter but, rather, a reaction to a complex of changes in the pre- and post-prandial intestinal lumen which occur as part of the hosts response to the physiological stimulus of a meal.

Hymenolepis diminuta: Effect of quality of host dietary carbohydrate on growth

Rats, each inoculated with 10 cysticercoids of H. diminuta were fed synthetic diets during the last 7 days of a 15-day experimental period. The diets were calorically and quantitatively identical. The effect of sugar quality in the host diet was compared using glucose, maltose, sucrose, galactose, and dextrin. Taking glucose as a standard, worm dry weight from rats fed on a maltose diet showed a decrease of 3.9%, dextrin a decrease of 11.8%, and sucrose a decrease of 22.8%. Galactose did not support worm growth. Changes in host body and liver weight were shown to be influenced by the different diets. The greatest body weight loss was associated with the galactose diet; the least with the dextrin diet. Glucose and sucrose diets occupied an intermediate position. The influence of starch quality in the diet was compared using potato, corn (maize), and wheat starch. With potato starch as a control, the increase in worm dry weight was 22% on wheat starch and 30% on corn starch. These two starches also resulted in a significant improvement (p < .05) in host liver weight. In all the experiments the availability of glucose to the worm in the intestinal lumen appears to be the limiting factor controlling parasite growth.

PURIFICATION AND PROPERTIES OF PHOSPHOENOLPYRUVATE CARBOXYKINASE FROM HYMENOLEPIS DIMINUTA (CESTODA)

A method is described for the purification of the enzyme phosphoenolpyruvate carboxykinase (PEPCK) from the cestode Hymenolepis diminuta. When purified to electrophoretic homogeneity, the enzyme had a molecular weight of 70,600 and an isoelectric point of 7.5. Kinetic studies indicated that the pH 5.6 was optimal for the carboxylation reaction and that Mn++ was the preferred divalent cation; there was no activity of the enzyme in the presence of Mg++. Apparent Km values for the carboxylation reaction were determined; those for GDP (20.6 muM) and PEP (38.9 muM) were lower than the values previously reported. GTP, GMP, ITP, IMP, fumarate, succinate and alpha-ketoglutarate were found to be competitive inhibitors and their Ki values determined.