Glucose absorption in vitro by the enteric stages of Trichinella spiralis

Glucose uptake and metabolism in the Trichinella spiralis nurse cell

Isolated Trichinella spiralis nurse cells transport a significantly greater amount of glucose/mg of protein than the normal skeletal muscle cell line (L6). V(max) and K(m) estimations revealed that nurse cells have a much higher saturation point than L6 cells for glucose. The effects of numerous physiological conditions (Na(+) concentration, pH, and temperature) on nurse cell glucose uptake were investigated. It was determined that sodium concentration had no effect on glucose uptake. Low (<6.5) and high (>7.3) pH and low (5 degrees C) temperatures significantly effected glucose uptake. The two hormones, insulin and epinephrine, appeared to have little, if any, influence on the rate of glucose uptake by nurse cells. Glucose uptake was inhibited in the presence of 6-carbon carbohydrates. The H(+)/glucose symport inhibitors, dicyclohexylcarbodiimide (DCCD) and Carbonyl cyanide 4-trifluoromethoxyphenlhydrazone (FCCP), and the facilitated diffusion inhibitor phloretin also inhibited glucose uptake. Oubain, a Na(+)/glucose symport inhibitor, did not inhibit glucose uptake. These data, in conjunction with Western blot analyses, revealed that the transport of glucose occurs via H(+)/glucose symport and facilitated diffusion, perhaps through the glucose transport proteins GLUT 1 and/or 4. It was also demonstrated that nurse cells are capable of synthesising glycogen. It appears that glycogen is in a constant state of flux and physiological conditions, such as glucose concentration, significantly influence the synthesis of this macromolecule. We conclude that these results are consistent with the hypothesis that nurse cells, at least maintained in vitro, are metabolically highly active but show significant divergence from normal muscle cells in several fundamental aspects of sugar metabolism.

Hypoglycaemia in experimental canine trichinellosis

This paper studies changes in serum glucose levels in dogs experimentally infected with Trichinella spiralis, and the histological causes of those changes. Hypoglycaemia is evident in 100% of experimental animals, and can be attributable to three factors: the reduced absorptive capacity of the intestine due to lesions (catarrhal and desquamative enteritis), high glucose consumption by parasites, or histopathological changes in the liver (glycogenic degeneration).

Carbohydrate reserves and infectivity in Trichinella spiralis isolated from carrion

Trichinous mice were killed and their carcasses maintained at room temperature or subzero temperatures for varying lengths of time. Some worm parameters were measured after direct isolation from carcasses while others were measured following passage through a second round of hosts. Glycogen and trehalose levels in infective 1st-stage larvae (L1) isolated directly from carcasses maintained at room temperature were significantly less than controls (day 0) after day 4 post-kill (p.k.). By day 21 p.k. among L1 isolated directly from mouse carcasses those observed coiled or moving had decreased by around 20% compared to day 0 p.k. The percentage of L1 isolated from carcasses on several days p.k., used to infect mice and recovered as pre-adult worms declined significantly after they had remained in carcasses for 14 days. Only 2.6% of muscle larvae isolated from carcasses on day 21 p.k. and used to infect mice were recoverable as pre-adults. Pre-adult worms raised in mice infected with larvae from day 7 carcasses had about 50% less glycogen than worms raised in mice infected with larvae isolated from fresh carcasses (day 0 p.k.). The fecundity in vitro of adult worms isolated from mice on day 7 following infection with infective L1 larvae maintained in carcasses held at room temperature for 0-16 days declined only when adult worms developed from larvae recovered from carcasses at 3 days following host death. Following 24 h at temperatures below freezing, infectivity of L1 larvae isolated from frozen carcasses was reduced by 97%. Carbohydrate levels remained high in larvae from carcasses frozen for up to 4 days.

The relative roles of the intestines and external surfaces in the nutrition of monogeneans, digeneans and nematodes

Several major groups of parasitic helminths (Monogenea, Digenea and Nematoda) possess two surfaces that are potentially absorptive in nature. These are an external surface, a tegument in the platyhelminths and cuticle in the nematodes, and the intestine. This paper discusses the relative contributions of these absorptive surfaces in the nutrition of these parasitic helminths. There are many factors that determine the availability of, and a parasite's ability to absorb nutrients via either of these surfaces, and this review discusses individually some of the more important morphological, physiological and environmental factors affecting the potential nutritional roles of these surfaces. It is clear from such a summary of previous studies that the intestines and teguments (cuticles) of helminth parasites can each serve an important nutritional role. However, insufficient data make it impossible at this time to determine the relative nutritional roles of these surfaces in any single parasitic helminth.

Ontogenetic changes in helminth membrane function

During their life-cycle many parasites experience a wide range of environments including free living and those provided by a variety of intermediate and final hosts. The nutritional requirements of parasites are met by physiological processes adapted to exploit the physicochemical characteristics provided by different hosts. In helminth parasites these adaptations are frequently expressed on the tegumentary surface. As an example of adaptations within the Trematoda, the control of monosaccharide transport in Proterometra sp. is described. Environmental sodium, although not directly involved in the uptake process, nevertheless regulates the expression of transport capabilities. In the Cestoda, the uptake of monosaccharides and amino acids is described for Hymenolepis diminuta. The metacestode of this tapeworm inhabits the blood system of an arthropod, and the adult the gut of a mammal. There are quantitative and qualitative differences in the amino acids and monosaccharides in these two environments and these are reflected in the transport mechanisms exhibited by the two forms of the life-cycle. In Echinococcus granulosus the transfer of amino acids, sugars and macromolecules across the membranes of hydatid cysts and protoscoleces is described. The major difference between these two stages in the life-cycle relates to the ability of hydatid cysts to absorb macromolecules, whereas protoscoleces are impermeable to these compounds. The potential for future work is emphasized.

Trichinella spiralis: behavior, structure, and biochemistry of larvae following exposure to components of the host enteric environment

Four layers are present on the surface of infective larvae of Trichinella spiralis isolated from host muscle in pepsin-HCl. Trypsin treatment of pepsin-HCl isolated worms caused partial degradation and removal of large patches of the two outer surface layers. Following exposure to bile, only traces of the outer layers remained on the worms surface. These changes in the worm surface were accompanied by a shift from Type I behavior, typical of pepsin-HCl isolated larvae, to Type II behavior, (snakelike) following exposure to either trypsin or bile. Worm behavior was also temperature dependent. Type I behavior was typical of worms maintained at room temperature regardless of treatment, while Type II behavior displayed by worms held at 37 C was treatment dependent. The absorption of in vitro glucose or beta-methyl-D-glucoside was lowest in pepsin-HCl isolated first stage infective larvae, significantly higher in trypsin treated worms and greatest in worms following exposure to bile. Sugar uptake by worms isolated from the host small intestine after 1 hr of enteral infection was similar to that seen in worms isolated from host muscle in pepsin-HCl. Sugar uptake in vitro in worms 2 hr following enteral infection was similar to worms following exposure to bile. The highest levels of sugar absorption in vitro occurred in worms which had resided in the small intestine for 3 hr. The lowest rates of incorporation of label into worm tissues was seen in 1 hr enteral and pepsin-HCl isolated worms. Infective larvae treated with trypsin or bile incorporated significantly greater amounts of label than the two former groups. The highest levels of incorporation of label into worm tissues was seen in 3 hr enteral worms. These findings support the view that trypsin, bile, and temperature serve as environmental cues which lead to alteration of the parasite's behavioral and nutritional status.