Nematodes excretion

D. J. Wright and D. R. Newall, Nitrogen excretion, osmotic and ionic regulation in nematodes. The Organisation of Nematodes (N. A. Croll, ed.). Academic Press, London, UK. 1976. p. 163. 

Enhanced nutrient cycling in both the rhizosphere and bulk soil may depend on the bacterial grazing by protozoa or nematodes with release of inorganic N. Nematodes appear to be the primary consumers of bacteria in the rhizosphere, whereas protozoa are equally prevalent in rhizosphere and bulk soil (41,97). Estimated C-to-N ratios of bacterial-feeding nematodes range from 5 1 to 10 1 (98,99) and are generally higher than those of their bacterial food source thus the excess N is excreted as ammonia (100,101) by nematodes. The estimated... 

Ammonia is also the major nitrogenous end product in some of the simpler aquatic and marine animal forms, such as protozoa, nematodes, and even bony fishes, aquatic amphibia, and amphibian larvae. Such animals are called am-monotelic. But in many animals, NH3 is toxic, and its removal by simple diffusion is difficult. Thus, in terrestrial snails and amphibia, as well as in other animals living in environments in which water is limited, urea is the principal end product (fig. 22.6). Urea formation also helps to maintain osmotic balance with seawater in cartilagenous fishes. In such animals, most of the urea secreted by the kidney glomerulus is reabsorbed by the tubules. Indeed, the amount of nitrogen excreted by the kidneys of fishes is small com-... 

There are many examples of crop rotation sequences that passively suppress nematode populations which will not be reviewed here. Examples of active nematode suppression in crop rotation sequences are typically found with plant species that produce and excrete allelopathic compounds. These compounds then affect plant-parasitic nematodes in the rhizosphere either directly or indirectly by altering rhizosphere microbial populations (Halbrendt, 1996). For the purpose of this chapter, allelopathic... 

Type 3 fermentation, characterised by a series of reactions between mitochondrial end-products that yield branched-chain fatty acids (e.g. 2-methylvalerate, 2-methylbutyrate), occurs in Ascaris, a number of other intestinal nematodes and in some trematodes (490). However, cestodes, with the exception of Bothriocephalus scorpii, which excretes methyl-butyrate (107), have not been shown to produce branched-chain fatty acids as end-products of respiratory metabolism. Some or all of the enzymes of the TCA cycle may be present in cestodes in addition to the type 1 and type 2 fermentation pathways. The extent to which the cycle may contribute to carbohydrate metabolism in cestodes is considered below. 

Next to fumarate reduction, some organisms use specific reactions in lipid biosynthesis as an electron sink to maintain redox balance in anaerobically functioning mitochondria. In anaerobic mitochondria two variants are known the production of branched-chain fatty acids and the production of wax esters. The parasitic nematode Ascaris suum reduces fumarate in its anaerobic mitochondria, but instead of only producing acetate and succinate or propionate, like most other parasitic helminths, this organism also use the intermediates acetyl-CoA and propionyl-CoA to form branched-chain fatty acids (Komuniecki et al. 1989). This pathway is similar to reversal of P-oxidation and a complex mixture of the end products acetate, propionate, succinate and branched-chain fatty acids is excreted. In this pathway, the... 

Levamisole is the levorotatory isomer of tetramisole. Originally used only as an antihelminthic drug, it acts by paralysing the musculature of susceptible nematodes so that they are expelled by peristalsis. It is rapidly metabolized and excreted, with a half-hfe of about 4 hours. 

The external surfaces of parasitic helminths, termed the tegument in cestodes and trematodes, and the cuticle in nematodes, are adapted to serve a wide range of biological functions. Though most research has focused on structural aspects or their roles in immune evasion (Chapter 16) and nutrient absorption, the external surfaces of helminths also serve important roles in locomotion, excretion and regulation of electrochemical and osmotic gradients. 

Excretion. Although direct evidence exists for outward transport of inorganic ions across the cuticle of A. suum (127), little is known about the relative importance of the cuticle, intestine or putative excretory canal system in nematodes for outward transport of metabolic end-products or other organic molecules. Organic acid end-products of carbohydrate metabolism are excreted across the cuticle in A. suum (129) and H. contortus (123). This process generates a microclimate pH within the aqueous pores of the cuticle which is maintained at pH 5.0, near the pK of the excreted organic acids (130). 

Little is known about the transport of amino acids across the intestine of nematodes. In vitro studies using isolated segments of intestine from A. suum indicate that uptake of methionine, glycine, histidine and valine is stereospecific and non-linear with respect to concentration, indicative of a mediated transport process (12). Most nematodes excrete a wide range of amino acids (149), and though some of these, such as alanine and proline, are true metabolic end-products, others must be derived from ingested materials. 

Pyrantel pamoate is poorly absorbed from the GI tract, a property that contributes to its selective action on GI nematodes. Less than 15% is excreted in the urine as parent drug and metabolites. Most of an administered dose is recovered in the feces. 

The major antigenic glycoconjugates found in excreted/secreted (ES) antigens synthesized by larvae of the parasitic nematodes T. canis and T. cati are 0-methylated... 

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