Essentiality, Synergism, and Antagonism

The use of phenylarsonic feed additives to promote growth in poultry and swine and to treat specific diseases does not seem to constitute a hazard to the animal or to its consumers. Animal deaths and elevated tissue arsenic residues occur only when the arsenicals are fed at excessive dosages for long periods. Arsenic can be detected at low levels in tissues of animals fed organoarsenicals, but it is rapidly eliminated when the arsenicals are removed from the feed for the required 5-day period before marketing. 

Selenium and arsenic are antagonists in several animal species. Dietary arsenic, as arsenate, alleviates the toxic effects of selenium, as seleno-DL-methionine, on mallard (Anas platyrhynchos) reproduction, duckling growth, and survival. Mallard ducklings fed arsenate in the diet at 200.0 mg As/kg ration were protected against the toxic effects 

The toxic effects of arsenic can be counteracted with (1) saline purgatives, (2) various demulcents that coat irritated gastrointestinal mucous membranes, (3) sodium thiosulfate, and (4) mono- and dithiol-containing compounds and 2,3-dimercaptopropanol. Arsenic uptake in rabbit intestine is inhibited by phosphate, casein, and various metal-chelating agents. Mice and rabbits are significantly protected against sodium arsenite intoxication by A-(2,3-dimercaptopropyl)phthalamidic acid. Conversely, the toxic effects of arsenite are potentiated by excess dithiols, cadmium, and lead, as evidenced by reduced food efficiency and disrupted blood chemistry in rodents. 

Although arsenic is not an essential plant nutrient, small yield increases have sometimes been observed at low soil arsenic levels, especially for tolerant crops such as potatoes, com, rye, and wheat. Arsenic ph5 otoxicity of soils is reduced with increasing lime, organic matter, iron, zinc, and phosphates. In most soil systems, the chemistry of As becomes the chemistry of arsenate the estimated half-time of arsenic in soils is about 6.5 years, although losses of 60% in 3 years and 67% in 7 years have been reported. Additional research is warranted on the role of arsenic in crop production, and in nutrition, with special reference to essentiality for aquatic and terrestrial wildlife. 

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Furthermore, both methyldopa and reserpine, that essentially interfere with the catecholamine synthesis as well as its storage, exacerbate the Parkinson syndrome and, therefore, antagonize the activity of levodopa. The pharmacological profile of levodopa actually synergized by antimuscarinics. 

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