Gastrointestinal tract nickel

Inhaled nickel is at least 100 times more toxic than ingested nickel because it is more readily absorbed from the lungs than from the gastrointestinal tract, and death is more often the result of respiratory failure than of nervous system effects. For example, oral ingestion of 0.05 mg Ni/kg BW and inhalation at 0.005 Ni/m3 are equally effective threshold doses in rats (USPHS 1977). 

Only a few percent of an injected dose of nickel is excreted via the gastrointestinal tract in the rat [315], In humans, there is indirect evidence of a significant biliary contribution to nickel excretion [263]. 

Mass fraction of nickel dose absorbed from the gastrointestinal tract (F, %) 27 17 0.7 0.4 ... 

No value was determined because of the small mass of nickel absorbed from the gastrointestinal tract and transferred from the serum into the tissues. 

Several chronic inhalation and oral studies and acute dermal studies in animals are reported in the literature. These studies exposed several species of animals to both soluble and less-soluble nickel compounds. The target organs were found to be the respiratory system for inhalation exposure and the respiratory system, gastrointestinal tract, hematological system, and kidneys for oral exposure at high levels. Reproductive and developmental effects were observed in animals after inhalation exposure and after oral exposure to nickel. Nickel sensitivity and dermatitis were also observed. 

Although copper is an essential element, it is much more toxic to cells than such nonessential elements as nickel and cadmium. Acute poisoning from ingestion of excessive amounts of copper salts, most frequently copper sulfate, results in nonspecific toxic-symptoms, a metallic taste, nausea, and vomiting (with vomitus possibly a blue-green color). The gastrointestinal tract can be damaged by ulceration. 

Humans are frequently exposed to metals due to their ubiquity, wide use in industries, and persistence in the environment. Many nickel compounds are released into the atmosphere during mining, smelting, and refining operations. Although nickel is poorly absorbed from the gastrointestinal tract, exposure... 

In addition to gastrointestinal absorption, nickel may also enter the body by inhalation, transcutaneous absorption, and parenteral administration. In humans, approximately 35% of inhaled nickel is absorbed from the respiratory tract the remainder is carried up the tracheobronchial mucociliary escalator and either swallowed or expectorated (Bennett 1984, Grandjean 1984, Sunderman 1986b). In penetration through the epidermis, nickel may be bound to urocanic acid and histidine, which occur in human sweat (Mali etal. 1964). Hostynek etal. 

Most of the nickel contained in food passes through the gastrointestinal tract without resorption. The effective absorption of nickel is usually less than 10%. Increased resorption of nickel (20%) can occur if the saturation with iron is low. Resorbed nickel is excreted from the body mainly in urine. In the cytosol of renal cells, nickel is bound to a glycoprotein (15 kDa). The protein component of this glycoprotein contains a high proportion of glycine and no cysteine, so it is not identical with metaUothionein. This glycoprotein also binds nickel in the urine. 

During occupational exposure, respiratory absorption of soluble and insoluble nickel compounds is the major route of entry, with gastrointestinal absorption secondary (WHO 1991). Inhalation exposure studies of nickel in humans and test animals show that nickel localizes in the lungs, with much lower levels in liver and kidneys (USPHS 1993). About half the inhaled nickel is deposited on bronchial mucosa and swept upward in mucous to be swallowed about 25% of the inhaled nickel is deposited in the pulmonary parenchyma (NAS 1975). The relative amount of inhaled nickel absorbed from the pulmonary tract is dependent on the chemical and physical properties of the nickel compound (USEPA 1986). Pulmonary absorption into the blood is greatest for nickel carbonyl vapor about half the inhaled amount is absorbed (USEPA 1980). Nickel in particulate matter is absorbed from the pulmonary tract to a lesser degree than nickel carbonyl however, smaller particles are absorbed more readily than larger ones (USEPA 1980). Large nickel particles (>2 pm in diameter) are deposited in the upper respiratory tract smaller particles tend to enter the lower respiratory tract. In humans, 35% of the inhaled nickel is absorbed into the blood from the respiratory tract the remainder is either swallowed or expectorated. Soluble nickel compounds... 

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