Absorption in Mammals

O Iron Absorption in Mammals with Particular Reference to Man... 

Decay in organisms relates to toxicity, and half-lives and excretion rates are dealt with elsewhere in this chapter. Toxicity arises because of easy absorption in mammals, leading to the loss of one alkyl group to form the trialkyl species. It is these trialkyl species which can most easily deliver lead and so cause toxicity. Decay does therefore take place by sequential loss of alkyl groups (similar to organotin species. Section 12.13.9), and so a series of alkyl, ionic, and inorganic lead species are excreted by mammals. 

Exposure to estrogenic compounds through diet will differ for herbivores and carnivores, the latter being most likely to encounter endogenous steroids in their prey. Efficient uptake of steroids in mammals is illustrated by the use of the contraceptive pill, but routes of absorption in invertebrates remain to be determined. The relationship between endocrine disruption and metabolic toxicity, with reduced reproductive viability a secondary consequence of metabolic disturbance, also merits further study in invertebrate species. 

In mammals, cadmium inhibits copper absorption across the intestinal mucosa (Aaseth and Norseth 1986). Intercorrelations of copper with cadmium and zinc in livers of polar bears (Ursus maritimus) are probably mediated by metallothioneins, which may contain all three metals (Braune etal. 1991). In rats, copper protects against nephrotoxicity induced by cadmium, provided that copper is administered 24 h prior to cadmium insult. Specifically, rats given 12.5 mg Cu/kg BW by way of subcutaneous injection 24 h before receiving 0.4 mg Cd/kg BW — when compared to a group receiving Cd alone — did not have excessive calcium in urine and renal cortex or excessive protein in urine. Thus, 2.8 mg Cu/kg BW protects against 0.25 mg Cd/kg BW (Liu et al. 1992). 

In mammals, copper absorption across the intestinal mucosa is inhibited by concomitant high oral intake of zinc (Aaseth and Norseth 1986). In livers from Weddell seals, copper is positively correlated with zinc (Szefer et al. 1994). The addition of zinc to swine diets protects against copper toxicosis caused by eating diets containing 250 mg Cu/kg ration (USEPA 1980). 

The absorption, bioavailability, and retention of radionuclides in mammals are modified by ... 

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