Neonatal animals absorption

Children s Susceptibility. No studies were located in which comparisons were made between the sensitivity of children and adults to the toxicity of americium. Animal studies indicate that juvenile dogs are less susceptible than adults to americium-induced bone cancer (Lloyd et al. 1999). No direct evidence was located to indicate that the pharmacokinetics of americium in children may be different from that in adults. Based on dosimetric considerations related to differences in the parameters of available models, as well as studies in animals, it seems likely that children may be more susceptible to americium toxicity than are adults by virtue of age-related differences in pharmacokinetics. Absorption of ingested americium may be as much as 200 times greater in neonatal animals than in adults. (Bomford and Harrison 1986 David and Harrison 1984 Sullivan et al. 1985). 

Sullivan MF. 1980a. Absorption of actinide elements from the gastrointestinal tract of neonatal animals. Health Phys 38 173-185. 

Absorption extent from the gastrointestinal tract (GIT) is very low (of the order of <1-2% of administered dose), although higher bioavailability may be achieved in neonatal animals and where there is dismption of the intestinal mucosa, caused by, for example, parvovirus infection. Within the GIT, aminoglycosides are stable and excreted unchanged in feces. 

More information is needed on the absorption of various forms of uranium in young animals. Also, studies are needed on whether maternally stored bone uranium is mobilized to blood during pregnancy and lactation and whether this can increase exposure to the fetus and neonate. Child health data needs relating to exposure are discussed in Section 5.8.1, Data Needs Exposures of Children. 

It can also be concluded that dermal absorption occurred as evidenced by the development of skin tumors (Boutwell and Bosch 1958 Lijinsky et al. 1957 Poel and Kammer 1957 Roe et al. 1958) and lung tumors (Roe et al. 1958) in mice following the dermal application of coal tar creosote (see Section 3.2.3.7). Other studies in animals support absorption of coal tar products after dermal application. Coal tar solution (0.05 mL of a 20% solution) was applied to the skin of six neonatal rats (4-6 days of age) and 24 hours later AHH activity was measured in the skin and liver (Bickers and Kappas 1978). There was greater than a 10-fold induction of skin AHH activity (298 13 versus 26.3 19 pmol hydroxy-benzo[a]pyrene/mg protein/hour in controls) and marked increased hepatic AHH activity (16,300 899 versus 750 35 pmol hydroxy-benzo[a]pyrene/mg protein/hour in controls) after topical application of the coal tar solution. 

The absorption of plutonium after oral administration was age- related in laboratory animals. From 3 to 6% of administered plutonium may be absorbed by neonatal rats, hamsters, guinea pigs, and dogs (Cristy and Leggett 1986). A rapid decrease in absorption has been seen with increasing age. 

The intestinal absorption of lead is also extremely variable, and can range from as much as 50% in the neonate (Momcilovic and Kostial, 1974) to as little as 0.1% in the adult (Kostial et al., 1971). In comparison, human absorption has been estimated at 5-10% in the adult (Kehoe, 1960) and 20-50% in children (Alexander, 1974). Estimation of lead intake as ng Pb/kg/day in experimental animals is thus a highly inaccurate measure of absorbed dose on a comparative basis. 

Since milk is the only food in the very young we assumed that milk diet might be one of the reasons for the high intestinal absorption in neonates. Indeed, older animals on milk diet also had a higher lead absorption than the controls (Kello and Kostial, 1973). 

From the results presented, it seems indisputable that metal metabolism in immature animals is different from that in adults. The high absorption of metals in neonates represents a risk of a higher body burden of metals in the immatures at the same level of environmental exposure. A higher body burden of toxic metals at the time of rapid growth and development is certainly undesirable. 

The existence of strong idiotypic cross-reactions among different mice of the same strain, with respect to certain antigens, made it feasible to attempt suppression of a particular idiotype with antiidiotypic antiserum. This could be analogous to suppression of an allotype in heterozygous animals with antiallotypic antiserum (Chapter 9). The appearance of an idiotype, characteristic of anti-p-azophenylarsonate (anti-Ar) antibodies of A/J mice was suppressed for periods up to 5 months, in neonatal or adult A/J mice, by intraperitoneal administration of a saline solution of 2 or 4 mg of an IgG fraction of rabbit anti-D antiserum (103). It was shown that suppression is not caused by simple absorption of anti-Ar antibodies by the antiidiotypic antibodies injected. There was no concomitant suppression of the total antihapten response or of production of antibody to the protein carrier. 

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