Effect of foreign compounds

Aluminium has a considerable influence on the kinetics and products of the process. Al-hydroxy cations promote hydrolysis of Fe in solution and lead to precipita- 

A Lepidocrocite with little ferrihydrite precipitated by rapid oxidation of 0.01 M Fe(Cl04)2 with purging of C02-free air B Close-up view of A C Lepidocrocite formed by slow oxidation by O2/ 

N2 = 0.002. D Ferrihydrite precipitated from 0.01 M Fe(Cl04)3 (Loeppert Clarke, 1984 with permission courtesy R. Loep-pert). 

Fe solutions have been aerated at pH 7.2 in the presence of various minerals and rocks including quartz and basalt (Posey Dowty et al., 1986). The major product in all cases except that of quartz (goethite) was lepidocrocite. These authors also noted that lowering the dielectric constant of the solvent (by replacing water with a mixture of water and dioxane) promoted goethite over lepidocrocite. Poorly crystalline lepidocrocite was also the sole product when Fe was oxidized at pH 7 and RT in the presence of bacteria (Bacillus suhtilis Escherichia coli) (Chatellier et al. 2001) (see also chap. 17). 

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Because the process of development of the embryo and then the fetus is a complex series of events, it is clear that many different mechanisms may cause the disruption that underlies the teratogenic effects of foreign compounds. In many cases, the initiating events probably occur at the subcellular or molecular level in the embryo, but may be only detectable as malformations or cell death. 

Timbrell, J.A., Delaney, J. Waterfield, C.J. (1996) Correlation between in vivo and in vitro toxic effects of foreign compounds. Comp. Haematol, int., 6, 232-236... 

Conney AH, Bums JJ. 1959. Stimulatory effect of foreign compounds on ascorbic acid biosynthesis and on drug-metabolizing enzymes. Nature 184 363-64... 

Conney, A, H, and Burns, J.J. Stimulatory effect of foreign compounds... 

Antibodies are glycoproteins found in body fluids including blood, milk, and mucous secretions and serve an essential role in the immune system that protects animals from infection or the cytotoxic effects of foreign compounds. Antibodies will bind with high affinity to an in-... 

The interaction of a foreign compound with a biological system is twofold there is the effect of the organism on the compound and the effect of the compound on the organism. 

The rates of movement of foreign compound into and out of the central compartment are characterized by rate constants kab and kei (Fig. 3.23). When a compound is administered intravenously, the absorption is effectively instantaneous and is not a factor. The situation after a single, intravenous dose, with distribution into one compartment, is the most simple to analyze kinetically, as only distribution and elimination are involved. With a rapidly distributed compound then, this may be simplified further to a consideration of just elimination. When the plasma (blood) concentration is plotted against time, the profile normally encountered is an exponential decline (Fig. 3.24). This is because the rate of removal is proportional to the concentration remaining it is a first-order process, and so a constant fraction of the compound is excreted at any given time. When the plasma concentration is plotted on a logio scale, the profile will be a straight line for this simple, one compartment model (Fig. 3.25). The equation for this line is... 

The selective uptake of paraquat is another excellent example of the importance of size and shape in the disposition and toxicity of foreign compounds (see chap. 3, pages 40-1, and chap. 7). Similarly, the chemical similarities between carbon monoxide and oxygen are important in the toxic effects caused as are discussed in detail in chapter 7. 

Intestinal motility may also be influenced by age, with various effects on the absorption of foreign compounds dependent upon the site of such absorption. The absence of gut flora in... 

As well as the sex hormones already mentioned (see above), many other hormones seem to affect the metabolism of foreign compounds and therefore may have effects on toxicity. A number of pituitary hormones may directly, as well as indirectly, affect metabolism, for example, growth hormone, follicle-stimulating hormone, adrenocorticotrophic hormone, luteinizing hormone, and prolactin. Thus, hypophysectomy in male rats results in a general decrease in metabolism, but the effects of some of the individual hormones may depend on the sex of the animal and the particular enzyme or metabolic pathway. For example, adrenocorticotrophic hormone (ACTH) administration decreases oxidative metabolism in males but increases N-demethylation in female rats. Removal of the adrenal gland reduces metabolism, such as ethylmorphine demethylation and aniline 4-hydroxylation, and this can... 

The disposition or localization, and in some cases metabolism, of foreign compounds may be dependent upon the characteristics of a particular tissue or organ, which may in turn affect the toxicity. There are many examples of organotropy in toxicology, but the mechanisms underlying such organ-specific toxic effects are often unknown. 

Levine WG, Millburn P, Smith RL, et al. The role of the hepatic endoplasmic reticulum in the biliary excretion of foreign compounds by the rat. The effect of phenobarbitone and SKF 525-A diethylaminoethyl diphenylpropylacetate Biochem Pharmac 1970 19 235-244. 

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