Species differences

The differences in effects of cholinesterase-inhibiting organophosphorus compounds are found not only between sexes and species, but also between phyla. It is because of these differences that the pesticidal activity of these compounds may be exploited. 

TABLE 35.1. Comparative Stratum Corneum Thickness, Epidermal Thickness, and the Number of Epidermal Cell Layers in the Ventral Abdomen (VAB) and at the Thoracolumbar Junction (TLJ) of Several Species (H E, Paraffin Sections) 

Species Area Cell Layers Mean + SE Epidermis (pm) Mean + SE Corneum (pm) Mean + SE 

Source Modified from Monteiro-Riviere N. A., et al. J. Invest. Dermatol. 95, 582-586,1990. 

A PPARa-null mouse model has been generated and the animals are viable and fertile.  

As we have seen from the discussion of toxicokinetics, the anatomy and physiology of an organism play key roles in defining the toxicity of a chemical to that organism. Birds have feathers rather than hair this impacts absorption. Aquatic mammals like muskrats have an insulating layer of fur that prevents water from reaching the skin. This will also affect absorption. Cattle have four stomachs and have a large 

Finally, physiological and anatomical differences can impact excretion. For example, the kangaroo rat lives in the desert yet requires no water to survive because its kidneys are extremely efficient at reabsorbing chemicals. However, this could also lead to increased retention of toxic chemicals, which could increase the toxicity of a chemical relative to other species. These issues are more specifically discussed below. 

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For gases, pure solids, pure liquids, and nonionic solutes, activity coefficients are approximately unity under most reasonable experimental conditions. For reactions involving only these species, differences between activity and concentration are negligible. Activity coefficients for ionic solutes, however, depend on the ionic composition of the solution. It is possible, using the extended Debye-Htickel theory, to calculate activity coefficients using equation 6.50... 

Oxytocin and Vasopressin Receptors. The actions of oxytocin and vasopressin are mediated through their interactions with receptors. Different receptor types as well as different second messenger responses help explain their diverse activities in spite of the hormones stmctural similarities. Thus oxytocin has at least one separate receptor and vasopressin has been shown to have two principal receptor types, and V2. Subclasses of these receptors have been demonstrated, and species differences further compHcate experimental analysis. It is apparent that both oxytocin and receptors function through the GP/1 phosphoHpase C complex (75), while the V2 receptors activate cycHc AMP (76). 

To fractionate various species, different configurations can be used. Figure 10 shows one such configuration for centrifugal force. 

Species Tested. In addition to the variation in susceptibiUty to chemically induced toxicity among members within a given population, there may be marked differences between species with respect to the relative potency of a given material to produce toxic injury. These species differences may reflect variations in physiological and biochemical systems, differences in distribution and metaboHsm, and differences in uptake and excretory capacity. 

Exposure studies have been made using mice and rats (257). These experiments have demonstrated species differences in butadiene toxicity and carcinogenicity. Butadiene was found to be a potent carcinogen in the mouse, but only a weak carcinogen in the rat. The interpretations have focused on differences in toxification rates and detoxification metaboHsms as causative factors (257). The metaboHsm is beHeved to proceed through intermediates involving butadiene monoepoxide and butadiene diepoxide (257). A similar mechanism has been proposed for its biodegradation pathway (258). 

There is an important practical distinction between electronic and dipole polarisation whereas the former involves only movement of electrons the latter entails movement of part of or even the whole of the molecule. Molecular movements take a finite time and complete orientation as induced by an alternating current may or may not be possible depending on the frequency of the change of direction of the electric field. Thus at zero frequency the dielectric constant will be at a maximum and this will remain approximately constant until the dipole orientation time is of the same order as the reciprocal of the frequency. Dipole movement will now be limited and the dipole polarisation effect and the dielectric constant will be reduced. As the frequency further increases, the dipole polarisation effect will tend to zero and the dielectric constant will tend to be dependent only on the electronic polarisation Figure 6.3). Where there are two dipole species differing in ease of orientation there will be two points of inflection in the dielectric constant-frequency curve. 

In the first category of solutions ( regular solutions ), it is the enthalpic contribution (the heat of mixing) which dominates the non-ideality, i.e. In such solutions, the characteristic intermolecular potentials between unlike species differ significantly from the average of the interactions between Uke species, i.e. 

The resin acids found in rosins are generally of the abietic- and pimaric-type. Rosins of various pine species differ in their content of abietic vs. pimaric-type acids. Rosins from species exhibiting high abietic-type acid compositions are preferred for production of rosin derivatives. However, the differences in properties of rosins are often associated with their non-resin acid content instead of their chemical compositions. On the other hand, the compositions of rosins from different sources greatly differ [22]. Table 8 shows a typical distribution of resin acids in rosins obtained from gum, tall oil and wood sources. 

Between various wood species great differences can occur in pH as well as in the buffer capacity. Even within the same wood species, differences might occur due to seasonal variations, portion of the wood substance under investigation, pH of the soil, age of the tree, time span after cutting, drying and processing parameters. 

Miltefosine, an alkylphosphocholine derivative, is a new antileishmanial drug and the first effective oral treatment of visceral leishmaniasis. However, there are concerns regarding teratogenicity, rapid emergence of resistance, and variable cure rates, possibly due to species differences in drug sensitivity. The mechanism of action of miltefosine is not known. 

Major species differences characterize the induction of CYP3A enzymes by diugs, steroids, and other chemicals. These species differences are a direct result... 

An excited state of a molecule can be regarded as a distinct chemical species, different from the ground state of the same molecule and from other excited states. It is obvious that we need some method of naming excited states. Unfortunately, there are several methods in use, depending on whether one is primarily interested in photochemistry, spectroscopy, or MO theory." One of the most common methods... 

It can be argued that the gut flora provides an additional trophic level in ruminants (Steinhour et al. 1982). This should result in a larger A N in ruminants than in non-ruminant herbivores. As many domesticated animals are ruminants this is a factor that has to be taken into account. Available 5 N data does not seem to show systematic differences between the categories ruminants and non-ruminants, although systematic species differences exist. 

When methyl parathion was given orally to rats at doses of 1.5 mg/kg and to guinea pigs at 50 mg/kg, plasma, erythrocyte, and brain cholinesterase activity was maximally inhibited within 30 minutes after administration. In rodents of both species that died after acute intoxication, brain cholinesterase levels decreased to 20% of control values and often to 5-7% (Miyamoto et al. 1963b). The species difference in susceptibility to orally administered methyl parathion is noted in Section 3.2.2.1. 

Chambers JE, Carr RE. 1995. Biochemical mechanisms contributing to species differences in insecticidal toxicity. Toxicology 105 291-304. 

Thompson HM, Langton SD, Hart ADM. 1995. Prediction of inter-species differences in the toxicity of organophosphorus pesticides to wildlife—a biochemical approach. Comp Biochem Physiol 111C 1-12. 

Renard, D. Lavenant-Gourgeon, L. Ralet, M. Sanchez, C. (2006). Acacia Senegal Gum Continuum of Molecular Species Differing by Their Protein to Sugar Ratio, Molecular Weight, and Charges. Biomacromolecules, Vol.7, No.9, (Augudt 2006), pp. 2637-2649, ISSN 1525-7797. 

Many of the physical changes in membrane structure of cells are reversible and species differences in the degree of disruption of dry membranes may relate to differences in composition, protective mechanisms or to additional damage occurring during desiccation (see below). 

Intravenous administration of endosulfan (7 3 ratio of a- and P-isomers) in rabbits produced slower elimination of the a-isomer (Gupta and Ehrnebo 1979). Excretion of the two isomers occurred primarily via the urine (29%) with much less excreted via the feces (2%). Given the earlier evidence in rats and mice describing the principal route of elimination of endosulfan and its metabolite to be via the feces, the differences in the excretion pattern in this study may be attributable to differences in exposure routes, to species differences, or to both. Nevertheless, studies in laboratory animals suggest that both renal and hepatic excretory routes are important in eliminating endosulfan from the body. Elimination of small doses is essentially complete within a few days. 

There are marked species differences in A-esterase activity. Birds have very low, often undetectable, levels of activity in plasma toward paraoxon, diazoxon, pirimi-phos-methyl oxon, and chlorpyrifos oxon (Brealey et al. 1980, Mackness et al. 1987, Walker et al. 1991 Figure 2.10). Mammals have much higher plasma A-esterase activities to all of these substrates. The toxicological implications of this are discussed in Chapter 10. Some species of insects have no measurable A-esterase activity, even in strains that have resistance to OPs (Mackness et al. 1982, Walker 1994). These include the peach potato aphid (Myzus persicae Devonshire 1991) and the... 

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