Animal models through diet

The proposed roles of oxysterols in atherosclerosis are based primarily on the results of cell-culture experiments. There are a number of in vivo studies in which investigators have exposed animals to oxysterols through diet or injection, but the overall results are not conclusive. For example, in a review by Brown and Jessup [19] of 13 oxysterol dietary studies, 6 showed an increase in atherosclerosis, but 4 demonstrated a decrease in lesion size and 3 showed no effect. Differences in animal models and types and doses of oxysterols undoubtedly account for some of these differences. 

Although it is impossible to describe all microbial interactions in the GI tract, some information has been discovered about the interactions of LAB supplementation and the impact on the GI tract microflora and inhibition of food-borne pathogens. We know that the carbohydrate concentration of a diet fed to an animal is changed as it passes through the GI tract, making an in vitro model inadequate to predict the behavior of LAB in a live animal (Fuller, 1992). Model systems have been developed but may not exactly... 

It was mentioned earlier in this chapter that alkaloids have no selective toxicity to invertebrates. Therefore, for many insects, these compounds are more attractive than toxins (Figure 4.5). The cases of butterfly or beetle behaviors just mentioned are very evident examples of the importance of plants for invertebrates. In both cases, alkaloids are secondary compounds that take part in the attraction for feeding. Moreover, it is also known that Manduca sexta flourish on alkaloid-rich Nicotiana plants and bmchid beetles BrucMdius villosus) on quinolizidine-alkaloid-iich plants.Such examples are a consequence of the herbivore model for choosing a specific plant diet. This model is based on the plant-herbivore interaction. The plant alone can either attract or deter the insect adult or larvae. It is necessary to highlight that alkaloids represent only one group of the secondary compounds through which plants worldwide interact with insects and other animals. 

Promotion in the urinary bladder is similar to other models since the lesions go through the stages of hyperplasia, hyperplastic nodules and later form carcinomas. Cell proliferation in the urinary bladder is an essential part of the promotion process (Hicks and Chowaniec, 1977). Focal hyperplasia, dysplasia and a high number of mitotic figures in transitional cells and urothelium are common in animals fed dietary saccharin (Chowaniec and Hicks, 1979). Male and female rats administered saccharin in the drinking water consumed less water and voluntarily less diet than if saccharin was mixed in the diet, and they did not develop bladder tumors (Chowaniec and Hicks, 1979). While increased cell proliferation is an essential component of the promotional process, hyperplasia may not be a sufficient stimulus for promotion. Isoproterenol given to rats caused urothelia hyperplasia but did not enhance MNU initiated bladder tumors (Hicks, 1980). Clearly, other biochemical properties of saccharin have to be investigated since hyperplasia... 

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