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In this study of 29-month-old male Fischer and Sprague-Dawley rats, the tumor pheochromocytoma occurred in seven of 20 Fischer rats (35%) and ten of 22 Sprague-Dawley rats (45%). Mean blood pressures and mean urinary vanillylmandelic acid levels of rats with pheochromocytomas did not vary significantly from rats with no tumors. Pheochromocytoma in our rats generally was non-functional or of minimal clinical significance. The content of chromaffin granules in tumor cells varied from abundant to not detectable, thus it was apparent that the absence of detectable chromaffin granules does not eliminate the diagnosis of pheochromocytoma.

The relative potencies for a series of sensory irritants, with structures based on toluene, were determined by measuring the airborne concentrations that caused a 50% decrease in respiratory rate in Swiss-Webster mice. This concentration is referred to as the RD50. Toluene, a relatively nonirritating compound, and compounds with chlorine, two chlorines, bromine, and iodine atoms substituted on the alpha carbon of toluene were tested. The RD50s for these compound types were determined to be 4900, 27, 27, 5.2, and 4.3 ppm, respectively. In addition, compounds with chlorine substituted at the ortho, meta, and para positions on the toluene ring were also tested. The RD50s were determined to be 4.9, 13, and 14 ppm, respectively. The structure-activity relationships of the compounds studied are explained by a model (Abraham et al., 1990; Nielsen and Alarie, 1982) that relates the interaction of sensory irritants with a receptor protein in a lipid bilayer. The trends in the RD50s, and thus sensory irritation, for the compounds studies are related to the development of a partial positive charge on the toluene alpha carbon by the positioning of a ring chlorine and the bond dissociation energies of the alpha carbon-halogen bond for the iodo, bromo, and chloro isomers of benzyl halide.

Arterial Fine Structure and Pathophysiological Change 3 Fine structure of muscular arteries 3 Fine structural alterations in the induced state Effects of inadequate nutrition, starvation, and refeeding on the cardiovascular and related systems Lipoproteins Physical and chemical properties of lipoproteins Human lipoprotein patterns Composition and distribution of human lipoproteins Nutritional alterations of composition and distribution of the human lipoproteins 49 Genetic and disease alterations of human lipoproteins 54 Relationship of human lipoprotein alterations and etiology of heart and blood vessel diseases 56 Dog lipoprotein patterns 60 Composition and distribution of dog lipoproteins 60 Nutritional alterations of composition and distribution of dog lipoproteins 63

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