Analysis of organ weight in toxicology studies is an important endpoint for identification of potentially harmful effects of chemicals. Differences in organ weight between treatment groups are often accompanied by differences in body weight between these groups, making interpretation of organ weight differences more difficult. Using data from control rats that were part of 26 toxicity studies conducted under similar conditions, we have evaluated the relationship between organ weight and body/brain weight to determine which endpoint (organ weight, organ-to-body weight ratio, or organ-to-brain weight ratio) is likely to accurately detect target organ toxicity. This evaluation has shown that analysis of organ-to-body weight ratios is predictive for evaluating liver and thyroid gland weights, and organ-to-brain weight ratios is predictive for evaluating ovary and adrenal gland weights. Brain, heart, kidney, pituitary gland, and testes weights are not modeled well by any of the choices, and alternative analysis methods such as analysis of covariance should be utilized.

BMS-645737, an inhibitor of vascular endothelial growth factor (VEGF) receptor-2 and fibroblast growth factor (FGF) receptor-1, has antiangiogenic activity and was evaluated in nonclinical studies as a treatment for cancer. This article characterizes the BMS-645737-induced clinical, gross, and histologic lesions of incisor teeth in Sprague-Dawley (SD) rats. Rats received 0 800 mg/kg BMS-645737 in a single-dose study or consecutive daily doses of 0 20 mg/kg/day in a 1-month study. The reversibility of these effects was assessed in the 1-month study. White discoloration and fracture of incisors were observed clinically and grossly in the 1-month study. In both studies, dose-dependent histopathologic lesions of incisors were degeneration and/or necrosis of odontoblasts and ameloblasts; decreased mineralization of dentin; inflammation and necrosis of the dental pulp; and edema, congestion, and hemorrhage in the pulp and periodontal tissue adjacent to the enamel organ. Partial recovery was observed at lower doses after a two-week dose-free period in the one-month study. Drug-induced incisor lesions were considered to be related to the pharmacologic inhibitory effects on VEGF and FGF signaling, that is, inhibition of growth and maintenance of small-diameter vessels that support the formation of dentin and enamel in growing teeth and/or to perturbances of function of odontoblasts and ameloblasts or their precursors.

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A simple dye-coupling assay has been developed to study gap junctional communication using a uterine cell line. The new dye-coupling assay was found to be of comparable sensitivity to an autoradiographic assay for transfer of radiolabelled nucleotide. To investigate the importance of protein synthesis in the establishment of dye-coupling under the conditions of this assay, cultures were treated with actinomycin-D and cycloheximide to inhibit transcription and translation, respectively. Inhibition of transcription had no significant effect on dye-coupling. The protein synthesis inhibitor, cycloheximide, also had no significant effect on dye-coupling at concentrations up to 1 uM, even though protein synthesis was inhibited to 19% of control.