Effects of reduced food intake for 4 weeks on physiological parameters in toxicity studies in dogs

This study sought to clarify the effects of reduced feeding on physiological parameters in dogs to enable appropriate evaluations of the safety and toxicity of test compounds. We measured alkaline phosphatase isozymes and the circulating blood volume, as well as clinical signs, body weight, hematology, blood chemistry, electrocardiography, organ weight, and histopathology, in male beagle dogs fed a diet consisting of 300 g/day or 150 g/day for 4 weeks. There were no abnormal clinical signs in any of the dogs. In the 150-g/day feeding group, a decreased alkaline phosphatase 3 suggesting effects on the bone and a decreased circulating blood volume associated with body weight loss were observed. Additionally, the following changes were also observed in the 150-g/day group: a decrease in body weight; hematologic changes including decreases in white blood cells, neutrophils, red blood cells, hemoglobin, hematocrit and reticulocytes; blood chemical changes including decreases in aspartate aminotransferase, lactate dehydrogenase and calcium and an increase in the creatinine at week 1 or thereafter; electrocardiographic changes including a decrease in the heart rate, a prolonged QRS duration and the occurrence of a second-degree atrioventricular block at week 3 or thereafter; and pathological changes including decreases in the weights of the liver and thymus, a decrease in hepatocyte rarefaction, and thymic atrophy. These results provide useful information for assessing the safety of compounds in toxicological studies, enabling direct treatment effects and secondary changes caused by decreased food intake to be distinguished.