Prediction of food intakes, weight gains, organ weights, and tumor size in tumor-bearing rats by the four-parameter mathematical model for physiological responses.

Groups of male weanling rats bearing the transplantable Novikoff ascites hepatoma were fed diets containing graded levels of protein. The food intakes and weight gains were recorded daily. Seven days after inoculation of the rats with the tumor (6 days in Experiment 2), the rats were sacrificed, their organs were weighed, and the tumor and ascites fluid volumes were determined. These results were analyzed by the four-parameter mathematical model for physiological responses. It was found that tumor-bearing rats eat and gain weight at the same rates as control rats fed identical diets, implying that this rapidly growing tumor does not interfere with the normal food intake and growth control mechanisms and that food intakes and weight gains are predictable by the four-parameter model. Organ growth was regulated in both normal and tumor-bearing rats but some actual organ weights in tumor-bearing rats were smaller than in control rats due to the presence of the tumor. However, other organs (spleen, lung, kidneys, and small intestine) of the tumor-bearing rats showed significant differences (p less than 0.01, Student's t test) from control rats. It was also possible to predict the growth of the tumor on the basis of the casein content of the diet.