Lathyritic lesions were induced in young growing rabbits by the administration of aminoacetonitrile. The animals with lathyritic lesions and those in a control group were sacrificed and frozen-dried sections were prepared from the epiphyseal plate of the femur after the method of Lowry. By use of specialized methods, the proliferating and hypertrophic cartilage-cell and primary-spongiosa areas of these animals were studied for their content of lactic, malic, and glucose-6-phosphate dehydrogenase, phosphoglucoisomerase, alkaline phosphate, and total phosphorus. Striking depression of lactic and glucose-6-phosphate dehydrogenase activity was observed in the areas of the hypertrophic cartilage cells and primary spongiosa. Phosphoglucoisomerase was reduced throughout all three areas. On the other hand, the content of total phosphorus, malic dehydrogenase, and alkaline phosphate in these areas was not disturbed. The most severe enzyme alterations occurred in those areas most disrupted by aminoacetonitrile.

From these and previous observations, it is felt that the morphological disruption of the epiphyseal plate associated with aminoacetonitrile treatment results from the reduction in activity of several enzyme systems normally providing metabolic intermediates and high-energy phosphate necessary for tissue synthesis. These observations are discussed in relation to the nutritional status of the animals, previous studies of the developing epiphyseal plate of the dog, and the protective effects of thyroxine and triiodothyronine against aminoacetonitrile lesions.