Microchemical determination of enzyme activities in the lathyritic chick embryo aorta.

In a study of lathyrism in the chick embryo, β-aminopropionitrile (β-APN) was found to alter the appearance of elastic material in the aortic media. Histochemical observations showed that, both in normal and in lathyritic aortas, alkaline phosphatase (APase) activity was localized to the endothelium. Glucose-6-phosphate dehydrogenase (G-6-PDH), malate dehydrogenase (MDH), lactate dehydrogenase (LDH) and acid phosphatase (AcPase) activities were demonstrable mainly in the endothelium and in the media. The activities of these 5 enzymes were measured microchemically in freezedried aortic sections. Simultaneous determinations were made in normal 17-day embryos and in 17-day embryos that had been treated with β-APN 3 days previously. In addition, G-6-PDH activity was measured in 15-day normal and 15-day lathyritic chick embryo aortas 24 hours after beginning treatment with the nitrile. The activities of the oxidative enzymes and AcPase expressed on a dry weight basis increased significantly in the aortas of the lathyritic animals. However, APase activity remained unchanged. It is suggested that β-APN influences the metabolic activity of aortic medial muscle cells in addition to inhibiting the cross-linking of extracellular elastin. This observation conforms with the electron microscopic evidence that the medial cells of lathyritic aortas display structural abnormalities. The possibility that the loss of preformed elastic material from the vessel wall in lathyrism may be the result of changed lysosomal permeability is discussed.