[Contribution to the study of aortic hetero-transplants by means of electron microscopy]

In this study the ultrastructure of aortic valves of the pig, fixed immediately upon removal from the animal is compared with that of grafts treated to suppress immune responses as well as grafts treated to suppress immune responses as well as grafts which had to be replaced upon deterioration after implantation in humans. Fresh pig valves are lined by an endothelium forming a continuous barrier between the valvular tissue and the surrounding medium and which acts as a selective filter. Aortic valves consist essentially of bundles of collagen fibres interspersed with elastic fibres. They are synthesized by sever fibroblasts located in this connective tissue network. The agents used in treatment destroy the endothelial cells and fibroblasts. Furthermore, the connective network does not remain fully intact; modifications occur in both the collagen fibres and the "ground substance". Modifications observed in deteriorated implants, though of similar appearance, are more profound; collagen fibers are thus more or less calcified. Cells which sometimes invade the implanted tissues belong to the macrophagic series and they produce enzymes which contribute to the degradation of heterografts easily accessible to enzymatic attack. It therefore, seems that treatment of the aortic valves cannot prevent antigenic reactions in the host and, furthermore, cannot confer sufficient resistance on implants to protect them from degradation which are sometimes incompatible with their proper functioning.