Histochemical and Ultrastructural study of the Platelet-Arterial Subendothelium Interaction

In order to characterize the subendothelial macromolecules able to interact with platelets rabbit aortas were de-endothelialized and incubated either with chymotrypsin (24 h at 37° C), with a highly purified bacterial collagenase (2 h at 37° C), or with chymotrypsin followed by collagenase or the reverse. Histochemical ultrastructural studies were performed before and after blood perfusion, using three different staining procedures: tannic acid (for the microfibrillar structures and elastin), ruthenium red (for the polyanions) and two peroxidase-labelled lectins (concanavalin A and ricinus communis (for the detection of saccharidic determinants)). After chymotrypsin, the tannic acid +ve, ruthenium red +ve and lectin +ve microfibrils had been digested; platelet adherence to the remaining sparse collagen fibrils persisted. After collagenase, these microfibrils are preserved, collagen has been digested, but the platelets can still adhere. After combined incubation with both enzymes, elastin is the only remaining constituent and no platelet adhesion can be observed.

These results show that in the rabbit aorta subendothelium besides collagen, microfibrillar glycoproteins are able to interact with human platelets.