Platelet adhesion in the rabbit abdominal aorta following the removal of the endothelium: a scanning and transmission electron microscopical study

Abstract

The initial reactions of the blood components and the intima of the rabbit abdominal aorta have been observed following mechanical trauma. The endothelium was removed by the insertion of a roughened metal probe into the lumen of the vessel, thus exposing the sub-endothelial fibres and the internal elastio lamina. On restoration of the blood flow, platelets and later leucocytes adhered to the injured surface. Only small clumps of platelets or single cells adhered to the surface. Under these conditions it was possible to study the morphology of the cells and vessel surface by scanning electron microscopy, as no large mass of thrombus material was present to obscure the picture. The platelets developed long branched projections on adhering to the injured surface. Platelets were found in larger numbers in areas where much collagen was present, such as the fenestrations of the internal elastic lamina, but were sometimes seen at sites where these fibres were absent. It was possible to observe that platelets were sometimes attached to endothelial basement membrane, but often they adhered to sites where neither basement membrane nor collagen could be seen. It would seem therefore that some other component from the damaged intima may be necessary for platelets to adhere to the injured surface. The presence of a subendothelial mucopolysaccharide layer was demonstrated with the dye ruthenium red. At no time was it possible to observe a complete covering of platelets over the whole injured area.

The Effect of Acetylsalicylic Acid on Platelet Adhesion in the Injured Abdominal Aorta

“…The release of ADP or some other platelet aggregation activators from damaged endothelial cells or smooth muscle cells of the media has also been suggested as a possible mechanism for platelet adhesion at injured sites in blood vessels [Honour and Mitchell, 1964;Born, 1966;Sheppard and French, 1971;Honour, Pickering and Sheppard, 1971]. In the present experiments exogenous ADP aggregated ASA treated platelets in vitro both with and without collagen, although in the presence of collagen, aggregation did not occur around the collagen fibres.…”

“…In this case more than endothelial removal was involved as damage occurred to the media. It has been shown that injury to the media, rather than just removal of endothelium, produces larger aggregates of platelets even in such areas which do not encourage gross thrombus formation [Sheppard and French, 1971]. As only endothelium was removed in the present experiments the platelets were probably adhering to subendothelial structures other than collagen and release of aggregation activators from the media was probably not involved.…”

“…Collagen fibres, mostly round fenestrations in the internal elastic lamina, are exposed when endothelium is mechanically removed from the rabbit abdominal aorta [Sheppard and French, 1971]. However it is doubtful whether the adhesion of platelets to the surface denuded of endothelium is solely due to the presence of collagen fibres [Sheppard andFrench, 1970, 1971;Sheppard, 1972].…”

“…The segment of aorta was attached to a frame so it could be fixed and dehydrated under pressure with all its normal dimensions preserved. Pieces of aorta were then prepared for both scanning and transmission electron microscopy [Sheppard and French, 1971].…”

“…In this paper some of the effects of ASA on platelet adhesion following a standard mechanical injury to the rabbit abdominal aorta [see Sheppard and French, 1971] are described together with studies in vitro on platelet-rich plasma from the same animals.…”