Ultrastructural modifications of the platelet plasma membrane in vascular diseases and the effect of a carbochromen derivative as studied by freeze-fracture and computer measurement.

A high surface density of the openings of the surface connected canalicular system (SCCS) has been observed in the freeze-fractured plasma membrane of circulating platelets in rabbits fed an atherogenic diet and in hypercholesterolemic type IIa patients. In vitro tests have revealed a correlation between the increased surface density of the SCCS openings and the initial steps of platelet activation. 8-Chlorocarbochromen, a new drug which enhances the in vivo release of prostacyclin from the arterial wall, has been found to be effective in reducing the high surface density of SCCS openings in platelets of rabbits on an atherogenic diet. The present study shows that circulating platelets from patients with peripheral vascular disease present a high surface density of SCCS openings compared to that observed in control subjects. After a single oral administration of 8-chlorocarbochromen, a reduction of the high number of these openings has been observed. Likewise, beta-thromboglobulin levels were found to be high in the patients and to be significantly reduced after oral administration of the drug. This study shows ultrastructural modifications of platelets in conditions related to atherosclerosis and includes data on the effectiveness of 8-chlorocarbochromen in reducing the platelet activation of these patients.