QUANTITATION OF PLATELET DEPOSITION ON HUMAN ARTERIES - ASSESSMENT OFTHE DISPARITY BETWEEN RESULTS OBTAINED WITH INDIUM-111(IN-111)-LABELING VERSUS SCANNING ELECTRON-MICROSCOPY

Quantitation techniques for measuring platelet deposition (PD) to vess el surfaces are important to an understanding of thrombogenesis. In pr evious studies, scanning electron microscopy (SEM) has been shown to i ndicate a lower extent of PD than platelet In-111-scintigraphy. Part o f this disparity may be explained by nonspecific binding of In-111 to the vessel surface during perfusion, or loss of adherent In-111-labell ed platelets by lysis or dissociation from the surface during specimen preparation for SEM. To assess whether these independent processes oc cur, we used a previously described human placental artery (HPA) perfu sion model to quantify vessel In-111 retention. Of the total In-111 th at bound to the vessel surface during perfusion, 77 +/- 42% (N=9) was platelet associated In-111 (In-111-labelled platelets) and 23 +/- 19% (N=9) was non-platelet associated In-111 (nonspecific binding). After specimen fixation, 67 +/- 32% (N=9) of the initial total surface In-11 1 remained. This decrease is due to dissociation of both adherent In-1 11-labelled platelets, and non-platelet associated In-111. After fixat ion, 57 +/- 34% (N=9) of the initial total surface In-111 remained as In-111-labelled platelets and 10 +/- 13% (N=9) remained as non-platele t associated In-111. Fixation caused no measurable lysis of platelets. These data suggest that PD may be overestimated by In-111-scintigraph y because of nonspecific binding of In-111 and underestimated by SEM b ecause of dissociation of adherent platelets during specimen preparati on for SEM.