ALIMENTARY LIPEMIA ENHANCES THE MEMBRANE EXPRESSION OF PLATELET P-SELECTIN WITHOUT AFFECTING OTHER MARKERS OF PLATELET ACTIVATION

The present study was conducted to determine whether alimentary lipemi a alters platelet activity in vivo. Normolipidemic volunteers were giv en a fatty meal and platelet function was assessed before, and 3 and 6 h after the meal. Platelet aggregability and secretion was determined using whole blood flow cytometry (expression of platelet P-selectin a nd fibrinogen binding), filtragometry ex vivo (reflecting platelet agg regability in vivo) and by measurements of platelet specific products in plasma (beta-thromboglobulin and platelet factor 4). Plasma triglyc erides increased from 0.8 (0.6:1.1; median, 25th and 75th percentiles) to 1.7 (1.0:2.3) mmol/l at 3 h and returned to baseline after 6 h (P < 0.001, one-way ANOVA). Apo B-100 and apo B-48 were both markedly inc reased 3 h postprandially in the Sf 60-400 fraction (large VLDLs, P < 0.001 for both), whereas the Sf 20-60 (small VLDLs) and Sf 12-20 fract ions (IDL) did not change. The platelet function assessments revealed that the percentage of platelets expressing P-selectin increased by 40 % (5%; 64%) after 3 h and by 51% (-7%; 85%) 6 h postprandially in unst imulated samples (P < 0.05 for both). In samples stimulated by ADP in vitro P-selectin expression increased by 45% (6%; 58%) after 3 h and b y 30% (12%; 58%) (P < 0.01 for both) after 6 h at 0.1 mu M. Platelet P -selectin expression was less influenced at higher ADP concentrations. The plasma levels of beta-thromboglobulin (approximate to 20 ng/ml) a nd platelet factor 4 (approximate to 0.3 ng/ml) were not affected by t he fat load. Flow cytometric analyses of fibrinogen binding and filtra gometry measurements also failed to reveal any postprandial alteration s. The present finding of enhanced platelet P-selectin expression sugg ests that platelets are mildly sensitized postprandially. Whether this is of importance for thrombus formation and atherosclerosis needs to be studied further. (C) 1998 Elsevier Science Ireland Ltd. All rights reserved.