PLATELET ACTIVITY IN-VIVO IN HYPERLIPOPROTEINEMIA - IMPORTANCE OF COMBINED HYPERLIPIDEMIA

Platelet hyperactivity in vitro is found in patients with isolated hyp ercholesterolemia. It is, however, less well established if platelet a ctivity in vivo is enhanced, and if there are differences between vari ous types of hyperlipoproteinemia. Platelet function in vivo was studi ed at rest and during mental stress in men with isolated hypercholeste rolemia (phenotype IIa; n = 21) or combined hyperlipidemia (phenotype IIb; n = 29), and age-matched normolipidemic controls (n = 41). The ur inary excretion of 11-dehydrothromboxane B-2 was elevated in patients compared to controls (IIa, p <0.05; IIb, p <0.001), and higher in type IIb than in IIa patients (p <0.05). Platelet secretion, assessed as p lasma beta-thromboglobulin levels, was higher in type IIb patients com pared to controls (p <0.01) and type IIa patients (p <0.05) during men tal stress. The urinary excretion of beta-thromboglobulin was also ele vated in type IIb patients compared to controls (p <0.05). Platelet ag gregability at rest, as measured by filtragometry ex vivo was, however , reduced in both patient groups compared to controls (p <0.05). No co rrelations were found between plasma lipoprotein levels and markers of platelet function in vivo. Type IIb patients had higher plasma fibrin ogen levels and higher leukocyte counts than controls (p <0.05 and p < 0.001) and type IIa patients (p <0.05 and p = 0.06). Thromboxane excre tion was positively related to fibrinogen levels and leukocyte counts (p <0.01 for both). Preliminary data regarding serum TNF-alpha also in dicated an elevation of this inflammatory cytokine in type IIb patient s (p <0.05 vs controls). In conclusion, thromboxane generation and pla telet secretion in vivo are enhanced in patients with hypercholesterol emia, and particularly so among patients with concomitant elevation of plasma triglycerides. The mechanism is unknown, but inflammatory medi ators may be involved. The present findings are of interest in relatio n to the role of triglycerides in coronary artery disease.