Alterations in plasma proteins and lipoproteins in acute myocardial infarction: effects on activation of lipoprotein lipase.

Plasma lipoprotein concentrations were followed in 21 men with acute myocardial infarction. HDL and LDL cholesterol concentrations showed similar time-courses with average maximal decreases of about 20%, 10-14 days after onset of symptoms. The decrease in HDL levels (measured as HDL cholesterol and apolipoprotein AI) was significantly correlated to the inflammatory response, as reflected by plasma orosomucoid concentrations, and to the extent of myocardial injury, as mirrored by serum activities of lactate dehydrogenase. In samples drawn 10 days after myocardial infarction we found marked changes in the ability of the patients' sera to enhance the activity of purified lipoprotein lipase. The maximal activating ability (at saturating serum concentrations) increased by about 30%; however, at suboptimal serum concentrations, the activating ability of the patients' sera declined (50% higher serum concentrations were required to reach half maximal reaction rate). The altered activation characteristics were correlated to the changes in HDL concentrations. By affecting the activity of lipoprotein lipase and thereby the rate of intravascular lipoprotein metabolism, this phenomenon may contribute to the lipoprotein alterations seen after myocardial infarction.