CIRCADIAN PLASMA-CONCENTRATION OF LIPOPROTEIN(A) AND DISTRIBUTION OF APOPROTEIN(A) IN HEALTHY-SUBJECTS

Most apolipoprotein(a) is present in the lipoprotein(a) [Lp(a)] complex, but a minor proportion has been found in the triglyceride-rich lipoprotein (TRL) fraction. Enrichment in the apo(a) content of the TRL fraction, as observed after fat load, might produce an increase in the atherosclerotic risk by increasing macrophage lipid uptake. Circadian levels of Lp(a) in whole serum and of apo(a) immunoreactivity in the TRL fraction were studied in ten healthy subjects on a regular diet (30 kcal/kg body weight; 30% fat, 15% protein, and 55% carbohydrates). Mean fasting Lp(a) in whole serum was 12.2 mg/dl (SEM 3.2, range 4.3-33.0 mg/dl) and did not show significant variations over the 24-h period. Percent apo(a) immunoreactivity in the TRL fraction ranged from 0% to 37% (mean 10%) of the apo(a) immunoreactivity in whole serum and did not change significantly during the study. Total and TRL triglycerides increased by 35% after lunch, and remained significantly higher than in the fasted state until midnight. In conclusion, Lp(a) concentration in whole serum and apo(a) immunoreactivity in the TRL fraction do not show significant circadian changes.