レチニールパルミテートを指標とした経口脂肪負荷時のカイロミクロン代謝回転速度に関する研究

Chylomicron is important not only for HDL metabolism but also for the metabolism of apoprotein B containing lipoproteins. Differences in the composition of dietary fatty acids must affect chylomicron metabolism. This study examined the effects of dietary saturated fatty acids, especially palmitic acid, linoleic acid, and oleic acid on chylomicron turnover, and the effects of chylomicron turnover on levels of plasma lipids and apoproteins.<br>Fifty-gram doses of creams derived from cow milk (palmitic acid-rich cream, PRC), safflower oil (linoleic acid-rich cream, LRC), and olive oil (oleic acid-rich cream, ORC) were administered with 90, 000 units of vitamin A consecutively at 2 or 3 days interval to 20 subjects. Olive oil only was administered to another 17 subjects. Blood samples were taken before, and 2, 4, and 6 hours after administration of oral cream. Plasma retinyl palmitate (RP) concentrations were measured as an indicator of chylomicron metabolism, using the HPLC method. Absorption-time constants (Ka) and eliminationtime constants (Ke) for plasma RP were calculated by one compartment model analysis.<br>Ka was 0.53±0.50/h for PRC, 0.82±1.44/h for LRC, and 1.30±1.93/h for ORC. Ke was 0.31±0.21/h for PRC, 0.31±0.19/h for LRC, and 0.48±0.17/h for ORC. Ka and Ke for ORC were significantly higher than those of PRC and LRC (P<0.05). Ka and Ke values for the 3 different cream types correlated positively with each other (N=20). Olive oil cream was therefore thought to be most appropriate for the oral-fat load test. Ka had positive correlations with plasma HDL-cholesterol (P<0.01), apoprotein AI (P<0.05), and apoprotein AII levels (P<0.01). Ke had also positive correlations with plasma HDL-cholesterol (P<0.01), apoprotein AI (P<0.05), and apoprotein AII levels (P<0.01), and had a negative correlation with plasma apoprotein B concentration (P<0.05). Those results indicated that rapid turnover of chylomicron increased the plasma HDL level and decreased levels of apoprotein B containing lipoproteins. Ke values were significantly low in type II and type IV hyperlipoproteinemias, which probably indicates that chylomicron interfered with uptake of apoprotein B containing lipoproteins via the LDL receptors.