B-1. 超低比重リポ蛋白のトリグリセライド脂肪酸代謝

抄録

Turnover of various size of endogeneously labeled very low density lipoprotein VLDL, d (1.006) was studied in the fasting rabbits. Triglyceride fatty acid of very low density lipoprotein (VLDL-TGFA) was labeled by either ¹⁴C- or ³H-palrnitate and labeled VLDL was subfractionated on 2% agarose column according to their size. Dose VLDL was prepared by mixing either large ¹⁴C-VLDL and small ³H-VLDL or small ¹⁴C-VLDL and large ³H-VLDL and was injected to recipient rabbits intravenously. Specific activity curves of VLDL-TGFA and LDL-TGFA (d 1.006 to 1.063) were obtained from the blood samples obtained at certain time intervals after the administration of Dose VLDL. In specific activity curves cif VLDL-TGFA two exponential components were ovserved; the rapid removal phase was followed by the slower removal phase. The values for half-life of VLDL-TGFA were taken directly from the observed slopes of initial rapid disappearance. The following results were obtained;
(1) Half-life of Dose VLDL-TGFA was ranging from 4.0 to 23.0 min.
(2) In every rabbit large VLDL disappeared faster than small VLDL from the circulation and there was statistically significant negative correlation between half-life of Dose VLDL and average diameter of Dose VLDL (n=20, r=-0.512, p<0.05). This result may suggest that the large VLDL are not all metabolized via small VLDL, for if that were so the half-life of each fraction would be the same.
(3) Statistically significant positive correlation was observed between half-life of Dose VLDL and VLDL-TG level of recipient rabbit (n=20, r= 0.671, p<0.01)
(4) Specific activity curves of VLDL-TGFA and LDL-TGFA was suggesting precursor-product relationship between these two lipoprotein fractions.
Some rabbits were exanquinated 15 and 30 min after the administration of Dose VLDL and distribution of radioactivity in VLDL subfractions were compared with those of Dose VLDL. The result was suggesting that VLDL-TG was not completely hydrolyzed by the enzyme when VLDL particles first bind to the capillary wall but they were partially hydrolyzed and decreased in their size gradually in the process of metabolism.