Distribution of C apolipoproteins between the vascular and lymph compartments of the rat

This study has investigated the kinetics of transfer of C apolipoproteins between the vascular and lymph compartments of the rat. Very-low-density lipoprotein, labeled with [125I]apolipoprotein C, was injected intravenously into lymph duct-cannulated rats and the redistribution of radioactivity between lymph and plasma followed at frequent intervals for 3 h. Equilibration between the two compartments was rapid (10-15 min), and thereafter removal from both compartments continued at similar rates. Specific radioactivity determinations showed that lymph C-III-0, C-III-3, and C-III-2,1 apolipoproteins rapidly reached values identical to those of corresponding plasma C apolipoproteins and the interrelationship between the curves were consistent with precursor-product relationships in which all, or most, of the product (lymph apolipoprotein C-III) was derived from the precursor (plasma). However, the specific radioactivity curves for C-II peptide did not cross; the lower value for lymph C-II apolipoprotein suggests that, unlike C-III apolipoproteins, a substantial proportion (approx. 40%) of lymph C-II peptide is not derived from the plasma compartment. The most likely source of the unlabeled lymph apolipoprotein C-II is synthesis and secretion from the intestine.