Catabolism of prothrombin-chylomicron complexes in vivo in the rat

The metabolism in vivo in the rat of 125I-prothrombin-chylomicron complexes was compared to that of free 125I-prothrombin injected in saline or together with chyle chylomicrons. The group that obtained 125I-prothrombin-chylomicron complexes exhibited a faster initial decrease of plasma 125I-prothrombin, a higher radioactivity in the liver and more trichloroacetic acid soluble 125I in plasma than in the other groups that did not differ. In the group injected with 125I-prothrombin-chylomicron complexes, 4% was in the HDL, 0.7% LDL, and 0.8% in VLDL 2 hours after injection. The data thus indicate that although most of the 125I-prothrombin is released during the metabolism of the prothrombin-chylomicron complexes, some is rapidly degraded and some is transferred to plasma lipoproteins and remains circulating for a considerable time period. The observations demonstrate that binding to chylomicrons influences the catabolism of prothrombin in vivo. Since chylomicrons did not influence the clearance of simultaneously injected free 125I-prothrombin, the prothrombin binding to chylomicrons or chylomicron remnants in vivo may, however, be too slow to influence the prothrombin catabolism under normal conditions.