Summary
When 125I-labeled canine prothrombin was given to normal adult dogs intravenously, it was
calculated that 240% of the plasma prothrombin crossed the capillary barrier per day,
410% of the interstitial prothrombin returned to the blood stream daily, and 79% of
the plasmatic prothrombin was catabolized per day. These data are in close agreement
with those observed for bovine prothrombin in calves by Takeda (1970).
When derived from normal dog prothrombin, prethrombin-1 is a mixture of 2 polypeptides,
one larger than the other, and both present in about equal amounts. The longer peptide,
“prethrombin-1-long,” was catabolized twice as fast as prothrombin, and the shorter,
“prethrombin-1-short,” 4 times faster. Prothrombin fragment-1 was catabolized by the
normal dog still more rapidly.
The catabolism of prothrombin was not accelerated in 3 dogs receiving continuous infusions
of a thromboplastic emulsion of dog brain. Nor was the level of prothrombin in their
plasma remarkably altered.
