Summary
Mouse liver slices incubated in a human serum medium displayed significantly greater
incorporation of glycine-14C into fibrinogen than when incubated with plasma. Preincubation of heat defibrinated
plasma with thrombin produced an increase in the level of biosynthesis comparable
to that induced by serum whereas defibrination of the plasma incubation medium exerted
no stimulatory effect on biosynthesis. Subcutaneous injection of 50 u of heterologous
thrombin into Swiss albino mice induced an increase (0.5 to 1.9 fold) in the rate
of biosynthesis of fibrinogen comparable to that induced in vitro by blood derived from aging or arteriosclerotic human subjects. Thrombin is not the
primary agent in the control of the synthesis of fibrinogen since the activity of
thrombin, when preincubated with plasma, had disappeared before the plasma was used
as a medium for stimulating the synthesis of fibrinogen. Also, incubation of serum
led to the production of a factor which greatly enhanced the biosynthesis of fibrinogen.
This condition is not known to lead to the production of thrombin.
