Rate of Clearance of Circulating Leukocytic Endogenous Mediator in the Rat

The rate of clearance of leukocytic endogenous mediator from the circulation of the rat was determined by measuring the rate of disappearance of activity from the plasma. Leukocytic endogenous mediator was injected iv into groups of rats and the plasma was periodically sampled for the activities that would lower plasma iron, increase plasma fibrinogen, or release bone marrow neutrophils. These activities were assayed by injecting the plasma into groups of normal rats. The t1/2 's for the clearance of leukocytic endogenous mediator ranged between 6 and 10 min.