Mechanisms of Leukocyte Production and Release

Abstract

A perfusion technique is described for assessing bone marrow function in isolated rat femurs. The marrows within these preparations are maintained in good physiological condition for 4-6 hours. Direct evidence is presented indicating that marrow leukocyte release is influenced by the blood flow rate through the marrow and the numbers of circulating white cells. Leukocytes were released from the marrow in a spurting pattern andthe release of neutrophils and lymphocytes were essentially associated events. Normal numbers of leukocytes in the perfusate suppressed white cell release and resulted in the sequestration of lymphocytes within the marrow. Whole blood containing the leukocytosis-inducing factor (LIF) produced either a marked increase in the blood flow rate through the marrow or prevented the progressive increase in vascular resistance observed in control preparations. Those effects accompanied the increased discharge of leukocytes into the perfusate. The addition of known vasoactive agents (i.e., acetylcholine, histamine and endotoxin) did not reproduce the flow rate patterns obtained with the LIF.