The effect of glucocorticosteroids on the kinetics of mononuclear phagocytes

The effect of glucocorticosteroids on the kinetics of mononuclear phagocytes, i.e., peripheral blood monocytes and peritoneal macrophages, was studied in normal mice, as well as in mice in which an inflammatory reaction was evoked in the peritoneal cavity. The administration of glucocorticosteroids resulted in a rapid decrease (within 3-6 hr) in the number of circulating monocytes, the duration being dependent on the nature and dose of the compound. The water-soluble dexamethasone sodium phosphate is only briefly active (less than 12 hr), but hydrocortisone acetate, which forms a subcutaneous depot, reduced the number of monocytes for more than 2 wk. In normal mice, hydrocortisone did not affect the number of macrophages already present in the peritoneal cavity, but the transit of mononuclear phagocytes from the circulation into the peritoneal cavity was arrested. During an inflammatory response in the peritoneal cavity, hydrocortisone suppresses both the increase in the number of monocytes in the peripheral blood and the increase in the number of peritoneal macrophages. This reduction of the inflammatory exudate appeared to be due to a diminished influx of mononuclear phagocytes from the peripheral blood. No lytic action of glucocorticosteroids on the mononuclear phagocytes could be demonstrated.