The effect of etiocholanolone on the entry of granulocytes into the peripheral blood.

P REVIOUS STUDIES of granulocyte kinetics in hematologically normal individuals employing tritiated thymidine ( H3TdR) have indicated that there is a 4-5 day period after administration of the radioisotope before labeled granulocytes appear in the peripheral blood.13 The large mass of non-proliferating granulocytic cells constitutes the marrow granulocyte reserve (MGR) from which the majority of mature granulocytes are released in an orderly fashion.4 however, in response to a variety of stimuli such as leukophoresis, bacterial endotoxin, and acute bacterial infection, entry of granulocytes into the peripheral blood from the MGR may be accelerated.2’58 The bone marrow constitutes the principal reservoir for granulocytes, and it has been established that cells of the myeloid series which leave the vascular tree normally do not return from the tissues.#{176} Etiocholanolone, a naturally occurring steroid metabolite, has been shown to cause leukocytosis consisting primarily of mature polymorphonuclear neutrophils when injected intramuscularly into man.9”’ Following injection, maximum granulocytosis is reached between 14 and 18 hours followed by a slow decline to normal at 24-36 hours.’#{176} Based on studies using tritiated diisopropylfluorophosphate labeling of autologous leukocytes, the increment in circulating granulocytes is associated with marked expansion of the total blood granulocyte pool with proportional increases of both the marginal and circulating granulocyte pools. These data give presumptive evidence that the granulocytes mobilized in response to etiocholanolone come from the bone marrow reserve.” We have studied the effect of etiocholanolone on the appearance of labeled