Abstract

Cyclophosphamide has been administered to rats in doses varying from 120 to 150 mg/kg i.p., and the effects on the eosinophilic leukocytes of bone marrow and other tissues (intestine, stomach, spleen, lung) have been studied by direct cell counts and estimates of the tissue content of an enzymatic marker (phospholipase B). The action of cyclophosphamide is primarily on marrow eosinophils (80-100% reduction) with less pronounced peripheral effects. The intestinal pool is the least affected (50-60%) and the first to present signs of recovery. The eosinopenic action of cyclophosphamide on peripheral tissues is augmented by the joint administration of dexamethasone (5 mg/kg i.p.). The effects of the two drugs are clearly additive and a permanent state of eosinopenia affecting all tissues studied can be maintained by administration of dexamethasone at the dose of 1.5 mg/kg i.p. on alternate days. Thus it appears feasible to control the eosinophilic population of rat tissue at abnormally low levels over a relatively extended period of time during which studies of the factors governing production and release of these cells from the marrow can be undertaken.