AbstractThe possible mechanisms underlying the suppression of erythropoiesis in hyperoxic animals were studied. Male Long-Evans rats were injected with cobaltous chloride hexahydrate, a known erythropoietic stimulant. One group was exposed to a hyperoxic environment for ten hours. Both serum levels of erythropoietin (Ep) and renal levels of erythrogenin were significantly lower (p< 0.005) in the hyperoxic animals compared to those left at room air. In addition, inhibitors to Ep or erythrogenin could not be detected in either the serum or renal tissue of the hyperoxic rats. These results indicate that the primary factor responsible for the erythropoietic suppression observed in a hyperoxic environment is a decreased production of erythrogenin which results in turn, in a lowered level of circulating Ep.