Plasma erythropoietin levels in mice. Response to hypoxia at different ages

Mice from newborn until adult age were exposed to hypobaric hypoxia of 0.5 atm for 6 h. In all age groups the animals responded with increased plasma erythropoietin (Ep) levels. A greater response was elicited from adult mice compared to newborn animals. No sex difference in response occurred. Twelve hours after the hypoxic exposure no plasma Ep activity was detectable. Though high plasma Ep levels were present in non-hypoxic mice 9 and 20 days old, hypoxia further increased the Ep activity. It is concluded that hypoxia stimulates Ep production during hepatic as well as during erythropoiesis. Though erythroid target cells may be maximally stimulated by Ep in the young mouse (9-20 days old) a reverse capacity for Ep production exists. Increased capacity for Ep production may develop towards adult age.