Enhanced effects of hypoxia on erythropoiesis in rabbits following beta-2 adrenergic activation with albuterol

The effects of long-term administration of albuterol, a selective beta-2 adrenergic agonist, on red cell production have been studied in rabbits under normoxic and hypoxic conditions. In normoxia albuterol (5 mg/kg s.c. daily for 8 weeks) was found to be moderately effective in stimulating erythropoiesis. A transient but significant increase in hematocrit values was seen in the albuterol-treated rabbits when compared to saline-treated normoxic rabbits. However, reticulocyte counts in peripheral blood remained unchanged, and no change in red cell mass was found after 8 weeks of treatment with albuterol when compared to the controls. In considering a possible negative feedback on erythropoiesis by oxygen availability, the erythropoietic activity of albuterol was also studied in combination with discontinuous hypoxia (0.42 atm for 9 hr every 2nd day) in rabbits for 6 weeks. Exposure to hypoxia resulted in a marked increase in erythropoiesis in all exposed rabbits. However, red cell mass and hematocrits were significantly higher when rabbits had been treated with albuterol before exposure to hypoxia. As we were unable to detect significant differences in plasma levels of erythropoietin during exposure to hypoxia after the injection of albuterol, it is concluded that this enhanced erythropoiesis is mainly due to beta receptor activation of bone marrow erythroid progenitor cells. These studies suggest a possible role of beta-2 adrenergic activation of erythropoiesis in adaptation to hypoxia.