Suppressive effects of E₂ on Epo induction stimulated by hypoxia, Co, and bleeding for 24 hours in rats. ▪ indicate without stimulation; □ and ▦, hypoxia (vehicle- and E₂-injected rats, respectively, confined to one hypoxic cage simultaneously); ▧, co-injection; and ▩, bleeding. Data are presented as mean values of plasma Epo levels with SD bars. The numbers of animals are shown on the tops of the bars. *Significant difference (P < .05) compared with each vehicle-injected group.