Hypoxia induces various adoptive signaling in cells that can cause several physiologic changes. In the present work, we have observed that exposure of bovine aortic endothelial cells (BAECs) to extreme hypoxia (1-5% O ₂) attenuates cellular respiration by a mechanism involving Hsp90-eNOS, so that the cells are conditioned to consume less oxygen and survive in prolonged hypoxic conditions. BAECs, exposed to 1% O ₂, showed a reduced respiration compared to 21% O ₂ maintained cells. Western blots and immunoprecipitation analyses showed an increase in the association of Hsp90-eNOS and enhanced NO generation upon hypoxia exposure, whereas there was no significant accumulation of HIF-1. The addition of inhibitors of Hsp90, PI3K and NOS significantly alleviated this hypoxia-induced attenuation of respiration. Thus, we conclude that hypoxia-induced excess NO and its derivatives such as ONOO- cause inhibition of the electron transport chain and attenuates O ₂ demand, leading to cell survival at extreme hypoxia. More importantly, such an attenuation is found to be independent of HIF-1, which is otherwise thought to be the key regulator of respiration in hypoxia exposed cells, through a non-phosphorylative glycolytic pathway. The present mechanistic insight will be helpful to understand the difference in the magnitude of endothelial dysfunction.