Trauma-hemorrhage (T-H) is known to impair tissue perfusion, leading to tissue hypoxia, and thus affecting mitochondria, the organelles with the highest oxygen demand. In a model of T-H and prolonged hypotension without fluid resuscitation, administration of a small volume of 17β-estradiol (E2), but not vehicle, prolonged the survival of rats for 3 h, even in the absence of fluid resuscitation. The main finding of this study is that T-H followed by prolonged hypotension significantly affects mitochondrial function, endoplasmic reticulum (ER) stress markers and free iron levels, and that E2 ameliorated all these changes. All of these changes were observed in the liver but not in the kidney. The sensitivity of mitochondrial respiration to exogenous cytochrome c can reflect increased permeability of the outer mitochondrial membrane for cytochrome c. Increased levels of free iron are indicative of oxidative stress, but neither oxidative nor nitrosylative stress markers changed. The spliced isoform of XBP1 mRNA (an early marker of ER stress) and the expression of C/EBP homologous protein (CHOP) (a protein regulating ER stress-induced apoptosis) were elevated in T-H animals but remained unchanged if T-H rats received E2. Both the prevention of elevated sensitivity of mitochondrial respiration to cytochrome c and a decrease in ER stress by E2 maintain functional integrity of the liver and may help the organ during prolonged hypotension and following resuscitation. A decrease in free iron levels by E2 is more relevant for resuscitation, often accompanied by oxidative stress reaction. Thus, E2 appears to be a novel hormonal adjunct that prolongs permissive hypotension during lengthy transportation of the injured patient between the injury site and the hospital in both civilian and military injuries. © 2010 The Feinstein Institute for Medical Research.