Objective:To assess the possible benefits of sympatholytics on uncontrolled hemorrhage in unanesthetized rats.Design:A randomized laboratory study using rats to test the effects of sympatholytics on uncontrolled hemorrhage.Setting:Research laboratory.Subjects:Forty female Sprague-Dawley rats, randomly assigned into four groups according to the treatment: untreated (Control); α-adrenergic blockade with phenoxybenzamine (Alpha); β-adrenergic blockade with propranolol (Beta); and a combined α- and β-adrenergic blockade by phenoxybenzamine and propranolol (Alpha/Beta).Intervention:After cannulation under light ether, the rats were allowed to awaken. A baseline blood sample was withdrawn. The uncontrolled hemorrhage was initiated by tail resection and allowed to continue without intervention for the duration of the experiment. After 15 mins, 80 mL/kg isotonic saline fluid was infused at 4.4 mL/min. At 60 mins, another blood sample was drawn; changes in mean arterial pressure, hematocrit, blood loss, and mortality were observed for up to 180 mins.Main Outcome Measure:Survival, mortality, blood loss (amount, prevalence, and rate), and hemodynamic variables (mean arterial pressure, pulse rate, hematocrit).Results:In the Alpha group, there was a reduction in spontaneous blood loss compared with the control group (2.9 vs. 10.6 mL/kg, respectively) and 100% survival. In contrast, the Beta group exhibited an increase in tail blood loss (21.1 mL) and a decreased survival (10%). Despite the enhanced hemorrhage in the Alpha/Beta group (17.0 mL/kg) compared with controls, the survival rate in both of these groups was 60%. In all groups, no significant increase in tail blood loss was observed after 60 mins.Conclusions:An α-adrenergic blockade increased survival in uncontrolled hemorrhage by significantly reducing spontaneous blood loss. Conversely, a β-adrenergic blockade significantly decreased survival and increased blood loss, whereas a combined blockade significantly increased blood loss without affecting survival.