Traumatic brain injury (TBI) is the most frequent cause of death in children and young adults in the United States. Besides emergency neurosurgical procedures, there are few medical treatment options to improve recovery in people who have experienced a TBI. Management of patients who survive TBI is complicated by both central nervous system and peripheral systemic effects. The pathophysiology of systemic inflammation and coagulopathy following TBI has been attributed to trauma-induced endothelial cell dysfunction; however, there is little knowledge of the mechanisms by which trauma might impact the functions of the vascular endothelium at sites remote from the injury. The endothelium lining these small vessels normally produces nitric oxide (NO), arachidonic acid metabolites, and endothelial-dependent hyperpolarizing factors to relax the surrounding vascular smooth muscle. For this research study we investigated the effects of fluid-percussion-induced TBI on endothelial-dependent vasodilatory functions in a remote tissue bed (the mesenteric circulation) 24 hours after injury. We hypothesized that TBI causes changes in the mesenteric artery endothelium that result in a loss of endothelial-dependent vasodilation. We found that vasodilations induced by the muscarinic-receptor agonist, acetylcholine, are attenuated following TBI. While the endothelial-derived hyperpolarizing component of vasodilation was preserved, the NO component was severely impaired. Therefore, we tested whether the loss of NO component was due to a decrease in bioavailablity of the NO synthase (NOS) cofactor BH4, the NOS substrate L-arginine, or to changes in expression/activity of the enzyme arginase, which competes with NOS for L-arginine. We found that supplementation of L-arginine and inhibition of the enzyme arginase rescues endothelial-dependent vasodilations in TBI arteries. This study demonstrates that there are pathological systemic effects outside the point of injury following TBI leading to a dysfunctional endothelial vasodilatory pathway. These data provide insight into the pathophysiology of endothelial dysfunction after trauma and may lead to new potential targets for drug therapy.