Scand J Clin Lab Invest 1998; 58: 161–166 161 Blood-free magnesium concentration declines following graded experimental traumatic brain injury D. L. HEATH & R. VINK Department of Physiology and Pharmacology, James Cook University of North Queensland, Townsville, Queensland, Australia Scand J Clin Lab 199858 161 166 ISSN 00364-5513 18 August 1997 28 January 1998 Deanne HeathDepartment of Physiology and Pharmacology, James Cook University, Townsville, Queensland 4811, Australia Heath DL, Vink R. Blood-free magnesium concentration declines following graded experimental traumatic brain injury. Scand J Clin Lab Invest 1998; 58: 161–166. Traumatic brain injury has been shown to result in a decrease in brain-free magnesium concentration that is associated with the development of neurologic motor deficits. Although these changes have been well characterized in the brain, changes in free magnesium homeostasis have not been characterized in other fluid compartments. The current experiments use ion selective electrodes to measure alterations in blood-free magnesium concentration following graded experimental brain injury in rats and to compare these changes with subsequent neurologic outcome. After severe impact-acceleration-induced injury, blood- free magnesium levels significantly declined (p<0.05) by 25% and remained depressed for at least 4 days after injury. After moderate injury, the decline in blood-free magnesium was less than that observed in the severe injury group, with respect to both degree of decline and duration of decline. The post- traumatic blood-free magnesium concentration correlated to observed motor deficits as assessed by rotarod evaluation (p<0.001). We conclude that blood- free magnesium levels may be a prognostic indicator of outcome following severe traumatic brain injury. Key words: head injury; ion-selective electrodes; ionised magnesium; trauma Deanne Heath, Department of Physiology and Pharmacology, James Cook University, Townsville, Queensland 4811, Australia Previous studies have demonstrated that both brain total and free magnesium concentration significantly decline following experimental traumatic brain injury and that this decline persists for at least 4 days after injury [1–3]. Moreover, such declines in free magnesium, and their attenuation by pharmacologic means, are associated with the degree of neurologic dysfunction that subsequently develops [4–6]. While the post-traumatic changes in brain magnesium homeostasis have now been well characterized, few studies have characterized free magnesium homeostasis outside of the brain. Indeed, a knowledge of blood-free magnesium concentration may also provide valuable information of post-traumatic mag- nesium homeostasis following traumatic brain injury and perhaps be of prognostic significance [7]. Moreover, such a technique would be far more practical and cost-effective in the clinical setting than the expensive magnetic resonance techniques used to date in all determinations of Scand J Clin Lab Invest Downloaded from informahealthcare.com by University Of South Australia on 07/19/15 For personal use only.