Acute elevation and recovery of intracellular [Mg 2+ ] following human focal cerebral ischemia

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Abstract
We used 31P magnetic resonance spectroscopy (MRS) to investigate changes in brain intracellular [Mg2+] following human focal cerebral ischemia. Mean brain pMg (where pMg = -log[Mg2+]) was significantly lower in the ischemic focus of all stroke patients (pMg = 3.34 ± 0.28, n = 45, p < 0.01) when compared with normal controls (pMg = 3.50 ± 0.08, n = 25). Ischemic brain pMg was also significantly reduced when the pH of the stroke region was acidotic (pH < 6.90, pMg = 3.07 ± 0.44, n = 11, p < 0.01) and when the phosphocreatine index (PCrI = PCr/[PCr + Pi (inorganic phosphate)]) was reduced (PCrI < 0.47, pMg = 3.12 ± 0.42, n = 13, p < 0.01). Mean brain pMg was significantly reduced at days 0 to 1 (acute) poststroke (pMg = 3.32 ± 0.28, n = 26, p < 0.01) and at days 2 to 3 (subacute) poststroke (pMg = 3.38 ± 0.28, n = 21, p = 0.03). There was also a significant (p < 0.01) correlation between decreased pMg and increased relative signal intensity of Pi (normalized by total phosphate signal, Pi/TP) for all stroke groups studied. During the temporal evolution of stroke, pH returned to normal levels by days 2 to 3, and pMg returned to normal by days 4 to 10 (subacute). PCrI and Pi/TP returned toward normal levels after 10 days (chronic), at a time when ischemic brain pH had become significantly alkalotic (pH = 7.10 ± 0.24, n = 15, p < 0.01). Elevation of ischemic brain [Mg2+] is temporally linked to the acidotic phase of human stroke as well as the breakdown of energy metabolism. These acute changes in [Mg2+] may contribute to, or be a marker for, cellular injury.

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