H-1-NMR ANALYSIS OF NERVE EDEMA IN THE STREPTOZOTOCIN-INDUCED DIABETIC RAT

To define the existence of intracellular hydration caused by metabolic derangements in the excised sciatic nerves of diabetic rats quantitat ively, relaxation times (T-1, T-2) and fraction of intracellular water content were measured with H-1-nuclear magnetic resonance (NMR) spect roscopy in normal rats (control group, n = 10), streptozotocin (STZ)-i nduced (50 mg/kg, IV) diabetic rats (DM group, n = 10), STZ-induced di abetic rats treated with an aldose reductase inhibitor (ARI, Epalresta t, 100 mg/kg) (ARI group, n = 8), and STZ-induced diabetic rats treate d with insulin (insulin group, n = 4). For selective measurement of in tracellular relaxation times, the inversion recovery (IR] method for c onventional T-1 and Carr-Purcell-Meiboom-Gill method for T-2 were used with an aqueous chemical shift reagent, 10 mmol/L dysprosium triethyl enetetramine-N, N, N', N'', N''', N'''-hexaacetic acid, resulting in d istinct separation of intracellular (Schwann cell, axon, endothelial c ell, and pericyte) and extracellular waters under the isotonic conditi on of the rat sciatic nerves. Furthermore, a new method of driven-equi librium single-pulse observation of T-1 (DESPOT) was used for rapid me asurement of T-1 for the purpose of clinical application on magnetic r esonance imaging (MRI). T-1 values measured by the DESPOT and IR metho ds were significantly correlated (p < 0.001). Total and intracellular water contents, sorbitol contents, and relaxation times of the sciatic nerve taken from the DM group were significantly elevated (p < 0.01), while myoinositol (p < 0.01) and extracellular water (p < 0.05) conte nts were significantly decreased as compared with the control group. B oth insulin and ARI treatments significantly improved relaxation times as compared with those in the DM group (p < 0.05-0.01). Relaxation ti mes correlated positively with total water (T-1, p < 0.05-0.01; T-2, p < 0.01), intracellular water (T-1, p < 0.001; T-2, p < 0.001), and so rbitol (T-1, p < 0.001; T-2, p < 0.001) contents of the excised nerve. Sorbitol content correlated positively with total and intracellular w ater contents (p < 0.01) but negatively with extracellular water conte nt (p < 0.05). These findings indicated that sorbitol itself and/or se condary sodium accumulation caused by an increase in sorbitol may be a major contributor to the increase in intracellular hydration and prol onged relaxation times associated with hyperglycemia, which are revers ible with insulin or ARI treatment. It was also suggested that rapid T -1 measurement would provide new insights into the pathogenesis of hum an diabetic neuropathy as a non-invasive evaluation method on MRI.