Protection against spinal cord ischemia with insulin-induced hypoglycemia

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✓ The effect of insulin-induced reduction in blood glucose to 65 ± 20 mg/dl (mean ± standard deviation) on recovery of electrophysiological function and extracellular lactate concentration was studied in a rabbit model of spinal cord ischemia. These results were compared to findings in animals with spinal cord ischemia that either were fasted overnight (fasted group: blood glucose 97 ± 26 mg/dl) or had no pretreatment (control group: blood glucose 172 ± 65 mg/dl). The aorta was occluded until the postsynaptic waves of the spinal somatosensory evoked potentials (SSEP's) had been absent for 20 minutes, a period of ischemia that produces paraplegia in 100% of untreated rabbits. The total aortic occlusion time was not significantly different in the three groups. Recovery of the SSEP's was significantly better in the insulin-treated animals than in the fasted or control animals. The N3 wave of the SSEP's, which has been found to correlate best with neurological recovery, returned to 65% ± 48% of the preischemia amplitude in the insulin-treated animals, compared to 40% ± 34% in the fasted group and 26% ± 24% in the control animals. Extracellular lactate concentration in the spinal cord increased immediately after occlusion of the aorta, reached a plateau as the postsynaptic waves disappeared from the SSEP's, and then increased a second time during the first 15 minutes of reperfusion. The peak lactate concentration during ischemia and during reperfusion correlated with the preischemia glucose concentration (r = 0.60336 and r = 0.76930, respectively). Lactate concentration in the spinal cord was higher during ischemia and throughout the first 2 hours of reperfusion in the control and fasted animals than in the insulin-treated animals. During the 2nd hour of reperfusion, lactate concentration was significantly higher in the control animals than in the fasted animals. Reduction in blood glucose with insulin improves recovery of electrophysiological function after spinal cord ischemia, probably because of reduced lactic acid production, especially during the early reperfusion period.

Article Information

Address reprint requests to: Claudia S. Robertson, M.D., Department of Neurosurgery, Baylor College of Medicine, One Baylor Plaza, Houston, Texas 77030.

© AANS, except where prohibited by US copyright law.

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Figures

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    Diagram of the experimental protocol and examples of spinal somatosensory evoked potential (SSEP) recordings.

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    The length of time required after inflation of the aortic balloon for the postsynaptic wave N3 to disappear from the spinal somatosensory evoked potentials (SSEP). The time was (mean ± standard deviation): 5.9 ± 3.8 minutes in the insulin-treated group, 8.7 ± 4.9 minutes in the fasted animals, and 8.4 ± 6.1 minutes in the control group.

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    Recovery of the individual spinal somatosensory evoked potential (SSEP) waves at 120 minutes after reperfusion, expressed as a percentage of their control amplitude.

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    Lactate concentration in the spinal cord dialysate (µmol/ml) during ischemia and the first 2 hours of reperfusion in the three experimental groups. * = different from control group, and + = different from fasted group (p < 0.05). SSEP = spinal somatosensory evoked potentials.

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