We have shown that glucose worsens hypoxic ischemic brain injury in the newborn pig and insulin reduces injury. We wish to see if this effect is caused by an increase in brain lactate, accompanied by an increase in brain ATP as in adult animals. Using the same protocol we had used to show the effect of glucose on brain injury, thirty-five 0-3 day old piglets had carotid snares and arterial and venus catheters placed under 1½% isoflurane anesthesia. They were randomly assigned to have their glucose increased to 300± 30 SE mg/dl with glucose infusion G, (n=12) or decreased to 67± 16 mg/dl with insulin I (n=13) or a sham group S (n=10). In the I and G groups at time 0, both carotid arteries were clamped and blood was withdrawn to reduce the blood pressure to two-thirds normal. At time 15 minutes inspired oxygen was reduced to 6%. At time 30 minutes, the brains were frozen in situ in liquid nitrogen, then removed and stored in liquid nitrogen. The shams were anesthetized and their brains were frozen in liquid nitrogen using an identical procedure but without inducing hypoxia or ischemia. Brains were homogenized and lactate and ATP were measured enzymatically, CSF amino acids by HPLC and H{3} MK801 binding by Scatchard Analysis. Brain ATP was 1.7±.09 mmoles/kg wet wt. in the S, 0.98 ± 0.09 in the G, and 0.52± 0.10 in the I, (all differences statistically significant p<.01). Brain lactate levels were 4.3 ± 1.0 mmoles/kg wet wt. in the S, 29.4± 2.6 in the G, and 18.3 ± 1.9 in the I, (all results statistically different p<.01). CSF glutamate was 12.9 ± 8.1 μM in G, 13.5 ± 8.7 in I, and 2.2 ± 0.9 in S (p=ns). Aspartate was 63 ± 21 μM in G, 42 ± 6 in I, and 58 ± 8 in S (p=ns), and glycine was 90 ± 22 μM in 6, 100 ± 22 in I and 84± 17 in S (p=ns). MK801 binding showed a Kd of 6.3 ± 0.4 nM in 6, 6.2 ± 0.3 in I, and 6.0 ± 0.6 in S (p=ns), and a Bmax of 2.3 ± 0.2 pMol/mg protein in G (p=ns), 2.6 ± 0.1 in I (p<.05 vs S), and 2.0 ± 0.2 in S. Although providing additional glucose preserves cellular ATP during hypoxic ischemic brain injury in the newborn pig, it does not change the glutaminergic system, and it worsens outcome by elevating cellular lactate levels above the threshold for cellular injury.
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