[Effect of different blood glucose levels on the expression of cerebral GLUT3 mRNA in neonatal rats with hypoxia-ischemia].

Objective: Concerns of the effect of glucose on perinatal hypoxic-ischemic brain damage are increasing. It was previously considered that the glucose transporter (GLUT) genes and their productions played an important role in the regulation of cerebral energy metabolism. The present study aimed to explore the effect of different blood glucose levels on the expression of cerebral GLUT3 mRNA in neonatal rats with hypoxia-ischemia (HI), and to evaluate the neuroprotective effect of glucose against HI insults.

Methods: A total of 250 7-day-old neonatal SD rats were randomly divided into 10 groups (n=25 each): Normal control, Sham-operated, HI, Hypoglycemia, Hypoglycemia pre- and post-HI, Mild hyperglycemia pre- and post-HI, Severe hyperglycemia pre- and post-HI. Blood glucose levels of normal, hypoglycemia, mild hyperglycemia and severe hyperglycemia were defined as 5-7 mmol/L, 3-4 mmol/L, 10-15 mmol/L and 16-25 mmol/L, respectively. The expression of GLUT3 mRNA was detected with RT-PCT technique at 2, 24, 48 and 72 hrs and at 7 days after HI.

Results: There was a correlation between increases in GLUT3 mRNA expression and postnatal age in the Normal control group. HI significantly enhanced the expression of GLUT3 mRNA from 2 hrs, peaking at 24 hrs after HI, and then significantly decreased at 72 hrs and 7 days after HI when compared with the Normal Control group (P < 0.01). GLUT3 mRNA expression in the Hypoglycemia pre-HI group was the lowest among all groups with HI at each time point after HI, and a statistically significant difference was found at 72 hrs after HI when compared with the HI group (P < 0.05). The expressional levels of GLUT3 mRNA in the Severe hyperglycemia pre-HI group were strikingly higher than those in any other groups with HI (P < 0.05 or 0.01). The GLUT3 mRNA expression patterns in the Mild and Severe hyperglycemia post-HI and the Hypoglycemia post-HI groups were similar to the Hypoglycemia pre-HI group.

Conclusions: GLUT3 mRNA expression and the synthesis of GLUT3 can be down-regulated by hypoglycemia pre-HI, coupled with aggravation of cerebral pathology, but up-regulated by higher hyperglycemia pre-HI, coupled with improvement of cerebral pathology. This suggested that adequate glucose supplement before HI can improve the cerebral function against HI insults in neonatal rats.