Diabetes in pregnancy is associated with fetal hyperglycemia and hyperinsulinemia resulting in abnormal fetal and neonatal hepatic glucose metabolism. As the transport of glucose into the cell represents the first step at which glucose utilization is controlled, we hypothesized that glucose transport would be altered in liver of fetal rats with hyperglycemia and hyperinsulinemia. In a rat model of LGA growth, selective ablation of alternate fetuses by uterine artery branch ligation produced tralhyperglycemia and hyperinsulinemia in the survivors. Ligations were performed on gestational day 15 (term=21.5)(n=12); litters from sham operated mothers served as controls (C) (n=10). Fetuses were delivered by hysterotomy on day 20. Glut protein expression was measured by Western blotting of extracted hepatic protein and quantified by autoradiograph densitiometry. Glut mRNA was measured by reverse transcription of RNA using an internal control (bovine retinal RNA) with subsequent PCR amplification (Glut 1, 2, and rhodopsin primers) and quantification by phosphorimaging. Levels of Glut mRNA were standardized to rhodopsin mRNA levels. Immunohistocytochemistry was performed on fixed liver samples to localize Glut protein. Body and liver weights were higher in LGA fetuses compared to C (Body: 3.99±.06 v. 3.51±.05 g; Liver: 0.28±.01 v. 0.23±.01 g, LGA vs C, respectively)(p<0.05). Glucose uptake was lower in LGA hepatocytes (1.09 pM/μg protein/min) compared to C (1.69 pM/μg protein/min). LGA Glut 1 and Glut 2 protein levels were significantly less than C (55%, 35% of C) (p<0.01). Immunohistochemistry revealed Glut 1 staining on hepatocytes and erythropoeitic elements, whereas Glut 2 staining was localized only to hepatocytes. The intensity of staining for Glut 1 and Glut 2 was qualitatively less in LGA liver. Glut 1 and Glut 2 mRNA levels were also decreased in LGA liver compared to C (35%, 15% of C) (p<0.01). We speculate that in the LGA fetus, increased glucose levels downregulate Glut 1 expression to minimize the potential detrimental effects of hyperglycemia to the hepatocyte. High insulin levels may downregulate Glut 2. The decrease in Glut 2, which transports glucose out of the hepatocyte, may contribute to the hypoglycemia observed in LGA neonates. These studies suggest that glucose and insulin availability regulate hepatic Glut expression under in vivo conditions in the fetal rat.
