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1 Agricultural Research Complex, Department of Animal Sciences, University of Arizona, Tucson, Arizona, United States
2 Perinatal Research Center, Department of Pediatrics, University of Colorado Health Sciences Center, Aurora, Colorado, United States
* To whom correspondence should be addressed. E-mail: limesand{at}ag.arizona.edu.
In this study we determined body weight-specific fetal (umbilical) glucose uptake (UGU), utilization (GUR), and production rates (GPR) and insulin action in IUGR fetal sheep. During basal conditions, UGU from the placenta was 33% lower in IUGR fetuses, but GUR was not different between IUGR and control fetuses. The difference between glucose utilization and UGU rates in the IUGR fetuses demonstrated the presence and rate of fetal GPR (41% of GUR). The mRNA concentrations of gluconeogenic enzymes, glucose-6-phophatase and PEPCK, were higher in the livers of IUGR fetuses, perhaps in response to CREB activation, as phosphorylated CREB/total CREB was increased 4.2 fold. A hyperglycemic clamp resulted in similar rates of glucose uptake and utilization in IUGR and control fetuses. The nearly identical GURs in IUGR and control fetuses at both basal and high glucose concentrations occurred at mean plasma insulin concentrations in the IUGR fetuses that were ~70% lower than controls, indicating increased insulin sensitivity. Furthermore, under basal conditions, hepatic glycogen content was similar, skeletal muscle glycogen was increased 2.2 fold, the fraction of fetal GUR that was oxidized was 32% lower, and GLUT 1 and GLUT 4 concentrations in liver and skeletal muscle were the same in IUGR fetuses compared with controls. These results indicate that insulin responsive fetal tissues (liver and skeletal muscle) adapt to the hypoglycemic-hypoinsulinemic IUGR environment with mechanisms that promote glucose utilization, particularly for glucose storage, including increased insulin action, glucose production, shunting of glucose utilization to glycogen production, and maintenance of glucose transporter concentrations.
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