Increased fetal insulin concentrations for one week fail to improve insulin secretion or β-cell mass in fetal sheep with chronically reduced glucose supply

Maternal undernutrition during pregnancy and placental insufficiency are characterized by impaired development of fetal pancreatic β-cells. Prolonged reduced glucose supply to the fetus is a feature of both. It is unknown if reduced glucose supply, independent of other complications of maternal undernutrition and placental insufficiency, would cause similar β-cell defects. Therefore, we measured fetal insulin secretion and β-cell mass following prolonged reduced fetal glucose supply in sheep. We also tested whether restoring physiological insulin concentrations would correct any β-cell defects. Pregnant sheep received either a direct saline infusion (CON = control, n = 5) or an insulin infusion (HG = hypoglycemic, n = 5) for 8 wk in late gestation (75 to 134 days) to decrease maternal glucose concentrations and reduce fetal glucose supply. A separate group of HG fetuses also received a direct fetal insulin infusion for the final week of the study with a dextrose infusion to prevent a further fall in glucose concentration [hypoglycemic + insulin (HG+I), n = 4]. Maximum glucose-stimulated insulin concentrations were 45% lower in HG fetuses compared with CON fetuses. β-Cell, pancreatic, and fetal mass were 50%, 37%, and 40% lower in HG compared with CON fetuses, respectively (P < 0.05). Insulin secretion and β-cell mass did not improve in the HG+I fetuses. These results indicate that chronically reduced fetal glucose supply is sufficient to reduce pancreatic insulin secretion in response to glucose, primarily due to reduced pancreatic and β-cell mass, and is not correctable with insulin.