Chronic fetal hypoglycemia inhibits the later steps of stimulus-secretion coupling in pancreatic β-cells

Abstract

We measured the impact of chronic late gestation hypoglycemia on pancreatic islet structure and function to determine the cause of decreased insulin secretion in this sheep model of fetal nutrient deprivation. Late gestation hypoglycemia did not decrease pancreas weight, insulin content, beta-cell area, beta-cell mass, or islet size. The pancreatic islet isolation procedure selected a group of islets that were larger and had an increased proportion of beta-cells compared with islets measured in pancreatic sections, but there were no morphologic differences between islets isolated from control and hypoglycemic fetuses. The rates of glucose-stimulated pancreatic islet glucose utilization (126.2 +/- 25.3 pmol glucose.islet(-1).h(-1), hypoglycemic, vs. 93.5 +/- 5.5 pmol glucose.islet(-1).h(-1), control, P = 0.47) and oxidation (10.5 +/- 1.7 pmol glucose.islet(-1).h(-1), hypoglycemic, vs. 10.6 +/- 1.6 pmol glucose.islet(-1).h(-1), control) were not different in hypoglycemic fetuses compared with control fetuses. Chronic late gestation hypoglycemia decreased insulin secretion in isolated pancreatic islets by almost 70% in response to direct nonnutrient membrane depolarization and in response to increased extracellular calcium entry. beta-Cell ultrastructure was abnormal with markedly distended rough endoplasmic reticulum in three of the seven hypoglycemic fetuses studied, but in vitro analysis of hypoglycemic control islets showed no evidence that these changes represented endoplasmic reticulum stress, as measured by transcription of glucose regulatory protein-78 and processing of X-box binding protein-1. In conclusion, these studies show that chronic hypoglycemia in late gestation decreases insulin secretion by inhibiting the later steps of stimulus-secretion coupling after glucose metabolism, membrane depolarization, and calcium entry.

Chronic late-gestation hypoglycemia upregulates hepatic PEPCK associated with increased PGC1α mRNA and phosphorylated CREB in fetal sheep

“…Cloning and real-time quantitative PCR for ovine ribosomal protein S15, PEPCK, glucose-6-phosphatase (G6Pase), and PGC1␣ (GenBank accession nos. AY949774, EF062862, EF062861, and AY957611, respectively) have been previously described (35,57). cDNA samples were run in triplicate, and the quantitative PCR was performed as previously described (57) with the standard curve method of relative quantification used to compare results (66).…”

Coordinated changes in hepatic amino acid metabolism and endocrine signals support hepatic glucose production during fetal hypoglycemia

“…Insulin is the primary hormone responsible for suppressing gluconeogenic gene expression and glucose production (7,36). Since fetal hypoglycemia results in decreased fetal (5,39,40), hypoinsulinemia is found in hypoglycemic models with increased glucose production (5,46). Whether hypoinsulinemia alone is sufficient for the induction of glucose production remains unclear, as pancreatectomized fetuses fail to induce glucose production (10,11), yet streptozotocin treated fetuses have increased glucose production (16).…”

Prolonged maternal amino acid infusion in late-gestation pregnant sheep increases fetal amino acid oxidation

“…The proportional area of the pancreas represented by ␤-and ␣-cells was measured as previously described (41).…”