Limesand, S., Leos, R. A., Anderson, M. J., Chen, X., Pugmire, J., Anderson, K. A., & Limesand, S. W. (2010). Chronic exposure to elevated norepinephrine suppresses insulin secretion in fetal sheep with placental insufficiency and intrauterine growth restriction. American journal of physiology. Endocrinology and metabolism, 298(4).
In this study, we examined chronic norepinephrine suppression of insulin secretion in sheep fetuses with placental insufficiency-induced intrauterine growth restriction (IUGR). Glucose-stimulated insulin secretion (GSIS) was measured with a square-wave hyperglycemic clamp in the presence or absence of adrenergic receptor antagonists phentolamine (alpha) and propranolol (beta). IUGR fetuses were hypoglycemic and hypoxemic and had lower GSIS responsiveness (P or = 0.05) than control fetuses. IUGR fetuses also had elevated plasma norepinephrine (3,264 +/- 614 vs. 570 +/- 86 pg/ml; P or = 0.05) and epinephrine (164 +/- 32 vs. 60 +/- 12 pg/ml; P or = 0.05) concentrations. In control fetuses, adrenergic inhibition increased baseline plasma insulin concentrations (1.7-fold, P or = 0.05), whereas during hyperglycemia insulin was not different. A greater (P or = 0.05) response to adrenergic inhibition was found in IUGR fetuses, and the average plasma insulin concentrations increased 4.9-fold at baseline and 7.1-fold with hyperglycemia. Unlike controls, basal plasma glucose concentrations fell (P or = 0.05) with adrenergic antagonists. GSIS responsiveness, measured by the change in insulin, was higher (8.9-fold, P or = 0.05) in IUGR fetuses with adrenergic inhibition than controls (1.8-fold, not significant), showing that norepinephrine suppresses insulin secretion in IUGR fetuses. Strikingly, in IUGR fetuses, adrenergic inhibition resulted in a greater GSIS responsiveness, because beta-cell mass was 56% lower and the maximal stimulatory insulin response tended (P 0.1) to be higher than controls. This persistent norepinephrine suppression appears to be partially explained by higher mRNA concentrations of adrenergic receptors alpha(1D), alpha(2A), and alpha(2B) in a cohort of fetuses that were naïve to the antagonists. Therefore, norepinephrine suppression of insulin secretion was maintained, in part, by upregulating adrenergic receptor expression, but the beta-cells also appeared to compensate with enhanced GSIS. These findings may begin to explain why IUGR infants have a propensity for increased glucose requirements if norepinephrine is suddenly decreased after birth.
Rozance, P. J., Limesand, S. W., Barry, J. S., Brown, L. D., & Hay Jr., W. W. (2009). Glucose replacement to euglycemia causes hypoxia, acidosis, and decreased insulin secretion in fetal sheep with intrauterine growth restriction. Pediatric Research, 65(1), 72-78.
PMID: 18704001;PMCID: PMC2678008;Abstract:
Nutritional interventions for intrauterine growth restriction (IUGR) have raised concerns for fetal toxicity, the mechanisms of which are unknown. Most of these attempts did not aim to normalize fetal metabolic conditions. Therefore, we used a model of IUGR to determine whether normalization of fetal hypoglycemia for 2 wks would be tolerated and increase insulin concentrations and pancreatic β-cell mass. IUGR fetuses received either a direct saline infusion (Sal, the control group) or a 30% dextrose infusion (Glu) to normalize glucose concentrations. Neither insulin concentrations (0.11 ± 0.01 Glu vs. 0.10 ± 0.01 ng/mL Sal) nor β-cell mass (65.2 ± 10.3 Glu vs. 74.7 ± 18.4 mg Sal) changed. Glucose stimulated insulin secretion (GSIS) was lower in the Glu group. Glu fetuses became progressively more hypoxic: O 2 content 1.4 ± 0.5 Glu vs. 2.7 ± 0.4 mM Sal, p 0.05. Partial pressure of carbon dioxide (Paco2) (53.6 ± 0.8 Glu vs. 51.6 ± 0.8 Sal, p 0.05) and lactate (7.74 ± 3.82 Glu vs. 2.47 ± 0.55 mM Sal, p 0.0001) were greater and pH lower (7.275 ± 0.071 Glu vs. 7.354 ± 0.003 Sal, p 0.01) in the Glu group. We conclude that correction of fetal hypoglycemia is not well tolerated and fails to increase insulin concentrations or ß-cell mass in IUGR fetuses. Copyright © 2008 International Pediatric Research Foundation, Inc.
Limesand, S. W., Jeckel, K. M., & Anthony, R. V. (2004). Purα, a Single-Stranded Deoxyribonucleic Acid Binding Protein, Augments Placental Lactogen Gene Transcription. Molecular Endocrinology, 18(2), 447-457.
PMID: 14645500;Abstract:
Placental lactogen (PL) is thought to alter maternal metabolism to increase the pool of nutrients available for the fetus and to stimulate fetal nutrient uptake. The ovine (o) PL gene is expressed in chorionic binucleate cells (oBNC) and cis-elements located within the proximal promoter (-124 to +16 bp) are capable of trophoblast-specific expression in human (BeWo) and rat (Rcho-1) choriocarcinoma cells. Protein-DNA interactions were identified with oBNC nuclear extracts, and mutational analysis of these regions revealed a previously undefined cis-element from -102/-123 bp that enhances promoter activity in BeWo cells but not Rcho-1 cells. Characterization of this region identified the nucleotide sequence CCAGCA (-105/ -110; o110) as the responsible cis-acting element. Southwestern analysis with this element identified a binding protein with an apparent Mr of approximately 41,000. Expression screening of an ovine placental cDNA library identified six homologous cDNAs, which shared identity with human (97%) and mouse (95%) Purα, a single-stranded DNA binding protein. The Purα-o110 interaction was confirmed by electrophoretic mobility-supershift assays with oBNC and BeWo extracts but was absent with Rcho-1 extracts. Furthermore, overexpression of ovine Purα enhanced transactivation of the oPL gene proximal promoter in both choriocarcinoma cell lines through this novel cis-element. This study identified a previously undefined cis-element, which interacts with Purα to augment PL gene transcription.
Macko, A. R., Yates, D. T., Chen, X., Shelton, L. A., Kelly, A. C., Davis, M. A., Camacho, L. E., Anderson, M. J., & Limesand, S. W. (2016). Adrenal Demedullation and Oxygen Supplementation Independently Increase Glucose-Stimulated Insulin Concentrations in Fetal Sheep With Intrauterine Growth Restriction. ENDOCRINOLOGY, 157(5), 2104-2115.
Yates, D. T., MacKo, A. R., Nearing, M., Chen, X., Rhoads, R. P., & Limesand, S. W. (2012). Developmental programming in response to intrauterine growth restriction impairs myoblast function and skeletal muscle metabolism. Journal of Pregnancy, 2012.
PMID: 22900186;PMCID: PMC3415084;Abstract:
Fetal adaptations to placental insufficiency alter postnatal metabolic homeostasis in skeletal muscle by reducing glucose oxidation rates, impairing insulin action, and lowering the proportion of oxidative fibers. In animal models of intrauterine growth restriction (IUGR), skeletal muscle fibers have less myonuclei at birth. This means that myoblasts, the sole source for myonuclei accumulation in fibers, are compromised. Fetal hypoglycemia and hypoxemia are complications that result from placental insufficiency. Hypoxemia elevates circulating catecholamines, and chronic hypercatecholaminemia has been shown to reduce fetal muscle development and growth. We have found evidence for adaptations in adrenergic receptor expression profiles in myoblasts and skeletal muscle of IUGR sheep fetuses with placental insufficiency. The relationship of β-adrenergic receptors shifts in IUGR fetuses because Adrβ2 expression levels decline and Adrβ1 expression levels are unaffected in myofibers and increased in myoblasts. This adaptive response would suppress insulin signaling, myoblast incorporation, fiber hypertrophy, and glucose oxidation. Furthermore, this β-adrenergic receptor expression profile persists for at least the first month in IUGR lambs and lowers their fatty acid mobilization. Developmental programming of skeletal muscle adrenergic receptors partially explains metabolic and endocrine differences in IUGR offspring, and the impact on metabolism may result in differential nutrient utilization. © 2012 D. T. Yates et al.
