Ontogeny of insulin-like growth factor 1 in a rabbit model of growth retardation

Ergot alkaloid exposure during gestation alters. I. Maternal characteristics and placental development of pregnant ewes1

Tall fescue [Lolium arundinaceum (Scheyreb.) Darbysh] is the primary cool season forage grass in the Southeastern United States. Most tall fescue contains an endophytic fungus (Epichloë coenophiala) that produces ergot alkaloids and upon ingestion induces fescue toxicosis. The objective of this study was to assess how exposure to endophyte-infected (E+; 1.77 mg hd-1 d-1 ergovaline and ergovalinine) or endophyte-free (E-; 0 mg hd-1 d-1 ergovaline and ergovalinine) tall fescue seed fed during 2 stages of gestation (MID, days 35-85/LATE, days 86-133) alters placental development. Thirty-six, fescue naïve Suffolk ewes were randomly assigned to 1 of 4 fescue treatments: E-/E-, E-/E+, E+/E-, or E+/E+. Ewes were individually fed the same amount of E+ or E- seed mixed into total mixed ration during MID and LATE gestation. Terminal surgeries were conducted on day 133 of gestation. Ewes fed E+ fescue seed had elevated (P < 0.001) ergot alkaloid excretion and reduced (P < 0.001) prolactin levels during the periods when fed E+ seed. Ewes switched on day 86 from E- to E+ seed had a 4% reduction (P = 0.005) in DMI during LATE gestation, which translated to a 2% reduction (P = 0.07) in DMI overall. Average daily gain was also reduced (P = 0.049) by 64% for E-/E+ ewes during LATE gestation and tended to be reduced (P = 0.06) by 33% overall. Ewes fed E+ seed during LATE gestation exhibited a 14% and 23% reduction in uterine (P = 0.03) and placentome (P = 0.004) weights, respectively. Caruncle weights were also reduced by 28% (P = 0.003) for E-/E+ ewes compared with E-/E- and E+/E-. Ewes fed E+ seed during both MID and LATE gestation exhibited a 32% reduction in cotyledon (P = 0.01) weights, whereas ewes fed E+ seed only during MID gestation (E+/E-) had improved (P = 0.01) cotyledon weights. The percentage of type A placentomes tended to be greater (P = 0.08) for E+/E+ ewes compared with other treatments. Other placentome types (B, C, or D) did not differ (P > 0.05). Total fetal weight per ewe was reduced (P = 0.01) for ewes fed E+ seed during LATE gestation compared with E-; however, feeding E+ seed during MID gestation did not alter (P = 0.70) total fetal weight per ewe. These results suggest that exposure to ergot alkaloids during LATE (days 86-133) gestation has the greatest impact on placental development by reducing uterine and placentome weights. This, in turn, reduced total fetal weight per ewe by 15% in ewes fed E+ seed during LATE gestation (E-/E+ and E+/E+).

A short periconceptional exposure to maternal type-1 diabetes is sufficient to disrupt the feto-placental phenotype in a rabbit model

Tight metabolic control of type-1 diabetes is essential during gestation, but it could be crucial during the periconception period. Feto-placental consequences of maternal type-1 diabetes around the time of conception need to be explored. Using a rabbit model, type-1 diabetes was induced by alloxan 7 days before mating. Glycemia was maintained at 15-20 mmol/L with exogenous insulin injections to prevent ketoacidosis. At 4 days post-conception (dpc), embryos were collected from diabetic (D) or normoglycemic control (C) dams, respectively, and transferred into non-diabetic recipients. At 28dpc, D- and C-feto-placental units were collected for biometry, placental analyses and lipid profiles. D-fetuses were growth-retarded, hyperglycemic and dyslipidemic compared to C-fetuses. The efficiency of D-placentas was associated with an increased gene expression related to nutrient supply and lipid metabolism whereas volume density of fetal vessels decreased. Fetal plasma, placental and fetal liver membranes had specific fatty acid signatures depending on embryonic origin. Tissues from D-fetuses contained more omega-6 polyunsaturated fatty acids. The concentrations of docosahexaenoic acid decreased while linoleic acid increased in the heart of D-fetuses. This study demonstrates that a short exposure to maternal type-1 diabetes in the periconception window, until the blastocyst stage, is able to irreversibly malprogram the feto-placental phenotype, through precocious and persistent structural and molecular adaptations of placenta.

Maternal exercise in rats upregulates the placental insulin-like growth factor system with diet- and sex-specific responses: minimal effects in mothers born growth restricted

KEY POINTS

The placental insulin-like growth factor (IGF) system is critical for normal fetoplacental growth, which is dysregulated following several pregnancy perturbations including uteroplacental insufficiency and maternal obesity. We report that the IGF system was altered in placentae of mothers born growth restricted compared to normal birth weight mothers, with maternal diet- and fetal sex-specific responses. Additionally, we report increased body weight and plasma IGF1 concentrations in fetuses from chow-fed normal birth weight mothers that exercised prior to and continued during pregnancy compared to sedentary mothers. Exercise initiated during pregnancy, on the other hand, resulted in placental morphological alterations and increased IGF1 and IGF1R protein expression, which may in part be modulated by reduced Let 7f-1 miRNA abundance. Growth restriction of mothers before birth and exercise differentially regulate the placental IGF system with diet- and sex-specific responses, probably as a means to improve fetoplacental growth and development, and hence neonatal survival. This increased neonatal survival may prevent adult disease onset.

ABSTRACT

The insulin-like growth factor (IGF) system regulates fetoplacental growth and plays a role in disease programming. Dysregulation of the IGF system is implicated in several pregnancy perturbations associated with altered fetal growth, including intrauterine growth restriction and maternal obesity. Limited human studies have demonstrated that maternal exercise enhances fetoplacental growth and decreases cord IGF ligands, which may restore the placental IGF system in complicated pregnancies. This study investigated the impact maternal exercise has on the placental IGF system in placentae from mothers born growth restricted and if these outcomes are dependent on maternal diet or fetal sex. Uteroplacental insufficiency (Restricted) or sham (Control) surgery was induced on embryonic day (E) 18 in Wistar-Kyoto rats. F1 offspring were fed a chow or high-fat diet from weaning, and at 16 weeks were randomly allocated an exercise protocol: Sedentary, Exercised prior to and during pregnancy (Exercise), or Exercised during pregnancy only (PregEx). Females were mated (20 weeks) with placentae associated with F2 fetuses collected at E20. The placental IGF system mRNA abundance and placental morphology was altered in mothers born growth restricted. Exercise increased fetal weight and Control plasma IGF1 concentrations, and decreased female placental weight. PregEx did not influence fetoplacental growth but increased placental IGF1 and IGF1R (potentially modulated by reduced Let 7f-1 miRNA) and decreased placental IGF2 protein. Importantly, these placental IGF system changes occurred with sex-specific responses. These data highlight that exercise differently influences fetoplacental growth and the placental IGF system depending on maternal exercise initiation, which may prevent the transgenerational transmission of deficits and dysfunction.

Validation of serum IGF-I as a biomarker to monitor the bioactivity of exogenous growth hormone agonists and antagonists in rabbits

The development of new growth hormone (GH) agonists and growth hormone antagonists (GHAs) requires animal models for pre-clinical testing. Ideally, the effects of treatment are monitored using the same pharmacodynamic marker that is later used in clinical practice. However, intact rodents are of limited value for this purpose because serum IGF-I, the most sensitive pharmacodynamic marker for the action of GH in humans, shows no response to treatment with recombinant human GH and there is little evidence for the effects of GHAs, except when administered at very high doses or when overexpressed. As an alternative, more suitable model, we explored pharmacodynamic markers of GH action in intact rabbits. We performed the first validation of an IGF-I assay for the analysis of rabbit serum and tested precision, sensitivity, linearity and recovery using an automated human IGF-I assay (IDS-iSYS). Furthermore, IGF-I was measured in rabbits of different strains, age groups and sexes, and we monitored IGF-I response to treatment with recombinant human GH or the GHA Pegvisomant. For a subset of samples, we used LC-MS/MS to measure IGF-I, and quantitative western ligand blot to analyze IGF-binding proteins (IGFBPs). Although recovery of recombinant rabbit IGF-I was only 50% in the human IGF-I assay, our results show that the sensitivity, precision (1.7–3.3% coefficient of variation) and linearity (90.4–105.6%) were excellent in rabbit samples. As expected, sex, age and genetic background were major determinants of IGF-I concentration in rabbits. IGF-I and IGFBP-2 levels increased after single and multiple injections of recombinant human GH (IGF-I: 286±22 versus 434±26 ng/ml; P<0.01) and were highly correlated (P<0.0001). Treatment with the GHA lowered IGF-I levels from the fourth injection onwards (P<0.01). In summary, we demonstrated that the IDS-iSYS IGF-I immunoassay can be used in rabbits. Similar to rodents, rabbits display variations in IGF-I depending on sex, age and genetic background. Unlike in rodents, the IGF-I response to treatment with recombinant human GH or a GHA closely mimics the pharmacodynamics seen in humans, suggesting that rabbits are a suitable new model to test human GH agonists and antagonists.

Placental gene transfer: transgene screening in mice for trophic effects on the placenta

OBJECTIVE

We hypothesized that gene transfer of select growth factors to the placenta may enhance placental and fetal growth. Thus, we examined the effect of 8 growth factor transgenes on murine placenta.

STUDY DESIGN

Adenoviral-mediated site-specific intraplacental gene transfer of 8 different growth factor transgenes at embryonic day (e) 14 was performed. Transgenes included angiopoietin-1, angiopoietin-2 (Ang-2), basic fibroblast growth factor, hepatocyte growth factor, insulin-like growth factor-1 (IGF-1), placenta growth hormone, platelet-derived growth factor-B (PDGF-B), and vascular endothelial growth factor(121). Fetuses and placentas were harvested at e17 and assessed for survival, gene transfer efficiency, placenta area, and fetal and placental weights.

RESULTS

Efficient gene transfer to the placenta was detected with minimal dissemination to the fetus. Overexpression of IGF-1, PDGF-B, and Ang-2 resulted in an increase in placenta cross-sectional area. Only Ang-2 gene transfer resulted in increased fetal weight, and only Ang-2 and basic fibroblast growth factor resulted in a change in placental weight.

CONCLUSION

Site-specific placental gene transfer results in efficient gene transfer with minimal dissemination to the fetus. Adenoviral-mediated IGF-1, adenoviral-mediated PDGF-B, and adenoviral-mediated Ang-2 significantly increase placenta growth.

Beneficial effect of insulin-like growth factor-1 on hypoxemic renal dysfunction in the newborn rabbit

Acute normocapnic hypoxemia can cause functional renal insufficiency by increasing renal vascular resistance (RVR), leading to renal hypoperfusion and decreased glomerular filtration rate (GFR). Insulin-like growth factor 1 (IGF-1) activity is low in fetuses and newborns and further decreases during hypoxia. IGF-1 administration to humans and adult animals induces pre- and postglomerular vasodilation, thereby increasing GFR and renal blood flow (RBF). A potential protective effect of IGF-1 on renal function was evaluated in newborn rabbits with hypoxemia-induced renal insufficiency. Renal function and hemodynamic parameters were assessed in 17 anesthetized and mechanically ventilated newborn rabbits. After hypoxemia stabilization, saline solution (time control) or IGF-1 (1 mg/kg) was given as an intravenous (i.v.) bolus, and renal function was determined for six 30-min periods. Normocapnic hypoxemia significantly increased RVR (+16%), leading to decreased GFR (-14%), RBF (-19%) and diuresis (-12%), with an increased filtration fraction (FF). Saline solution resulted in a worsening of parameters affected by hypoxemia. Contrarily, although mean blood pressure decreased slightly but significantly, IGF-1 prevented a further increase in RVR, with subsequent improvement of GFR, RBF and diuresis. FF indicated relative postglomerular vasodilation. Although hypoxemia-induced acute renal failure was not completely prevented, IGF-1 elicited efferent vasodilation, thereby precluding a further decline in renal function.

Effect of esophageal ligation on small intestinal development in normal and growth-retarded fetal rabbits

OBJECTIVE

The uninterrupted passage of amniotic fluid through the gastrointestinal tract is hypothesized to influence both intestinal and overall fetal somatic development. The effect of in utero esophageal ligation (EL) and therefore the exclusion of AF on somatic growth, small intestinal (SI) morphology and proliferation, and the expression of the glucose transporter sodium-glucose cotransporter 1 (SGLT-1) in both normal and intrauterine growth-retarded (IUGR) fetal rabbits were evaluated.

METHODS

Thirteen pregnant New Zealand white rabbits underwent surgery on day 24 of their normal 31-day gestation. Ipsilateral normal and IUGR fetuses underwent EL; the contralateral normal and IUGR fetuses underwent cervical exploration only forming 4 study groups (control-normal, control-IUGR, EL-normal and EL-IUGR). Rabbits were killed on day 31. Small intestinal villus height was measured, and epithelial cell proliferation was deter mined by proliferating cell nuclear antigen staining. Sodium-glucose cotransporter 1 messenger RNA (mRNA) and protein expressions were analyzed. Statistical analysis was performed using 2-way analysis of variance.

RESULTS

Esophageal ligation reduced fetal weight in IUGR by 15% and in normal by 10%. Villus height was significantly reduced in IUGR versus normal in both control and EL (control, P = 0.01; EL, P = 0.05). Intrauterine growth-retarded fetuses had reduced SI proliferation versus normal in both control and EL. Sodium-glucose cotransporter 1 mRNA production in EL fetuses was equal to control fetuses. Esophageal ligation-normal and EL-IUGR fetuses exhibited reduced protein levels and decreased staining for SGLT-1 in villus enterocytes.

CONCLUSIONS

Amniotic fluid exclusion by in utero EL reduced fetal weight. Small intestinal proliferation was not affected by EL. Although SGLT-1 mRNA and protein were produced in all 4 groups, exposure of the fetal gastrointestinal tract to amniotic fluid appears necessary for proper brush border expression of nutrient transporter proteins.

Effect of epidermal growth factor on small intestinal sodium/glucose cotransporter-1 expression in a rabbit model of intrauterine growth retardation

INTRODUCTION

Intrauterine growth-retarded (IUGR) infants have impaired gastrointestinal function with feeding difficulties and predisposition to necrotizing enterocolitis. The rabbit provides a model of IUGR based on uterine position. Sodium/glucose cotransporter-1 (SGLT-1) is a membrane protein responsible for carbohydrate transport across the intestinal brush border membrane. Previous studies demonstrate increases in small intestinal (SI) nutrient uptake in response to amniotic fluid supplementation with epidermal growth factor (EGF). To determine whether SGLT-1 expression plays a role in the intestinal response to EGF supplementation, this IUGR rabbit model was evaluated.

METHODS

Eight pregnant rabbits underwent placement of intraamniotic catheters into 2 normal (Nl) and 2 IUGR fetuses per mother on gestational day 24. Mini-osmotic pumps infused either EGF (300 microg/kg per day) or control solution forming 4 study groups (EGF-Nl vs Cont-Nl; EGF-IUGR vs Cont-IUGR). On gestational day 31, the fetal SI was harvested. Sodium/glucose cotransporter-1/glyceraldehyde-3-phosphate dehydrogenase messenger RNA (mRNA) densitometric band ratios were measured by reverse transcriptase polymerase chain reaction. Immunohistochemistry SGLT-1 staining was performed on middle SI. Statistical analysis was performed using the analysis of variance.

RESULTS

Sodium/glucose cotransporter-1 was expressed in the gastrointestinal tract throughout the last one third of gestation. There were no native differences in SGLT-1 mRNA expression between Nl and IUGR fetuses at term. Epidermal growth factor infusion did not significantly affect SI SGLT-1 mRNA expression in either Nl or IUGR fetuses vs controls (EGF-Nl = 1.94 vs Cont-Nl = 1.94, P = .98; EGF-IUGR = 1.77 vs Cont-IUGR = 1.85, P = .74). Immunohistochemistry revealed increased SGLT-1 SI protein expression in infused IUGR fetuses.

CONCLUSIONS

Increases in previously documented up-regulation in SI nutrient transport after EGF infusion are independent of SGLT-1 mRNA expression. Further studies are warranted investigating SGLT-1 protein expression, localization, and functional kinetics in response to amniotic fluid supplementation with EGF.

Effect of epidermal growth factor infusion on fetal rabbit intrauterine growth retardation and small intestinal development

BACKGROUND/PURPOSE

Intrauterine growth retardation (IUGR) infants have impaired gastrointestinal function with resultant feeding difficulties and predisposition to necrotizing enterocolitis. Supplemented amniotic fluid swallowed by the developing fetus is a potential prenatal treatment for IUGR. Rabbits have naturally occurring IUGR fetuses based on uterine position. To determine intestinal response to epidermal growth factor (EGF) infusion, this rabbit model of IUGR was studied.

METHODS

Eight pregnant rabbits underwent placement of intraamniotic catheters into 2 normal and 2 IUGR fetuses per mother on gestational day 24 of a 31-day gestation. Miniosmotic pumps infused either EGF (about 300 microg/kg/d) or control solution forming 4 study groups (EGF-Favored [Fav] v. Cont-Fav; EGF-IUGR v. Cont-IUGR). On gestational day 31, the fetal gastrointestinal tracts were harvested for analysis. Intestinal epithelial cell proliferation was studied by 5-bromo-2-deoxyuridine (BrdU) incorporation, villus heights were measured, and EGF mRNA was measured by reverse transcriptase polymerase chain reaction (RT-PCR). Statistical analysis was performed using Students' t test.

RESULTS

Fetal survival rate was 87%. EGF-IUGR fetal weights were increased compared with Cont-IUGR fetuses. EGF infusion significantly increased IUGR fetal small intestinal villus height and BrdU-positive small intestinal (SI) crypt cells, all approaching Cont-Fav levels. EGF mRNA was expressed throughout the gastrointestinal tract.

CONCLUSIONS

Supplemental amniotic EGF normalizes fetal weight and intestinal proliferation in the IUGR fetal rabbit. The inclusion of EGF in supplemental amniotic feeding solutions is supported.

Fetal therapy with rhIGF-1 in a rabbit model of intrauterine growth retardation

BACKGROUND

Intrauterine growth retardation (IUGR) may, in part, be due to a deficiency of insulin-like growth factor-1 (IGF-1). The objectives of this study were to determine the relationship between fetal serum IGF-1 levels and fetal and placental size in a rabbit model of IUGR and to compare two techniques of selective, exogenous IGF-1 administration (transamniotic and branch uterine arterial catheter infusion) to growth-retarded fetuses in utero.

MATERIALS AND METHODS

Pregnant rabbits (n = 6) had their fetuses harvested near term (31 days) for fetal and placental weighing and serum collection. Growth-retarded fetuses were selectively infused for 7 days with recombinant human IGF-1 (rhIGF-1; 1,440 ng/day) either through a transamniotic catheter (n = 8) or via an adjacent uterine arterial branch catheter (n = 6). Opposite horn runts were sham catheterized, but not infused. At term, the fetal runt pairs and their placentas were harvested and weighed, and their serum was collected. The correlation between fetal and placental weight and endogenous serum IGF-1 was calculated (Pearson coefficient, r), while paired t-tests were used to compare the means between the IGF-1-infused and control groups.

RESULTS

There was a significant correlation between fetal (r = 0.4230; P = 0.022) and placental weight (r = 0.4166; P = 0.025) and endogenous serum levels of IGF-1. Transamniotic infusion of rhIGF-1 was associated with an increase in serum IGF-1 level (254 +/- 79 vs 351 +/- 101 ng/ml, P = 0.04) and placental weight (5.4 +/- 2.3 vs 7.1 +/- 3.2 g, P = 0.005), and with a trend toward increased fetal weight between matched fetal runt pairs. Fetal mortality in the uterine arterial catheterized group was 76%, and there was no significant difference in fetal or placental weight or IGF-1 levels between infused and noninfused survivors.

CONCLUSIONS

Endogenous fetal serum levels correlate with fetal and placental size in the rabbit IUGR model. Transamniotic administration of rhIGF-1 significantly increases serum IGF-1 levels and placental weight of fetal runts, while uterine vessel catheterization results in prohibitive fetal mortality and does not increase fetal or placental growth or IGF-1 levels.