Adrenocortical responsiveness is blunted in twin relative to singleton ovine fetuses

MitoQ as an antenatal antioxidant treatment improves markers of lung maturation in healthy and hypoxic pregnancy

Chronic fetal hypoxaemia is a common pregnancy complication that increases the risk of infants experiencing respiratory complications at birth. In turn, chronic fetal hypoxaemia promotes oxidative stress, and maternal antioxidant therapy in animal models of hypoxic pregnancy has proven to be protective with regards to fetal growth and cardiovascular development. However, whether antenatal antioxidant therapy confers any benefit on lung development in complicated pregnancies has not yet been investigated. Here, we tested the hypothesis that maternal antenatal treatment with MitoQ will protect the developing lung in hypoxic pregnancy in sheep, a species with similar fetal lung developmental milestones as humans. Maternal treatment with MitoQ during late gestation promoted fetal pulmonary surfactant maturation and an increase in the expression of lung mitochondrial complexes III and V independent of oxygenation. Maternal treatment with MitoQ in hypoxic pregnancy also increased the expression of genes regulating liquid reabsorption in the fetal lung. These data support the hypothesis tested and suggest that MitoQ as an antenatal targeted antioxidant treatment may improve lung maturation in the late gestation fetus. KEY POINTS: Chronic fetal hypoxaemia promotes oxidative stress, and maternal antioxidant therapy in hypoxic pregnancy has proven to be protective with regards to fetal growth and cardiovascular development. MitoQ is a targeted antioxidant that uses the cell and the mitochondrial membrane potential to accumulate within the mitochondria. Treatment of healthy or hypoxic pregnancy with MitoQ, increases the expression of key molecules involved in surfactant maturation, lung liquid reabsorption and in mitochondrial proteins driving ATP synthesis in the fetal sheep lung. There were no detrimental effects of MitoQ treatment alone on the molecular components measured in the present study, suggesting that maternal antioxidant treatment has no effect on other components of normal maturation of the surfactant system.

Predictors of a non-response to prophylactic indomethacin for patent ductus arteriosus in preterm infants

BACKGROUND

Preterm infants are recommended for prophylactic indomethacin (PIND) to promote closure of patent ductus arteriosus (PDA) and reduce morbidity and mortality. This study investigated the predictive factors of a non-response to PIND for PDA in preterm-birth infants.

METHODS

Consecutive preterm-birth infants (gestational age: < 28 weeks) who received PIND between 2009 and 2019 were retrospectively enrolled. Seventy-six eligible participants were classified as PIND responders (N = 42) or non-responders (N = 34). Information on potential confounders in maternal obstetric and perinatal data were collected from medical records. Multiple logistic regression analysis was carried out to identify the prognostic factors of a PIND response in preterm-birth infants.

RESULTS

The prevalence of intrauterine infection and multiple births was significantly different between responders and non-responders to PIND (intrauterine infection: 2 [4.8%] vs. 8 [23.5%], P = 0.036; twins: 3 [7.1%] vs. 9 [ 26.5%], P = 0.029, respectively). In multivariate logistic regression analysis after adjustment for multiple births, intrauterine infection was a significant and independent predictive factor of a non-response to PIND (odds ratio [OR] 5.54, 95% confidence interval [CI] 1.05-29.2, P = 0.044). A remarkable association was also noted for multiple births with a non-response to PIND (OR 4.22, 95% CI 0.99-17.8, P = 0.050).

CONCLUSIONS

Intrauterine infection and multiple births were identified as potential risk factors of a non-response to PIND for PDA in preterm infants.

Metabolic Consequences of Glucocorticoid Exposure before Birth

Glucocorticoids have an important role in development of the metabolic phenotype in utero. They act as environmental and maturational signals in adapting feto-placental metabolism to maximize the chances of survival both before and at birth. They influence placental nutrient handling and fetal metabolic processes to support fetal growth, fuel storage and energy production with respect to nutrient availability. More specifically, they regulate the transport, utilization and production of a range of nutrients by the feto-placental tissues that enables greater metabolic flexibility in utero while minimizing any further drain on maternal resources during periods of stress. Near term, the natural rise in fetal glucocorticoid concentrations also stimulates key metabolic adaptations that prepare tissues for the new energy demanding functions after birth. Glucocorticoids, therefore, have a central role in the metabolic communication between the mother, placenta and fetus that optimizes offspring metabolic phenotype for survival to reproductive age. This review discusses the effects of maternal and fetal glucocorticoids on the supply and utilization of nutrients by the feto-placental tissues with particular emphasis on studies using quantitative methods to assess metabolism in rodents and sheep in vivo during late pregnancy. It considers the routes of glucocorticoid overexposure in utero, including experimental administration of synthetic glucocorticoids, and the mechanisms by which these hormones control feto-placental metabolism at the molecular, cellular and systems levels. It also briefly examines the consequences of intrauterine glucocorticoid overexposure for postnatal metabolic health and the generational inheritance of metabolic phenotype.

Developmental outcomes in small-for-gestational age twins using a singleton vs twin birthweight reference in Upstate KIDS

BACKGROUND

Limited data exist about the potential developmental delays in appropriately grown twins; furthermore, twins may be at higher risk of developmental delay than singletons. Small-for-gestational age is a risk factor for developmental delay and is based on singleton birthweight references, which may misclassify small-for-gestational age in a subset of appropriately grown twins.

OBJECTIVE

This study aimed to evaluate the risk of developmental delay in twins classified as small-for-gestational age according to the twin and singleton birthweight references (<10th percentile).

STUDY DESIGN

In a birth cohort (2008-2010) of twins (n=1790) and singletons (n=3829) where parents completed Ages & Stages Questionnaires for child development between 4 and 36 months, we used a US population-based birthweight reference to categorize singletons and twins as small-for-gestational age. Uncertain small-for-gestational age twins were defined as small-for-gestational age by a singleton reference (<10th percentile) and not by a twin reference, and twin-reference small-for-gestational age twins were defined as small-for-gestational age by a twin reference. Adjusted generalized linear mixed-effects models were used to estimate the odds of failure on any Ages & Stages Questionnaires domain and on each of the 5 domains (fine motor, gross motor, communication, personal-social, and problem-solving domains); random intercepts accounted for repeated measures and twin clustering.

RESULTS

Compared with non-small-for-gestational age twins (>10th percentile), uncertain small-for-gestational age twins did not have higher odds of Ages & Stages Questionnaires failure (adjusted odds ratio, 1.28; 95% confidence interval, 0.91-1.80). Compared with non-small-for-gestational age singletons, both twin-reference and uncertain small-for-gestational age twins had higher odds of Ages & Stages Questionnaires failure, with the highest risk conferred to twin-reference small-for-gestational age twins (twin-reference adjusted odds ratio, 3.14 [95% confidence interval, 1.94-5.10]; uncertain adjusted odds ratio, 2.35 [95% confidence interval, 1.69-3.26]; P<.01 for trend). Results remained consistent when limiting analyses to term births (≥37 weeks' gestation).

CONCLUSION

Although a singleton reference may overestimate small-for-gestational age in twins, the findings indicated that a singleton birthweight reference may be appropriate for twins because it identifies more twins at risk of developmental delay than a twin reference.

Attenuation of ductus arteriosus intimal thickening in preterm sheep twins compared with singletons

Preterm twins have a higher morbidity rate of patent ductus arteriosus (PDA) than do singletons. However, the effect of multiple births on maturation of the ductus arteriosus (DA) has not been reported. Because intimal thickening (IT) is required for DA anatomical closure, we examined IT development in the DA of preterm twins and singletons. Sheep DA tissues obtained from preterm fetuses were subjected to elastica van Gieson staining to evaluate IT. The total IT score in each DA was the sum of the IT scores obtained from six evenly divided parts of the DA, which was positively correlated with gestational ages in singletons. Total IT scores were smaller in preterm twins than in singletons, although no difference in gestational age, birth weight, or gender ratio was observed. These data suggest that IT development of the DA is attenuated in sheep preterm twins, which may affect the higher morbidity of PDA.

Transcriptomics Modeling of the Late-Gestation Fetal Pituitary Response to Transient Hypoxia

Background

The late-gestation fetal sheep responds to hypoxia with physiological, neuroendocrine, and cellular responses that aid in fetal survival. The response of the fetus to hypoxia represents a coordinated effort to maximize oxygen transfer from the mother and minimize wasteful oxygen consumption by the fetus. While there have been many studies aimed at investigating the coordinated physiological and endocrine responses to hypoxia, and while immunohistochemical or in situ hybridization studies have revealed pathways supporting the endocrine function of the pituitary, there is little known about the coordinated cellular response of the pituitary to the hypoxia.

Results

Thirty min hypoxia (from 17.0±1.7 to 8.0±0.8 mm Hg, followed by 30 min normoxia) upregulated 595 and downregulated 790 genes in fetal pituitary (123–132 days’ gestation; term = 147 days). Network inference of up- and down- regulated genes revealed a high degree of functional relatedness amongst the gene sets. Gene ontology analysis revealed upregulation of cellular metabolic processes (e.g., RNA synthesis, response to estrogens) and downregulation of protein phosphorylation, protein metabolism, and mitosis. Genes found to be at the center of the network of upregulated genes included genes important for purine binding and signaling. At the center of the downregulated network were genes involved in mRNA processing, DNA repair, sumoylation, and vesicular trafficking. Transcription factor analysis revealed that both up- and down-regulated gene sets are enriched for control by several transcription factors (e.g., SP1, MAZ, LEF1, NRF1, ELK1, NFAT, E12, PAX4) but not for HIF-1, which is known to be an important controller of genomic responses to hypoxia.

Conclusions

The multiple analytical approaches used in this study suggests that the acute response to 30 min of transient hypoxia in the late-gestation fetus results in reduced cellular metabolism and a pattern of gene expression that is consistent with cellular oxygen and ATP starvation. In this early time point, we see a vigorous gene response. But, like the hypothalamus, the transcriptomic response is not consistent with mediation by HIF-1. If HIF-1 is a significant controller of gene expression in the fetal pituitary after hypoxia, it must be at a later time.

Fetal endocrine and metabolic adaptations to hypoxia: the role of the hypothalamic-pituitary-adrenal axis

In utero, hypoxia is a significant yet common stress that perturbs homeostasis and can occur due to preeclampsia, preterm labor, maternal smoking, heart or lung disease, obesity, and high altitude. The fetus has the extraordinary capacity to respond to stress during development. This is mediated in part by the hypothalamic-pituitary-adrenal (HPA) axis and more recently explored changes in perirenal adipose tissue (PAT) in response to hypoxia. Obvious ethical considerations limit studies of the human fetus, and fetal studies in the rodent model are limited due to size considerations and major differences in developmental landmarks. The sheep is a common model that has been used extensively to study the effects of both acute and chronic hypoxia on fetal development. In response to high-altitude-induced, moderate long-term hypoxia (LTH), both the HPA axis and PAT adapt to preserve normal fetal growth and development while allowing for responses to acute stress. Although these adaptations appear beneficial during fetal development, they may become deleterious postnatally and into adulthood. The goal of this review is to examine the role of the HPA axis in the convergence of endocrine and metabolic adaptive responses to hypoxia in the fetus.

Effect of periconceptional nutrition on the growth, behaviour and survival of the neonatal lamb

Periconceptional nutrition (PCN) can influence foetal hypothalamo-pituitary adrenal (HPA) axis function and alter cortisol secretion with possible consequences for maturation and growth of major organs, gestation length and behaviour. We examined effects of PCN on phenotype and survival of the neonatal lamb in 466 Merino ewes allocated to treatments providing 70%, 100% and 150% respectively, of maintenance requirements for 17 days prior and 6 days after insemination. Gestation length and birth weight for lambs in PCN treatment groups was similar (P > 0.05) but low PCN decreased the size of the neonate (crown-rump-length and metacarpal length P < 0.05). A subset of lambs euthanased at 5 days of age further showed that low PCN decreased the amount of peri-renal fat (P < 0.05) and increased liver mass (P < 0.05) while high PCN increased neck thymus and ovary mass (P < 0.05). Neonatal lambs from low PCN ewes returned faster to their mothers after release (P < 0.05) and contacted the udder in the shortest time (P < 0.05). Significant interactions between PCN treatment and sex (P < 0.05) and between PCN treatment and ewe age (P < 0.05) were also observed for time lambs took to follow the ewe. Survival of lambs was similar but potential differences may have been masked by favourable weather conditions. In conclusion, this study provides evidence of significant changes in lamb growth and development dependent on PCN and, for the first time, links these changes with significant changes in behaviour of the neonate. The impact of these effects on lamb survival and potential reproductive capacity of female offspring remains to be determined.

Impact of size at birth and prematurity on adult anthropometry in 4744 middle-aged Danes - The Inter99 study

Low birth weight is related to increased risk of developing cardiovascular disease and type 2 diabetes in adult life. Since obesity is closely associated with type 2 diabetes and cardiovascular disease, the relationship between size at birth and adult anthropometry is of interest as a mediator of the relationship between birth weight and metabolic diseases. The aim of this study was, therefore, to examine the effect of size at birth and prematurity on measures of adult anthropometry taking adult socio-economic status and lifestyle variables into account. Midwife records with information on mother's age and parity as well as weight, length and maturity at birth were traced in 4744 Danes born between 1939 and 1970. Measures of adult anthropometry (weight, height, body mass index (BMI), waist circumference, hip circumference and waist/hip ratio) had previously been recorded together with information on socio-economic factors, lifestyle and parental diabetes status. Mother's age, parity and diabetes status were associated with offspring birth weight. Size at birth was positively associated with adult height and weight, but only weakly associated with BMI and not associated with waist/hip ratio when adjusted for socio-economic and lifestyle factors. Infants born preterm were less growth restricted at birth and grew to be taller and heavier compared with term infants born small for gestational age. Altogether, this study does not find evidence that obesity or a central fat distribution is mediating the relationship between low birth weight and risk of cardiovascular disease or type 2 diabetes in later life.

Embryo number and periconceptional undernutrition in the sheep have differential effects on adrenal epigenotype, growth, and development

Exposure to poor maternal nutrition around the time of conception results in an early prepartum activation of the fetal pituitary-adrenal axis and in increased adrenal growth and stress response after birth associated with epigenetic changes in a differentially methylated region (DMR) of adrenal IGF2/H19. We have determined the effects of maternal undernutrition during the periconceptional period (PCUN: 70% of control intake from 60 days before until 6 days after conception) and early preimplantation period (PIUN: 70% of control intake for 6 days after conception) on fetal plasma ACTH and cortisol concentrations and fetal adrenal ACTHR, StAR, 3βHSD, CYP11B, CYP17, TGFβ1, IGF1, IGF1R, IGF2, and IGF2R mRNA expression and the methylation level of sites within the DMRs of IGF2/H19 and IGF2R in the adrenal of twin and singleton fetuses at 136-138 days gestation. Being a twin resulted in a delayed prepartum increase in fetal ACTH and in a lower cortisol response to CRH in the control but not PCUN and PIUN groups. PCUN, but not PIUN, resulted in an increase in adrenal weight and CYP17 expression in singletons, a decrease in adrenal IGF2 expression in singletons, and an increase in adrenal IGF2R expression in both twins and singletons. IGF2/H19 and IGF2R DMR methylation levels and ACTHR expression were lower in the twin adrenal. Thus, exposure of the oocyte and embryo to maternal undernutrition or to the environment of a twin pregnancy have differential effects on epigenetic and other factors that regulate fetal adrenal growth and IGF2 and IGF2R expression.

Maternal undernutrition during the first week after conception results in decreased expression of glucocorticoid receptor mRNA in the absence of GR exon 17 hypermethylation in the fetal pituitary in late gestation

Exposure to maternal undernutrition during the periconceptional period results in an earlier prepartum activation of the fetal hypothalamo–pituitary–adrenal (HPA) axis and altered stress responsiveness in the offspring. It is not known whether such changes are a consequence of exposure of the oocyte and/or the early embryo to maternal undernutrition in the periconceptional period. We have compared the effects of ‘periconceptional’ undernutrition (PCUN: maternal undernutrition imposed from at least 45 days before until 6 days after conception), and ‘early preimplantation’ undernutrition (PIUN: maternal undernutrition imposed for only 6 days after conception) on the expression of genes in the fetal anterior pituitary that regulate adrenal growth and steroidogenesis, proopiomelanorcortin (POMC), prohormone convertase 1 (PC1), 11β-hydroxysteroid dehydrogenase type 1 and 2 (11βHSD1 and 2) and the glucocorticoid receptor (GR) in fetal sheep at 136–138 days of gestation. Pituitary GR mRNA expression was significantly lower in the PCUN and PIUN groups in both singletons and twins compared with controls, although this suppression of GR expression was not associated with hypermethylation of the exon 17 region of the GR gene. In twin fetuses, the pituitary 11βHSD1 mRNA expression was significantly higher in the PIUN group compared with the PCUN but not the control group. Thus, exposure of the single or twin embryo to maternal undernutrition for only 1 week after conception is sufficient to cause a suppression of the pituitary GR expression in late gestation. These changes may contribute to the increased stress responsiveness of the HPA axis in the offspring after exposure to poor nutrition during the periconceptional period.

Hypoxaemia-induced catecholamine secretion from adrenal chromaffin cells inhibits glucose-stimulated hyperinsulinaemia in fetal sheep

Abstract  Hypoxaemia elicits adrenergic suppression of fetal glucose-stimulated hyperinsulinaemia. We postulate that this effect is mediated by catecholamines, exclusively, from fetal adrenal chromaffin cells. To investigate this hypothesis, square-wave hyperglycaemic clamp studies were performed under normoxaemic (26 ± 0.9 mmHg) and hypoxaemic (14 ± 0.3 mmHg) steady-state conditions in near-term fetal sheep that had undergone either surgical sham or bilateral adrenal demedullation (AD), values mentioned are ± SEM. Under normoxaemic conditions plasma noradrenaline concentrations were lower in AD fetuses than in sham-operated fetuses (457 ± 122 versus 1073 ± 103 pg ml(-1), P < 0.05). Plasma insulin concentrations were not different at euglycaemia between shams (0.46 ± 0.07 ng ml(-1)) and AD fetuses (0.44 ± 0.04 ng ml(-1)) and increased (P < 0.05) with hyperglycaemia in both groups although to a lesser extent in AD fetuses (0.94 ± 0.19 ng ml(-1)) compared to shams (1.31 ± 0.15 ng ml(-1); P < 0.05). Hypoxaemia increased plasma adrenaline (26-fold) and noradrenaline (5-fold) in shams but elicited no change in AD fetuses. Under hypoxaemic conditions, euglycaemic plasma insulin concentrations were reduced (P < 0.05) in both sham and AD fetuses to 0.30 ± 0.05 ng ml(-1) and 0.27 ± 0.01 ng ml(-1) respectively, and the insulin response to hyperglycaemia was abolished in shams but not affected in AD fetuses (0.33 ± 0.06 versus 0.73 ± 0.02 ng ml(-1), P < 0.05). Hypoxaemia also induced hyperlactacaemia and hypocarbia to a greater extent in shams than in AD fetuses, indicating that catecholamines potentiate reductions in oxidative metabolism independently of insulin. These findings demonstrate that the fetal adrenal chromaffin cells are the source for acute hypoxaemia-induced elevations in fetal plasma catecholamines and suppression of glucose-stimulated hyperinsulinaemia, but other factors reduce plasma insulin at euglycaemia.

Insulin deficiency alters the metabolic and endocrine responses to undernutrition in fetal sheep near term

Insulin deficiency affects the adult metabolic response to undernutrition, but its effects on the fetal response to maternal undernutrition remain unknown. This study examined the effects of maternal fasting for 48 h in late gestation on the metabolism of fetal sheep made insulin deficient by pancreatectomy (PX). The endocrine and metabolic responses to maternal fasting differed between intact, sham-operated and PX fetuses, despite a similar degree of hypoglycemia. Compared with intact fetuses, there was no increase in the plasma concentrations of cortisol or norepinephrine in PX fetuses during maternal fasting. In contrast, there was a significant fasting-induced rise in plasma epinephrine concentrations in PX but not intact fetuses. Umbilical glucose uptake decreased to a similar extent in both groups of fasted animals but was associated with a significant fall in glucose carbon oxidation only in intact fetuses. Pancreatectomized but not intact fetuses lowered their oxygen consumption rate by 15-20% during maternal fasting in association with increased uteroplacental oxygen consumption. Distribution of uterine oxygen uptake between the uteroplacental and fetal tissues therefore differed with fasting only in PX fetuses. Both groups of fetuses produced glucose endogenously after maternal fasting for 48 h, which prevented any significant fall in the rate of fetal glucose utilization. In intact but not PX fetuses, fasting-induced glucogenesis was accompanied by a lower hepatic glycogen content. Chronic insulin deficiency in fetal sheep therefore leads to changes in the counterregulatory endocrine response to hypoglycemia and an altered metabolic strategy in dealing with nutrient restriction in utero.

Periconceptional events perturb postnatal growth regulation in sheep

Periconceptional undernutrition and twin conception alter intrauterine growth and metabolism and are associated with later adverse metabolic outcomes. The contribution of postnatal growth to these outcomes is less well defined. We investigated whether maternal periconceptional undernutrition or twin conception altered postnatal growth regulation in ways that could lead to metabolic disease. Single and twin offspring of ewes undernourished (UN) from 61 d before until 30 d after mating, fed to achieve and maintain 10-15% weight loss (UN), were compared with offspring of maintenance-fed controls (N). At 2 h and 1, 6, and 12 wk after birth, lambs were weighed and plasma hormone and metabolite concentrations analyzed. Milk intake, measured by deuterium oxide dilution, was inversely related to birth weight only in N singles, although twins had the greatest postnatal growth velocity. Positive associations were seen between milk intake, growth velocity, and leptin concentrations in N, but not UN, offspring. We conclude that periconceptional undernutrition alters the relationships between regulators of postnatal growth, including nutrient intake and key hormonal axes, in both singles and twins without affecting size at birth or postnatal growth velocity. Dissociation of growth from its key regulators is one possible mechanism underlying adverse metabolic outcomes after periconceptional undernutrition.

Are twins growth restricted?

It is now well established that IUGR is associated with an increased risk of a range of adult onset diseases, including cardiovascular disease, obesity, and type 2 diabetes. Infants from twin pregnancies are generally born smaller than singletons; therefore, it has been suggested that twins represent a naturally occurring model of IUGR. Although twin gestations contribute significantly to the population burden of preterm birth and small size at birth, whether twins have the same long-term health consequences as IUGR singletons remains unclear. The purpose of this review is to consider what is currently known about the clinical implications of twinning, the differences that exist between the growth and developmental profiles of singleton and twin fetuses, and to use this as a basis for exploring the question of whether fetuses conceived as twins are analogous to IUGR singletons of similar birthweight and gestation. This question is increasingly important in both the clinical and research settings, because the incidence of twinning is increasing and the long-term implications of reduced size at birth are mostly investigated in species which bear multiple offspring.

Characterization of glucose-insulin responsiveness and impact of fetal number and sex difference on insulin response in the sheep fetus

GSIS is often measured in the sheep fetus by a square-wave hyperglycemic clamp, but maximal β-cell responsiveness and effects of fetal number and sex difference have not been fully evaluated. We determined the dose-response curve for GSIS in fetal sheep (0.9 of gestation) by increasing plasma glucose from euglycemia in a stepwise fashion. The glucose-insulin response was best fit by curvilinear third-order polynomial equations for singletons (y = 0.018x(3) - 0.26x(2) + 1.2x - 0.64) and twins (y = -0.012x(3) + 0.043x(2) + 0.40x - 0.16). In singles, maximal insulin secretion was achieved at 3.4 ± 0.2 mmol/l glucose but began to plateau after 2.4 ± 0.2 mmol/l glucose (90% of maximum), whereas the maximum for twins was reached at 4.8 ± 0.4 mmol/l glucose. In twin (n = 18) and singleton (n = 49) fetuses, GSIS was determined with a square-wave hyperglycemic clamp >2.4 mmol/l glucose. Twins had a lower basal glucose concentration, and plasma insulin concentrations were 59 (P < 0.01) and 43% (P < 0.05) lower in twins than singletons during the euglycemic and hyperglycemic periods, respectively. The basal glucose/insulin ratio was approximately doubled in twins vs. singles (P < 0.001), indicating greater insulin sensitivity. In a separate cohort of fetuses, twins (n = 8) had lower body weight (P < 0.05) and β-cell mass (P < 0.01) than singleton fetuses (n = 7) as a result of smaller pancreata (P < 0.01) and a positive correlation (P < 0.05) between insulin immunopositive area and fetal weight (P < 0.05). No effects of sex difference on GSIS or β-cell mass were observed. These findings indicate that insulin secretion is less responsive to physiological glucose concentrations in twins, due in part to less β-cell mass.

Influence of gestational diabetes mellitus on weight discrepancy in twin pregnancies

OBJECTIVE

To evaluate the influence of gestational diabetes mellitus on weight discrepancy in twin pregnancies.

METHODS

200 twin pregnancies were included in the study. 157 nondiabetic pregnant women with twin gestations and 43 twin pregnancies with gestational diabetes mellitus (GDM) with viable fetuses born after 24 weeks of gestation were enrolled. Influence of maternal age, body-mass-index at the time of the oral glucose tolerance test, parity, smoking, chorionicity, gestational age at delivery and diagnosis of GDM on weight discrepancy of the twins was evaluated.

RESULTS

Mean weight discrepancy of all analyzed twin pregnancies was 285 grams (+/- 231), relative weight discrepancy was 11.3% (+/- 8.6). Univariate regression analyses showed that GDM, chorionicity and gestational age at delivery were significantly associated with weight discrepancy. In the multivariate model only diagnosis of GDM was significantly associated with weight discrepancy.

CONCLUSION

Twin pregnancies with insulin requiring gestational diabetes seem to have less birth weight discrepancy than twin pregnancies with normal glucose tolerance.

Sex differences in the ovine fetal cortisol response to stress

This study tested the hypothesis that the sexually dimorphic adrenocortical response to stress is already established before birth. Chronically instrumented late gestation pregnant sheep carrying 16 male and 15 female age-matched singleton fetuses were subjected to an acute episode of hypoxic stress. Maternal and fetal blood gases, adrenocorticotrophic hormone (ACTH), and cortisol were measured. In addition, six male and six female fetuses received the ACTH analog, Synacthen, and plasma cortisol was measured. During hypoxic stress, the increment in plasma cortisol was 2-fold greater in male versus females fetuses (30.6 ± 3.2 versus 14.3 ± 2.0 ng/mL; p < 0.001) mediated, in part, by greater adrenocortical sensitivity to ACTH. The data support the hypothesis tested and show that sex-specific differences in the cortisol stress response are present before birth with the output of cortisol being much greater in male than in female fetuses.

Relationship between litter birthweight and litter size in five goat genotypes

The aim of the present study was to use a non-linear regression approach to investigate the relationship between litter birthweight and litter size of five breeds of goat under intensive conditions in a hot arid environment. Litter-size and litter-weight data on 20 117 kids from 13 685 litters representing five breeds, namely Saanen, Toggenburg, French Alpine, Anglo-Nubian and Granadina, were compared to evaluate this relationship. Regardless of breed, birthweight for kids born as twins, triplets and quadruplets was, on average, 92%, 87% and 83%, respectively, of that of singleton kids; litter size accounted for 81% of the variation in litter weight. The coefficient of the power regression differed (P < 0.01) among breeds, with similar slopes for French Alpine, Toggenburg and Saanen goats and a smaller litter-weight increase for every additional fetus in Anglo-Nubian and Granadina goats than in other breeds of goat. These results support the hypothesis that, regardless of parity, litter weight in dairy and Granadina goats increases at a reduced rate with increases in litter size, although the rate of change with the increasing number of fetuses was moderate, as indicated by a power regression of the form y = axb between these variables across age categories and breeds of goat.

Influence of estradiol and fetal stress on luteinizing hormone, follicle-stimulating hormone, and prolactin in late-gestation fetal sheep

BACKGROUND

Hypotension and reduced cerebral blood flow secondary to brachiocephalic occlusion (BCO) stimulate various homeostatic physiological and endocrine responses. Our previous studies have also suggested a role of estradiol in augmenting the fetal stress response to BCO.

OBJECTIVES

We tested the hypothesis that gonadotropins and/or prolactin (PRL) are upregulated in fetal pituitary in response to fetal stress and play a role in the response to BCO-induced stress.

METHODS

We performed 3 studies: one in which we measured ovine fetal pituitary PRL, luteinizing hormone (LH), and follicle-stimulating hormone (FSH) mRNA throughout the latter half of gestation in order to better understand the ontogenetic changes upon which dynamic responses are superimposed; one in which we measured these mRNA abundances in response to BCO and/or estrogen treatment, and one in which we measured plasma LH responses to BCO in chronically catheterized late-gestation fetal sheep.

RESULTS

PRL gene expression is increased dramatically in the last 20% of gestation. LH and FSH mRNAs were unchanged except for a transient dip in the expression of LH in the last few days before the normal time of spontaneous parturition. Chronic treatment with estradiol decreased LH and FSH mRNA, but increased PRL mRNA abundance after BCO. In contrast, BCO alone increases the abundance of LH, but not FSH or PRL mRNA in fetal pituitary. Plasma LH concentrations were not increased in response to BCO.

CONCLUSIONS

We conclude that the late-gestation fetal sheep responds to hypotensive stress with increases in LH mRNA but not LH secretion. LH, FSH and PRL changes are therefore unlikely to contribute to the fetal response to cerebral hypoperfusion.

Sex- and age-specific effects of nutrition in early gestation and early postnatal life on hypothalamo-pituitary-adrenal axis and sympathoadrenal function in adult sheep

The early-life environment affects risk of later metabolic disease, including glucose intolerance, insulin resistance and obesity. Changes in hypothalamo-pituitary-adrenal (HPA) axis and sympathoadrenal function may underlie these disorders. To determine consequences of undernutrition in early gestation and/or immediately following weaning on HPA axis and sympathoadrenal function, 2- to 3-year-old Welsh Mountain ewes received 100% (C, n = 39) or 50% nutritional requirements (U, n = 41) from 1-31 days gestation, and 100% thereafter. From weaning (12 weeks) to 25 weeks of age, male and female offspring were then either fed ad libitum (CC, n = 22; UC, n = 19) or were undernourished (CU, n = 17; UU, n = 22) such that body weight was reduced to 85% of their individual target, based on a growth trajectory calculated from weights taken between birth and 12 weeks. From 25 weeks, ad libitum feeding was restored for all offspring. At 1.5 and 2.5 years, adrenocorticotropic hormone (ACTH) and cortisol concentrations were measured at baseline and in response to corticotropin-releasing factor (CRF) (0.5 microg kg(1)) plus arginine vasopressin (AVP) (0.1 microg kg(1)). At 2.5 years, HPA axis and sympathoadrenal (catecholamine) responses to a transport and isolation stress test were also measured. In females, post-weaning undernutrition reduced pituitary output (ACTH) but increased adrenocortical responsiveness (cortisol:ACTH area under curve) during CRF/AVP challenge at 1.5 years and increased adrenomedullary output (adrenaline) to stress at 2.5 years. In males, cortisol responses to stress at 2.5 years were reduced in those with slower growth rates from 12 to 25 weeks. Early gestation undernutrition was associated with increased adrenocortical output in 2.5-year-old females only. Pituitary and adrenal responses were also related to adult body composition. Thus, poor growth in the post-weaning period induced by nutrient restriction has sex- and age-specific effects on HPA and sympathoadrenal function. With altered glucose tolerance previously reported in this model, this may have long-term detrimental effects on metabolic homeostasis and cardiovascular function.

Effects of dam parity and rearing rank on the glucose and fat metabolism, and adrenal function of post-pubertal single and twin-ewe progeny

In an effort to increase the number of lambs produced per ewe’s productive lifetime in New Zealand, an increasing number of ewe lambs (8–9 months old) are being bred. This, in turn, results in an increased proportion of second-parity 2-year-old ewes in New Zealand’s breeding flock, rather than the more usual first-parity 2-year olds. The longer-term effects of dam parity on resulting ewe progeny are of interest and few studies have examined this. The present study was designed to determine whether parity (first or second) of Romney 2-year-old dams had any effect on the metabolic function of their single- and twin-born and reared ewe lamb progeny at 10 months of age. Ten-month-old, single and twin ewe lamb progeny born to first- or second-parity dams (n = 8 per group) were catheterised and given intravenous glucose (0.17 g/kg liveweight) (GTT), insulin (0.15 IU/kg liveweight) (ITT) and epinephrine (1 μg/kg liveweight) (ETT) tolerance tests to assess their glucose and fat metabolism and adrenal function. Rearing rank reduced (P < 0.05) the insulin response of twins to a glucose challenge, but increased (P < 0.05) their glucose response to an insulin challenge. Offspring from first-parity dams had higher (P < 0.05) basal plasma concentrations of cortisol and cortisone, whereas their cortisol/cortisone responses to an insulin challenge were unaffected by either dam parity or rearing rank. Neither dam parity nor rearing rank appeared to influence responses to an epinephrine challenge. The present study suggests that both dam parity and rearing rank alter the glucose and insulin metabolism of the offspring, which may have longer-term impacts on the growth and reproductive efficiency of the animal.

Blunted stress response in small for gestational age neonates

There is evidence that adverse conditions during intrauterine development affect future health of the offspring. Hypothalamus-pituitary-adrenal (HPA) axis dysregulation is assumed to play an important role in the association of small for gestational age (SGA) and the pathogenesis of hypertension and the metabolic syndrome. Stress response patterns in SGA neonates may identify a link with intrauterine-induced permanent maladaptation of the HPA axis. Salivary cortisol and cortisone levels were therefore analyzed during resting conditions and in response to a pain-induced stress event in SGA (<5th percentile) and appropriate for gestational age (AGA) neonates born > or =34 wk of gestation. In AGA neonates, salivary cortisol and cortisone levels significantly increased after the stress event (p < 0.05). In contrast, SGA infants exhibited a blunted steroid release after stress induction (p = 0.76, p = 0.65, respectively). No influence of mode of delivery (p = 0.93), gender (p = 0.21), and gestational age (p = 0.57) on stress response patterns was observed in a multiple stepwise regression. SGA neonates show a blunted physiologic activation of the HPA axis in response to a stress stimulus. Thus, intrauterine-induced alteration of HPA axis regulation seems to persist into the postnatal period and represents a prerequisite for the hypothesis of HPA axis involvement in the fetal origin of adult diseases.

Twin-pregnancy increases susceptibility of ewes to hypoglycaemic stress and pregnancy toxaemia

Pregnancy toxaemia is a metabolic disorder with a high mortality rate and occurs in twin-bearing ewes in late gestation. Maternal hypoglycaemia is a characteristic symptom of the disease and has been attributed to an increase in glucose uptake by the twin-bearing uterus. The possibility that a reduced maternal glucose production rate might cause hypoglycaemia, has received little attention in the past. It was the aim of this study to investigate this explanation as a possible alternative. Six ewes were sequentially subjected to two types of hypoglycaemic stress, firstly by fasting for 14 h and secondly through induction of moderate hyperketonaemia. Glucose kinetics were assessed in each animal during the dry non-gestational period, during late gestation, and during early lactation. Application of these stress factors was associated with variation of plasma glucose concentration from 4.9 to 0.87 mmol L(-1). The plasma glucose concentration was always significantly related to the glucose production rate. The greatest stress-induced reductions in glucose concentration and glucose production rate were seen during late gestation in twin-bearing ewes. The decline in the glucose production rate after an overnight fast and during induced hyperketonaemia was greater in twin-bearing ewes than in single-bearing ewes (59% and 43%, respectively, p<0.05). The stress conditions resulted in the lowest levels of glucose concentration and glucose turnover rates in the stressed, hyperketonaemic, late gestation twin-bearing ewes. This illustrates that the glucose homoeostatic system of ewes bearing twins is significantly more susceptible to hypoglycaemic stress than that of ewes bearing single lambs. These findings also show that the primary cause of hypoglycaemia in late gestation twin-pregnant ewes is an increased susceptibility to a stress related reduction in glucose production rate. This metabolic condition leaves the twin-pregnant ewe predisposed for the development of pregnancy toxaemia.

Effects of twinning and periconceptional undernutrition on late-gestation hypothalamic-pituitary-adrenal axis function in ovine pregnancy

The relationships between reduced size at birth, increased activity of the hypothalamic-pituitary-adrenal (HPA) axis, and increased risk of disease in adulthood are well described in singletons but are much less clear in twins. This may be because the physiological processes underlying reduced size at birth are different in singletons and twins. Periconceptional undernutrition can cause altered activity of the fetal and postnatal HPA axis without altering size at birth. However, the independent effects of periconceptional undernutrition and twinning on activity of the maternal and fetal HPA axes are not well described. We therefore studied maternal and fetal HPA axis function during late gestation in twin and singleton sheep pregnancies, either undernourished around conception or fed ad libitum. We found that twinning led to suppressed baseline HPA axis function and decreased adrenal sensitivity to ACTH stimulation but increased fetal pituitary ACTH response both to direct stimulation by CRH (ACTH area under the curve response: 29.7 +/- 2.2 vs. 17.1 +/- 1.6 ng/min x ml, P < 0.01) and to decreased cortisol negative feedback. In contrast, periconceptional undernutrition resulted in a decreased pituitary response (ACTH area under the curve response: 19.4 +/- 1.6 vs. 26.1 +/- 2.2 ng/min x ml, P = 0.02) but no difference in adrenal response. Thus, the HPA axis function of twin sheep fetuses in late gestation is very different from that of control and undernourished singletons. If the HPA axis is an important mediator between fetal adaptations and adult disease, these data may help explain why the relationship between fetal growth and postnatal physiology and disease risk is inconsistent in twins.

Maternal nutrient restriction alters renal development and blood pressure regulation of the offspring

Studies have shown that the risk of hypertension in adulthood can be affected by the in utero environment. It is established that hypertension is linked to compromised kidney function and that factors affecting organogenesis can increase the risk of later disease. Prostaglandins (PG) and growth factors are known to play an important role in regulating kidney function and renal organogenesis. The extent, however, to which global energy restriction (where all nutrients are reduced) of the mother can programme later blood pressure control or renal PG and growth factor status is unknown. A study is described that aimed to examine the long-term effects of maternal nutrient restriction (NR) and elucidate their relationship with compromised kidney development. First, it was necessary to establish animal models. A sheep model of 50% NR during specific stages of gestation was used to investigate fetal renal development, whilst a rat model of 50% NR throughout pregnancy was used to investigate postnatal kidney development and adult functioning. Molecular analysis has shown that expression of the growth hormone–insulin-like growth factor (GH–IGF) axis is affected by NR in the fetal sheep kidneys, and that changes are dependent on the timing of NR and whether the fetus is a singleton or a twin. Analysis of the kidneys from the rat model has shown nutritional differences in the expression of PG receptors and the enzymes responsible for PG synthesis and degradation that persist into adulthood. In conclusion, NR does affect the GH–IGF and PG axes, and these changes may be important in the nutritional programming of renal functioning and adult blood pressure control.

The emergence of the cortisol circadian rhythm in monozygotic and dizygotic twin infants: the twin-pair synchrony

OBJECTIVE

Studies on the influence of genetic factors on the ontogeny of cortisol circadian rhythm in infants are lacking. This study evaluated the influence of twinning and the heritability on the age of emergence of salivary cortisol rhythm.

DESIGN AND SUBJECTS

A longitudinal study was performed using salivary samples obtained during morning and night, at 2, 4, 8, 12, 16, 20 and 24 weeks of postnatal life in 34 infants, 10 monozygotic (MZ) and 7 dizygotic (DZ) twin pairs. Salivary cortisol was determined by radioimmunoassay (RIA). Zigosity was verified by DNA analysis of at least 13 short tandem repeat polymorphisms. Difference of the emergence of cortisol circadian rhythm, within each twin pair, the intraclass correlation coefficient and the heritability index (h(2)) were calculated.

RESULTS

The mean (+/- SEM) age of emergence of salivary cortisol circadian rhythm was similar in MZ and DZ (7.8 +/- 1.0 vs 7.4 +/- 1.3 weeks). Seven pairs showed coincidence of the emergence of cortisol rhythm. Ten pairs were not coincident; among them the within-pair difference of emergence of salivary circadian rhythm was similar in both MZ and DZ groups. The intraclass correlation coefficients were rMZ = 0.60, P = 0.02; and rDZ = 0.65, P = 0.03, respectively. The heritability index (h(2)) was 0.21 (ns).

CONCLUSIONS

Salivary circadian rhythm appeared at the same postnatal age in MZ and DZ twin infants. Although several physiological aspects might be involved, the heritability index, obtained in the present study, suggests less genetic than environmental impact on the age of the onset of the cortisol circadian rhythm. Our data also indicated that each twin-pair show synchrony because they probably shared prenatal and postnatal environmental synchronizers.

Effects of twinning, birth size, and postnatal growth on glucose tolerance and hypothalamic-pituitary-adrenal function in postpubertal sheep

Low birth weight is associated with postnatal physiological changes, including impaired glucose tolerance and increased cortisol secretion, that may predispose to disease in adulthood. Twins are born lighter than singletons, but there are conflicting data regarding the association between birth weight and postnatal physiology in twins. We studied glucose tolerance and ACTH and cortisol responses to a combined corticotropin-releasing hormone and arginine vasopressin (CRH + AVP) challenge in postpubertal female twin (n = 7 twin pairs) and singleton (n = 13) sheep from the same flock. There were no differences in glucose tolerance between twins and singletons and no association with birth weight. Twins had a greater ACTH (P < 0.05), but not cortisol, response to CRH + AVP than singletons. ACTH area under the curve was inversely related to birth weight in both singletons [R(2) = 0.31, P = 0.05; -8,311 (SD 3,736) pg.min.ml(-1).kg(-1)] and twins (R(2) = 0.49); in twins, this was due to the within-twin pair rather than the between-twin pair coefficient in the regression analysis [P = 0.02, -26,856 (9,806) vs. P = 0.1, 8,619 (4,950) pg.min.ml(-1).kg(-1)]. We conclude that the reduced fetal growth in twins has postnatal consequences for hypothalamic-pituitary-adrenal function and that this is determined by factors specific to the fetus (within-twin pair) rather than by shared maternal factors (between-twin pair). Studies investigating the associations between fetal growth and postnatal outcomes in twins benefit from an appropriate singleton control group and from analyses evaluating the contribution from both between- and within-pair coefficients in twins.

Myocyte enlargement, differentiation, and proliferation kinetics in the fetal sheep heart

The generation of new myocytes is an essential process of in utero heart growth. Most, or all, cardiac myocytes lose their capacity for proliferation during the perinatal period through the process of terminal differentiation. An increasing number of studies focus on how experimental interventions affect cardiac myocyte growth in the fetal sheep. Nevertheless, fundamental questions about normal growth of the fetal heart remain unanswered. In this study, we determined that during the last third of gestation the hearts of fetal sheep grew primarily by four processes. 1) Myocyte proliferation contributed substantially to daily cardiac mass gain, and the number of cardiac myocytes continued to increase to term. 2) The (hitherto unrecognized) contribution to cardiac growth by the increase in myocyte size associated with the transition from mononucleation to binucleation (terminal differentiation) became considerable from approximately 115 days of gestational age (dGA) until term (145dGA). Because binucleation became the more frequent outcome of myocyte cell cycle activity after approximately 115dGA, the number of binucleated myocytes increased at the expense of the number of mononucleated myocytes. Both the interval between nuclear divisions and the duration of cell cycle activity in myocytes decreased substantially during this same period. Finally, cardiac growth was in part due to enlargement of 3) mononucleated and 4) binucleated myocytes, which grew in cross-sectional diameter but not length during the last third of gestation. These data on normal cardiac growth may enable a more detailed understanding of the consequences of experimental and pathological interventions in prenatal life.

Influence of maternal pre-pregnancy body composition and diet during early-mid pregnancy on cardiovascular function and nephron number in juvenile sheep

The prenatal diet can program an individual's cardiovascular system towards later higher resting blood pressure and kidney dysfunction, but the extent to which these programmed responses are directly determined by the timing of maternal nutritional manipulation is unknown. In the present study we examined whether maternal nutrient restriction targeted over the period of maximal placental growth, i.e. days 28-80 of gestation, resulted in altered blood pressure or kidney development in the juvenile offspring. This was undertaken in 6-month-old sheep born to mothers fed control (100-150 % of the recommended metabolisable energy (ME) intake for that stage of gestation) or nutrient-restricted (NR; 50 % ME; n 6) diets between days 28 and 80 of gestation. Controls were additionally grouped according to normal (>3, n 7) or low body condition score (LBCS; <2, n 6), thereby enabling us to examine the effect of maternal body composition on later cardiovascular function. From day 80 to term (approximately 147 d) all sheep were fed to 100 % ME. Offspring were weaned at 12 weeks and pasture-reared until 6 months of age when cardiovascular function was determined. Both LBCS and NR sheep tended to have lower resting systolic (control, 85 (se 2); LBCS, 77 (se 3); NR, 77 (se 3) mmHg) and diastolic blood pressure relative to controls. Total nephron count was markedly lower in both LBCS and NR relative to controls (LBCS, 59 (se 6); NR, 56 (se 12) %). Our data suggest that maternal body composition around conception is as important as the level of nutrient intake during early pregnancy in programming later cardiovascular health.

Endocrine and metabolic programming during intrauterine development

In humans, low birth weight is associated with an increased risk of metabolic dysfunction in adult life. Many of these metabolic disorders have an endocrine origin and are accompanied by abnormal hormone concentrations. This has led to the hypothesis that adult metabolic disease arises in utero as a result of programming of key endocrine systems during suboptimal intrauterine conditions associated with fetal growth retardation. This review examines the experimental evidence for prenatal endocrine programming with particular emphasis on endocrine axes involved in growth and metabolism, namely, the hypothalamic-pituitary-adrenal axis, the endocrine pancreas and the somatotrophic axis. It also considers how changes in these endocrine systems contribute to the programming of metabolism in later life.

Programming of glucose-insulin metabolism in adult sheep after maternal undernutrition

The present study examines the effects of late vs. early gestation undernutrition on adult glucose-insulin homeostasis in sheep and investigates whether the lower birth weight of twins alters glucose-insulin handling in adult life. Pregnant sheep were fed to requirement (100% intake) from day 0 of gestation to term [ approximately 147 days of gestation (dGA), control singles (CS) n = 5; control twins (CT) n = 5] or to 50% requirement from days 0-30 dGA [nutrient restricted during early gestation (NRE); n = 5] or day 110-term [NR during late nutrition (NRL); n = 4]. At all other times, NR sheep received 100% intake. All sheep lambed naturally; offspring were weaned at 10 wk and were reared on pasture until 1 yr of age. At this time, indwelling catheters were inserted, and 2-4 days later, basal metabolic and endocrine status and responses to an intravenous glucose tolerance test (IVGTT) and feeding were assessed. Adipose and skeletal muscle were then sampled after humane euthanasia and were analyzed for expression of insulin-signaling proteins and GLUT4. Between groups, birth weight of singletons was similar and increased relative to twins. At 1 yr of age, weights were similar between groups. The areas under the curve for glucose and insulin during the IVGTT were greater in NRL vs. other groups, indicating glucose intolerance. This was associated with reduced adipose, but not muscle, GLUT4, and increased adipose tissue mass. Adult glucose-insulin homeostasis in sheep was unaffected by fetal number. In conclusion, prenatal undernutrition, specifically during late gestation, affects adult offspring intermediary metabolism, and, in particular, glucose-insulin homeostasis.

Early embryonic environment, the fetal pituitary-adrenal axis and the timing of parturition

It is well established in the sheep, that the normal timing of parturition is dependent on a prepartum activation of the fetal pituitary-adrenal axis. We have recently demonstrated for the first time that embryo number, embryo sex, and alterations in the environment of the early embryo, including exposure to maternal undernutrition during the periconceptional period, alter the timing and level of activation of the pituitary-adrenal axis in the sheep fetus during late gestation. There is a delay in activation of the fetal HPA axis in twin fetuses and we speculate that the diminished adrenocortical responsiveness in the twin fetus may be an adaptive response, which counters the impact of the potential enhanced intrauterine stress experienced by a twin fetus, thereby reducing the possibility of preterm delivery. We have also reported that a moderate restriction of maternal nutrition to during the periconceptional period (from 60 days before and for one week after conception) resulted in an earlier activation of the pituitary-adrenal axis of twin, but not singleton, fetuses during late gestation. A series of studies using assisted reproductive technologies have also found that perturbation of the early embryonic environment results in a dysregulation of placental and fetal growth and development and in the timing of normal parturition. In summary, after several decades of work focussed on events in late gestation associated with the prepartum activation and stress responsiveness of the fetal HPA axis, our recent studies indicate that the environment of the early embryo may have a significant role to play in determining the timing and level of the prepartum activation of this axis and potentially on the functional capacity of the axis to respond to acute or chronic stress in later life.