Ovine uteroplacental and fetal metabolism during and after fetal cortisol overexposure in late gestation

Cortisol modifies fetal metabolism in preparation for delivery, but whether preterm cortisol exposure programs persisting changes in fetoplacental metabolism remains unknown. This study infused fetal sheep with saline ( n = 36) or cortisol ( n = 27) to raise fetal plasma cortisol to normal prepartum concentrations for 5 days from day 125 of gestation (term: ≈145 days). Fetal uptake and uteroplacental metabolism of glucose, oxygen, and lactate, together with fetal hepatic glucogenic capacity, were measured on the final day of infusion or 5 days later. Cortisol reduced adrenal weight and umbilical glucose uptake during infusion but increased fetal glucose concentrations, hepatic glycogen content, and hepatic glucogenic enzyme activity (fructose-1,6-bisphosphatase and glucose-6-phosphatase) and gene expression ( PC and G6PC) compared with saline infusion. Postcortisol infusion, umbilical glucose uptake, and hepatic glucose-6-phosphatase activity remained low and high, respectively, whereas fetal glucose levels normalized and hepatic glycogen was lower with higher adrenal weights than in controls. Cortisol infusion increased the proportion of total uterine glucose uptake consumed by the uteroplacental tissues, irrespective of age. Placental tracer glucose transport capacity was also increased after, but not during, cortisol infusion, without changes in placental glucose transporter gene expression. Blood lactate concentration and Pco2 were higher, whereas pH and O2 content were lower in cortisol-infused than saline-infused fetuses, although uteroplacental metabolism and fetal uptake of oxygen and lactate were unaltered. The results suggest that preterm cortisol overexposure alters fetoplacental metabolism and adrenal function subsequently with persisting increases in uteroplacental glucose consumption at the expense of the fetal supply.

Maternal low-dose porcine somatotropin treatment in late gestation increases progeny weight at birth and weaning in sows but not in gilts

Birth weight positively predicts postnatal growth and performance in pigs and can be increased by sustained maternal porcine ST (pST) treatment from d 25 to 100 of pregnancy (term ∼115 d). The objective of this study was to test whether a shorter period of maternal pST treatment in late pregnancy (d 75 to 100) could also increase birth and weaning weights of progeny under commercial conditions. Gilts (parity 0) and sows (parities 2 and 3) were not injected (controls) or injected daily with pST (gilts: 2.5 mg•d(-1), sows: 4.0 mg•d(-1), both ∼13 to 14 μg•kg(-1)•d(-1)) from d 75 to 100 of pregnancy. Litter size and BW were recorded at birth and weaning, and dams were followed through the subsequent mating and pregnancy. Maternal pST injections from d 75 to 100 increased litter average progeny weight at birth (+96 g, P = 0.034) and weaning (+430 g, P = 0.038) in sows, but had no effect on progeny weight in gilts (each P > 0.5). Maternal pST treatment did not affect numbers of live-born piglets and increased numbers of stillborn piglets in sows only (+0.4 pigs/litter, P = 0.034). Maternal pST treatment did not affect subsequent reproduction of dams. Together with our previous data, these results suggest that sustained increases in maternal pST are required to increase fetal and postnatal growth in gilt progeny, but that increasing maternal pST in late pregnancy may only be an effective strategy to increase fetal and possibly postnatal growth in sow progeny.

Review: Placental programming of postnatal diabetes and impaired insulin action after IUGR

Being born small due to poor growth before birth increases the risk of developing metabolic disease, including type 2 diabetes, in later life. Inadequate insulin secretion and decreasing insulin sensitivity contribute to this increased diabetes risk. Impaired placental growth, development and function are major causes of impaired fetal growth and development and therefore of IUGR. Restricted placental growth (PR) and function in non-human animals induces similar changes in insulin secretion and sensitivity as in human IUGR, making these valuable tools to investigate the underlying mechanisms and to test interventions to prevent or ameliorate the risk of disease after IUGR. Epigenetic changes induced by an adverse fetal environment are strongly implicated as causes of later impaired insulin action. These have been well-characterised in the PR rat, where impaired insulin secretion is linked to epigenetic changes at the Pdx-1 promotor and reduced expression of this transcription factor. Present research is particularly focussed on developing intervention strategies to prevent or reverse epigenetic changes, and normalise gene expression and insulin action after PR, in order to translate this to treatments to improve outcomes in human IUGR.

316. MATERNAL DIETARY ARGININE SUPPLEMENTATION DURING LATE GESTATION IMPROVES REPRODUCTIVE EFFICIENCY IN PIGS

Arginine (a non-essential amino acid) and its conversion to nitric oxide (NO) can promote formation of new blood vessels and cause vasodilation. This may reduce resistance and increase blood flow to the uterus and placenta, and the delivery of nutrients for fetal growth and survival. In pregnant rats, dietary arginine deficiency causes IUGR and increases fetal death and perinatal mortality, whereas dietary arginine supplementation reverses this. Human IUGR is associated with impaired NO synthesis, and eNOS activity in umbilical vein endothelial cells, but maternal arginine supplements have produced inconclusive results. We hypothesised that maternal arginine supplementation (MAS) in the pig (a species with naturally occurring IUGR), during late gestation, when placental angiogenesis and vascularity increase, would increase birth and placental weights. Large White (LW) and Landrace (LR) gilts (n = 285) and sows (n = 326), were fed either a control or arginine supplemented (+25 g/d arginine, Nutreco Progenos premix) diet (2.5 kg/d) in late gestation (d75-term at ~114 days). Number born, born alive, still born and mummified, birth weight and d10 weight of progeny were measured. Data were analysed using Univariate ANOVA. MAS in late gestation in gilts and sows reduced the number of still born (Con: 1.17 ± 0.13 piglets/litter; Arg: 0.84 ± 0.09 piglets/litter; P = 0.046). In LW gilts, MAS increased birth weight (Con: 1.21 ± 0.05kg; Arg: 1.34 ± 0.05kg; P < 0.05), and litter birth weight (Con: 13.38 ± 0.72 kg; Arg: 15.27 ± 0.73 kg; P < 0.05). MAS also increased birth weight in LW (Con: 1.17 ± 0.06 kg; Arg: 1.30 ± 0.06 kg; P < 0.05) and LR (Con: 1.47 ± 0.05 kg; Arg: 1.60 ± 0.05 kg; P < 0.05) sows, and reduced still borns in LW sows (Con: 1.12 ± 0.14 piglets/litter; Arg: 0.77 ± 0.09 piglets/litter; P < 0.05). MAS in late gestation improves pregnancy outcomes in terms of piglet survival and birth weight, in LW and LR gilts and sows. MAS during critical periods of placental development may enhance placental-fetal blood flow and nutrient transfer, thereby improving fetal growth and survival.

Maternal responses to daily maternal porcine somatotropin injections during early-mid pregnancy or early-late pregnancy in sows and gilts

Piglet neonatal survival and postnatal growth and efficiency are positively related to birth weight. In gilts, daily maternal porcine ST (pST) injections from d 25 to 100 (term approximately 115 d), but not d 25 to 50, of pregnancy increase progeny birth weight. Daily maternal pST injections from d 25 to 50 increase fetal weight at d 50 in gilts and sows. We therefore hypothesized that daily pST injections from d 25 to 100, but not d 25 to 50, of pregnancy would increase birth weight similarly in both parities. Landrace x Large White gilts and sows were uninjected (controls) or were injected daily with pST (gilts: 2.5 mg/d; sows: 4.0 mg/d, each approximately 15 microg of pST/kg per day) from d 25 to 50 or 100 of pregnancy. Litter size and BW were recorded at birth, midlactation, and weaning. Dams were followed through the subsequent mating and pregnancy. Maternal pST injections from d 25 to 100, but not d 25 to 50, increased mean piglet birth weight by 11.6% in sows (P <or= 0.001) and by 5.6% in gilts (P = 0.008). Both pST treatments decreased litter size by approximately 0.6 live-born piglets (each P <or= 0.025). In sows, maternal pST treatment from d 25 to 100 increased culls at weaning (P = 0.037). In remated dams, prior treatments did not affect (P > 0.1) the weaning-remating interval, conception rate, or subsequent litter size. Greater pST-induced birth weight increases in sows than in gilts may mean that underlying metabolic or placental mechanisms for pST action are constrained by maternal competition for nutrients in rapidly growing gilts.

Maternal exposure to dexamethasone or cortisol in early pregnancy differentially alters insulin secretion and glucose homeostasis in adult male sheep offspring

An adverse intrauterine environment increases the risk of developing various adult-onset diseases, whose nature varies with the timing of exposure. Maternal undernutrition in humans can increase adiposity, and the risk of coronary heart disease and impaired glucose tolerance in adult life, which may be partly mediated by maternal or fetal endocrine stress responses. In sheep, dexamethasone in early pregnancy impairs cardiovascular function, but not glucose homeostasis in adult female offspring. However, male offspring are often more susceptible to early life "programming". Pregnant sheep were infused intravenously with saline (0.19 ml/h), dexamethasone (0.48 mg/h), or cortisol (5 mg/h), for 2 days from 26 to 28 days of gestation. In male offspring, size at birth and postnatal growth were measured, and glucose tolerance [intravenous glucose tolerance test (IVGTT)], insulin secretion, and insulin sensitivity of glucose, alpha-amino nitrogen, and free fatty acid metabolism were assessed at 4 yr of age. We show that cortisol, but not dexamethasone, treatment of mothers causes fasting hyperglycemia in adult male offspring. Maternal cortisol induced a second-phase hyperinsulinemia during IVGTT, whereas maternal dexamethasone induced a first-phase hyperinsulinemia. Dexamethasone improved glucose tolerance, while cortisol had no impact, and neither affected insulin sensitivity. This suggests that maternal glucocorticoid exposure in early pregnancy alters glucose homeostasis and induces hyperinsulinemia in adult male offspring, but in a glucocorticoid-specific manner. These consequences of glucocorticoid exposure in early pregnancy may lead to pancreatic exhaustion and diabetes longer term and are consistent with stress during early pregnancy contributing to such outcomes in humans.

Sex-specific effects of placental restriction on components of the metabolic syndrome in young adult sheep

Prenatal and early postnatal life experiences, reflected by size at birth and postnatal catch-up growth, contribute to the risk of developing the metabolic syndrome in adulthood, but their relative importance is unclear. Therefore, we determined the effects of restricted placental and fetal growth on components of the metabolic syndrome in young adult sheep and the relationships of the latter to size at birth and early postnatal growth. Fasting plasma metabolites, glucose tolerance (by intravenous glucose tolerance test, IVGTT), insulin secretion and sensitivity, and resting blood pressure were measured in 22 control and 20 placentally restricted (PR) 1-yr-old sheep. In male sheep, PR increased the initial rise in glucose during an IVGTT and reduced diastolic blood pressure, and small size at birth independently predicted reduced adult size, glucose tolerance, and fasting plasma insulin and insulin disposition of glucose metabolism but increased insulin disposition of circulating FFAs. Also in males, high fractional growth rates in early postnatal life independently predicted impaired early glucose clearance during an IVGTT. In female animals, PR increased insulin sensitivity of glucose metabolism and reduced fasting plasma FFAs, and thinness at birth predicted increased adult size, fasting blood glucose, and pulse pressure. In conclusion, PR and small size at birth are associated with more components of the metabolic syndrome in adult male than in adult female sheep, with few independent effects of early postnatal growth. These sex differences in the onset and extent of adverse metabolic consequences after prenatal restraint in the sheep are consistent with observations in humans.

Postnatal ontogeny of glucose homeostasis and insulin action in sheep

Glucose tolerance declines with maturation and aging in several species, but the time of onset and extent of changes in insulin sensitivity and insulin secretion and their contribution to changes in glucose tolerance are unclear. We therefore determined the effect of maturation on glucose tolerance, insulin secretion, and insulin sensitivity in a longitudinal study of male and female sheep from preweaning to adulthood, and whether these measures were related across age. Glucose tolerance was assessed by intravenous glucose tolerance test (IVGTT, 0.25 g glucose/kg), insulin secretion as the integrated insulin concentration during IVGTT, and insulin sensitivity by hyperinsulinemic-euglycemic clamp (2 mU insulin.kg(-1).min(-1)). Glucose tolerance, relative insulin secretion, and insulin sensitivity each decreased with age (P < 0.001). The disposition index, the product of insulin sensitivity, and various measures of insulin secretion during fasting or IVGTT also decreased with age (P < 0.001). Glucose tolerance in young adult sheep was independently predicted by insulin sensitivity (P = 0.012) and by insulin secretion relative to integrated glucose during IVGTT (P = 0.005). Relative insulin secretion before weaning was correlated positively with that in the adult (P = 0.023), whereas glucose tolerance, insulin sensitivity, and disposition indexes in the adult did not correlate with those at earlier ages. We conclude that glucose tolerance declines between the first month of life and early adulthood in the sheep, reflecting decreasing insulin sensitivity and absence of compensatory insulin secretion. Nevertheless, the capacity for insulin secretion in the adult reflects that early in life, suggesting that it is determined genetically or by persistent influences of the perinatal environment.

285.Increased perinatal mortality following restriction of placental and fetal growth

Intrauterine growth restriction and subsequent low birth weight in humans are associated with increased perinatal mortality and morbidity. Impaired placental function is a major cause of IUGR in humans, but its impact on perinatal survival has not been clearly defined. We have therefore investigated the effect of restriction of placental and fetal growth on perinatal survival and behaviour in the neonatal lamb. Placental growth was surgically restricted (PR) by removal of the majority of endometrial implantation sites prior to pregnancy, leaving either 6 to 7 (moderate PR) or 3 to 4 (severe PR) visible caruncles in each uterine horn, and ewes were mated following at least 10 weeks recovery. Perinatal outcomes (stillbirths and neonatal death before 3 days of age) were recorded in a cohort of 48 control (30 singleton, 18 twin) and 28 moderate PR (14 singleton, 14 twin), and 21 severe PR (11 singleton, 10 twin) lambs, and effects of PR or twinning were evaluated by Chi-square analysis. Rates of stillbirth (P = 0.006) and total perinatal deaths (P < 0.001) were higher in severe PR pregnancies than in control or moderate PR lambs, overall (see Table in PDF file). Similarly, severe PR increased stillbirths and perinatal deaths in twins alone (P = 0.003 and P = 0.015 respectively), but the effects of PR were not significant in singletons (P = 0.10, P = 0.26 respectively). Twinning increased stillbirths and perinatal deaths overall (P = 0.002, P = 0.001) and in control lambs alone (P = 0.038, P = 0.017). Restricted fetal growth due to twinning or severe surgical restriction of placental growth thus decreases perinatal survival, due to increased stillbirths. We will further investigate the characteristics of neonatal morbidity following PR by recording neonatal behaviour, including time taken to stand and suckle, in a subsequent cohort of control and PR lambs.

Perinatal growth and plasma GH profiles in adolescent and adult sheep

Poor prenatal growth is associated with limited evidence of GH deficiency in adult humans, which may contribute to their increased risk of cardiovascular and metabolic disease. We therefore examined the effects of placental restriction of fetal growth (PR) on size at birth, neonatal fractional growth rate (FGR) and the circulating GH profile in adolescent and young adult sheep of both sexes. Moderate or severe PR decreased birth size and increased neonatal FGR of weight, crown-rump length and abdominal circumference. In adolescent males, mean and baseline GH concentrations correlated negatively and independently with birth weight and FGR of weight, and mean GH concentrations correlated negatively with current weight. In young adult males, mean GH concentrations correlated negatively and independently with birth shoulder height and FGR of shoulder height whilst, in young adult females, these correlations were positive. This suggests that restricted fetal growth and reduced neonatal growth rate in sheep are followed by elevated circulating GH in adolescent and adult males, but GH deficiency or increased GH clearance in adult females.

Treatment of underfed pigs with GH throughout the second quarter of pregnancy increases fetal growth

Circulating growth hormone (GH) concentrations increase in pregnancy and administration of GH during early-mid pregnancy increases fetal growth in well-fed pigs. To determine whether increased maternal GH could promote fetal growth when feed availability is restricted, fifteen cross-bred primiparous sows (gilts) were fed at approximately 30% of ad libitum intake, from mating onwards and were injected daily i.m. with recombinant porcine GH (pGH) at doses of 0, 13.4+/-0.3 and 25.6+/-0.5 microg/kg live weight from day 25 to day 51 of pregnancy (term approximately 115 days). Treatment with pGH increased maternal backfat loss between day 25 and day 51 of pregnancy, and increased maternal plasma IGF-I concentrations measured at day 51 of pregnancy. Fetal body weight, length and skull width at day 51 of pregnancy were increased by maternal treatment with pGH. Fetal plasma glucose concentrations were increased and maternal/fetal plasma glucose concentration gradients were decreased by maternal pGH treatment at 13.4, but not 25.6 microg/kg.day. Fetal plasma concentrations of urea were decreased by both levels of pGH treatment. Overall, fetal weight was negatively correlated with fetal plasma concentrations of urea, positively correlated with maternal plasma alpha-amino nitrogen concentrations and unrelated to glucose concentrations in either maternal or fetal plasma. This suggests that the availability of amino acids, not glucose, limits fetal growth in the first half of pregnancy in underfed gilts, and that maternal GH treatment may improve amino acid delivery to the fetus.

Differential timing for programming of glucose homoeostasis, sensitivity to insulin and blood pressure by in utero exposure to dexamethasone in sheep

Numerous epidemiological studies have related an increased risk of adult-onset cardiovascular and metabolic disease to an adverse intra-uterine environment at critical periods. We have shown that fetal sheep exposed to dexamethasone for only 2 days at 27 days of gestation (term approximately 150 days) became hypertensive adults, whereas those exposed at 64 days of gestation remained normotensive, as did controls. In the same sheep, now nearly 5 years old, we performed glucose tolerance tests and hyperinsulinaemic euglycaemic clamps to study the insulin sensitivity of glucose, amino acid and non-esterified fatty acid metabolism. Glucose tolerance, calculated as the area under the curve, after intravenous administration of bolus glucose and insulin secretion in response to a glucose challenge were not altered in any group. There were no significant differences in the insulin sensitivity of net whole-body glucose or amino acid uptake. However, suppression of lipolysis by insulin, measured as the proportional decrease in the circulating concentration of non-esterified fatty acids during the hyperinsulinaemic clamp, was 69+/-1.2% at steady-state plasma insulin levels ( approximately 1000 m-units/l) in the group exposed to dexamethasone at 27 days of gestation, but only 50.8+/-6.5% in the controls (P<0.05). In the group exposed to dexamethasone at 64 days of gestation, the decrease was 66.4+/-5.1%, which did not reach significance compared with the controls (P=0.10). Thus brief dexamethasone exposure during early gestation programmed hypertension independently of insulin resistance of glucose or amino acid metabolism; however, it did lead to increased insulin sensitivity of the inhibition of lipolysis, which may increase susceptibility to the development of obesity postnatally.