Lindsay Heasman

Influence of Restricted Maternal Nutrition in Early to Mid Gestation on Placental and Fetal Development at Term in Sheep

We investigated the influence of restricted maternal nutrition between 28 and 77 d of gestation on placental weight and appearance, and on fetal weight and conformation. Single-bearing ewes were fed either twice [i.e. controls (n = 19)] or half [i.e. nutrient-restricted (n = 28)] their energy requirements from 28 to 77 d of gestation, after which all ewes were fed to fully meet the energy requirements for maintenance and pregnancy. Close to term (145 ± 1 d) placental weight was higher in the nutrient-restricted group [nutrient-restricted, 416.3 ± 12.6 g; controls, 347.4 ± 17.6 g (p < 0.01)], as was the abundance of everted placentomes. There was no significant difference in total fetal weight, or weights of individual organs between groups, but crown-rump length was significantly greater in lambs born to nutrient-restricted ewes [nutrient-restricted, 50.4 ± 0.4 cm; controls, 48.2 ± 0.6, cm (p < 0.01)]. Fetal to placental weight ratio was lower in the nutrient-restricted group [nutrient-restricted, 9.51 ± 0.23; controls, 10.81 ± 0.39 (p < 0.01)]. A stronger relationship between the total weight of the fetal component of the placental and fetal weight was observed in controls (r2 = 0.50) than in nutrient-restricted ewes (r2 = 0.18). In conclusion, maternal nutrient restriction over the period of rapid placental growth results in a larger placenta and altered placental to fetal weight ratio if ewes are subsequently fed to requirements for the remainder of gestation.

Maternal nutrition in early-mid gestation and placental size in sheep

We investigated the influence of restricted maternal nutrition between 30 and 80 d gestation on placental growth. Singleton-bearing ewes were fed on either 0.6 (i.e. nutrient restricted) times their energy requirements of 2.25 times this amount (i.e. controls) up to 80 d gestation, when their placentas and fetuses were sampled and analysed. Nutrient-restricted ewes lost body condition score but not body weight and had lower plasma thyroid hormone concentrations than controls, but there were no differences in plasma glucose, non-esterified fatty acids or 3-hydroxybutyrate concentrations between groups. There was no effect of maternal nutrient restriction on fetal weight, conformation or organ weight with the exception of brain weight which was lower nutrient-restricted ewes. Nutrient restriction had no effect on total placental weight, or proportion of inverted placentomes, but was associated with an increased abundance of small placentomes and decreased weight of the fetal but not maternal components of the placenta. Fetal cotyledons form nutrient-restricted ewes also had a lower DNA but higher haemoglobin concentration than those sampled from controls. The plasma concentration of triiodothyronine in umbilical cord plasma was also increased in fetuses from nutrient-restricted ewes. In conclusion, maternal nutrient restriction during early-mid gestation is associated with a smaller placenta.

Effect of Maternal Nutrition on Brown Adipose Tissue and Its Prolactin Receptor Status in the Fetal Lamb

We investigated the influence of maternal nutritional enhancement during the second half of gestation on prolactin receptor (PRLR) abundance in fetal brown adipose tissue (BAT) and liver close to term (i.e. 141–144 d gestation). Ewes were provided with 100% (i.e. control;n = 8) or 150% (i.e. well-fed;n = 7) of their metabolic requirements from 80 to 144 d gestation. Crude plasma membranes were prepared from fetal BAT and hepatic tissue, and individual molecular weight isoforms for the long and short forms of the PRLR were detected by immunoblotting. Mitochondrial preparations were prepared from BAT to measure the amount of the BAT-specific mitochondrial uncoupling protein-1 and its thermogenic activity (i.e. guanosine 5′-diphosphate binding). Fetuses sampled from well-fed ewes were heavier (controls, 3927 ± 196 g; well-fed, 4783 ± 219 g;p = 0.01) but possessed less BAT per kilogram body weight (controls, 5.92 ± 0.43 g/kg; well-fed, 3.85 ± 0.19 g/kg;p = 0.001), which had a greater uncoupling protein-1 abundance (controls, 56 ± 5% of reference; well-fed, 78 ± 9% of reference;p < 0.01) and higher thermogenic activity (controls, 157 ± 41 pmol guanosine 5′-diphosphate per milligram mitochondrial protein; well-fed, 352 ± 36 pmol guanosine 5′-diphosphate per milligram mitochondrial protein;p < 0.01) than controls. Multiple isoforms of the long and short forms of the PRLR were detected in all tissues. BAT from well-fed fetuses had a higher abundance of the 15-kD isoform of the long form of the PRLR (controls, 1.6 ± 0.4 densitometric units; well-fed, 16.3 ± 2.0 densitometric units;p < 0.001). This isoform was not detected in hepatic tissue. Maternal nutrient intake had no effect on any other isoforms of the PRLR in BAT or liver. In conclusion, increasing the quantity of feed provided in late gestation acts to promote fetal weight and BAT maturation, the combination of which will enhance neonatal viability.

The influence of maternal nutrient restriction in early to mid-pregnancy on placental and fetal development in sheep

Placental weight is a primary factor determining size at birth in many species. In sheep, placental weight peaks at approximately mid-gestation, with structural remodelling occurring over the second half of pregnancy to meet the increasing nutritional demands of the growing fetus. Numerous factors influence placental growth and development in sheep, and many workers (see Kelly, 1992) have investigated the role of maternal nutrition as a regulator of placental and fetal size. We have studied the effects of feeding ewes approximately 50% of their recommended energy requirements during early to mid-pregnancy on fetal and placental indices measured at mid-gestation (i.e. 80 d) and close to term (i.e. 145 d). Maternal nutrient restriction is associated with a reduction in placental weight at 80 d, but an increase in placental weight at 145 d of gestation, compared with ewes fed adequately in early pregnancy. No significant effect on fetal weight was observed at either 80 or 145 d gestation, although differences in body dimensions and the insulin-like growth factor-1 axis were found in lambs from nutrient-restricted ewes delivered close to term. Maternal nutrition during pregnancy plays a pivotal role in the regulation of fetal and placental development in sheep, and therefore has the potential to influence both short- and longer-term health outcomes.

Influence of relative size at birth on growth and glucose homeostasis in twin lambs during juvenile life

The effect of differences in size at birth on growth and glucose homeostasis between female twin lambs during juvenile life was examined. Twenty-six sets of twins were entered into the study, of which ten were used for organ sampling at birth and 16 were studied over the first year of life. Eleven sets were defined as being mismatched for birthweight as the weight difference between twins was >25%, with light lambs weighing 4.1 +/- 0.3 kg and heavy lambs weighing 5.1 +/- 0.1 kg. All remaining twins were matched in bodyweight, weighing 4.6 +/- 0.5 kg. During the rapid period of juvenile growth (i.e. one, three and six months of age) and following stabilization of bodyweight (i.e. 12 months of age) glucose tolerance tests were performed by intravenously injecting 0.8 mg kg(-1) bodyweight glucose. This was followed the next day with an insulin tolerance test, performed by intravenously injecting 0.08 units kg(-1) bodyweight insulin. At birth there were no differences in organ weight as a fraction of total bodyweight between matched and mismatched twins, but the ratio of liver to brain weight was lower in light compared with heavy twins. Light lambs remained lighter than their twins up to six months of age, and crown-rump length was also shorter. At one and three months of age there were no differences in basal plasma glucose concentrations between the groups, but glucose tolerance was greater in light compared with heavy lambs at one and six months of age. Insulin tolerance was greater in light compared with matched lambs at one and six months of age. In conclusion, it has been shown that size at birth of one twin in relation to its co-twin is one factor determining glucose regulation during postnatal life. This not only affects glucose and insulin tolerance but also growth over the first six months of age.

Maternal nutrient restriction during early to mid gestation alters the relationship between insulin-like growth factor I and bodyweight at term in fetal sheep.

The present study was designed to determine whether altered placental size, as a consequence of maternal nutrient restriction in sheep between 28 and 77 days gestation, is associated with a modified relationship between fetal weight or dimensions and plasma insulin-like growth factor (IGF) I concentration or abundance of hepatic IGF-I and IGF-II mRNA close to term. Singleton-bearing ewes consumed either 1.2x (controls, n = 19) or 0.5x (nutrient restricted, n = 28) their metabolizable energy (ME) requirements from 28 to 77 days gestation, after which all ewes were fed in order to fully meet their ME requirements for maintenance and pregnancy. Close to term (145 +/- 1 days) plasma IGF-I concentration in cord blood was similar between groups, but only significantly correlated with fetal bodyweight, thoracic circumference, crown-rump length and lean body mass in lambs born to control (r2 0.38, 0.76, 0.33, 0.42; P<0.001), and not to nutrient-restricted (r2 = 0.01, 0.11, 0.01, 0.02) ewes. There were no differences in fetal hepatic expression of IGF-I and IGF-II mRNA between groups close to term. In conclusion, maternal nutrient restriction in early to mid gestation followed by feeding to requirements up to term alters the relationship between fetal IGF-I, bodyweight and length. Increasing maternal nutrition in later gestation after a prolonged period of nutrient restriction may stimulate fetal nutrient supply such that fetal growth is enhanced without an increase in plasma IGF-I. As a result, there is a loss of the relationship between fetal weight and plasma IGF-I concentration observed in fetuses whose mothers are fed adequately throughout gestation.

Effect of maternal dexamethasone treatment and ambient temperature on prolactin receptor abundance in Brown adipose and hepatic tissue in the foetus and new-born lamb.

We investigated the influence of maternal dexamethasone treatment and ambient temperature on prolactin receptor (PRLR) abundance in brown adipose tissue (BAT) and hepatic tissue from foetuses and 6‐h‐old lambs delivered by caesarean section. Lambs were either delivered into a warm (30 °C; WD) or cool (15 °C; CD) ambient temperature at 140 days gestation, 2 days after dexamethasone treatment, or at 146 days gestation for controls. Uncoupling protein‐1 (UCP1) content of BAT was higher in dexamethasone‐treated groups compared to controls. A range of tissue‐specific PRLR isoforms was detected. For the long form of PRLR in BAT these isoforms had molecular weights of 66, 54, 34 and 19 kD compared with 88, 76, 66, 58, 54 and 48 kD in liver. In BAT, isoforms of the short form of PRLR had molecular weights of 66, 62, 54, 48, 33 and 31 kD compared with 82, 66, 56, 54, 48, 40 and 33 kD in liver. Dexamethasone treatment in CD lambs resulted in higher abundance of the 54 kD isoform of the short form of PRLR in liver, whilst in BAT dexamethasone resulted in a greater abundance of the 48 kD isoform of the short form, and lower abundance of the 66 kD isoform of the long form of PRLR, compared to controls. A negative correlation (r2=0.52) was observed between abundance of 66 kD isoform for the long form of PRLR and UCP1, compared with positive correlations (r2=0.58–0.60) for the abundance of the 54 and 48 kD isoforms for the short form of PRLR and UCP1. In conclusion, maternal dexamethasone treatment 1 week before term alters the abundance of PRLR isoforms in a tissue‐specific manner. This response is dependent on ambient temperature after birth and may provide a critical endocrine signal for maximising non‐shivering thermogenesis.

Plasma prolactin concentrations after caesarean section or vaginal delivery.

The umbilical venous plasma prolactin concentrations of three groups of term infants were compared immediately after birth. Samples were taken following seven vaginal deliveries, eight emergency caesarean sections performed during labour, and 12 elective caesarean sections before labour. Mean concentrations of prolactin were significantly lower in the elective caesarean section group compared with the labour groups. This result indicates that the fetal hypothalamic–pituitary axis is stimulated during labour which could explain the increase in plasma prolactin concentrations at birth.

Effect of maternal nutrient restriction in early to mid gestation and thyrotrophin-releasing hormone on lamb survival following Caesarean section delivery near to term

We investigated the influence of restricted maternal nutrition between 28 and 77 days gestation on survival and thermoregulatory adaptation following Caesarean section delivery near to term. This study was designed to examine the hypothesis that adaptation after birth would be compromised in those lambs born to nutrient restricted ewes. We further hypothesised that this would be due in part to inadequate hypothalamic-pituitary-thyroidal function. Lambs born to nutrient restricted ewes were untreated (RU) or treated with thyrotrophin-releasing hormone (TRH; RT) immediately prior to umbilical cord clamping. Single bearing ewes consumed either 6.60 MJ x day(-1) (controls, n = 4) or 3.00 MJ x day(-1) (nutrient restricted, n = 15) from 28-77 days gestation, after which all ewes consumed 7.20 MJ x day(-1). All lambs born to control ewes commenced continuous breathing and began to shiver following Caesarean section delivery and survived to 6 h after birth. Only 4 out of 9 RU lambs established continuous breathing and survived to 6 h after birth compared with all RT lambs. Six hours after birth, RT lambs possessed perirenal brown adipose tissue with a higher thermogenic activity than 6 h old RU or control lambs. Lamb birth weight was similar in all groups. In conclusion, near-term lambs born to ewes nutrient restricted in early to mid gestation are at increased risk of death following Caesarean section delivery. Survival after birth can be significantly enhanced if TRH is administered to the lambs immediately before delivery.

Influence of Thyrotrophin‐Releasing Hormone on Thermoregulatory Adaptation after Birth in Near‐Term Lambs Delivered by Caesarean Section

We investigated the hypothesis that exogenous stimulation with thyrotrophin‐releasing hormone (TRH) immediately prior to umbilical cord clamping can improve thermoregulatory adaptation after birth in near‐term lambs delivered by Caesarean section. Lambs received an umbilical vein injection of saline ± TRH (8 μg) prior to cord clamping. The rate of change in colonic temperature and oxygen consumption after birth were not influenced by TRH, but TRH‐treated lambs exhibited a greater incidence of shivering compared with controls over the first hour of neonatal life. Two and a half hours after birth, TRH‐treated lambs possessed brown adipose tissue (BAT) with a higher thermogenic activity (i.e. GDP binding to mitochondrial protein), but their BAT had a reduced DNA content and they had less hepatic glycogen than control lambs. TRH administration had no effect on iodothyronine 5′ deiodinase activity in BAT and liver, or on plasma concentrations of total triiodothyronine, thyroxine, cortisol or free fatty acids. Three TRH‐treated but no control lambs, failed to establish continuous breathing, so tissues from these treated lambs together with time‐matched controls were sampled 25 min after birth. These ‘non‐surviving’ TRH‐treated lambs had very high plasma catecholamine concentrations, but their lung weights were similar to controls. ‘Surviving’ TRH‐treated lambs possessed lungs with less DNA than non‐surviving TRH‐treated lambs. It is concluded that umbilical vein injection of TRH prior to umbilical cord clamping increases the recruitment of both shivering and non‐shivering thermogenesis after birth.