Effect of maternal nutrient restriction in early gestation on responses of the hypothalamic-pituitary-adrenal axis to acute isocapnic hypoxaemia in late gestation fetal sheep

Epidemiological and experimental evidence suggests that maternal undernutrition during pregnancy may alter development of fetal organ systems. We have demonstrated previously that fetal hypothalamic-pituitary-adrenal (HPA) axis responses to exogenous corticotropin-releasing hormone (CRH) + arginine vasopressin (AVP), or adrenocorticotrophin hormone (ACTH), are reduced in fetuses of mildly undernourished ewes. To examine these effects further we tested HPA axis responses to acute isocapnic hypoxaemia in fetal sheep at 114-129 days gestation (dGA), following 15% reduction in maternal nutritional intake between 0 and 70 dGA. Fetuses from control (C) and nutrient-restricted (R) ewes were chronically catheterised and plasma ACTH and cortisol responses were determined at 114-115, 120-123 and 126-129 dGA during hypoxaemia (1 h) induced by lowering the maternal inspired O2 fraction (FI,O2). Basal plasma cortisol concentrations and HPA axis responses at 114-115 and 120-123 dGA did not differ between C and R fetuses. At 126-129 dGA, both plasma ACTH (P < 0.01) and cortisol (P < 0.05) responses were smaller in R fetuses compared to C fetuses. Fetal blood gas status, fetal body weight, body proportions and organ weights did not differ between the groups. We conclude that mild maternal undernutrition alters development of the fetal HPA axis producing a reduction in pituitary and adrenal responsiveness to endogenous stimuli.     

Fetal exposure to excess glucocorticoid is unlikely to explain the effects of periconceptional undernutrition in sheep

Periconceptional undernutrition alters fetal growth, metabolism and endocrinology in late gestation. The underlying mechanisms remain uncertain, but fetal exposure to excess maternal glucocorticoids has been hypothesized. We investigated the effects of periconceptional undernutrition on maternal hypothalamic–pituitary–adrenal axis function and placental 11β-hydroxysteroid dehydrogenase type 2 (11βHSD2) activity. Ewes received maintenance feed (N, n = 20) or decreased feed from −60 to +30 days from mating to achieve 15% weight loss after an initial 2-day fast (UN, n = 21). Baseline plasma samples and arginine vasopressin (AVP)–corticotrophin-releasing hormone (CRH) challenges were performed on days −61, −57, −29, −1, +29, 33, and 49 from mating (day 0). Maternal adrenal and placental tissue was collected at 50 days. Baseline plasma levels of adrenocorticotrophic hormone (ACTH) and cortisol decreased in the UN group ( P < 0.0001). ACTH response to AVP–CRH was greater in UN ewes during undernutrition ( P = 0.03) returning to normal levels after refeeding. Cortisol response to AVP–CRH was greater in UN ewes after the initial 2-day fast, but thereafter decreased and was lower in UN ewes from mating until the end of the experiment ( P = 0.007). ACTH receptor, StAR and p450c17 mRNA levels were down-regulated in adrenal tissue from UN ewes. Placental 11βHSD2 activity was lower in UN than N ewes at 50 days ( P = 0.014). Moderate periconceptional undernutrition results in decreased maternal plasma cortisol concentrations during undernutrition and after refeeding, and adrenal resistance to ACTH for at least 20 days after refeeding. Fetal exposure to excess maternal cortisol is unlikely during the period of undernutrition, but could occur later in gestation if maternal plasma cortisol levels return to normal while placental 11βHSD2 activity remains low.     

The composition of maternal plasma and foetal urine after feeding and drinking in chronically catheterized ewes during the last two months of pregnancy

1. The fluid sacs and bladders of sixteen foetuses in fourteen ewes were catheterized between 81 and 92 days gestational age and the rumens of four ewes were also catheterized.2. Between 95 and 145 days gestational age in forty-six 24 hr experiments hourly samples of maternal plasma and foetal urine were obtained and in fifteen experiments foetal fluid samples were also taken at 4- to 6-hr intervals.3. The osmolality, pH, and concentrations of sodium, potassium, chloride, glucose, fructose and urea were measured on all samples.4. During experiment there was no significant variation in the composition of amniotic or allantoic fluid. Marked changes in osmolality occurred in maternal plasma and foetal urine when ewes drank after feeding, but not in ewes that received water intrarumenally via catheter while feeding or in fasting ewes. Post-prandial changes in maternal plasma osmolality may have altered transplacental water fluxes and as a result foetal plasma volume and osmolality.5. The results suggest that the foetus alters renal water retention by varying antidiuretic hormone (ADH) secretion in response to changes in blood volume and at later gestational ages plasma osmolality as well.6. Post-prandial changes in the [Na(+)]/[K(+)] ratio of foetal urine suggested that foetal adrenocorticotrophin (ACTH) secretion is influenced by variations in foetal blood volume and glucose concentrations.7. The post-prandial changes in foetal urine composition observed here support previous suggestions (Mellor & Slater, 1972) about the role of foetal urine in foetal fluid formation which were based on gestational changes in the composition of foetal fluids and urine sampled once daily during the post-absorptive state.     

Interactions between maternal subtotal nephrectomy and salt: effects on renal function and the composition of plasma in the late gestation sheep fetus

Effects of altered maternal salt intake between 122 and 127 days gestation (term is 150 days) were studied in eight fetuses carried by ewes which had renal insufficiency caused by subtotal nephrectomy (STNxF) and seven fetuses carried by intact ewes (IntF). Plasma sodium and osmolality were increased in ewes with subtotal nephrectomy on a high-salt intake (0.17 m NaCl in place of drinking water for 5 days; P < 0.05). The STNxF had normal body weights. A high maternal salt intake did not affect fetal blood pressure or heart rate. Plasma osmolality was higher in STNxF (P < 0.001), and plasma sodium and osmolality were increased by high salt (P < 0.001 and P < 0.04, respectively). The STNxF had higher urinary osmolalities (P = 0.002), which were also increased by a high maternal salt intake (P = 0.03). Renal blood flow fell in STNxF in response to a high maternal salt intake, but increased in IntF (P = 0.003). In STNxF but not IntF, glomerular filtration rate and urinary protein excretion were positively related to fetal plasma renin levels (P < or = 0.01). It is concluded that the salt intake of pregnant ewes with renal insufficiency affects maternal and fetal osmolar balance, fetal plasma sodium and fetal renal function. Since STNxF also had altered renal haemodynamic responses to high maternal salt and evidence of renin-dependent glomerular filtration and protein excretion, we suggest that interactions between dietary salt and pre-existing maternal renal disease impair glomerular integrity and function in the fetus.     

Increased uncoupling protein-2 mRNA abundance and glucocorticoid action in adipose tissue in the sheep fetus during late gestation is dependent on plasma cortisol and triiodothyronine

The endocrine regulation of uncoupling protein-2 (UCP2), an inner mitochondrial protein, in fetal adipose tissue remains unclear. The present study aimed to determine if fetal plasma cortisol and triiodothyronine (T₃) influenced the mRNA abundance of UCP2, glucocorticoid receptor (GR) and 11β-hydroxysteroid dehydrogenase type 1 (11βHSD1) and 2 (11βHSD2) in fetal adipose tissue in the sheep during late gestation. Perirenal–abdominal adipose tissue was sampled from ovine fetuses to which either cortisol (2–3 mg kg⁻¹ day⁻¹) or saline was infused for 5 days up to 127–130 days gestation, or near term fetuses (i.e. 142–145 days gestation) that were either adrenalectomised (AX) or remained intact. Fetal plasma cortisol and T₃ concentrations were higher in the cortisol infused animals and lower in AX fetuses compared with their corresponding control group, and increased with gestational age. UCP2 and GR mRNA abundance were significantly lower in AX fetuses compared with age-matched controls, and increased with gestational age and by cortisol infusion. Glucocorticoid action in fetal adipose tissue was augmented by AX and suppressed by cortisol infusion, the latter also preventing the gestational increase in 11βHSD1 mRNA and decrease in 11βHSD2 mRNA. When all treatment groups were combined, both fetal plasma cortisol and T₃ concentrations were positively correlated with UCP2, GR and 11βHSD2 mRNA abundance, but negatively correlated with 11βHSD1 mRNA abundance. In conclusion, plasma cortisol and T₃ are both required for the late gestation rise in UCP2 mRNA and differentially regulate glucocorticoid action in fetal adipose tissue in the sheep during late gestation.     

Distribution of ionic sulfate, lithium, and bromide across the sheep placenta.

Salts of sulfate, lithium, and bromine were injected or infused intravenously into ewes in the last trimester of gestation. Ewes and fetuses had indwelling catheters; most fetuses were nephrectomized. Concentrations were measured in paired maternal and fetal samples over periods of 4--14 days. Maternal excretion of sulfate was too rapid to permit near equilibration of fetal and maternal plasma concentrations; the results, however, did not support the existence of a large potential difference across the exchange barrier. The concentrations of Li+ (given by continuous infusion) and 82Br- in maternal plasma did not change rapidly. The concentrations of these tracers in fetal plasma rose until they were nearly equal to the maternal plasma concentrations. Steady-state transplacental potentials, calculated by use of the Nernst equation, were 5.2 +/- 2.0 (SEM) mV (n = 26) for Li+ and -2.2 +/- 0.8 (SEM) mV (n = 10) for Br-. Nernst potentials calculated from previously measured maternal and fetal plasma concentrations of Na+, K+, Mg2+, and Cl- were +0.4, +3.6, +0.5, and -1.4 mV. We concluded that, of the total potential difference of about -50 mV (fetus negative) between the fetal lamb and the ewe, only a few mV are dropped across the placental exchange barrier.     

Effect of cortisol on blood pressure and vascular reactivity in the ovine fetus.

The aim of this study was to investigate the cardiovascular effects of exogenous cortisol in fetal sheep, (a) between 100 and 120 days of gestation when cortisol production is minimal and (b) after 130 days when endogenous plasma cortisol starts to rise. Chronically cannulated ovine fetuses (103-120 days, n = 9; 130-137 days, n = 7), received sequentially a 24 h infusion of vehicle (0.9% sodium chloride) and a 24 h infusion of cortisol at 100 micrograms/h. Blood pressure and heart rate changes to bolus injections each of angiotensin II and noradrenaline (0.2, 0.5, 1.0, 2.0 micrograms) were measured before and after the saline and cortisol infusions. Fetuses in each age group, served as additional controls receiving 48 h saline infusions. In both immature and mature age groups, the cortisol infusion increased basal fetal blood cortisol concentrations by 33.7 and 35.4 nmol/l respectively. In the immature group, cortisol, but not saline, caused significant 14.3 and 15.3% increases in basal systolic and diastolic pressures respectively. Basal blood pressure was higher in the mature group, but did not increase further despite the increase in cortisol levels. Furthermore, vascular responsiveness to angiotensin II but not to noradrenaline was significantly enhanced following the cortisol infusion, at both ages. Fetal heart rate did not change following the cortisol infusion. Exogenous cortisol contributes to the regulation of fetal blood pressure in the immature fetus, when other mechanisms have not developed. Cortisol might achieve this, in part, by enhancing vascular sensitivity to angiotensin II.     

Effect of maternal starvation on fetal tissue nucleic acid, plasma amino acid and growth hormone concentration in sheep

The measurement of nucleic acids in fetal tissues as well as plasma growth hormone and amino acids was used in conjunction with fractional protein synthetic rates to investigate the mechanism of reduced fetal protein synthesis following acute maternal starvation. The nucleic acid analysis of fetal tissues from fed and 48 h starved ewes (120-130 days gestation) demonstrated a significant reduction in kidney RNA and heart DNA concentration in the starved fetuses. The RNA synthetic capacity (RNA/protein) was also seen to decrease in the starved fetuses both for liver and kidney tissue as was the protein/DNA in the lung tissue. Most revealing, however, were the measurements of RNA and DNA activity or the extent to which the protein synthesizing capacity was realized (g protein/g RNA or DNA/day). Significant reductions were observed in liver and brain RNA activity as well as the DNA activity of liver, lung, kidney and muscle. Plasma aminograms demonstrated reductions in maternal histidine, methionine and isoleucine as well as reductions in fetal glutamate and phenylalanine following starvation. Conversely, the fetal growth hormone levels were seen to rise under the influence of maternal starvation. The impact of maternal nutrient deprivation during gestation on fetal metabolism appears to depend on the ontogenic stage of development of specific tissues at the time the deprivation occurs.     

The effects of pregnancy and maternal nutrition on the maternal renin-angiotensin system in sheep

Physiological changes occurring in the mother during pregnancy can determine the outcome of pregnancy in terms of birthweight and neonatal viability. Maternal adaptations include plasma volume expansion linked to enhanced activity of the renin-angiotensin system (RAS). The present study was designed to determine whether these changes occur very early in gestation, and the extent to which maternal nutrient restriction may compromise the maternal RAS. Using sheep, we have investigated the effects of pregnancy per se, maternal nutrient restriction and later restoration of maternal diet on maternal body weight, plasma volume and plasma renin concentration (PRC), and angiotensinogen (Aogen) and arginine vasopressin (AVP) concentration. During the period of placental growth (i.e. 28-80 days gestation) ewes were fed either a nutrient-restricted (NR) diet or were well fed (WF). NR ewes consumed between 3.2 and 3.8 MJ day(-1) of metabolisable energy (ME) which is close to 60 % of requirements taking into account the ME required for both ewe maintenance and growth of the conceptus in order to produce a 4.5 kg lamb at term. WF ewes consumed 150 % of ME requirements. Restoration of maternal diet between 80 and 140 days gestation (i.e. fed to satiety and consuming between 8 and 10.9 MJ day(-1), which is close to 150 % of ME requirements) followed previous nutrient restriction. Between pre-conception and 28 days gestation, plasma volume increased in conjunction with a decline in PRC and Aogen concentration. During the period of nutrient restriction ewe body weight did not increase and plasma volume was lower in NR than WF ewes. During this time there was no effect of maternal nutrition on PRC; however, Aogen concentration was lower in the NR group. From 80 days gestation following the rise in food intake for previously NR ewes, greater increases in ewe body weight, plasma volume and PRC occurred up to term compared with ewes that were well fed throughout gestation. Plasma AVP concentration was not significantly affected by either maternal nutrition or gestational age. In conclusion, the stimulus of moderately severe maternal nutrient restriction evoked smaller rises in maternal weight, plasma volume and Aogen concentration than occurred in ewes that were well fed throughout gestation. Following the restoration of maternal diet after 80 days gestation, PRC gradually rose to peak at term. These adaptations in the maternal RAS during the critical period of placental growth may have long-term effects on fetal development.     

Serum hormones and metabolites in fetally decapitated pigs

The effects of fetal decapitation on serum hormones and metabolites were studied in utero in the pig. Pig fetuses were decapitated at 45 days of gestation and serum sampled from the umbilical vein and artery of each fetus and from the uterine artery at 110 days of gestation. Serum levels of cortisol were reduced in decapitated fetuses when compared to intact controls. The data suggest that the decapitated fetus derived its cortisol primarily from maternal sources. Decapitation produced a deficiency of serum RIA growth hormone, T3 and T4. The absence of these hormones produced no effect on fetal growth. Serum insulin, glucagon and triglycerides were elevated in decapitated fetuses. Arterial venous differences in blood glucose indicated that the decapitated fetuses were utilizing glucose at a higher rate than intact fetuses. The alterations seen in serum insulin and triglycerides suggest that neural mechanism may be involved in prenatal lipid deposition.     

Pancreatic α Cell Function in the Fetal Foal During Late Gestation

Plasma glucagon concentrations were measured in chronically catheterized fetal ponies and their mothers between 260 days of gestation and term (approximately 335 days). Fetal alpha cell responses to arginine and variations in fetal glycaemia were also examined during late gestation. Immunoreactive glucagon was present in fetal plasma at 260 days of gestation and its concentration in utero increased after 320 days and then again at birth. Maternal plasma glucagon concentrations were higher after 300 days than earlier in gestation but were lower than the corresponding fetal value throughout the period of gestation studied. Fetal alpha cells responded rapidly to intravenous arginine infusion but not to changes in the fetal glucose level induced by maternal fasting for 36 h or by intrafetal infusion of glucose. The maximal increment in fetal plasma glucagon in response to arginine occurred at the end of the 5 min infusion and was positively correlated to the basal pre-infusion plasma glucagon concentrations. Fetal plasma glucagon concentrations were unaffected by either hyper- or hypoglycaemia. In contrast, maternal plasma glucagon levels were significantly increased by fasting. These observations indicate that equine pancreatic alpha cells are functional in utero but that they are unresponsive to variations in glycaemia until after birth.     

Maternal melatonin selectively inhibits cortisol production in the primate fetal adrenal gland

We tested the hypothesis that in primates, maternal melatonin restrains fetal and newborn adrenal cortisol production. A functional G-protein-coupled MT1 membrane-bound melatonin receptor was detected in 90% gestation capuchin monkey fetal adrenals by (a) 2-[¹²⁵I] iodomelatonin binding ( K _d, 75.7 ± 6.9 p m ; B _max, 2.6 ± 0.4 fmol (mg protein)⁻¹), (b) cDNA identification, and (c) melatonin inhibition of adrenocorticotrophic hormone (ACTH)- and corticotrophin-releasing hormone (CRH)-stimulated cortisol but not of dehydroepiandrosterone sulphate (DHAS) production in vitro . Melatonin also inhibited ACTH-induced 3β-hydroxysteroid dehydrogenase mRNA expression. To assess the physiological relevance of these findings, we next studied the effect of chronic maternal melatonin suppression (induced by exposure to constant light during the last third of gestation) on maternal plasma oestradiol during gestation and on plasma cortisol concentration in the 4- to 6-day-old newborn. Constant light suppressed maternal melatonin without affecting maternal plasma oestradiol concentration, consistent with no effect on fetal DHAS, the precursor of maternal oestradiol. However, newborns from mothers under constant light condition had twice as much plasma cortisol as newborns from mothers maintained under a normal light–dark schedule. Newborns from mothers exposed to chronic constant light and daily melatonin replacement had normal plasma cortisol concentration. Our results support a role of maternal melatonin in fetal and neonatal primate cortisol regulation.     

The late gestation fetal cardiovascular response to hypoglycaemia is modified by prior peri-implantation undernutrition in sheep

Undernourished late gestation fetuses display asymmetric growth restriction, suggestive of a redistribution of nutritional resources. The modification of fetal organ blood supply in response to acute hypoxia is well characterized, but it is not known whether similar responses occur in response to acute reductions in nutrition, or if such late gestation responses can be influenced by early gestation nutrition. In pregnant sheep, total nutrient requirements were restricted during the peri-implantation period (PI40, 40%; PI50, 50% of total, days 1–31) or in late gestation (L, 50% total, days 104–postmortem). Control animals were fed 100% nutrient requirements. Fetal organ blood flows were measured at baseline, and during acute fetal hypoglycaemia induced by maternal insulin infusion at 125 dGA. Baseline heart rate was increased in PI40 fetuses. During hypoglycaemia, an initial rise in fetal heart rate was followed by a slower fall. Fetal femoral artery blood flow decreased, and adrenal blood flow and femoral vascular resistance increased in all fetuses during hypoglycaemia. These changes were accompanied by increased fetal plasma adrenaline and cortisol, and reduced plasma insulin levels. The maximum femoral artery blood flow response to hypoglycaemia occurred earlier in PI50 and PI40 compared with control fetuses. The late gestation fetal cardiovascular response to acute hypoglycaemia was consistent with a redistribution of combined ventricular output away from the periphery and towards central organs. One element of the peripheral vascular response was modified by peri-implantation nutrient restriction, indicating that nutritional challenges early in gestation can have an enduring impact on cardiovascular control.     

Teratogenicity of N-(4-hydroxyphenyl)-all-trans-retinamide in rats and rabbits

N-(4-hydroxyphenyl)-all-trans-retinamide (HPR) has potential efficacy in the treatment of dermatologic, arthritic, and neoplastic disorders. The teratogenicity of such a compound is of special concern in light of the known adverse effects of retinoids, in general, on the developing conceptus. In these studies, Sprague-Dawley rats and New Zealand White rabbits were treated orally from gestation days 6 to 15 and 6 to 18, respectively, with 0, 20, 125, or 800 mg/kg/day of HPR. In rat fetuses, low incidences of hydrocephaly (mid- and high-dosage groups) were observed. Fetal tissue (ng/g) and maternal plasma (ng/ml) concentrations of HPR, its major metabolite (N-[4-methoxyphenyl] retinamide [MPR]) and retinol were determined in separate groups of similarly-treated rats 3 h following the last dose on gestation day 15. Fetal tissue concentrations of HPR and MPR were approximately one-half maternal plasma concentrations. A dose related reduction in maternal plasma and fetal tissue concentrations of retinol were also observed. In mid- and high-dosage rabbit fetuses, a dose-related increase in the incidence of dome-shaped head was observed. Subsequent skeletal evaluation revealed delays in skull bone ossification and a widening of the frontal and frontoparietal sutures. Microphthalmia was also observed in two high-dosage fetuses. A dose-dependent and statistically significant reduction in maternal plasma retinol levels was observed across all dosage groups.     

Effect of acute maternal starvation on tyrosine metabolism and protein synthesis in fetal sheep

To determine the effects of acute maternal starvation on intrauterine growth, tyrosine concentration and specific activity values in plasma, intracellular free and protein bound pools were determined in catheterized ovine fetuses following an 8 h continuous infusion of L-[2,3,5,6 3H] or L-[U-14C] tyrosine into the ewe and fetus respectively at 115-125 days of gestation. From the kinetic data the rates of whole body and tissue fractional protein synthesis were calculated. Although placental protein synthesis was not significantly changed as a result of acute maternal starvation, fetal whole body protein synthesis was reduced from 63 g/d/kg in the fed to 25 g/d/kg in the starved condition. There was also a 10 fold reduction in the net placental transfer of tyrosine to the fetus in the starved ewes. In addition, a three fold increase was observed in the quantity of tyrosine used for oxidation by the fetuses of starved ewes, changing from 5.2% of tyrosine net utilization in the fed to 13.7% in the starved condition. Significant reductions in tissue fractional protein synthesis rates were also seen in the liver, brain, lung kidney and GIT tissues from 78, 37, 65, 45 and 71%/d respectively in the fed to 12, 10, 23, 22 and 35%/d in the fetuses of starved ewes. The data indicate that during acute maternal starvation the sheep fetus utilizes more tyrosine for oxidation and less for anabolic purposes which is reflected in a decrease both in whole body and tissue fractional rates of protein synthesis.     

Fetal motor activity and maternal cortisol

The contemporaneous association between maternal salivary cortisol and fetal motor activity was examined at 32 and 36 weeks gestation. Higher maternal cortisol was positively associated with the amplitude of fetal motor activity at 32 weeks, r(48) = .39, p < .01, and 36 weeks, r(77) = .27, p < .05, and the amount of time fetuses spent moving at 32 weeks during the 50 min observation period, r(48) = 33, p < .05. Observation of periods of unusually intense fetal motor activity were more common in fetuses of women with higher cortisol, Mann–Whitney U = 58.5. There were no sex differences in fetal motor activity, but the associations between maternal cortisol and fetal motor amplitude and overall movement were significantly stronger for male than female fetuses. © 2009 Wiley Periodicals, Inc. Dev Psychobiol 51: 505–512, 2009     

ACTH-producing cells of 21-day-old rat fetuses after maternal dexamethasone exposure

Adrenocorticotrophic hormone (ACTH) is essential for developmental maturation of numerous organ systems during the fetal period and for adaptation to environmental challenges. Immunocytochemical and stereological methods were used in the present study to examine the effects of dexamethasone (Dx) administration during pregnancy on fetal rat pituitary ACTH-producing cells. Doses of 0.5, 0.5 and 1.0 mg Dx/kg body weight/day were given to the dams on 3 consecutive days starting on day 16 of gestation. Morphometric analysis of the ACTH-producing cells of fetuses at 21 days of gestation revealed significant inhibition by 24% and 27%, respectively, of cell volume and cell number after maternal Dx administration, whereas the volume of cell nuclei and volume density of ACTH-stained cells were insignificantly decreased. Immunocytochemical analysis showed reduced numbers, sizes and immunopositivity of ACTH cells of 21-day-old fetuses from Dx-treated dams as compared with the control group. Maternal Dx treatment in the period of intense differentiation of the hypothalamo-hypophyseal-adrenal system had an inhibitory effect on fetal function and proliferative activity of ACTH-producing cells at 21 days of gestation. Thus, inhibition of activity of fetal ACTH-producing cells may lead to adrenal suppression, modified activity of the hypothalamo-pituitary-adrenal axis and reduced body weight possibly causing lasting functional abnormalities.     

Effects of twin pregnancy and periconceptional undernutrition on maternal metabolism, fetal growth and glucose-insulin axis function in ovine pregnancy

Although twins have lower birthweights than singletons, they may not experience the increased disease risk in adulthood reportedly associated with low birthweight. In contrast, another periconceptional event, maternal undernutrition, does not reduce birthweight but does affect fetal and postnatal physiology in sheep. We therefore studied maternal and fetal metabolism, growth and glucose–insulin axis function in late gestation in twin and singleton sheep pregnancies, either undernourished from 60 days before until 30 days after conception or fed ad libitum . We found that twin-bearing ewes had decreased maternal food intake in late gestation and lower maternal and fetal plasma glucose and insulin levels. Twin fetuses had fewer everted placentomes, grew slower in late gestation, and had a greater insulin response to a glucose challenge, but lesser response to arginine. In contrast, periconceptional undernutrition led to increased maternal food intake and a more rapid fall in maternal glucose levels in response to fasting. Periconceptional undernutrition increased the number of everted placentomes, and abolished the difference in insulin responses to glucose between twins and singletons. Thus, the physiology of twin pregnancy is quite different from that of singleton pregnancy, and is probably determined by a combination of factors acting in both early and late gestation. The inconsistency of the relationships between low birthweight and postnatal disease risk of twins may lie in their very different fetal development. These data suggest that twin pregnancy may be another paradigm of developmental programming, and indicate that twins and singletons must be examined separately in any study of fetal or postnatal physiology.     

不同妊娠状态下孕妇外周血中游离胎儿DNA定量分析

目的对不同妊娠状态下孕妇外周血中游离胎儿DNA(f DNA)定量分析,确定其平均浓度及临床参考值范围,初步探讨在不同妊娠状态下母血中f DNA的浓度变化,为临床应用提供科学依据。方法从孕妇外周血浆中提取fDNA,用实时荧光定量聚合酶链反应(FQ-PCR)方法检测其中Y性别决定区的SRY基因。结果在正常早期的孕妇组38例血浆标本中有32例检测到SRY基因,其平均浓度149.25拷贝数/ml,参考值范围为33.28~265.22拷贝数/ml;在正常晚期的孕妇组32例血浆标本中全部检测到SRY基因,其平均浓度为212.14拷贝数/ml,参考值范围为142.76~281.52拷贝数/ml;在晚期患有子痫前期的孕妇30例血浆标本中全部检测到SRY基因,其平均浓度为678.70拷贝数/ml,参考值范围为595.01~726.40拷贝数/ml。实验数据用单因素方差分析,组间差异显著性检验用LSD-t检验。妊娠晚期孕妇血浆中f DNA的含量较妊娠早期升高,约为1.4倍,有统计学意义(P<0.01);晚期患子痫前期的孕妇血浆f DNA的水平是同期正常对照组的3.9倍,有统计学意义(P<0.01)。结论1.用FQ-PCR法最早在孕48天孕妇外周血中即可检测到fDNA。2.随着妊娠的进展孕妇血浆中f DNA的含量升高。3.晚期患子痫前期孕妇其血浆f DNA的水平是同期正常对照组的3.9倍,有统计学意义(P<0.01)。4.f DNA在进行无创伤性产前诊断中有重要价值。     

Synthesis of taurocholate by rat fetal liver in organ culture: effects of cortisol in vitro.

Taurocholate production by fetal hepatic organ cultures was measured by radioimmunoassay. Taurocholate production was maximal on day 1 of in vitro incubation, but was demonstrable in organ cultures maintained for periods up to 15 days. Explants obtained from fetuses of 18 gestational days of age produced only 82 pmol taurocholate per milligram dry weight of tissue during the first 24 h of incubation. Explants obtained from fetuses 21 gestational days of age produced 1,043 pmol taurocholate per milligram dry weight. The presence of cortisol (2.0 X 10(-6) M) in the incubation medium increased synthesis of taurocholate by rat fetal liver in which total taurocholate rose 50-fold above control after 120 h of incubation. In increasing concentrations from 2.0 X 10(-9) M to 2.0 X 10(-7) M, cortisol produced an incremental rise in taurocholate. However, additional increases in cortisol dose failed to provide further stimulation, and taurocholate production was inhibited by cortisol concentrations of 2.0 X 10(-5) M. The results provide further validation for the technique of fetal hepatic organ culture. They demonstrate that taurocholate synthesis is increasing rapidly during the final stages of gestation and show that cortisol augments taurocholate synthesis in a dose-response pattern.