Impact of placental restriction on the development of the sympathoadrenal system

Size at birth and autonomic function during psychological stress

Small size at birth is associated with exaggerated blood pressure responses to psychological stressors, which increase the risk of developing sustained hypertension in adult life. Explanatory mechanisms for this association are not well characterized. We investigated the hypothesis that an adverse fetal environment, reflected by small size at birth, persistently alters autonomic nervous system and baroreflex control of cardiovascular function, resulting in exaggerated blood pressure and heart rate responses to stressors. Men and women from an Australian prospective cohort study underwent a series of 3 psychological stressors (Stroop, mirror-tracing, and speech) while their blood pressure was recorded continuously using a Portapres. Indices of autonomic function were derived using spectrum analysis (wavelet packet transform), and baroreflex function was estimated using an adaptive autoregressive model. We found that women who were small at birth demonstrated increased levels of low-frequency blood pressure variability at rest (r=-0.28; P<0.05) and during stress (r=-0.42; P<0.001), reduced levels of high-frequency heart period variability (r=0.22; P<0.05), and reduced baroreflex sensitivity (r=0.34; P<0.01). These findings were not present in the men. This study provides evidence that markers of impaired fetal growth are related to autonomic cardiovascular control involving modulation of both sympathetic and parasympathetic function but in a sex-specific manner. We also provide the first human evidence of a relationship between size at birth and baroreflex function.

Restricted fetal growth and lung development: a morphometric analysis of pulmonary structure

Intrauterine growth restriction (IUGR) in humans increases the risk of lung disease and impaired function suggesting that adverse intra-uterine conditions can alter lung development. We hypothesized that placental restriction (PR) of fetal growth would alter lung structure in late gestation. PR involved removal of implantation sites in pre-pregnant ewes. Normal (n = 7) and PR (n = 11) fetuses were delivered at day 140 gestation. Lungs were fixed by tracheal infusion, processed and analyzed by morphometry. PR reduced ponderal index (PI) of lambs by 13%, increased lung volume:body weight (BW) (19%), and decreased the proportion of lung volume that comprised parenchyma from 86.5(2.6)% to 76.7(2.1)% with no change in absolute volume of non-parenchyma. Within the parenchyma, PR increased the proportion comprising airspace from 42.0(2.2)% to 55.5(1.7)% with smaller (-13%) more dense (18%) airsacs/alveoli present. The overall effect was a reduction in total gas-exchange surface density (-10%). Lung wet-weight and volume, parenchymal volume, gas-exchange tissue, and airspace volumes and gas-exchange surface area correlated positively with BW and crown-rump length (CRL) for all animals. The relative lung weight and volume correlated negatively with BW, CRL, and lung weight:BW with PI. Lung weight, lung volume, parenchymal volume, airspace perimeter, percent of parenchymal gas-exchange tissue, gas-exchange surface density, and area correlated positively with PI. The results indicate increased sparing of lung growth but with increasing structural changes, predominantly within lung parenchyma, with increasing growth restriction. Structural alterations associated with PR and poor fetal growth may be important in the pathogenesis of impaired lung function associated with IUGR.

Fetal programming of hypertension

Numerous epidemiological studies suggest an inverse relationship between low birth weight (LBW) and hypertension, an observation now supported by numerous animal studies. The mechanisms linking LBW and hypertension appear to be multifactorial and involve alterations in the normal regulatory systems and renal functions involved in the long-term control of arterial pressure. Recent studies using animal models of fetal programming suggest that programming during fetal life occurs in response to an adverse fetal environment and results in permanent adaptive responses that lead to structural and physiological alterations and the subsequent development of hypertension. This review summarizes the adaptive responses observed in the different models used to induce a suboptimal fetal environment and discusses insights into the mechanisms mediating the fetal programming of hypertension.

Management of preterm infants with intrauterine growth restriction

Preterm intrauterine growth restriction (IUGR) is strongly associated with increased mortality and morbidity. In the management of these infants, complications of preterm birth can be amplified by the effect of suboptimal fetal growth. It is important that pregnancies with IUGR are detected before birth, so that delivery can be arranged in a high-risk maternity unit with the appropriate neonatal staff in attendance. The provision of full support for resuscitation and stabilisation of these infants is crucial to the short-term and long-term health of these infants, who have suffered chronic hypoxia and malnutrition in utero. The long term outcome studies of these infants are retrospective and they include SGA infants. The effects of prematurity affect the outcome of IUGR infants. IUGR is associated with cerebral palsy in those delivered more than 32 weeks gestation. Infants less than 32 weeks of gestation may have poor developmental outcome if the head growth is affected, these infants may have associated cognitive and behavioural problems. Children who fail to grow by 2-4 years are at risk of long term growth problems. This paper outlines the acute and long-term management of these infants.

Developmental origins of the metabolic syndrome: prediction, plasticity, and programming

The "fetal" or "early" origins of adult disease hypothesis was originally put forward by David Barker and colleagues and stated that environmental factors, particularly nutrition, act in early life to program the risks for adverse health outcomes in adult life. This hypothesis has been supported by a worldwide series of epidemiological studies that have provided evidence for the association between the perturbation of the early nutritional environment and the major risk factors (hypertension, insulin resistance, and obesity) for cardiovascular disease, diabetes, and the metabolic syndrome in adult life. It is also clear from experimental studies that a range of molecular, cellular, metabolic, neuroendocrine, and physiological adaptations to changes in the early nutritional environment result in a permanent alteration of the developmental pattern of cellular proliferation and differentiation in key tissue and organ systems that result in pathological consequences in adult life. This review focuses on those experimental studies that have investigated the critical windows during which perturbations of the intrauterine environment have major effects, the nature of the epigenetic, structural, and functional adaptive responses which result in a permanent programming of cardiovascular and metabolic function, and the role of the interaction between the pre- and postnatal environment in determining final health outcomes.

Differential effects of maternal hypoxia or nutrient restriction on carotid and femoral vascular function in neonatal rats

In response to reduced oxygen or nutrient supply, the fetus may redistribute cardiac output to conserve brain and heart growth, at the expense of the peripheral tissues; however, it is not known whether alterations in vascular function are maintained after birth or whether reduced fetal oxygen versus nutrient supply produces distinct effects. Using a pressure myograph, we examined isolated carotid and femoral artery responses to phenylephrine and endothelin-1 in neonatal rats, after either reduced maternal oxygen or global nutrient restriction during late gestation. Timed-pregnant Sprague-Dawley rats were randomly assigned to control ( n = 10), hypoxia (12% O2, n = 9), or nutrient restriction (NR, 40% of control diet, n = 7) protocol and treated from day 15–21 of pregnancy. Pups were collected 3–12 h after birth. Neonatal weights ( P < 0.001) and relative liver weights ( P < 0.001) were lower in hypoxia and nutrient restriction treatments compared with control, while relative heart weights were greater in the hypoxia than in the control or nutrient restriction groups ( P < 0.01). Constriction to phenylephrine was reduced in carotid arteries from the hypoxia and nutrient restriction groups compared with control ( P < 0.001), while the femoral artery response was greater in hypoxia-treated neonates compared with control or nutrient-restricted neonates ( P < 0.01). Only the hypoxia reduced carotid responses to endothelin-1, while no differences were observed in the endothelin-1 responses in femoral arteries. Maternal hypoxia and maternal nutrient restriction produced distinct effects on heart growth and neonatal vascular function, suggesting that regional changes in cardiovascular function after poor fetal growth are dependent on the nature of the insult in utero.

Restriction of placental growth results in greater hypotensive response to alpha-adrenergic blockade in fetal sheep during late gestation

Placental insufficiency resulting in restriction of fetal substrate supply and fetal hypoxaemia is a major cause of restricted fetal growth and increased neonatal morbidity. Fetal adaptations to placental restriction (PR) include increases in circulating catecholamines and cortisol and decreased fetal body growth, with relative sparing of brain growth. The mechanisms underlying the redistribution of fetal cardiac output in PR fetuses are not known and the aim of this study was to determine whether maintenance of fetal blood pressure (BP) in the PR fetus is dependent on alpha-adrenergic stimulation. PR was induced by removing the majority of uterine caruncles in the ewe before conception. Sterile vascular surgery was performed on seven PR and six control fetuses at 113-120 days' gestation (term = 150 +/- 3 days). Fetuses with a mean arterial PO2 < 17 mmHg between 123 and 127 days' gestation were defined as hypoxic. There was a greater fall (P < 0.05) in fetal BP during phentolamine infusion (i.v: 5 mg bolus, 0.2 mg kg(-1) min(-1) for 2 h) in the hypoxic PR group (-15 +/- 2 mmHg) compared with normoxic controls (-5 +/- 1 mmHg). The fall in fetal BP during phentolamine infusion was directly related to the level of fetal PO2. Fetal BP and HR responses to phenylephrine (i.v.: 40 microg kg(-1)) were not different between PR and control fetuses. The maintenance of BP in the chronically hypoxic fetus is therefore dependent on alpha-adrenergic activation, and this fetal adaptation to a suboptimal intrauterine environment pre-dates the development of significant growth restriction. While this adaptation may play a critical role in the redistribution of fetal cardiac output to ensure the sparing of brain growth, it may have adverse consequences for peripheral vascular function in the neonatal period and in adult life.

Impact of periconceptional nutrition on maternal and fetal leptin and fetal adiposity in singleton and twin pregnancies

It has been proposed that maternal nutrient restriction may alter the functional development of the adipocyte and the synthesis and secretion of the adipocyte-derived hormone, leptin, before birth. We have investigated the effects of restricted periconceptional undernutrition and/or restricted gestational nutrition on fetal plasma leptin concentrations and fetal adiposity in late gestation. There was no effect of either restricted periconceptional or gestational nutrition on maternal or fetal plasma leptin concentrations in singleton or twin pregnancies during late gestation. In ewes carrying twins, but not singletons, maternal plasma leptin concentrations in late gestation were directly related to the change in ewe weight that occurred during the 60 days before mating [maternal leptin = 0.9 (change in ewe weight) + 7.8; r = 0.6, P < 0.05]. In twin, but not singleton, pregnancies, there was also a significant relationship between maternal and fetal leptin concentrations (maternal leptin = 0.5 fetal leptin + 4.2, r = 0.63, P < 0.005). The relative mass of perirenal fat was also significantly increased in twin fetal sheep in the control-restricted group (6.0 ± 0.5) compared with the other nutritional groups (control-control: 4.1 ± 0.4; restricted-restricted: 4.4 ± 0.4; restricted-control: 4.3 ± 0.3). In conclusion, the impact of maternal undernutrition on maternal plasma leptin concentrations during late gestation is dependent on fetal number. Furthermore, we have found that there is an increased fetal adiposity in the twins of ewes that experienced restricted nutrition throughout gestation, and this may be important in the programming of postnatal adiposity.

Prenatal stress changes rat arterial adrenergic reactivity in a regionally selective manner

A suboptimal fetal environment has been linked to increased risk of cardiovascular disease in adulthood. We investigated whether intrauterine stress (IUS) alters the development of adrenergic reactivity in different types of rat arteries. Intrauterine stress was induced by ligation of the uterine arteries at day 13 of pregnancy in Wistar rats. First-order mesenteric, renal, femoral and saphenous arteries of the 21-day-old male offspring were studied in a myograph. IUS in the rat changes arterial adrenergic reactivity in a regionally selective manner. Adrenoceptor-mediated responses are altered in the renal artery. Maximal contractile responses to phenylephrine were increased, while sensitivity to the alpha(1)-adrenoceptor agonist was decreased. Intrauterine stress significantly reduced contractile responses to norepinephrine and enhanced relaxing responses to isoproterenol in the renal artery. Adrenergic responses were not modified in mesenteric, femoral and saphenous arteries. In the kidneys the densities of [(3)H]prazosin binding sites, periarterial adrenergic nerves and of the glomeruli were not altered after intrauterine stress at day 13 of gestation. The observed regionally selective alterations in arterial reactivity might link a suboptimal fetal environment to the development of cardiovascular disease in the adult.

Nutritional Manipulation of Fetal Adipose Tissue Deposition and Uncoupling Protein 1 Messenger RNA Abundance in the Sheep: Differential Effects of Timing and Duration

A range of epidemiological and experimental studies have indicated that suboptimal nutrition at different stages of gestation is associated with an increased prevalence of adult hypertension, cardiovascular disease, and obesity. The timing of prenatal nutrient restriction is important in determining postnatal outcomes-including obesity. The present study, aimed to determine the extent to which fetal adiposity and expression of the key thermogenic protein, uncoupling protein (UCP)1, are altered by restriction of maternal nutrient intake imposed during four different periods, starting from before conception. Maternal nutrient intake was restricted from 60 days before until 8 days after mating (periconceptional nutrient restriction; R-C), from 60 days before mating and throughout gestation (R-R), from 8 days gestation until term (C-R), or from 115 days gestation until term. Fetal perirenal adipose tissue (PAT) was sampled near to term at approximately 143 days. UCP1 mRNA, but not protein, abundance in PAT was increased in fetuses in the R-R group (C-C 63 +/- 18; R-C 83 +/- 43; C-R 103 +/- 38; R-R 167 +/- 50 arbitrary units (P < 0.05)). In contrast, the abundance of UCP1 mRNA, but not protein, in fetal PAT was decreased when maternal nutrition was restricted from 115 days gestation. The major effect of maternal nutrient restriction on adipose tissue deposition occurred in the C-R group, in which the proportion of fetal fat was doubled, whereas maternal nutrient restriction from 115 days gestation reduced fetal fat deposition. In conclusion, there are differential effects of maternal and therefore fetal nutrient restriction on UCP1 mRNA expression and fetal fat mass and these effects are dependent on the timing and duration of nutrient restriction.

Reduced uteroplacental blood flow alters renal arterial reactivity and glomerular properties in the rat offspring

Fetal malnutrition and hypoxia may modify organ system maturation and result in cardiovascular diseases in the adult. We tested whether intrauterine stress (IUS) leads to persistent alterations of renal biology. In rats, intrauterine stress was induced by ligation of the uterine arteries at day 17 of pregnancy. Renal arteries of the 21-day-old male offspring were isolated to study pharmacological reactivity. Kidneys were dissected to analyze renal structure and beta-adrenoceptor expression. At 21 days of age, half of the animals underwent unilateral left nephrectomy. At the age of 12 weeks, rats were instrumented for blood pressure monitoring, blood sampling, and renal function measurements. After IUS, litter size and birth weight were reduced, whereas the hematocrit was increased. Renal arterial responses to beta-adrenergic stimulation and sensitivity to adenylyl cyclase activation were increased, along with the renal expression of beta2-adrenoceptors. At 21 days and at 6 months of age, the number and density of the glomeruli were reduced, whereas their size was increased. The filtration fraction and urinary albumin concentration were increased 12 weeks after intrauterine stress. In control rats, removal of the left kidney at 21 days of age did not affect kidney function and blood pressure. However, after IUS, the remaining right kidney failed to compensate for the loss of the left kidney, and blood pressure was increased. In conclusion, prenatal stress transiently modifies renal arterial reactivity and results in long-lasting adverse effects on renal structure and function and on renal compensatory mechanisms.

The effect of birth weight on hypothalamo-pituitary-adrenal axis function in juvenile and adult pigs

Programming of the hypothalamo-pituitary-adrenal (HPA) axis during prenatal and early postnatal life may explain, in part, the association between low birth weight (BW) and the increased incidence of cardiovascular and metabolic disease in later life. This study examined the effect of natural variations in BW on HPA axis function in juvenile and adult pigs. Low (< 1.47 kg) and high (> 1.53 kg) BW pure-bred Large White piglets from 15 litters were studied at 3 (n = 47) and 12 (n = 17) months of age. At each age, HPA axis function was tested by hypoglycaemic challenge (I.V. insulin; 0.5 IU (kg body weight)(-1)) and ACTH challenge (I.V. Synacthen, 2 microg (kg body weight)(-1)). At 3 months of age, adrenal size, the ratio of adrenal cortical to medullary area and stimulated cortisol concentrations were elevated in pigs that were of low BW and that remained small after birth. At 12 months of age, thinness at birth was associated with elevated adrenal responsiveness to insulin-induced hypoglycaemia. These results are consistent with the hypothesis that impaired fetal and early postnatal growth are associated with altered HPA axis function in later life.

Impact of maternal undernutrition during the periconceptional period, fetal number, and fetal sex on the development of the hypothalamo-pituitary adrenal axis in sheep during late gestation

Evidence from epidemiologic, clinical, and experimental studies has shown that a suboptimal intrauterine environment during early pregnancy can alter fetal growth and gestation length and is associated with an increased prevalence of adult hypertension and cardiovascular disease. It has been postulated that maternal nutrient restriction may act to reprogram the development of the pituitary-adrenal axis, resulting in excess glucocorticoid exposure and adverse health outcomes in later life. It is unknown, however, whether maternal nutrient restriction during the periconceptional period alters the development of the fetal pituitary-adrenal axis or whether the effects of periconceptional undernutrition can be reversed by the provision of an adequate level of maternal nutrition throughout the remainder of pregnancy. We have investigated the effect of restricted periconceptional nutrition (70% of control feed allowance) from 60 days before until 7 days after mating and the effect of restricted gestational nutrition from Day 8 to 147 of gestation on the development of the fetal hypothalamo-pituitary adrenal (HPA) axis in the sheep. In these studies, we have also investigated the effects of fetal number and sex on the pituitary-adrenal responses to periconceptional and gestational undernutrition. In ewes maintained on a control diet throughout the periconceptional and gestational periods, fetal plasma ACTH concentrations were higher and the prepartum surge in cortisol occurred earlier in singletons compared with twins. Plasma ACTH concentrations were also significantly higher in male compared with female singletons, and in twin fetuses, the prepartum surge in cortisol concentrations occurred earlier in males than in females. Periconceptional undernutrition resulted in higher fetal plasma concentrations of ACTH between 110 and 145 days of gestation and a significantly greater cortisol response to a bolus dose of corticotropin-releasing hormone in twin, but not singleton, fetuses in late gestation. We have therefore demonstrated that fetal number and sex each has an impact on the timing of the prepartum activation of the HPA axis in the sheep. Restriction of the level of maternal nutrition before and in the first week of a twin pregnancy results in stimulation of the fetal pituitary-adrenal axis in late gestation, and this effect is not reversed by the provision of a maintenance control diet from the second week of pregnancy.

Effects of prevailing hypoxaemia, acidaemia or hypoglycaemia upon the cardiovascular, endocrine and metabolic responses to acute hypoxaemia in the ovine fetus

Although it is established that the fetus can successfully withstand a single, acute hypoxaemic challenge during gestation, little is known about what effects prevailing adverse intrauterine conditions might have on the fetal response to acute hypoxaemia. The aims of this study were therefore: (1) to characterise the effects of prevailing and sustained hypoxaemia, acidaemia or hypoglycaemia on the fetal cardiovascular responses to an episode of acute hypoxaemia; and (2) to determine the effects of these adverse intrauterine conditions on mechanisms mediating these cardiovascular responses. Thirty-three Welsh Mountain sheep fetuses were chronically instrumented (1-2 % halothane) between 117 and 125 days of gestation (term is ca 145 days) with amniotic and vascular catheters and with a transit-time flow probe around a femoral artery. The animals were divided retrospectively into four groups based upon post-surgical, sustained, basal blood oxygen (chronically hypoxaemic; P(a,O2), 17.3 +/- 0.5 mmHg; n = 8), glucose (chronically hypoglycaemic; blood glucose, 0.49 +/- 0.03 mmol l(-1); n = 6) and acid-base (chronically acidaemic; pH(a), 7.25 +/- 0.01; n = 5) status. Values for compromised fetuses were -2 S.D. from a group of control (n = 14) fetuses. At 130 +/- 4 days, a 1 h episode of acute, isocapnic hypoxaemia (9 % O(2) in N(2), to reduce carotid P(a,O2) to 12 +/- 1 mmHg) was induced in all fetuses by reducing the maternal inspired O(2) fraction (F(I,O2)). Fetal cardiovascular variables were recorded at 1 s intervals throughout the experimental protocol and arterial blood samples taken at appropriate intervals for biophysical (blood gases, glucose, lactate) and endocrine (catecholamines, vasopressin, cortisol, ACTH) measures. During acute hypoxaemia all fetuses elicited hypertension, bradycardia and femoral vasoconstriction. However, prevailing fetal compromise altered the cardiovascular and endocrine responses to a further episode of acute hypoxaemia, including: (1) enhanced pressor and femoral vasoconstriction; (2) greater increments in plasma noradrenaline and vasopressin during hypoxaemia; and (3) basal upward resetting of hypothalamic-pituitary-adrenal axis function. Only chronically hypoxaemic fetuses had significantly elevated basal concentrations of noradrenaline and enhanced chemoreflex function during acute hypoxaemia. These data show that prevailing adverse intrauterine conditions alter the capacity of the fetus to respond to a subsequent episode of acute hypoxaemia; however, the partial contributions of hypoxaemia, acidaemia or hypoglycaemia to mediating these responses can vary.

The effects of birth weight on basal cardiovascular function in pigs at 3 months of age

In man, epidemiological studies have shown that low birth weight (BW) is associated with an increased risk of cardiovascular disease in later life. In this study, the long-term consequences of variations in natural BW on basal cardiovascular function were investigated in pigs at 3 months of postnatal age. Low (< 1.41 kg; n = 20) and high (> 1.52 kg; n = 20) BW Large White piglets were selected from a total of 12 litters for study at 3 months of age. Basal mean arterial pressure (MAP) and heart rate (HR) were recorded for approximately 30 min using standard recording equipment and basal arterial blood samples were taken for hormone analyses. Concentrations of angiotensin-converting enzyme (ACE) were also measured in kidney, lung and plasma. Basal MAP, but not HR, in 3-month-old pigs was significantly inversely related to BW and positively related to the ratio of head length to BW. Postnatal growth rate of low BW pigs was slower than that of high BW pigs such that low BW piglets remained significantly smaller at 3 months of age. There were no differences in basal plasma adrenaline or cortisol concentrations between low and high BW pigs. However, basal plasma noradrenaline concentrations were significantly elevated in low BW compared to high BW pigs. Renal and pulmonary ACE levels were significantly reduced in low BW compared to high BW pigs. These data show that basal MAP in 3-month-old pigs is negatively associated with BW and positively correlated to disproportionate size at birth. This effect was associated with an increase in basal plasma noradrenaline concentrations.

Evaluation of gestational deficiencies in cloned sheep fetuses and placentae

Sheep fetal development at 35 days of gestation was examined following natural mating, in vitro production (IVP) of fertilized embryos, or somatic cell nuclear transfer (NT). Five crossbred (Blackface x Black Welsh) and four purebred (Black Welsh) fetuses and their associated placentae produced by natural mating were morphologically normal and consistent with each other. From 10 ewes receiving 21 IVP embryos, 17 fetuses (81%) were recovered, and 15 of these (88%) were normal. The NT fetuses were derived from two Black Welsh fetal fibroblast cell lines (BLW1 and 6). Transfer of 21 BLW1 and 22 BLW6 NT embryos into 12 and 11 ewes, respectively, yielded 7 (33%) and 8 (36%) fetuses, respectively. Only three (43%) BLW1 and two (25%) BLW6 NT fetuses were normal, with the rest being developmentally retarded. The NT fetal and placental deficiencies included liver enlargement, dermal hemorrhaging, and lack of placental vascular development reflected by reduced or absent cotyledonary structures. Fibroblasts isolated from normal and abnormal cloned fetuses did not differ in their karyotype from sexually conceived fetuses or nuclear donor cell lines. Our results demonstrate that within the first quarter of gestation, cloned fetuses are characterized by a high incidence of developmental retardation and placental insufficiency. These deficiencies are not linked to gross defects in chromosome number.

Catecholamine levels and receptor expression in low protein rat offspring

AIMS

Low birthweight in humans has been shown to lead to increased resting pulse rate in adult life, suggesting possible increased sympathoadrenal activity. The hypothesis that early growth restriction is associated with permanent alterations in catecholamine metabolism was tested.

METHODS

Circulating catecholamine concentrations (by radioimmunoassay) and adipocyte adrenoceptor expression from different fat depots (by Western blot) were estimated in 12-week-old male offspring of rat dams fed a reduced protein diet during pregnancy and lactation.

RESULTS

In the fed state, median (interquartile range) plasma adrenaline concentrations for male control and low protein offspring rats were: 0.65 (0.48-0.86) vs. 1.42 (0.89-1.87) nmol/l (P < 0.005), respectively. Equivalent noradrenaline concentrations were: 2.71 (2.16-3.46) vs. 3.45 (3.00-4.28) nmol/l (P < 0.05). After 24 h starvation, plasma adrenaline concentrations of controls rose to become similar to those of low protein offspring: 1.03 (0.95-1.31) vs. 1.41 (0.69-1.62) nmol/l (P = 0.3), respectively. Noradrenaline concentrations rose in both groups to become similar: 3.84 (3.33-4.54) vs. 4.32 (3.70-6.54) nmol/l (P = 0.3). In epididymal adipocytes adrenoceptor expression (relative to that of controls) was: alpha2A 0.79 (0.66-0.94) (P = 0.08), beta1 2.60 (2.27-3.07) (P = 0.04), beta3 1.37 (1.27-1.46) (P = 0.02). Similar-pattern differences in adrenoceptor expression were observed in subcutaneous and intra-abdominal adipocytes.

CONCLUSIONS

These results are consistent with the suggestion that long-term alterations in catecholamine metabolism are present in adult offspring of rats fed a reduced protein diet during pregnancy and lactation.

Effect of maternal undernutrition in early gestation on ovine fetal blood pressure and cardiovascular reflexes

Human epidemiological and animal experimental studies suggest that maternal undernutrition during pregnancy may alter cardiovascular development of the offspring. The extent to which these effects involve changes in fetal cardiovascular function and whether they are necessarily linked to reduced fetal growth is unknown. In sheep, we investigated the effect of a 15% reduction in maternal global nutrition for the first 70 days of gestation (term = 147 days) on fetal blood pressure development, baroreflex control of fetal heart rate (FHR), and cardiovascular responses to acute hypoxemia in late gestation. Basal mean arterial pressure (P < 0.05), systolic blood pressure (P < 0.05), diastolic blood pressure (P < 0.05), and rate-pressure product (P < 0.001) were significantly lower in fetuses of nutritionally restricted ewes (R) compared with controls (C). FHR was not altered. The operating point for the fetal baroreflex was significantly lower in R fetuses compared with C (P < 0.01), but there was no difference between the groups in the cardiovascular response to hypoxemia. We conclude that mild maternal undernutrition alters fetal cardiovascular development, producing low blood pressure and resetting of baroreflex control mechanisms. This effect occurs without any changes in fetal growth or blood gas status.

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 P1LR 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.

Impact of restriction of placental and fetal growth on expression of 11beta-hydroxysteroid dehydrogenase type 1 and type 2 messenger ribonucleic acid in the liver, kidney, and adrenal of the sheep fetus

We have investigated the effects of fetal growth restriction, induced by restriction of placental growth and function (PR), on 11beta-hydroxysteroid dehydrogenase type 1 (11betaHSD-1) and 11betaHSD-2 messenger RNA (mRNA) expression in fetal tissues in the sheep, using Northern blot analysis. Fetal liver, kidney, and adrenals were collected from normally grown fetuses at 90 days (n = 6), 125 days (n = 6), and 141-145 days (n = 7) and from PR fetuses at 141-145 days (n = 6). Expression of 11betaHSD-1 mRNA in the fetal liver increased significantly between 125 days (7.4+/-0.8) and 141-145 days gestation (27+/-5.3). There was also an approximately 2-fold increase in the ratio of 11betaHSD-1 mRNA/18S rRNA expression in the PR group (53.8+/-7.9) compared with that in control animals at 141-145 days gestation. There was a significant decrease in 11betaHSD-2 mRNA in fetal adrenals between 125 days (41.6+/-2.4) and 141-145 days (26.7+/-1.1) gestation, but there was no effect of PR on the expression of adrenal 11betaHSD-2 mRNA. 11betaHSD-2 mRNA expression in the fetal kidney increased between 90 days (16.8+/-1.7) and 141-145 days gestation (31.7+/-4.3), but there was no effect of PR on the levels of 11betaHSD-2 mRNA in the fetal kidney. In summary, 11betaHSD-2 mRNA is differentially regulated in the fetal adrenal and kidney in the sheep fetus during late gestation. There is also a specific increase in the expression of 11betaHSD-1 mRNA in the liver of growth-restricted fetuses in late gestation. This suggests that there is increased hepatic exposure to cortisol in the growth-restricted fetus, which may be important in the reprogramming of hepatic physiology that occurs after growth restriction in utero.

Total body catecholamine kinetics before and after birth in spontaneously hypoxemic fetal lambs

To study the effect of fetal hypoxemia on perinatal norepinephrine and epinephrine total body kinetics, 13 near-term fetal lambs were instrumented with vascular catheters under general anesthesia. One week later, norepinephrine and epinephrine kinetics were measured in normoxemic (n = 7) or spontaneously hypoxemic fetuses (n = 6) with isotope dilution methodology. Hypoxemic fetuses had lower body (P < 0.02) and placental (P = 0.01) weights and a threefold elevation in plasma norepinephrine (P < 0.005) and epinephrine (P < 0.025) associated with correspondingly higher total body norepinephrine (P < 0.005) and epinephrine (P < 0.05) spillovers. After birth, total body norepinephrine and epinephrine spillover increased 45% and 3.2-fold, respectively, in normoxemic animals (both P < 0.001). However, in the hypoxemic group, norepinephrine total body spillover was unchanged between fetal and 1-h lambs and then fell in 4-h lambs (P < 0.005). In addition, total body epinephrine release rose postnatally (P < 0.05) but less than in the normoxemic group (P < 0.02). No differences in norepinephrine or epinephrine total body clearance occurred between normoxemic and hypoxemic groups in either fetal or newborn lambs. These findings indicate that in hypoxemic and growth-restricted fetuses 1) elevated circulating norepinephrine and epinephrine levels are related to increased sympathoadrenal activity and 2) birth is associated with an initial maintenance and subsequent decline in global sympathetic activity but a blunting of adrenal medullary activation.

Restriction of placental and fetal growth in sheep alters fetal blood pressure responses to angiotensin II and captopril

1. We have measured arterial blood pressure between 115 and 145 days gestation in normally grown fetal sheep (control group; n = 16) and in fetal sheep in which growth was restricted by experimental restriction of placental growth and development (PR group; n = 13). There was no significant difference in the mean gestational arterial blood pressure between the PR (42.7 +/- 2.6 mmHg) and control groups (37.7 +/- 2.3 mmHg). Mean arterial blood pressure and arterial PO2 were significantly correlated in control animals (r = 0.53, P < 0.05, n = 16), but not in the PR group. 2. There were no changes in mean arterial blood pressure in either the PR or control groups in response to captopril (7.5 microg captopril min-1; PR group n = 7, control group n = 6) between 115 and 125 days gestation. After 135 days gestation, there was a significant decrease (P < 0.05) in the fetal arterial blood pressure in the PR group but not in the control group during the captopril infusion (15 microg captopril min-1; PR group n = 7, control group n = 6). 3. There was a significant effect (F = 14.75; P < 0.001) of increasing doses of angiotensin II on fetal diastolic blood pressure in the PR and control groups. The effects of angiotensin II were different (F = 8.67; P < 0.05) in the PR and control groups at both gestational age ranges. 4. These data indicate that arterial blood pressure may be maintained by different mechanisms in growth restricted fetuses and normally grown counterparts and suggests a role for the fetal renin-angiotensin system in the maintenance of blood pressure in growth restricted fetuses.

Placental restriction alters adrenal medullary development in the midgestation sheep fetus

The aims of this study were to determine whether placental restriction (PR) alters the pattern of localization of the catecholamine-synthesizing enzymes, dopamine-beta-hydroxylase and phenylethanolamine N-methyltransferase, and enkephalin (ENK)-containing peptides in the adrenal gland of the midgestation sheep fetus. We also determined the effect of PR on the content and profile of the molecular mass forms of ENK-containing peptides in the fetal adrenal medulla. Placental growth was restricted by removal of most of the placental implantation sites in the uterus before mating. In midgestation, placental and fetal body weight were reduced (p < 0.05) in the PR group (n = 8; 237.9 +/- 39.5 g, 564.7 +/- 41.6 g, respectively) when compared with the control group (n = 9; 479.1 +/- 36.9 g, 721.2 +/- 22.8 g, respectively). However, combined fetal adrenal weight and adrenal cortical and medullary area were similar in the PR and control fetuses. In PR fetuses, distribution of staining for dopamine-beta-hydroxylase, phenylethanolamine N-methyltransferase, and ENK-containing peptides in the adrenal medulla was similar when compared with the control group; however, staining was less intense and not all adrenomedullary cells were stained. The total adrenal content of ENK-containing peptides was also significantly (p < 0.05) less in the PR group (103.4 +/- 18.6 ng/adrenal) than in the control group (243.6 +/- 24.8 ng/adrenal). However, the molecular mass profile of ENK-containing peptides was not altered in the PR fetuses compared with controls. These data suggest that placental restriction in utero may alter the synthesis and/or secretion of catecholamines and ENK-containing peptides from the fetal adrenal medulla from as early as 90 d gestation.

Prolactin receptor gene expression and foetal adipose tissue

We have investigated the effects of increasing gestational age, maternal undernutrition or restricted placental growth on prolactin receptor (PRLR) gene expression in perirenal adipose tissue collected from foetal sheep during late gestation (term = 147 d +/- 3 d of gestation). Foetal nutrient supply was reduced by either restriction of placental growth following removal of endometrial caruncles before mating or by reducing maternal feed intake by 50% from 115 d of gestation. Total RNA was extracted from adipose tissue taken from foetal sheep between 90 and 145 d of gestation, and only at 141-145 d in placentally restricted, nutrient restricted and control foetuses. Messenger RNAs encoding the long (PRLR1) and short (PRLR2) forms of the PRLR and glyceraldehyde-phosphate-dehydrogenase (GAPDH) were detected and quantified in a ribonuclease protection assay using an antisense RNA probe complementary to ovine PRLR2 and GAPDH. There was a 7.5-fold increase in the amount of perirenal adipose tissue between 90 and 125 d of gestation, compared with a 1.3-fold increase between 125 and 145 d of gestation. The abundance of mRNA encoding PRLR1 and PRLR2 in perirenal adipose tissue increased 10- and sixfold, respectively, between 90 and 125 d of gestation, and then declined by 145 d of gestation. Both placental restriction and maternal undernutrition significantly reduced foetal adipose tissue deposition. The abundance of PRLR1 but not PRLR2 mRNA was reduced in adipose tissue from the placentally restricted group, where as GAPDH mRNA was three times higher than in controls. In contrast, maternal undernutrition from 115 d of gestation did not affect PRLR1, PRLR2 or GAPDH mRNA expression in foetal adipose tissue. It is concluded that during the period of rapid deposition of perirenal adipose tissue, there is a concomitant increase in PRLR gene expression. This indicates that prolactin may play an important role in the growth and maturation of foetal adipose tissue which occurs before birth.