Preeclampsia and risk of maternal pulmonary hypertension at high altitude in Bolivia

Women with a history of preeclampsia (PE) have a greater risk of pulmonary arterial hypertension (PAH). In turn, pregnancy at high altitude is a risk factor for PE. However, whether women who develop PE during highland pregnancy are at risk of PAH before and after birth has not been investigated. We tested the hypothesis that during highland pregnancy, women who develop PE are at greater risk of PAH compared to women undergoing healthy highland pregnancies. The study was on 140 women in La Paz, Bolivia (3640m). Women undergoing healthy highland pregnancy were controls (C, n = 70; 29 ± 3.3 years old, mean±SD). Women diagnosed with PE were the experimental group (PE, n = 70, 31 ± 2 years old). Conventional (B- and M-mode, PW Doppler) and modern (pulsed wave tissue Doppler imaging) ultrasound were applied for cardiovascular íííassessment. Spirometry determined maternal lung function. Assessments occurred at 35 ± 4 weeks of pregnancy and 6 ± 0.3 weeks after birth. Relative to highland controls, highland PE women had enlarged right ventricular (RV) and right atrial chamber sizes, greater pulmonary artery dimensions and increased estimated RV contractility, pulmonary artery pressure and pulmonary vascular resistance. Highland PE women had lower values for peripheral oxygen saturation, forced expiratory flow and the bronchial permeability index. Differences remained 6 weeks after birth. Therefore, women who develop PE at high altitude are at greater risk of PAH before and long after birth. Hence, women with a history of PE at high altitude have an increased cardiovascular risk that transcends the systemic circulation to include the pulmonary vascular bed.

Parental ancestry and risk of early pregnancy loss at high altitude

High altitude pregnancy is associated with increased frequency of low birth weight infants and neonatal complications, the risks of which are higher in women of low-altitude ancestry. Does ancestry also influence the risk of miscarriage (pregnancy loss <20 weeks) in high-altitude pregnancy? To answer this, 5386 women from La Paz, Bolivia (3300-4150 m) with ≥1 live-born infant were identified. Data were extracted from medical records including maternal and paternal ancestry, demographic factors, and reproductive history. The risk of miscarriage by ancestry was assessed using multivariate logistic regression, adjusting for parity, and maternal age. Andean women experienced first live-births younger than Mestizo or European women (21.7 ± 4.6 vs 23.4 ± 8.0 vs 24.1 ± 5.1, P < .001). Andeans experienced more pregnancies per year of reproductive life (P < .001) and had significantly higher ratios of live-births to miscarriages than women of Mestizo or European ancestry (P < .001). Andean women were 24% less likely to have ever experienced a miscarriage compared to European women (OR:0.76; CI:0.62-0.90, P < .001). The woman's partner's ancestry wasn't a significant independent predictor of miscarriage. In conclusion, the risk of miscarriage at high altitude is lower in Andean women. The lack of a paternal ancestry effect suggests underlying mechanisms relate more to differential maternal adaptation in early pregnancy than fetal genetics.

Translatable mitochondria-targeted protection against programmed cardiovascular dysfunction

The prenatal origins of heart disease in offspring have been established. However, research in species with developmental milestones comparable to humans is lacking, preventing translation of this knowledge to clinical contexts. Using sheep and chickens, two species with similar cardiovascular developmental milestones to humans, we combined in vivo experiments with in vitro studies at organ, cellular, mitochondrial, and molecular levels. We tested mitochondria-targeted antioxidant intervention with MitoQ against cardiovascular dysfunction programmed by developmental hypoxia, a common complication in human pregnancy. Experiments in sheep determined in vivo fetal and adult cardiovascular function through surgical techniques not possible in humans, while those in chicken embryos isolated effects independent of maternal or placental influences. We show that hypoxia generates mitochondria-derived oxidative stress during cardiovascular development, programming endothelial dysfunction and hypertension in adult offspring. MitoQ treatment during hypoxic development protects against this cardiovascular risk via enhanced nitric oxide signaling, offering a plausible intervention strategy.

Perinatal cardiopulmonary adaptation to the thin air of the Alto Andino by a native Altiplano dweller, the llama

Most mammals have a poor tolerance to hypoxia, and prolonged O₂ restriction can lead to organ injury, particularly during fetal and early postnatal life. Nevertheless, the llama (Lama Glama) has evolved efficient mechanisms to adapt to acute and chronic perinatal hypoxia. One striking adaptation is the marked peripheral vasoconstriction measured in the llama fetus in response to acute hypoxia, which allows efficient redistribution of cardiac output toward the fetal heart and adrenal glands. This strong peripheral vasoconstrictor tone is triggered by a carotid body reflex and critically depends on α-adrenergic signaling. A second adaptation is the ability of the llama fetus to protect its brain against hypoxic damage. During hypoxia, in the llama fetus there is no significant increase in brain blood flow. Instead, there is a fall in brain O₂ consumption and temperature, together with a decrease of Na⁺-K⁺-ATPase activity and Na⁺ channels expression, protecting against seizures and neuronal death. Finally, the newborn llama does not develop pulmonary hypertension in response to chronic hypoxia. In addition to maintaining basal pulmonary arterial pressure at normal levels the pulmonary arterial pressor response to acute hypoxia is lower in highland than in lowland llamas. The protection against hypoxic pulmonary arterial hypertension and pulmonary contractile hyperreactivity is partly due to increased hemoxygenase-carbon monoxide signaling and decreased Ca²⁺ sensitization in the newborn llama pulmonary vasculature. These three striking physiological adaptations of the llama allow this species to live and thrive under the chronic influence of the hypobaric hypoxia of life at high altitude.

Physiological development of the equine fetus during late gestation

In many species, the pattern of growth and physiological development in utero has an important role in determining not only neonatal viability but also adult phenotype and disease susceptibility. Changes in fetal development induced by a range of environmental factors including maternal nutrition, disease, placental insufficiency and social stresses have all been shown to induce adult cardiovascular and metabolic dysfunction that often lead to ill health in later life. Compared to other precocious animals, much less is known about the physiological development of the fetal horse or the longer-term impacts on its phenotype of altered development in early life because of its inaccessibility in utero, large size and long lifespan. This review summaries the available data on the normal metabolic, cardiovascular and endocrine development of the fetal horse during the second half of gestation. It also examines the responsiveness of these physiological systems to stresses such as hypoglycaemia and hypotension during late gestation. Particular emphasis is placed on the role of the equine placenta and fetal endocrine glands in mediating the changes in fetal development seen towards term and in response to nutritional and other environmental cues. The final part of the review presents the evidence that the early life environment of the horse can alter its subsequent metabolic, cardiovascular and endocrine phenotype as well as its postnatal growth and bone development. It also highlights the immediate neonatal environment as a key window of susceptibility for programming of equine phenotype. Although further studies are needed to identify the cellular and molecular mechanisms involved, developmental programming of physiological phenotype is likely to have important implications for the health and potential athletic performance of horses, particularly if born with abnormal bodyweight, premature or dysmature characteristics or produced by assisted reproductive technologies, indicative of an altered early life environment.

Altered autonomic control of heart rate variability in the chronically hypoxic fetus

KEY POINTS

Fetal heart rate variability (FHRV) has long been recognised as a powerful predictor of fetal wellbeing, and a decrease in FHRV is associated with fetal compromise. However, the mechanisms by which FHRV is reduced in the chronically hypoxic fetus have yet to be established. The sympathetic and parasympathetic influences on heart rate mature at different rates throughout fetal life, and can be assessed by time domain and power spectral analysis of FHRV. In this study of chronically instrumented fetal sheep in late gestation, we analysed FHRV daily over a 16 day period towards term, and compared changes between fetuses of control and chronically hypoxic pregnancy. We show that FHRV in sheep is reduced by chronic hypoxia, predominantly due to dysregulation of the sympathetic control of the fetal heart rate. This presents a potential mechanism by which a reduction in indices of FHRV predicts fetuses at increased risk of neonatal morbidity and mortality in humans. Reduction in overall FHRV may therefore provide a biomarker that autonomic dysregulation of fetal heart rate control has taken place in a fetus where uteroplacental dysfunction is suspected.

ABSTRACT

Although fetal heart rate variability (FHRV) has long been recognised as a powerful predictor of fetal wellbeing, the mechanisms by which it is reduced in the chronically hypoxic fetus have yet to be established. In particular, the physiological mechanism underlying the reduction of short term variation (STV) in fetal compromise remains unclear. In this study, we present a longitudinal study of the development of autonomic control of FHRV, assessed by indirect indices, time domain and power spectral analysis, in normoxic and chronically hypoxic, chronically catheterised, singleton fetal sheep over the last third of gestation. We used isobaric chambers able to maintain pregnant sheep for prolonged periods in hypoxic conditions (stable fetal femoral arterial P O 2 10-12 mmHg), and a customised wireless data acquisition system to record beat-to-beat variation in the fetal heart rate. We determined in vivo longitudinal changes in overall FHRV and the sympathetic and parasympathetic contribution to FHRV in hypoxic (n = 6) and normoxic (n = 6) ovine fetuses with advancing gestational age. Normoxic fetuses show gestational age-related increases in overall indices of FHRV, and in the sympathetic nervous system contribution to FHRV (P < 0.001). Conversely, gestational age-related increases in overall FHRV were impaired by exposure to chronic hypoxia, and there was evidence of suppression of the sympathetic nervous system control of FHRV after 72 h of exposure to hypoxia (P < 0.001). This demonstrates that exposure to late gestation isolated chronic fetal hypoxia has the potential to alter the development of the autonomic nervous system control of FHRV in sheep. This presents a potential mechanism by which a reduction in indices of FHRV in human fetuses affected by uteroplacental dysfunction can predict fetuses at increased risk.

Influence of gestational diabetes on fetal autonomic nervous system: a study using phase-rectified signal-averaging analysis

OBJECTIVES

Maternal gestational diabetes mellitus (GDM) is known to influence fetal physiology. Phase-rectified signal averaging (PRSA) is an innovative signal-processing technique that can be used to investigate fetal heart signals. The PRSA-calculated variables average acceleration capacity (AAC) and average deceleration capacity (ADC) are established indices of autonomic nervous system (ANS) function. The aim of this study was to evaluate the influence of GDM on the fetal cardiovascular and ANS function in human pregnancy using PRSA.

METHODS

This was a prospective clinical case-control study of 58 mothers with diagnosed GDM and 58 gestational-age matched healthy controls in the third trimester of pregnancy. Fetal cardiotocography (CTG) recordings were performed in all cases at entry to the study, and a follow-up recording was performed in 19 GDM cases close to delivery. The AAC and ADC indices were calculated by the PRSA method and fetal heart rate short-term variation (STV) by CTG software according to Dawes-Redman criteria.

RESULTS

Mean gestational age of both groups at study entry was 35.7 weeks. There was a significant difference in mean AAC (1.97 ± 0.33 bpm vs 2.42 ± 0.57 bpm; P < 0.001) and ADC (1.94 ± 0.32 bpm vs 2.28 ± 0.46 bpm; P < 0.001) between controls and fetuses of diabetic mothers. This difference could not be demonstrated using standard computerized fetal CTG analysis of STV (controls, 10.8 ± 3.0 ms vs GDM group, 11.3 ± 2.5 ms; P = 0.32). Longitudinal fetal heart rate measurements in a subgroup of women with diabetes were not significantly different from those at study entry.

CONCLUSIONS

Our findings show increased ANS activity in fetuses of diabetic mothers in late gestation. Analysis of human fetal cardiovascular and ANS function by PRSA may offer improved surveillance over conventional techniques linking GDM pregnancy to future cardiovascular dysfunction in the offspring. Copyright © 2017 ISUOG. Published by John Wiley & Sons Ltd.

The highs and lows of programmed cardiovascular disease by developmental hypoxia: studies in the chicken embryo

It is now established that adverse conditions during pregnancy can trigger a fetal origin of cardiovascular dysfunction and/or increase the risk of heart disease in later life. Suboptimal environmental conditions during early life that may promote the development of cardiovascular dysfunction in the offspring include alterations in fetal oxygenation and nutrition as well as fetal exposure to stress hormones, such as glucocorticoids. There has been growing interest in identifying the partial contributions of each of these stressors to programming of cardiovascular dysfunction. However, in humans and in many animal models this is difficult, as the challenges cannot be disentangled. By using the chicken embryo as an animal model, science has been able to circumvent a number of problems. In contrast to mammals, in the chicken embryo the effects on the developing cardiovascular system of changes in oxygenation, nutrition or stress hormones can be isolated and determined directly, independent of changes in the maternal or placental physiology. In this review, we summarise studies that have exploited the chicken embryo model to determine the effects on prenatal growth, cardiovascular development and pituitary-adrenal function of isolated chronic developmental hypoxia.

Fetal in vivo continuous cardiovascular function during chronic hypoxia

Although the fetal cardiovascular defence to acute hypoxia and the physiology underlying it have been established for decades, how the fetal cardiovascular system responds to chronic hypoxia has been comparatively understudied. We designed and created isobaric hypoxic chambers able to maintain pregnant sheep for prolonged periods of gestation under controlled significant (10% O2) hypoxia, yielding fetal mean P(aO2) levels (11.5 ± 0.6 mmHg) similar to those measured in human fetuses of hypoxic pregnancy. We also created a wireless data acquisition system able to record fetal blood flow signals in addition to fetal blood pressure and heart rate from free moving ewes as the hypoxic pregnancy is developing. We determined in vivo longitudinal changes in fetal cardiovascular function including parallel measurement of fetal carotid and femoral blood flow and oxygen and glucose delivery during the last third of gestation. The ratio of oxygen (from 2.7 ± 0.2 to 3.8 ± 0.8; P < 0.05) and of glucose (from 2.3 ± 0.1 to 3.3 ± 0.6; P < 0.05) delivery to the fetal carotid, relative to the fetal femoral circulation, increased during and shortly after the period of chronic hypoxia. In contrast, oxygen and glucose delivery remained unchanged from baseline in normoxic fetuses. Fetal plasma urate concentration increased significantly during chronic hypoxia but not during normoxia (Δ: 4.8 ± 1.6 vs. 0.5 ± 1.4 μmol l(-1), P<0.05). The data support the hypotheses tested and show persisting redistribution of substrate delivery away from peripheral and towards essential circulations in the chronically hypoxic fetus, associated with increases in xanthine oxidase-derived reactive oxygen species.

Hypoxia, AMPK activation and uterine artery vasoreactivity

Genes near adenosine monophosphate-activated protein kinase-α1 (PRKAA1) have been implicated in the greater uterine artery (UtA) blood flow and relative protection from fetal growth restriction seen in altitude-adapted Andean populations. Adenosine monophosphate-activated protein kinase (AMPK) activation vasodilates multiple vessels but whether AMPK is present in UtA or placental tissue and influences UtA vasoreactivity during normal or hypoxic pregnancy remains unknown. We studied isolated UtA and placenta from near-term C57BL/6J mice housed in normoxia (n = 8) or hypoxia (10% oxygen, n = 7-9) from day 14 to day 19, and placentas from non-labouring sea level (n = 3) or 3100 m (n = 3) women. Hypoxia increased AMPK immunostaining in near-term murine UtA and placental tissue. RT-PCR products for AMPK-α1 and -α2 isoforms and liver kinase B1 (LKB1; the upstream kinase activating AMPK) were present in murine and human placenta, and hypoxia increased LKB1 and AMPK-α1 and -α2 expression in the high- compared with low-altitude human placentas. Pharmacological AMPK activation by A769662 caused phenylephrine pre-constricted UtA from normoxic or hypoxic pregnant mice to dilate and this dilatation was partially reversed by the NOS inhibitor l-NAME. Hypoxic pregnancy sufficient to restrict fetal growth markedly augmented the UtA vasodilator effect of AMPK activation in opposition to PE constriction as the result of both NO-dependent and NO-independent mechanisms. We conclude that AMPK is activated during hypoxic pregnancy and that AMPK activation vasodilates the UtA, especially in hypoxic pregnancy. AMPK activation may be playing an adaptive role by limiting cellular energy depletion and helping to maintain utero-placental blood flow in hypoxic pregnancy.

Pathophysiological mechanisms of high-intensity focused ultrasound-mediated vascular occlusion and relevance to non-invasive fetal surgery

High-intensity focused ultrasound (HIFU) is a non-invasive technology, which can be used occlude blood vessels in the body. Both the theory underlying and practical process of blood vessel occlusion are still under development and relatively sparse in vivo experimental and therapeutic data exist. HIFU would however provide an alternative to surgery, particularly in circumstances where serious complications inherent to surgery outweigh the potential benefits. Accordingly, the HIFU technique would be of particular utility for fetal and placental interventions, where open or endoscopic surgery is fraught with difficulty and likelihood of complications including premature delivery. This assumes that HIFU could be shown to safely and effectively occlude blood vessels in utero. To understand these mechanisms more fully, we present a review of relevant cross-specialty literature on the topic of vascular HIFU and suggest an integrative mechanism taking into account clinical, physical and engineering considerations through which HIFU may produce vascular occlusion. This model may aid in the design of HIFU protocols to further develop this area, and might be adapted to provide a non-invasive therapy for conditions in fetal medicine where vascular occlusion is beneficial.

Ascorbate prevents placental oxidative stress and enhances birth weight in hypoxic pregnancy in rats

This study isolated the effects of maternal hypoxia independent of changes in maternal nutrition on maternal circulatory and placental molecular indices of oxidative stress and determined whether maternal antioxidant treatment conferred protection. Pregnant rats were subjected to normoxic pregnancy or 13% O2 chronic hypoxia for most of gestation with and without maternal treatment with vitamin C in the drinking water. Maternal hypoxia with and without vitamin C did not affect maternal food or water intake and led to a significant increase in maternal and fetal haematocrit. At gestational day 20, maternal plasma urate and L-cysteine concentrations, and placental levels of 4-hydroxynonenal and heat shock protein 70 were increased while placental heat shock protein 90 levels were decreased in hypoxic pregnancy. The induction of maternal circulatory and placental molecular indices of oxidative stress in hypoxic pregnancies was prevented by maternal treatment with vitamin C. Maternal hypoxia during pregnancy with or without vitamin C increased placental weight, but not total or compartmental volumes. Maternal treatment with vitamin C increased birth weight in both hypoxic and normoxic pregnancies. The data show that maternal hypoxia independent of maternal undernutrition promotes maternal and placental indices of oxidative stress, effects that can be prevented by maternal treatment with vitamin C in hypoxic pregnancy. While vitamin C may not be the ideal candidate of choice for therapy in pregnant women, and taking into consideration differences in ascorbic acid metabolism between rats and humans, the data do underlie that antioxidant treatment may provide a useful intervention to improve placental function and protect fetal growth in pregnancy complicated by fetal hypoxia.

A role for xanthine oxidase in the control of fetal cardiovascular function in late gestation sheep

Virtually nothing is known about the effects on fetal physiology of xanthine oxidase inhibition. This is despite maternal treatment with the xanthine oxidase inhibitor allopurinol being considered in human complicated pregnancy to protect the infant’s brain from excessive generation of ROS.We investigated the in vivo effects of maternal treatment with allopurinol on fetal cardiovascular function in ovine pregnancy in late gestation. Under anaesthesia, pregnant ewes and their singleton fetus were instrumented with vascular catheters and flow probes around an umbilical and a fetal femoral artery at 118±1 dGA (days of gestational age; termca. 145 days). Five days later, mothers were infused I.V. with either vehicle (n =11) or allopurinol (n =10). Fetal cardiovascular function was stimulated with increasing bolus doses of phenylephrine (PE) following maternal vehicle or allopurinol. The effects of maternal allopurinol on maternal and fetal cardiovascular function were also investigated following fetal NO blockade (n =6) or fetal β1-adrenergic antagonism (n =7). Maternal allopurinol led to significant increases in fetal heart rate, umbilical blood flow and umbilical vascular conductance, effects abolished by fetal β1-adrenergic antagonism but not by fetal NO blockade. Maternal allopurinol impaired fetal α1-adrenergic pressor and femoral vasopressor responses and enhanced the gain of the fetal cardiac baroreflex. These effects of maternal allopurinol were restored to control levels during fetal NO blockade. Maternal treatment with allopurinol induced maternal hypotension, tachycardia and acid–base disturbance. We conclude that maternal treatment with allopurinol alters in vivo maternal, umbilical and fetal vascular function via mechanisms involving NO and β1-adrenergic stimulation. The evidence suggests that the use of allopurinol in clinical practice should be approached with caution.

Redox modulation of the fetal cardiovascular defence to hypoxaemia

Episodes of hypoxia in utero present a potentially serious challenge to the fetus, but are counteracted by defence responses including marked redistribution of blood flow from peripheral circulations to the brain. Here, we report the novel observation that the oxidant tone is an important modulator of this cardiovascular defence. Using pregnant Welsh Mountain sheep surgically prepared for long-term recording, we investigated in vivo the effects on the fetal cardiovascular defence to acute hypoxaemia of fetal treatment with the antioxidant vitamin C. The mechanisms via which vitamin C may affect the vascular oxidant tone were investigated by monitoring fetal plasma concentrations of nitrates and nitrites, by determining changes in the activity of superoxide dismutase (SOD) in fetal plasma, and by investigating the effect of vitamin C treatment on the fetal cardiovascular defence to hypoxaemia following nitric oxide (NO) synthase blockade. Fetal treatment with vitamin C markedly depressed the normal femoral constrictor response to acute hypoxaemia in the fetus (5.2 ± 1.0 vs. 1.1 ± 0.3 mmHg (ml min(-1))(-1), mean ± s.e.m.; P < 0.05) an effect which was completely restored following NO synthase blockade (6.2 ± 1.3 mmHg (ml min(-1))(-1)). Compared to saline infusion, fetal treatment with vitamin C during acute hypoxaemia also significantly increased fetal plasma SOD activity from normoxic baseline (-8.9 ± 6.5 vs. 15.0 ± 6.6% inhibition, P < 0.05) and decreased the plasma concentration ratio of nitrate:nitrite from normoxic baseline (ΔNO3(-):NO2(-); 0.15 ± 0.30 vs. -0.29 ± 0.11, P < 0.05). The data provide in vivo evidence of redox modulation of redistribution of blood flow in the fetus, part of the fetal brain sparing during acute hypoxaemic stress.

Prenatal hypoxia independent of undernutrition promotes molecular markers of insulin resistance in adult offspring

Molecular mechanisms predisposing people to insulin resistance are starting to emerge. Altered insulin signaling for hepatic gluconeogenesis and muscle glucose uptake is thought to play a central role. Development under suboptimal conditions is also known to increase the risk of insulin resistance in adulthood. However, the partial contributions of reduced oxygen vs. nutrient delivery to the fetus, two common adverse conditions in utero, to developmental programming of insulin resistance remain unknown. The aim of this study was to determine the effects of developmental hypoxia or undernutrition on the expression of insulin-signaling proteins in liver and skeletal muscle in adult rat offspring. We show that the expression of hepatic phospho-Akt and muscle Akt2 were significantly reduced in offspring of hypoxic, relative to offspring from normoxic or undernourished, pregnancies. Hepatic Akt-1, Akt-2, and PKCζ protein expression was reduced in offspring from both hypoxic and undernourished pregnancies. Muscle GLUT4 expression was decreased in undernourished, and further decreased in hypoxic, offspring. These findings link prenatal hypoxia to down-regulation of components of hepatic and muscle Akt expression in adult offspring. Akt may represent a pharmaceutical target for clinical intervention against the developmental programming of metabolic disease resulting from prenatal hypoxia.

Effects of acute acidemia on the fetal cardiovascular defense to acute hypoxemia

In complicated pregnancy, fetal hypoxemia rarely occurs in isolation but is often accompanied by fetal acidemia. There is growing clinical concern about the combined effects of fetal hypoxemia and fetal acidemia on neonatal outcome. However, the effects on the fetal defense responses to acute hypoxemia during fetal acidemia are not well understood. This study tested the hypothesis that fetal acidemia affects the fetal defense responses to acute hypoxemia. The hypothesis was tested by investigating, in the late-gestation sheep fetus surgically prepared for long-term recording, the in vivo effects of acute fetal acidemia on 1) the fetal cardiovascular responses to acute hypoxemia and 2) the neural and endocrine mechanisms mediating these responses. Under general anesthesia, five sheep fetuses at 0.8 gestation were instrumented with catheters and Transonic flow probes around the femoral and umbilical arteries. After 5 days, animals were subjected to an acute hypoxemia protocol during intravenous infusion of saline or treatment with acidified saline. Treatment with acidified saline reduced fetal basal pH from 7.35 +/- 0.01 to 7.29 +/- 0.01 but did not alter basal cardiovascular variables, blood glucose, or plasma concentrations of catecholamines, ACTH, and cortisol. During hypoxemia, treatment with acidified saline increased the magnitude of the fetal bradycardia and femoral vasoconstriction and concomitantly increased chemoreflex function and enhanced the increments in plasma concentrations of catecholamines, ACTH, and cortisol. Acidemia also reversed the increase in umbilical vascular conductance during hypoxemia to vasoconstriction. In conclusion, the data support our hypothesis and show that acute acidemia markedly alters fetal hemodynamic, metabolic, and endocrine responses to acute hypoxemia.

Effects of dexamethasone on the glucogenic capacity of fetal, pregnant, and non-pregnant adult sheep

Fetal glucocorticoids have an important role in the pre-partum maturation of physiological systems essential for neonatal survival such as glucogenesis. Consequently, in clinical practice, synthetic glucocorticoids, like dexamethasone, are given routinely to pregnant women threatened with pre-term delivery to improve the viability of their infants. However, little is known about the effects of maternal dexamethasone treatment on the glucogenic capacity of either the fetus or mother. This study investigated the effects of dexamethasone treatment using a clinically relevant dose and regime on glycogen deposition and the activities of glucose-6-phosphatase (G6Pase) and phosphoenolpyruvate carboxykinase (PEPCK) in the liver and kidney of pregnant ewes and their fetuses, and of non-pregnant ewes. Dexamethasone administration increased the glycogen content of both the fetal and adult liver within 36 h of beginning treatment. It also increased G6Pase activity in the liver and kidney of the fetuses but not of their mothers or the non-pregnant ewes. Neither hepatic nor renal PEPCK activity was affected by dexamethasone in any group of animals. These changes in glycogen content and G6Pase activity were accompanied by rises in the plasma glucose and insulin concentrations and by a fall in the plasma cortisol level in the fetus and both groups of adult animals. In addition, dexamethasone treatment raised fetal plasma tri-iodothyronine (T(3)) concentrations and reduced maternal levels of plasma T(3) and thyroxine, but had no effect on thyroid hormone concentrations in the non-pregnant ewes. These findings show that maternal dexamethasone treatment increases the glucogenic capacity of both the mother and fetus and has major implications for glucose availability both before and after birth.

The role of calcitonin gene-related Peptide in the in vivo pituitary-adrenocortical response to acute hypoxemia in the late-gestation sheep fetus

This study tested the hypothesis that calcitonin gene-related peptide (CGRP) has a role in mediating the in vivo fetal adrenal glucocorticoid response to acute stress. The hypothesis was tested by investigating the effects of fetal treatment with a selective CGRP antagonist on plasma ACTH and cortisol responses to acute hypoxemia in the late-gestation sheep fetus. Under anesthesia, six fetuses at 0.8 of gestation were surgically instrumented with vascular catheters. Five days later, fetuses were subjected to 0.5-h hypoxemia during treatment with either iv saline or a CGRP antagonist, in randomized order, on different days. Treatment started 30 min before hypoxemia and ran continuously until the end of the challenge. Arterial blood samples were collected for plasma ACTH and cortisol measurements (RIA) and blood gas monitoring. CGRP antagonism did not alter basal arterial blood gas or endocrine status. During hypoxemia, similar falls in arterial partial pressure of oxygen occurred in all fetuses. During saline infusion, acute hypoxemia induced significant increases in fetal ACTH and cortisol concentrations. During CGRP antagonism, the pituitary-adrenal responses were markedly attenuated. Correlation of paired plasma ACTH and cortisol values from all individual fetuses during normoxia and hypoxemia showed positive linear relationships; however, neither the slope nor the intercept of the peptide-steroid relationship was affected by CGRP antagonism. These data support the hypothesis that CGRP is involved in the in vivo regulation of fetal adrenocortical steroidogenesis during acute hypoxemia. In addition, the data reveal that CGRP may have a role in the control of other components of the hypothalamo-pituitary-adrenal axis during stimulated conditions in fetal life.

Role of Nitric Oxide in Mediating In Vivo Vascular Responses to Calcitonin Gene-Related Peptide in Essential and Peripheral Circulations in the Fetus

Background— The role of calcitonin gene-related peptide (CGRP) in cardiovascular regulation is gaining clinical and scientific interest. In the adult, in vivo studies have shown that CGRP-stimulated vasodilation in several vascular beds depends, at least in part, on nitric oxide (NO). However, whether CGRP acts as a vasodilator in the fetus in vivo and whether this effect is mediated via NO have been addressed only minimally. This study tested the hypothesis that CGRP has potent NO-dependent vasodilator actions in essential and peripheral vascular beds in the fetus in late gestation.

Methods and Results— Under anesthesia, 5 fetal sheep at 0.8 gestation were instrumented with vascular catheters and Transonic flow probes around an umbilical artery and a femoral artery. Five days later, fetuses received 2- and 5-μg doses of exogenous CGRP intra-arterially in randomized order. Doses were repeated during NO blockade with the NO clamp. This technique permits blockade of de novo synthesis of NO while compensating for tonic production of the gas, thereby maintaining basal cardiovascular function. CGRP resulted in potent and long-lasting NO-dependent dilation in the umbilical and femoral circulations, hypotension, and a positive cardiac chronotropic effect. During NO blockade, the femoral vasodilator response to CGRP was diminished. In contrast, in the umbilical vascular bed, the dilator response was not only prevented but reversed to vasoconstriction.

Conclusions— CGRP has potent NO-dependent vasodilator actions in fetal essential and peripheral vascular beds. CGRP-induced NO-dependent effects in the umbilical vascular bed may provide an important mechanism in the control and maintenance of umbilical blood flow during pregnancy.

Chronic umbilical cord compression results in accelerated maturation of lung and brown adipose tissue in the sheep fetus during late gestation

Umbilical cord compression (UCC) sufficient to reduce umbilical blood flow by 30% for 3 days, results in increased fetal plasma cortisol and catecholamines that are likely to promote maturation of the fetal lung and brown adipose tissue (BAT). We determined the effect of UCC on the abundance of uncoupling protein (UCP)1 (BAT only) and -2, glucocorticoid receptor (GR), and 11beta-hydroxysteroid dehydrogenase (11beta-HSD)1 and -2 mRNA, and mitochondrial protein voltage-dependent anion channel (VDAC) and cytochrome c in these tissues. At 118 +/- 2 days of gestation (dGA; term approximately 145 days), 14 fetuses were chronically instrumented. Eight fetuses were then subjected to 3 days of UCC from 125 dGA, and the remaining fetuses were sham operated. All fetuses were then exposed to two 1-h episodes of hypoxemia at 130 +/- 1 and 134 +/- 1 dGA before tissue sampling at 137 +/- 2 dGA. In both tissues, UCC upregulated UCP2 and GR mRNA, plus VDAC and cytochrome c mitochondrial proteins. In lung, UCC increased 11beta-HSD1 mRNA but decreased 11beta-HSD2 mRNA abundance, a pattern reversed for BAT. UCC increased UCP1 mRNA and its translated protein in BAT. UCP2, GR, 11beta-HSD1 and -2 mRNA, plus VDAC and cytochrome c protein abundance were all significantly correlated with fetal plasma cortisol and catecholamine levels, but not thyroid hormone concentrations, in the lung and BAT of UCC fetuses. In conclusion, chronic UCC results in precocious maturation of the fetal lung and BAT mitochondria, an adaptation largely mediated by the surge in fetal plasma cortisol and catecholamines that accompanies UCC.

Maturation of pancreatic beta-cell function in the fetal horse during late gestation

At birth, the endocrine pancreas becomes more directly involved in the control of glycaemia than in utero. However, compared with other tissues, relatively little is known about the maturational changes that occur in the fetal endocrine pancreas in preparation for extrauterine life. This study examined the pancreatic beta-cell response to exogenous administration of glucose and arginine in fetal horses with respect to their gestational age and concentration of cortisol, the hormone responsible for prepartum maturation of other fetal tissues. Glucose administration had no effect on fetal insulin secretion between 175 and 230 days of gestation but evoked a rapid insulin response in fetuses closer to term (290-327 days). In late gestation, the beta-cell response was more rapid and greater in magnitude in fetuses with basal cortisol levels higher than 15 ng/ml than in those with lower cortisol values at the time of glucose administration. The fetal beta-cell response to arginine was unaffected by the rise in fetal plasma cortisol towards term. These findings show that there are maturational changes in pancreatic beta-cell function in fetal horses as cortisol levels rise close to term. Primarily, these prepartum maturational changes were in the mechanisms of glucose-stimulated insulin secretion, which would enable the beta cells to regulate glycaemia at the higher glucose levels observed postnatally.

Calcitonin gene-related peptide antagonism attenuates the haemodynamic and glycaemic responses to acute hypoxaemia in the late gestation sheep fetus

The fetal defence to acute hypoxaemia involves cardiovascular and metabolic responses, which include peripheral vasoconstriction and hyperglycaemia. Both these responses are mediated via neuroendocrine mechanisms, which require the stimulation of the sympathetic nervous system. In the adult, accumulating evidence supports a role for calcitonin gene-related peptide (CGRP) in the activation of sympathetic outflow. However, the role of CGRP in stimulated cardiovascular and metabolic functions before birth is completely unknown. This study tested the hypothesis that CGRP plays a role in the fetal cardiovascular and metabolic defence responses to acute hypoxaemia by affecting sympathetic outflow. Under anaesthesia, five sheep fetuses at 0.8 of gestation were surgically instrumented with catheters and a femoral arterial Transonic flow-probe. Five days later, fetuses were subjected to 0.5 h hypoxaemia during either i.v. saline or a selective CGRP antagonist in randomised order. Treatment started 30 min before hypoxaemia and ran continuously until the end of the challenge. Arterial samples were taken for blood gases, metabolic status and hormone analyses. CGRP antagonism did not alter basal arterial blood gas, metabolic, cardiovascular or endocrine status. During hypoxaemia, similar falls in Pa,O2 occurred in all fetuses. During saline infusion, hypoxaemia induced hypertension, bradycardia, femoral vasoconstriction, hyperglycaemia and an increase in haemoglobin, catecholamines and neuropeptide Y (NPY). In contrast, CGRP antagonism markedly diminished the femoral vasoconstrictor and glycaemic responses to hypoxaemia, and attenuated the increases in haemoglobin, catecholamines and NPY. Combined, these results strongly support the hypothesis that CGRP plays a role in the fetal cardiovascular and metabolic defence to hypoxaemia by affecting sympathetic outflow.

Fetal cardiovascular, metabolic and endocrine responses to acute hypoxaemia during and following maternal treatment with dexamethasone in sheep

In sheep, direct fetal treatment with dexamethasone alters basal cardiovascular function and the cardiovascular response to acute hypoxaemia. However, in human clinical practice, dexamethasone is administered to the mother, not to the fetus. Hence, this study investigated physiological responses to acute hypoxaemia in fetal sheep during and following maternal treatment with dexamethasone in doses and at dose intervals used in human clinical practice. Under anaesthesia, 18 fetal sheep were instrumented with vascular and amniotic catheters, a carotid flow probe and a femoral flow probe at 118 days gestation (term ca 145 days). Following 6 days recovery at 124 days gestation, 10 ewes received dexamethasone (2 x 12 mg daily i.m. injections in saline). The remaining animals were saline-injected as age-matched controls. Two episodes of hypoxaemia (H) were induced in all animals by reducing the maternal F(IO2)for 1 h (H1, 8 h after the second injection; H2, 3 days after the second injection). In fetuses whose mothers received saline, hypoxaemia induced significant increases in fetal arterial blood pressure, carotid blood flow and carotid vascular conductance and femoral vascular resistance, significant falls in femoral blood flow and femoral vascular conductance and transient bradycardia. These cardiovascular responses were accompanied by a fall in arterial pH, increases in blood glucose and blood lactate concentrations and increased plasma concentrations of catecholamines. In fetuses whose mothers were treated with dexamethasone, bradycardia persisted throughout hypoxaemia, the magnitude of the femoral vasoconstriction, the glycaemic, lactacidaemic and acidaemic responses and the plasma concentration of neuropeptide Y (NPY) were all enhanced during H1. However, during H2, all of these physiological responses were similar to saline controls. In dexamethasone fetuses, the increase in plasma adrenaline was attenuated during H1 and the increase in carotid vascular conductance during hypoxaemia failed to reach statistical significance both during H1 and during H2. These data show that maternal treatment with dexamethasone in doses and intervals used in human obstetric practice modified the fetal cardiovascular, metabolic and endocrine defence responses to acute hypoxaemia. Furthermore, dexamethasone-induced alterations to these defences depended on whether the hypoxaemic challenge occurred during or following maternal dexamethasone treatment.

The effects of pregnancy on the cardiovascular response to acute systemic isocapnic hypoxia in conscious sheep

OBJECTIVE

This study tested the hypothesis that pregnancy affects the cardiovascular responses to hypoxia by altering the outputs of the peripheral components of the stress system and independent of changes in P(a)CO(2).

DESIGN

Comparison of cardiovascular and endocrine responses to acute isocapnic hypoxia between pregnant and non-pregnant ewes.

SETTING

Experimental laboratory.

SAMPLE

Fifteen pregnant (118 days of gestation; term is ca. 145 days) and 8 non-pregnant sheep.

METHODS

Chronically instrumented pregnant and non-pregnant ewes were subjected to 1 hour normoxia, 1 hour of acute systemic isocapnic hypoxia and 1 hour recovery.

MAIN OUTCOME MEASURES

Arterial blood pressure, heart rate, femoral blood flow and femoral vascular conductance were recorded continuously throughout and arterial blood samples were taken during normoxia, hypoxia and recovery for the measurement of blood gas, metabolic and endocrine status.

RESULTS

Basal blood pressure and blood glucose and lactate concentrations were lower in pregnant animals (P < 0.05). In contrast, basal cardiovascular variables and plasma concentrations of noradrenaline, adrenaline, neuropeptide Y, adrenocorticotropic hormone (ACTH) and cortisol were similar in pregnant and non-pregnant ewes. During hypoxia similar reductions in P(a)O(2) occurred in pregnant and non-pregnant animals, without alterations in P(a)CO(2) or pH(a). In non-pregnant ewes, acute hypoxia induced a transient increase in arterial pressure and sustained tachycardia without significant changes in femoral haemodynamics. Pregnancy attenuated the cardiovascular response, significantly diminishing the magnitude of the increment in heart rate throughout the hypoxic challenge (P < 0.001). However, hypoxia did not induce significant changes in blood metabolites or in plasma concentrations of any stress hormone measured in either pregnant or non-pregnant animals.

CONCLUSION

Pregnancy not only affects basal but also stimulated cardiovascular function in the mother. The diminished chronotropic response to hypoxia in pregnancy is mediated via mechanisms independent of changes in P(a)CO(2) or in plasma concentrations of hormones or metabolites associated with activation of the stress system.

Development of baroreflex and endocrine responses to hypotensive stress in newborn foals and lambs

OBJECTIVE

The aims of this study were to compare and contrast the development of the cardiac baroreflex and endocrine responses to acute hypotensive stress in healthy newborn pony foals and lambs during the first two weeks of postnatal life.

METHODS

Under general anaesthesia, seven Welsh pony foals and six Welsh Mountain lambs were catheterised with hind limb artery and vein catheters. Following post-surgical recovery, at 1 week and 2 weeks of age, blood pressures of the animals were raised and lowered acutely by intravenous infusion of phenylephrine and sodium nitroprusside, respectively. During hypotension, blood samples were taken for measurement of plasma hormones associated with activation of the stress axis.

RESULTS

Basal arterial blood pressure increased significantly (P<0.05) between week 1 and week 2 in the absence of any significant change in basal heart rate in foals and with a significant reduction in basal heart rate in lambs. In foals, the slope of the heart rate-blood pressure relationship decreased in response to acute hypertension, and it increased in response to acute hypotension, from week 1 to week 2 (all P<0.05). In contrast, in lambs, the slope of the heart rate-blood pressure relationship decreased with both acute hypertension and acute hypotension from week 1 to week 2 (all P<0.05). In foals, there were significant increases in plasma concentrations of noradrenaline, neuropeptide Y (NPY), vasopressin, adrenocorticotrophic hormone (ACTH) and cortisol in response to hypotension (P<0.05). In lambs, there were also significant increases in plasma concentrations of ACTH and cortisol during hypotension. Plasma concentrations of noradrenaline, NPY and vasopressin were not measured during hypotension in lambs. In foals, although the magnitude of the ACTH response to hypotension was smaller at week 2 than week 1, the increment in plasma cortisol was similar in the two age groups. In contrast, in lambs, the profile of both the ACTH and cortisol responses was similar at week 1 and week 2.

CONCLUSION

These data suggest that the increase in basal arterial blood pressure in the foal and the lamb during the first 2 weeks of postnatal life is accompanied by differential maturational changes in the vagal and sympathetic components of the cardiac baroreflex between the two species. These developmental cardiac baroreflex changes occur together with increased adrenocortical responsiveness to acute hypotensive stress, which appears comparatively more mature in lambs than in foals.

Calcitonin gene-related peptide contributes to the umbilical haemodynamic defence response to acute hypoxaemia

Despite clinical advances in obstetric practice, undiagnosed fetal hypoxaemia still contributes to a high incidence of perinatal morbidity. The fetal defence to hypoxaemia involves a redistribution of blood flow away from peripheral circulations towards essential vascular beds, such as the umbilical, cerebral, myocardial and adrenal circulations. In marked contrast to other essential vascular beds, the mechanisms mediating maintained perfusion of the umbilical circulation during hypoxaemia remain unknown. This study determined the role of calcitonin gene-related peptide (CGRP) in the maintenance of umbilical blood flow during basal and hypoxaemic conditions. Under anaesthesia, five sheep fetuses were instrumented with catheters and a Transonic probe around an umbilical artery, inside the fetal abdomen, at 0.8 of gestation. Five days later, fetuses were subjected to 0.5 h hypoxaemia during either i.v. saline or a selective CGRP antagonist in randomised order. Treatment started 30 min before hypoxaemia and ran continuously until the end of the challenge. The CGRP antagonist did not alter basal blood gas or cardiovascular status in the fetus. A similar fall in Pa,O2 occurred in fetuses during either saline (21 +/- 0.8 to 9 +/- 0.9 mmHg) or antagonist treatment (20 +/- 0.9 to 9 +/- 1.2 mmHg). Hypoxaemia during saline led to significant increases in arterial blood pressure, umbilical blood flow and umbilical vascular conductance. In marked contrast, hypoxaemia during CGRP antagonist treatment led to pronounced falls in both umbilical blood flow and umbilical vascular conductance without affecting the magnitude of the hypertensive response. In conclusion, CGRP plays an important role in the umbilical haemodynamic defence response to hypoxaemia in the late gestation fetus.

Developmental changes in pulmonary and renal angiotensin-converting enzyme concentration in fetal and neonatal horses

Angiotensin-converting enzyme (ACE) has an active role in the control of blood pressure and body fluid homeostasis both before and after birth. This study investigated the ontogeny of pulmonary and renal ACE concentrations in fetal and neonatal horses. Fetal pulmonary ACE concentration increased from 250 days towards term (c. 335 days). Newborn foals showed significantly higher mean concentrations of pulmonary ACE (4.40 +/- 0.62 nmol min(-1) mg protein(-1)) than both fetuses during late gestation (1.23 +/- 0.51 nmol min(-1) mg protein(-1)) and animals aged 1 day to 2 weeks of postnatal age (0.85 +/- 0.15 nmol min(-1) mg protein(-1)). Renal ACE was detected in fetal horses from 100 days of gestation but showed no developmental trend during the second half of gestation or in early postnatal life. Overall in the fetus, mean concentrations of renal ACE were also approximately 10 times lower than mean pulmonary values. Renal ACE concentration may be related to the functional immaturity of the equine kidneys. The increase in pulmonary ACE concentration seen towards term in the fetal horse may be induced by the prepartum cortisol surge that occurs very close to delivery in this species. Therefore, premature delivery in this species may interrupt the onset of ACE production in the fetal lungs and circumvent the normal maturation of the renin-angiotensin system.

Adrenocortical responsiveness is blunted in twin relative to singleton ovine fetuses

Twin fetuses experience much higher rates of perinatal mortality/morbidity than age- and weight-matched singletons. Across species, the prepartum increase in fetal plasma cortisol is responsible for maturing a number of systems in preparation for birth and the immediate postnatal period. In sheep, it is known that basal adrenocortical function is delayed in twins relative to singletons. Thus, it could be argued that relative immaturity in twins may explain their increased susceptibility to stress in the perinatal period and their relatively poor perinatal outcome. However, whether adrenocortical responsiveness to stress is also diminished in the twin fetus and whether the fetal cardiovascular, metabolic and endocrine defences to acute stress are comparatively weak in the twin fetus is unknown. This study investigated the effect of twinning on adrenocortical responsiveness to either the physiological stress of acute hypoxaemia or to an exogenous ACTH test, and on the fetal cardiovascular, metabolic and endocrine responses to acute hypoxaemic stress. Twenty Welsh Mountain sheep fetuses were chronically instrumented (1-2% halothane) at 121 +/- 3 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 into two groups based upon fetal number (singletons, n= 10; twins, n= 10), as determined at surgery. At 130 +/- 2 days, a 1 h episode of acute, isocapnic hypoxaemia (to reduce carotid P(O(2)) to 12 +/- 1 mmHg) was induced in all fetuses by reducing the maternal inspired O(2) fraction (F(IO(2)); 9% O(2) in N(2)). 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. At 133 +/- 2 days a 2.5 microg bolus dose of synthetic ACTH (Synacthen; Ciba Pharmaceuticals, UK) was injected i.v. into eight of the singleton and six of the twin fetuses to determine adrenocortical steroidogenic sensitivity to exogenous ACTH. Under basal conditions, twins had lower plasma cortisol concentration, arterial blood pressure and femoral blood flow relative to singleton fetuses. Twins responded to acute hypoxaemia with similar pressor and vasopressor responses compared to singleton fetuses. However, the rate pressure product, an index of myocardial work, tended to decrease during hypoxaemia in twins, in contrast to the increase observed in singletons. Similar increases in the fetal plasma concentrations of ACTH, AVP, noradrenaline and adrenaline were observed during hypoxaemia in both groups; however, both the increments in fetal plasma concentration of cortisol in response to acute hypoxaemia and to exogenous ACTH were blunted in twins relative to singletons. This study shows that basal adrenocortical function as well as adrenocortical responsiveness is blunted in the twin relative to the singleton fetus. Further, the mechanism for adrenocortical blunting resides at the level of the adrenal cortex rather than higher up the axis. Relative adrenocortical immaturity in the twin fetus may reflect a specific endocrine adaptation to prolong gestation in multiple ovine pregnancies; however, such an adaptation does not affect the cardiovascular, metabolic or endocrine defence responses to acute hypoxaemia in the twin fetus.

Life before birth: effects of cortisol on future cardiovascular and metabolic function

The concept of fetal programming is an area that is now under rigorous investigation in many laboratories throughout the world. We need to engender a fascination in all segments of society, not just pregnant women, about life in the womb.

CONCLUSION

Everyone needs to understand that improving the condition of the fetus will have personal, social and economic benefits. The time has come to realize that, in a sense, it is not just women who are pregnant but it is the family and the whole of society.

Hindlimb glucose and lactate metabolism during umbilical cord compression and acute hypoxemia in the late-gestation ovine fetus

The metabolic adaptation of the hindlimb in the fetus to a reversible period of adverse intrauterine conditions and, subsequently, to a further episode of acute hypoxemia has been examined. Sixteen sheep fetuses were chronically instrumented with vascular catheters and transit-time flow probes. In nine of these fetuses, umbilical blood flow was reversibly reduced by 30% from baseline for 3 days (umbilical cord compression), while the remaining fetuses acted as sham-operated, age-matched controls. Acute hypoxemia was subsequently induced in all fetuses by reducing maternal fractional inspired oxygen concentration for 1 h. Paired hindlimb arteriovenous blood samples were taken at appropriate intervals during cord compression and acute hypoxemia, and by using femoral blood flow and the Fick principle, substrate delivery, uptake, and output were calculated. Umbilical cord compression reduced blood oxygen content and delivery to the hindlimb and increased hindlimb oxygen extraction and blood glucose and lactate concentration in the fetus. However, hindlimb glucose and oxygen consumption were unaltered during umbilical cord compression. In contrast, hindlimb oxygen delivery and uptake were significantly reduced in all fetuses during subsequent acute hypoxemia, but glucose extraction, oxygen extraction, and hindlimb lactate output significantly increased in sham-operated control fetuses only. Preexposure of the fetus to a temporary period of adverse intrauterine conditions alters the metabolic response of the fetal hindlimb to subsequent acute stress. Additional data suggest that circulating blood lactate may be derived from sources other than the fetal hindlimb under these circumstances. The lack of hindlimb lactate output during acute hypoxemia in umbilical cord-compressed fetuses, despite a significant fall in oxygen delivery to and uptake by the hindlimb, suggests that the fetal hindlimb may not respire anaerobically after exposure to adverse intrauterine conditions. hypoxia

The effect of a reversible period of adverse intrauterine conditions during late gestation on fetal and placental weight and placentome distribution in sheep

Adverse intrauterine conditions occurring during early to mid-gestation or throughout the whole of gestation influence placental weight and the distribution of placentome types in sheep. However, no study to date has investigated the effect of a reversible period of adverse intrauterine conditions during late gestation upon fetal and placental weight and placentome distribution in sheep. Twenty-two sheep fetuses were chronically instrumented with an inflatable cord occluder, amniotic and vascular catheters and with a Transonic flow probe around an umbilical artery. At 125 days (term isca.145 days) the occluder was inflated to reduce umbilical blood flow by ca.30 per cent for 3d in 12 fetuses (umbilical cord compressed, UCC). The occluder was then deflated and umbilical blood flow allowed to return to baseline. The remaining 10 fetuses acted as sham-operated controls in which the occluder remained deflated at all times. At 135-137dGA ewes were humanely killed and tissues collected, weighed and placentomes classified. A reduction in umbilical blood flow by approximately 30 per cent from baseline for 3 days in UCC fetuses led to mild fetal asphyxia throughout the period of cord-compression. After deflation of the occluder cuff, umbilical blood flow returned to a level that was significantly greater than that measured during baseline. Umbilical cord compression had no effect on fetal body weight but significantly increased fetal adrenal weight relative to body weight. While the total number of placentomes was not altered by cord-compression, total placentome weight and the total weight of C/D-type placentomes were both reduced in UCC relative to control placentae. In addition, the mean weight of placentomes, and of C/D-type placentomes specifically, was significantly lower in UCC relative to control placentae. When expressed as a percentage of the total number of placentomes in the placenta, there was a significantly lower percentage of C/D-type placentomes in UCC relative to control placentae. In addition, there was a significant relationship between the total number of placentomes and the percentage C/D-type placentomes in control, but not UCC, placentae. The data suggest that a temporary, reversible period of adverse intrauterine conditions occurring late in gestation in sheep has persisting effects upon the placenta, mean placentome weight and placentome distribution.

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.

Plasma leptin concentration in fetal sheep during late gestation: ontogeny and effect of glucocorticoids

The ontogeny and developmental control of plasma leptin concentration in the fetus are poorly understood. The present study investigated plasma leptin concentration in chronically catheterized sheep fetuses near term, and in neonatal and adult sheep. The effect of glucocorticoids on plasma leptin in utero was examined by fetal adrenalectomy and exogenous cortisol or dexamethasone infusion. In intact, untreated fetuses studied between 130 and 140 d (term, 145 +/- 2 d), plasma leptin concentration increased in association with the prepartum cortisol surge. Positive relationships were observed between plasma leptin in utero and both gestational age and plasma cortisol. Plasma leptin was also inversely correlated with fetal p(a)O(2). The ontogenic rise in plasma leptin was abolished by fetal adrenalectomy. In intact fetuses at 123-127 d, plasma leptin was increased by infusions of cortisol (3-5 mg kg(-1)d(-1), +127 +/- 21%) for 5 d and dexamethasone (45-60 microg kg(-1)d(-1), +268 +/- 61%) for 2 d. However, the cortisol-induced rise in plasma leptin was transient; by the fifth day of infusion, plasma leptin was restored to within the baseline range. These findings show that, in the sheep fetus, an intact adrenal gland is required for the normal ontogenic rise in plasma leptin near term. Furthermore, fetal treatment with exogenous and endogenous glucocorticoids increases circulating leptin concentration in utero.

Sympathetic control of the cardiovascular response to acute hypoxemia in the chick embryo

In response to an acute hypoxemic insult, the mammalian fetus shows a redistribution of the cardiac output in favor of the heart and brain. Peripheral vasoconstriction contributes to this response and is partly mediated by the release of catecholamines. Two mechanisms of catecholamine release in the fetus are reported: 1) neurogenic sympathetic stimulation and 2) a nonneurogenic mechanism via a direct effect of hypoxemia on chromaffin tissues. In the present study, the effects of sympathetic blockade on plasma catecholamine release and cardiac output distribution in response to acute hypoxemia were studied in the chick embryo at different stages of incubation. Only at the end of the incubation period, sympathetic blockade markedly attenuated the increase in plasma catecholamine concentrations and resulted in a greater fraction of the cardiac output distributed to the carcass. However, these effects did not prevent a significant increase in cardiac output to the brain and heart during acute hypoxemia. These data imply that in the chick embryo the contribution of neurogenic mechanisms to the catecholaminergic response to acute hypoxemia becomes greater by the end of the incubation period.

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.

Regulation of 11 beta-hydroxysteroid dehydrogenase type 2 activity in ovine placenta by fetal cortisol

The effect of fetal cortisol on the activity of the type 2 isoform of the enzyme, 11 beta-hydroxysteroid dehydrogenase (11 beta-HSD2), was examined in ovine placenta and fetal kidney by measuring tissue 11 beta-HSD2 activity during late gestation when endogenous fetal cortisol levels rise and after exogenous cortisol administration to immature fetuses before the prepartum cortisol surge. Placental 11 beta-HSD2 activity decreased between 128-132 days and term (approximately 145 days of gestation) in association with the normal prepartum increase in fetal plasma cortisol. Raising fetal cortisol levels to prepartum values in the immature fetus at 128--132 days of gestation reduced placental 11 beta-HSD2 activity to term values. In contrast, 11 beta-HSD2 activity in the fetal renal cortex was unaffected by gestational age or cortisol infusion. When all the data were combined, there was an inverse correlation between the log fetal plasma cortisol level at delivery and placental 11 beta-HSD2 activity, expressed both on a weight-specific basis and per mg placental protein. Fetal cortisol therefore appears to be a physiological regulator of placental, but not renal, 11 beta-HSD2 activity in fetal sheep during late gestation. These findings have important implications, not only for glucocorticoid exposure in utero, but also for the local actions of cortisol within the placental tissues that are involved in initiating parturition in the sheep.

Alpha-adrenergic contribution to the cardiovascular response to acute hypoxemia in the chick embryo

Fetal responses to acute hypoxemia include bradycardia, increase in blood pressure, and peripheral vasoconstriction. Peripheral vasoconstriction contributes to the redistribution of the cardiac output away from ancillary vascular beds toward myocardial, cerebral, and adrenal circulations. We investigated the effect of alpha-adrenergic receptor blockade on this fetal response. Fluorescent microspheres were used to measure cardiac output distribution during basal and hypoxemic conditions with and without phentolamine treatment. Phentolamine altered basal cardiac output distribution, indicating a basal alpha-adrenergic tone, but this was mainly noted at the earlier stages of incubation. During hypoxemia, phentolamine prevented vasoconstriction in the carcass. At day 19 of incubation, the percent cardiac output distributed to the carcass increased by 20% compared with a decrease in the control group by 17%. Phentolamine markedly attenuated the subsequent redistribution of the cardiac output toward the brain (from +102% in the control group to -25% in the phentolamine-treated group) and the heart (from +196% in the control group to +69% in the phentolamine-treated group). In the chick embryo, alpha-adrenergic mechanisms contribute to the maintenance of basal vascular tone and to the redistribution of the cardiac output away from the peripheral circulations toward the brain and heart during hypoxemic conditions.

An in vivo nitric oxide clamp to investigate the influence of nitric oxide on continuous umbilical blood flow during acute hypoxaemia in the sheep fetus

1. The aims of this study in the ovine fetus were to (1) characterise continuous changes in umbilical blood flow and vascular conductance during acute hypoxaemia and (2) determine the effects of nitric oxide blockade on umbilical blood flow and vascular conductance during normoxic and hypoxaemic conditions using a novel in vivo 'nitric oxide clamp'. 2. Under 1-2% halothane anaesthesia, seven ovine fetuses were instrumented between 118 and 125 days of gestation (term is ca 145 days) with vascular and amniotic catheters and a flow probe around an umbilical artery. At least 5 days after surgery, all fetuses were subjected to a 3 h protocol: 1 h of normoxia, 1 h of hypoxaemia and 1 h of recovery during fetal I.V. infusion with saline or, 1-2 days later, during combined fetal treatment with the nitric oxide (NO) inhibitor N (G)-nitro-L-arginine methyl ester (L-NAME, 100 mg x kg(-1)) and the NO donor sodium nitroprusside (NP, 5.1 +/- 2.0 microg x kg(-1) x min(-1), the 'nitric oxide clamp'). Following the end of the 3 h experimental protocol, the infusion of NP was withdrawn to unmask any persisting effects of fetal treatment with L-NAME alone. 3. During acute hypoxaemia, the reduction in arterial partial pressure of O2 (Pa,O2) was similar in fetuses infused with saline or treated with the nitric oxide clamp. In all fetuses, acute hypoxaemia led to a progressive increase in mean arterial blood pressure and a fall in heart rate. In saline-infused fetuses, acute hypoxaemia led to a rapid, but transient, decrement in umbilical vascular conductance. Thereafter, umbilical vascular conductance was maintained and a significant increase in umbilical blood flow occurred, which remained elevated until the end of the hypoxaemic challenge. In contrast, while the initial decrement in umbilical vascular conductance was prevented in fetuses treated with the nitric oxide clamp, the increase in umbilical blood flow during hypoxaemia was similar to that in fetuses infused with saline. After the 1 h recovery period of the acute hypoxaemia protocol, withdrawal of the sodium nitroprusside infusion from fetuses undergoing the nitric oxide clamp led to a significant, but transient, hypertension and a sustained umbilical vasoconstriction. 4. In conclusion, the data reported in this study of unanaesthetised fetal sheep (1) show that minute-by-minute analyses of haemodynamic changes in the umbilical vascular bed reveal an initial decrease in umbilical vascular conductance at the onset of hypoxaemia followed by a sustained increase in umbilical blood flow for the duration of the hypoxaemic challenge, (2) confirm that the increase in umbilical blood flow after 15 min hypoxaemia is predominantly pressure driven, and (3) demonstrate that nitric oxide plays a major role in the maintenance of umbilical blood flow under basal, but not under acute hypoxaemic, conditions.

A novel method for controlled and reversible long term compression of the umbilical cord in fetal sheep

1. In fetal sheep during late gestation the aims of the present study were to (1) develop a technique for inducing prolonged but reversible periods of controlled compression of the umbilical cord and (2) characterise the cardiovascular, endocrine and metabolic responses to this challenge. 2. Under 1-2 % halothane anaesthesia, 16 Welsh Mountain sheep fetuses were chronically instrumented at 118 +/- 2 days of gestation (term is ca 145 days) with an inflatable occluder cuff around the umbilical cord, amniotic and femoral vascular catheters and with transit-time flow probes around the contra-lateral femoral artery and an umbilical artery. At 125 days, umbilical blood flow was reduced by 30 % from a pre-determined 24 h baseline for 3 days by automated servo-controlled inflation of the occluder cuff (n = 8). The occluder was then deflated allowing return of umbilical blood flow to baseline. The remaining eight fetuses were used as sham-operated controls in which the occluder was not inflated throughout the protocol. Fetal cardiovascular variables were recorded at 8 s intervals and arterial blood samples taken for measurement of blood gases, glucose and lactate and plasma adrenaline, noradrenaline and vasopressin concentration throughout the study. 3. Automated servo-controlled inflation of the occluder cuff, programmed to reduce umbilical blood flow by 30 % from baseline, reduced umbilical blood flow by 30.2 +/- 1.7 %, with a coefficient of variation during compression of 6.5 +/- 1.1 %. Sustained partial compression of the umbilical cord produced falls in fetal arterial pH, P(a,O2), percentage O(2) saturation of haemoglobin, and hindlimb oxygen delivery, and increases in P(a,CO2), haemoglobin concentration, arterial blood oxygen carrying capacity and in blood glucose and lactate concentrations. While the reductions in P(a,O2), percentage saturation of haemoglobin and hindlimb oxygen delivery and the increase in P(a,CO2) were sustained throughout compression, the reduction in arterial pH and the increase in arterial oxygen carrying capacity had returned towards baseline values by 48 h compression. Fetal blood lactate concentrations reached a peak at 8 h of compression and, thereafter, were maintained at an elevated level relative to baseline. 4. Partial compression of the umbilical cord produced fetal hypertension, a reduction in femoral blood flow and, consequently, an increase in calculated fetal femoral vascular resistance for the duration of the challenge. In addition, the fall in heart rate measured in sham control fetuses by the end of the study, did not occur in cord-compressed fetuses. Cosinor analysis on 24 h rhythms of cardiovascular data indicated a significant increase in the amplitude of the 24 h rhythm in heart rate in cord-compressed fetuses relative to sham controls during the period of compression or sham-compression. Furthermore, cord compression led to an increase in fetal plasma noradrenaline, but not adrenaline and vasopressin concentrations relative to sham control fetuses. 5. In conclusion, a novel reversible method for controlled, long-term compression of the umbilical cord in sheep has been developed. The data show that sustained, partial compression of the umbilical cord produced moderate but sustained asphyxia, which resolved after the end of the compression period, and induced changes in fetal cardiovascular, endocrine and metabolic functions.

Effects of altitude versus economic status on birth weight and body shape at birth

The compelling evidence linking small size at birth with later cardiovascular disease has renewed and amplified a clinical and scientific interest in the determinants of fetal growth. Although the effects of maternal nutrition on fetal growth have been extensively studied, comparatively little is known about the effects of maternofetal hypoxia. This study tested the hypothesis that in highland regions, high altitude rather than maternal economic status is associated with reduced and altered fetal growth by investigating the effects of high altitude versus economic status on birth weight and body shape at birth in Bolivia. Bolivia is geographically and socioeconomically unique. It contains several highland (>3500 m above sea level) and lowland (<500 m) cities that are inhabited by very economically divergent populations. Birth weight, body length, and head circumference were compared between a high- (n = 100) and low- (n = 100) income region of La Paz (3649 m; largest high-altitude city) and a high- (n = 100) and low- (n = 100) income region of Santa Cruz (437 m; largest low-altitude city). In addition, the frequency distribution across the continuum of birth weights was plotted for babies born from high- and low-income families in La Paz and Santa Cruz. Mean birth weights were lower in babies from La Paz than in babies from Santa Cruz in both high- and low-income groups. The cumulative frequency curve across all compiled birth weights was shifted to the left in babies from La Paz compared with those from Santa Cruz, regardless of economic status. The frequency of low birth weight (<2500 g) was higher in babies from La Paz than from Santa Cruz in both high- and low-income groups. In addition, at high altitude but not at low altitude, high income was associated with an increase in the head circumference:birth weight ratio. These findings suggest that high altitude rather than economic status is associated with low birth weight and altered body shape at birth in babies from Bolivia.

Purinergic contribution to circulatory, metabolic, and adrenergic responses to acute hypoxemia in fetal sheep

This study investigated the effects on femoral vascular resistance, blood glucose and lactate levels, and plasma catecholamine concentrations of fetal treatment with an adenosine receptor antagonist during acute hypoxemia in fetal sheep during late gestation. Under anesthesia, seven fetal sheep were instrumented between 117 and 118 days gestation (term is approximately 145 days) with vascular and amniotic catheters and an ultrasonic probe around a femoral artery. Six days after surgery, all fetuses were randomly subjected to a 3-h experiment consisting of 1 h of normoxia, 1 h of hypoxemia, and 1 h of recovery. This was done during either intravenous infusion of vehicle or the adenosine receptor antagonist [8-(p-sulfophenyl)-theophylline; 8-SPT] dissolved in vehicle. During vehicle infusion, all fetuses responded to hypoxemia with bradycardia, an increase in arterial blood pressure, and femoral vasoconstriction. Increases in blood glucose and lactate concentrations and in plasma epinephrine and norepinephrine concentrations also occurred in all fetuses during hypoxemia. Fetal treatment with 8-SPT markedly attenuated the bradycardic, hypertensive, vasoconstrictor, glycemic, and adrenergic responses to hypoxemia, but it did not affect the increase in blood lactate concentrations during hypoxemia. These data show that adenosine is involved in the mechanisms mediating fetal cardiovascular, metabolic, and adrenergic responses to hypoxemia in fetal sheep. Fetal treatment with 8-SPT mimics the effects of carotid sinus nerve section on fetal cardiovascular function during hypoxemia, suggesting a role for adenosine in mediating fetal cardiovascular chemoreflexes.

Plasma adrenocorticotropin and cortisol concentrations during acute hypoxemia after a reversible period of adverse intrauterine conditions in the ovine fetus during late gestation

The present study determined the pituitary-adrenal responses to acute hypoxemia after a period of reversible adverse intrauterine conditions produced by partial compression of the umbilical cord for 3 days in the sheep fetus during late gestation. At 118 +/- 2 days gestation (term is approximately 145 days), 12 sheep fetuses were instrumented under halothane anesthesia with an occluder cuff around the umbilical cord, amniotic and vascular catheters, and a transit-time flow probe around an umbilical artery. In 6 of the fetuses at 125 days, umbilical blood flow was reduced by about 30% from baseline for 3 days (UCC), after which the occluder was deflated. The remaining 6 fetuses acted as sham-operated controls in which the occluder was not inflated. All fetuses were then subsequently subjected to 2 periods of acute hypoxemia, elicited by reducing the maternal inspired fraction of oxygen (FiO(2)) at 2 +/- 1 and 5 +/- 2 days after the end of cord compression or sham compression. In addition, 4 fetuses from each group were subjected to an ACTH challenge 1-2 days after the final episode of acute hypoxemia. Maternal and fetal arterial blood samples were taken at appropriate intervals during cord compression, acute hypoxemia, and ACTH challenge for analyses of blood gases, pH, and plasma ACTH and cortisol concentrations. Partial compression of the umbilical cord produced reversible mild fetal asphyxia, a transient increase in fetal plasma ACTH, and a progressive increase in fetal plasma cortisol. At 5 +/- 2 days after the end of compression, despite similar blood gas status between the groups, basal plasma cortisol, but not ACTH, concentrations were significantly greater in compressed fetuses relative to sham controls. However, this dissociation did not affect a similar increment in fetal plasma ACTH and cortisol concentrations during acute hypoxemia or in the fetal plasma cortisol response to the ACTH challenge in either group. An increase in adrenocortical mass occurred in fetuses preexposed to partial compression of the umbilical cord relative to sham controls. The data suggest that fetal exposure to a reversible period of adverse intrauterine conditions produced by partial compression of the umbilical cord does not affect the magnitude of the fetal hypothalamic-pituitary-adrenal axis response to subsequent acute hypoxemia, but it leads to resetting of basal hypothalamic-pituitary-adrenal axis function in the fetus. The mechanism for this resetting may include an increase in adrenocortical steroidogenic synthetic capacity, but it is not due to a change in adrenocortical sensitivity to ACTH. Inappropriate fetal glucocorticoid exposure after reversible periods of adverse intrauterine conditions has important implications for fetal and postnatal development.

Neuropeptide Y in the sheep fetus: effects of acute hypoxemia and dexamethasone during late gestation

Plasma concentrations of neuropeptide Y (NPY) were measured in pregnant ewes and their fetuses under basal conditions and in response to acute hypoxemia during late gestation. The effects of fetal treatment with dexamethasone on these NPY responses were also examined. Under general anesthesia, 10 Welsh Mountain ewes and their fetuses were chronically instrumented between 117-120 days gestation (dGA; term is approximately 145 dGA) with vascular and amniotic catheters, and an ultrasonic probe around a femoral artery of each fetus. At 124 dGA, five fetuses were continuously infused i.v. with dexamethasone for 48 h at a rate of 1.73 +/- 0.16 microg x kg(-1) x h(-1) while the remaining five fetuses received vehicle at the same rate. At 126 dGA, 45 h from the onset of either infusion, 1 h of materno-fetal hypoxemia was induced by reducing maternal FiO2. During normoxia, maternal plasma NPY concentrations were three times those measured in fetal plasma in both groups. During hypoxemia, PaO2 fell to similar levels in the control and dexamethasone-treated groups in both mothers and fetuses. In control animals, there was a significant increase in the NPY concentration in fetal, but not maternal, plasma during hypoxemia. Fetal treatment with dexamethasone significantly enhanced the fetal NPY response to acute hypoxemia but had no effects on basal NPY levels in the fetal or maternal plasma or on the maternal response to acute hypoxemia. These data show: 1) differences between the maternal and fetal plasma NPY response to maternal inhalation hypoxia; 2) that NPY may play a role in mediating fetal defense responses to acute hypoxemia; and 3) that fetal exposure to glucocorticoids modifies the fetal plasma NPY response to acute hypoxemia.

Developmental changes in plasma catecholamine concentrations during normoxia and acute hypoxia in the chick embryo

In the mammalian fetus, the cardiovascular responses to acute hypoxaemia include a redistribution of the cardiac output away from the periphery towards the adrenal, myocardial and cerebral circulations. A component of the peripheral vasoconstriction is mediated by increased release of catecholamines into the fetal circulation during acute hypoxaemia. Previously, we have shown that the chick embryo also shows an increase in peripheral vascular resistance during acute hypoxaemia and that this response becomes progressively larger towards the end of the incubation period. However, the ontogeny of the catecholaminergic response to acute hypoxaemia has not been investigated in this species. Fertilised chicken eggs were studied on days 10, 13, 16 and 19 of incubation (hatching is at 21 days). At each stage of incubation, blood samples were obtained from the chorioallantoic artery of the chick embryos during normoxia and after 5 min of hypoxaemia for measurement of plasma concentrations of adrenaline and noradrenaline by HPLC. Basal plasma adrenaline and noradrenaline concentrations by the end of the incubation period were much higher in the chick embryo than values reported for mammalian fetuses during late gestation. During normoxia, basal plasma noradrenaline concentration remained unchanged during development but plasma adrenaline concentration showed a developmental increase from < 25.1 pmol l-1 at day 10 to 3 nmol l-1 at day 19 of incubation. Acute hypoxaemia caused an increase in plasma noradrenaline and adrenaline from day 13 and day 16 of incubation, respectively. In addition, the increase in plasma adrenaline and noradrenaline and in the ratio of plasma adrenaline to noradrenaline during acute hypoxaemia became progressively larger by the end of the incubation period. These data show an ontogenic increase in basal plasma catecholamines and in the catecholaminergic response to acute hypoxaemia in the chick embryo during the last third of the incubation period.

Androstenedione treatment of pregnant baboons at 0.7-0.8 of gestation promotes a premature forward shift in the nocturnal maternal plasma estradiol surge relative to progesterone and increases myometrial contraction activity

Androstenedione treatment of pregnant monkeys at 0.8 of gestation reproduces endocrine, biophysical, and biochemical changes similar to those measured during spontaneous, term labor in the pregnant monkey. In the pregnant baboon, the spontaneous onset of labor at term has been attributed to a forward shift in the nocturnal estradiol surge relative to that of progesterone in maternal plasma. This study investigated whether androstenedione treatment of the pregnant baboon at 0.7-0.8 of gestation promotes a premature forward shift in the nocturnal surge of maternal plasma estradiol relative to progesterone and whether this shift is associated with premature increases in nocturnal myometrial activity. Eight pregnant baboons were prepared surgically under general anesthesia with vascular catheters and myometrial electromyogram electrodes between 121 and 139 days of gestation (term is ca. 185 days). Catheters were maintained patent by continuous infusion of heparinized saline from the time of surgery until one of two treatments began following at least 9 days of postoperative recovery. In four baboons (Group I), the saline administration was replaced by a continuous infusion of 10% intralipid vehicle during Day 1 of the experimental protocol. During Day 2 and Day 3, the intralipid infusion was switched for a continuous infusion of androstenedione dissolved in intralipid set at a low (0.8 mg x kg(-1) x h(-1)) and at a high (1.6 mg x kg(-1) x h(-1)) dose, each delivered for 24 h. The other four pregnant baboons (Group II) received 10% intralipid vehicle for Days 1, 2, and 3 of the experimental protocol. One baboon from Group I received an additional dose of 0.4 mg x kg(-1) x h(-1) for 24 h before the low and the high dose of androstenedione. In each baboon, during each experimental day, maternal arterial blood samples (1 ml) were taken at 1 h intervals for 12 h, starting 3 h before the onset of darkness in the animal's environment, for measurement of maternal plasma estradiol and progesterone concentrations via RIA. Myometrial contractions were counted during each night-time period of the experimental protocol. All pregnant baboons demonstrated increases in maternal plasma estradiol and progesterone concentrations at night-time. Androstenedione had a dose-dependent effect in elevating day-time maternal plasma estradiol concentrations and in promoting a forward shift in the nocturnal surge of maternal plasma estradiol without affecting the nocturnal progesterone profile in maternal plasma. Maternal treatment with androstenedione also led to an increase in nocturnal myometrial contraction activity. We conclude that androstenedione treatment of the pregnant baboon at 0.7-0.8 of gestation promotes a premature forward shift in the nocturnal estradiol surge relative to that of progesterone in maternal plasma and that this shift is associated with an increase in nocturnal myometrial contraction activity, in a similar way to that measured during spontaneous onset of labor at term in this species.