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Chronic High-Altitude Hypoxia Alters Iron and Nitric Oxide Homeostasis in Fetal and Maternal Sheep Blood and Aorta. Antioxidants (Basel) 2022; 11:antiox11091821. [PMID: 36139895 PMCID: PMC9495375 DOI: 10.3390/antiox11091821] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/15/2022] [Revised: 09/09/2022] [Accepted: 09/12/2022] [Indexed: 11/16/2022] Open
Abstract
The mammalian fetus thrives at oxygen tensions much lower than those of adults. Gestation at high altitude superimposes hypoxic stresses on the fetus resulting in increased erythropoiesis. We hypothesized that chronic hypoxia at high altitude alters the homeostasis of iron and bioactive nitric oxide metabolites (NOx) in gestation. To test for this, electron paramagnetic resonance was used to provide unique measurements of iron, metalloproteins, and free radicals in the blood and aorta of fetal and maternal sheep from either high or low altitudes (3801 or 300 m). Using ozone-based chemiluminescence with selectivity for various NOx species, we determined the NOx levels in these samples immediately after collection. These experiments demonstrated a systemic redistribution of iron in high altitude fetuses as manifested by a decrease in both chelatable and total iron in the aorta and an increase in non-transferrin bound iron and total iron in plasma. Likewise, high altitude altered the redox status diversely in fetal blood and aorta. This study also found significant increases in blood and aortic tissue NOx in fetuses and mothers at high altitude. In addition, gradients in NOx concentrations observed between fetus and mother, umbilical artery and vein, and plasma and RBCs demonstrated complex dynamic homeostasis of NOx among these circulatory compartments, such as placental generation and efflux as well as fetal consumption of iron-nitrosyls in RBCs, probably HbNO. In conclusion, these results may suggest the utilization of iron from non-hematopoietic tissues iron for erythropoiesis in the fetus and increased NO bioavailability in response to chronic hypoxic stress at high altitude during gestation.
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Reyes RV, Herrera EA, Ebensperger G, Sanhueza EM, Giussani DA, Llanos AJ. Perinatal cardiopulmonary adaptation to the thin air of the Alto Andino by a native Altiplano dweller, the llama. J Appl Physiol (1985) 2020; 129:152-161. [PMID: 32584666 DOI: 10.1152/japplphysiol.00800.2019] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/07/2023] Open
Abstract
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.
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Affiliation(s)
- R V Reyes
- Programa de Fisiopatología, Instituto de Ciencias Biomédicas, Facultad de Medicina, Universidad de Chile, Santiago, Chile.,International Center for Andean Studies (INCAS), Universidad de Chile, Santiago, Chile
| | - E A Herrera
- Programa de Fisiopatología, Instituto de Ciencias Biomédicas, Facultad de Medicina, Universidad de Chile, Santiago, Chile.,International Center for Andean Studies (INCAS), Universidad de Chile, Santiago, Chile
| | - G Ebensperger
- Programa de Fisiopatología, Instituto de Ciencias Biomédicas, Facultad de Medicina, Universidad de Chile, Santiago, Chile.,International Center for Andean Studies (INCAS), Universidad de Chile, Santiago, Chile
| | - E M Sanhueza
- Programa de Fisiopatología, Instituto de Ciencias Biomédicas, Facultad de Medicina, Universidad de Chile, Santiago, Chile
| | - D A Giussani
- Department of Physiology, Development and Neuroscience, University of Cambridge, Cambridge, United Kingdom
| | - A J Llanos
- Programa de Fisiopatología, Instituto de Ciencias Biomédicas, Facultad de Medicina, Universidad de Chile, Santiago, Chile.,International Center for Andean Studies (INCAS), Universidad de Chile, Santiago, Chile
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Abstract
The human cerebral vasculature originates in the fourth week of gestation and continues to expand and diversify well into the first few years of postnatal life. A key feature of this growth is smooth muscle differentiation, whereby smooth muscle cells within cerebral arteries transform from migratory to proliferative to synthetic and finally to contractile phenotypes. These phenotypic transformations can be reversed by pathophysiological perturbations such as hypoxia, which causes loss of contractile capacity in immature cerebral arteries. In turn, loss of contractility affects all whole-brain cerebrovascular responses, including those involved in flow-metabolism coupling, vasodilatory responses to acute hypoxia and hypercapnia, cerebral autoregulation, and reactivity to activation of perivascular nerves. Future strategies to minimize cerebral injury following hypoxia-ischemic insults in the immature brain might benefit by targeting treatments to preserve and promote contractile differentiation in the fetal cerebrovasculature. This could potentially be achieved through inhibition of receptor tyrosine kinase-mediated growth factors, such as vascular endothelial growth factor and platelet-derived growth factor, which are mobilized by hypoxic and ischemic injury and which facilitate contractile dedifferentiation. Interruption of the effects of other vascular mitogens, such as endothelin and angiotensin-II, and even some miRNA species, also could be beneficial. Future experimental work that addresses these possibilities offers promise to improve current clinical management of neonates who have suffered and survived hypoxic, ischemic, asphyxic, or inflammatory cerebrovascular insults.
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Affiliation(s)
- William J Pearce
- From the Center for Perinatal Biology, Loma Linda University School of Medicine, Loma Linda, CA.
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Ducsay CA, Goyal R, Pearce WJ, Wilson S, Hu XQ, Zhang L. Gestational Hypoxia and Developmental Plasticity. Physiol Rev 2018; 98:1241-1334. [PMID: 29717932 PMCID: PMC6088145 DOI: 10.1152/physrev.00043.2017] [Citation(s) in RCA: 105] [Impact Index Per Article: 17.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/05/2023] Open
Abstract
Hypoxia is one of the most common and severe challenges to the maintenance of homeostasis. Oxygen sensing is a property of all tissues, and the response to hypoxia is multidimensional involving complicated intracellular networks concerned with the transduction of hypoxia-induced responses. Of all the stresses to which the fetus and newborn infant are subjected, perhaps the most important and clinically relevant is that of hypoxia. Hypoxia during gestation impacts both the mother and fetal development through interactions with an individual's genetic traits acquired over multiple generations by natural selection and changes in gene expression patterns by altering the epigenetic code. Changes in the epigenome determine "genomic plasticity," i.e., the ability of genes to be differentially expressed according to environmental cues. The genomic plasticity defined by epigenomic mechanisms including DNA methylation, histone modifications, and noncoding RNAs during development is the mechanistic substrate for phenotypic programming that determines physiological response and risk for healthy or deleterious outcomes. This review explores the impact of gestational hypoxia on maternal health and fetal development, and epigenetic mechanisms of developmental plasticity with emphasis on the uteroplacental circulation, heart development, cerebral circulation, pulmonary development, and the hypothalamic-pituitary-adrenal axis and adipose tissue. The complex molecular and epigenetic interactions that may impact an individual's physiology and developmental programming of health and disease later in life are discussed.
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Affiliation(s)
- Charles A. Ducsay
- The Lawrence D. Longo, MD Center for Perinatal Biology, Department of Basic Sciences, Loma Linda University School of Medicine, Loma Linda, California
| | - Ravi Goyal
- The Lawrence D. Longo, MD Center for Perinatal Biology, Department of Basic Sciences, Loma Linda University School of Medicine, Loma Linda, California
| | - William J. Pearce
- The Lawrence D. Longo, MD Center for Perinatal Biology, Department of Basic Sciences, Loma Linda University School of Medicine, Loma Linda, California
| | - Sean Wilson
- The Lawrence D. Longo, MD Center for Perinatal Biology, Department of Basic Sciences, Loma Linda University School of Medicine, Loma Linda, California
| | - Xiang-Qun Hu
- The Lawrence D. Longo, MD Center for Perinatal Biology, Department of Basic Sciences, Loma Linda University School of Medicine, Loma Linda, California
| | - Lubo Zhang
- The Lawrence D. Longo, MD Center for Perinatal Biology, Department of Basic Sciences, Loma Linda University School of Medicine, Loma Linda, California
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Thompson LP, Aguan K, Zhou H. Chronic Hypoxia Inhibits Contraction of Fetal Arteries by Increased Endothelium-Derived Nitric Oxide and Prostaglandin Synthesis. ACTA ACUST UNITED AC 2016; 11:511-20. [PMID: 15582495 DOI: 10.1016/j.jsgi.2004.05.008] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
OBJECTIVE Chronic hypoxia causes redistribution of fetal cardiac output by mechanisms poorly understood. We tested the hypothesis that chronic hypoxia alters vascular reactivity of arteries from near-term fetal guinea pigs. METHODS Pregnant guinea pigs (50 days, term = 65 days) were exposed to either normoxia (room air) or hypoxia (12% O2) for 14 days. Carotid artery ring segments from anesthetized fetuses were mounted onto myographs for measurement of force. Contractile responses to cumulative addition of prostaglandin F2alpha (PGF2alpha, 10(-9) M to 10(-5) M), U46619, a thromboxane mimetic (10(-12) M to 12(-6) M), and KCl (10 to 120 mM) were measured in the presence and absence of INDO (INDO, 10(-5) M) alone and INDO plus nitro-L-arginine (LNA, 10(-4) M), or INDO plus N6-iminoethyl-L-lysine (LNIL, 5 x 10(-5) M, a selective iNOS inhibitor), and measured in endothelium-intact and denuded arteries. Nitric oxide synthase (NOS) activity was measured in isolated arteries by 14C-L-arginine to 14C-L-citrulline conversion. RESULTS Hypoxia decreased contractile responses to both PGF2alpha and U46619 under control conditions. Maximal contraction to both agonists was increased in hypoxemic arteries after INDO alone and INDO + LNA compared to normoxic controls. Endothelium-denudation abolished the differences between the groups. KCl contraction was unaffected by hypoxia. LNIL potentiated maximal PGF(2alpha) contraction but was similar between groups. Hypoxia increased (P < .05) total and Ca(2+)-dependent NOS activities by 1.7- and 2.1-fold, respectively, but had no effect on Ca(2+)-independent activity. CONCLUSION Chronic hypoxia alters vascular reactivity of fetal carotid arteries by increasing the contribution of both vasodilator prostaglandins and nitric oxide and suggests that changes in local vascular mechanisms may be altered by chronic hypoxia.
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Affiliation(s)
- Loren P Thompson
- Department of Obstetrics, Gynecology and Reproductive Sciences, University of Maryland School of Medicine, Baltimore, Maryland 21201, USA.
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Silpanisong J, Pearce WJ. Vasotrophic regulation of age-dependent hypoxic cerebrovascular remodeling. Curr Vasc Pharmacol 2014; 11:544-63. [PMID: 24063376 DOI: 10.2174/1570161111311050002] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/29/2012] [Revised: 06/08/2012] [Accepted: 07/12/2012] [Indexed: 02/07/2023]
Abstract
Hypoxia can induce functional and structural vascular remodeling by changing the expression of trophic factors to promote homeostasis. While most experimental approaches have been focused on functional remodeling, structural remodeling can reflect changes in the abundance and organization of vascular proteins that determine functional remodeling. Better understanding of age-dependent hypoxic macrovascular remodeling processes of the cerebral vasculature and its clinical implications require knowledge of the vasotrophic factors that influence arterial structure and function. Hypoxia can affect the expression of transcription factors, classical receptor tyrosine kinase factors, non-classical G-protein coupled factors, catecholamines, and purines. Hypoxia's remodeling effects can be mediated by Hypoxia Inducible Factor (HIF) upregulation in most vascular beds, but alterations in the expression of growth factors can also be independent of HIF. PPARγ is another transcription factor involved in hypoxic remodeling. Expression of classical receptor tyrosine kinase ligands, including vascular endothelial growth factor, platelet derived growth factor, fibroblast growth factor and angiopoietins, can be altered by hypoxia which can act simultaneously to affect remodeling. Tyrosine kinase-independent factors, such as transforming growth factor, nitric oxide, endothelin, angiotensin II, catecholamines, and purines also participate in the remodeling process. This adaptation to hypoxic stress can fundamentally change with age, resulting in different responses between fetuses and adults. Overall, these mechanisms integrate to assure that blood flow and metabolic demand are closely matched in all vascular beds and emphasize the view that the vascular wall is a highly dynamic and heterogeneous tissue with multiple cell types undergoing regular phenotypic transformation.
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Affiliation(s)
- Jinjutha Silpanisong
- Center for Perinatal Biology, Loma Linda University School of Medicine, Loma Linda, CA 92350, USA.
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Chronic fetal hypoxia produces selective brain injury associated with altered nitric oxide synthases. Am J Obstet Gynecol 2011; 204:254.e16-28. [PMID: 21272843 DOI: 10.1016/j.ajog.2010.11.032] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/27/2010] [Revised: 10/18/2010] [Accepted: 11/09/2010] [Indexed: 11/21/2022]
Abstract
OBJECTIVE The purpose of this study was to investigate the impact of chronic hypoxia on the nitric oxide synthase isoenzymes in specific brain structures. STUDY DESIGN Time-mated pregnant guinea pigs were exposed to 10.5% molecular oxygen for 14 days (animals with chronic fetal hypoxia; HPX) or room air (control animals; NMX); L-N6-(1-iminoethyl)-lysine (L-NIL; an inducible nitric oxide synthase inhibitor, 1 mg/kg/d) was administered to HPX group for 14 days (L-NIL + HPX). Fetal brains were harvested at term. Multilabeled immunofluorescence was used to generate a brain injury map. Laser capture microdissection and quantitative polymerase chain reaction were applied; cell injury markers, apoptosis activation, neuron loss, total nitric oxide, and the levels of individual nitric oxide synthase isoenzymes were quantified. RESULTS Chronic hypoxia causes selective fetal brain injury rather than global. Injury is associated with differentially affected nitric oxide synthases in both neurons and glial cells, with inducible macrophage-type nitric oxide synthase up-regulated at all injury sites. L-NIL attenuated the injury, despite continued hypoxia. CONCLUSION These studies demonstrate that chronic hypoxia selectively injures the fetal brain in part by the differential regulation of nitric oxide synthase isoenzymes in an anatomic- and cell-specific manner.
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Guo R, Hou W, Dong Y, Yu Z, Stites J, Weiner CP. Brain injury caused by chronic fetal hypoxemia is mediated by inflammatory cascade activation. Reprod Sci 2010; 17:540-8. [PMID: 20360591 DOI: 10.1177/1933719110364061] [Citation(s) in RCA: 58] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/17/2022]
Abstract
The prevalence of cerebral palsy (CP) shows little temporal or geographic variation and is associated with preterm birth, maternal/fetal infection/inflammation, and fetal growth restriction (IUGR), a potential surrogate for chronic fetal hypoxemia (CHX). We previously demonstrated CHX causes a fetal inflammatory response syndrome (FIRS). Herein, we test the hypothesis that CHX may cause fetal brain injury by upregulating inflammatory cytokine cascades, culminating in apoptosis pathway activation. Time-mated guinea pigs were housed in 12% or 10.5% O(2) for the last 21% of gestation. Chronic fetal hypoxemia increased the lactate/pyruvate and decreased the glutathione (GSH)/oxidized glutathione (GSSH) ratios, confirming a shift to a prooxidant state. The end result was a >30% decrease in hippocampal neuron density. Based on a microarray spotted with 113 cytokines and receptors, 22 genes were upregulated by CHX in proportion to the degree of hypoxia; the findings were confirmed by quantitative polymerase chain reaction (PCR). Thus, CHX triggers fetal brain inflammation inversely proportional to its severity characterized by increased apoptosis and neuronal loss. We suggest CHX fetal brain injury is not directly caused by oxygen deprivation but rather is an adaptive response that becomes maladaptive.
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Affiliation(s)
- Rong Guo
- Department of Pathophysiology, Xian Jiaotong University School of Medicine, Xian, Shannxi, PR China
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Sankaran S, Kyle PM. Aetiology and pathogenesis of IUGR. Best Pract Res Clin Obstet Gynaecol 2009; 23:765-77. [PMID: 19666240 DOI: 10.1016/j.bpobgyn.2009.05.003] [Citation(s) in RCA: 120] [Impact Index Per Article: 8.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/10/2008] [Revised: 04/02/2009] [Accepted: 05/04/2009] [Indexed: 01/06/2023]
Abstract
Intrauterine growth restriction (IUGR) is a major cause of perinatal mortality and morbidity. A complex and dynamic interaction of maternal, placental and fetal environment is involved in ensuring normal fetal growth. An imbalance or lack of coordination in this complex system may lead to IUGR. Animal studies have given us an insight into some aspects of the basic pathophysiology of IUGR, and recent technologies such as Doppler studies of maternal and fetal vessels have added further information. The aetiologies of IUGR are diverse, involving multiple complex mechanisms, which make understanding of the pathophysiology difficult. However, particular focus is placed on the mechanisms involved in uteroplacental insufficiency as a cause of IUGR, as (1) it is common, (2) outcome can be good if timing of delivery is optimal and (3) it may be amenable to therapy in the future. While the research into the pathophysiology of IUGR continues, there have been interesting discoveries related to the genetic contribution to IUGR and the intrauterine programming of adult-onset diseases attributed to IUGR.
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Affiliation(s)
- Srividhya Sankaran
- Guy's & St Thomas' NHS Foundation Trust, Westminster Bridge Road, London SE1 7EH, UK
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Morrison JL. SHEEP MODELS OF INTRAUTERINE GROWTH RESTRICTION: FETAL ADAPTATIONS AND CONSEQUENCES. Clin Exp Pharmacol Physiol 2008; 35:730-43. [DOI: 10.1111/j.1440-1681.2008.04975.x] [Citation(s) in RCA: 201] [Impact Index Per Article: 12.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/21/2023]
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Pena JP, Tomimatsu T, Hatran DP, McGill LL, Longo LD. Cerebral blood flow and oxygenation in ovine fetus: responses to superimposed hypoxia at both low and high altitude. J Physiol 2007; 578:359-70. [PMID: 17068100 PMCID: PMC2075128 DOI: 10.1113/jphysiol.2006.119925] [Citation(s) in RCA: 30] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/24/2006] [Accepted: 10/21/2006] [Indexed: 01/09/2023] Open
Abstract
For the fetus, although the roles of arterial blood gases are recognized to be critical in the regulation of cerebral blood flow (CBF) and cerebral oxygenation, the relation of CBF, cortical tissue P(O2) (tP(O2)), sagittal sinus P(O2), and related indices of cerebral oxygenation to arterial blood gases are not well defined. This is particularly true for that fetus subjected to long-term hypoxia (LTH). In an effort to elucidate these interrelations, we tested the hypothesis that in the fetus acclimatized to high altitude, cerebral oxygenation is not compromised relative to that at low altitude. By use of a laser Doppler flowmeter with a fluorescent O2 probe, in near-term fetal sheep at low altitude (n = 8) and those acclimatized to high altitude hypoxia (3801 m for 90 +/- 5 days; n = 6), we measured laser Doppler CBF (LD-CBF), tP(O2), and related variables in response to 40 min superimposed hypoxia. At both altitudes, fetal LD-CBF, cerebral O2 delivery, tP(O2), and several other variables including sagittal sinus P(O2), correlated highly with arterial P(O2) (P(a,O2)). In response to superimposed hypoxia (P(a,O2) = 11 +/- 1 Torr), LD-CBF was significantly blunted at high altitude, as compared with that at low altitude. In the two altitude groups fetal cerebral oxygenation was similar under both control conditions and with superimposed hypoxia, cortical tP(O2) decreasing from 8 +/- 1 and 6 +/- 1 Torr, respectively, to 2 +/- 1 Torr. Also, for these conditions sagittal sinus P(O2) and [HbO2] values were similar. In response to superimposed hypoxia, cerebral metabolic rate for O(2) decreased approximately 50% in each group (P < 0.05). For both the fetus at low altitude and that acclimatized to high altitude LTH, we present the first dose-response data on the relation of LD-CBF, cortical tP(O2), and sagittal sinus blood gas values to P(a,O2). In addition, despite differences in several variables, the fetus at high altitude showed evidence of successful acclimatization, supporting the hypothesis that such fetuses demonstrate no compromise in cerebral oxygenation.
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Affiliation(s)
- Jorge Pereyra Pena
- Center for Perinatal Biology, Department of Physiology, Obstetrics and Gynecology, Loma Linda University, School of Medicine, Loma Linda, CA 92350, USA
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Abstract
Fetal cerebrovascular responses to acute hypoxia are fundamentally different from those observed in the adult cerebral circulation. The magnitude of hypoxic vasodilatation in the fetal brain increases with postnatal age although fetal cerebrovascular responses to acute hypoxia can be complicated by age-dependent depressions of blood pressure and ventilation. Acute hypoxia promotes adenosine release, which depresses fetal cerebral oxygen consumption through action of adenosine on neuronal A1 receptors and vasodilatation through activation of A2 receptors on cerebral arteries. The vascular effect of adenosine can account for approximately half the vasodilatation observed in response to hypoxia. Hypoxia-induced release of nitric oxide and opioids can account for much of the adenosine-independent cerebral vasodilatation observed in response to hypoxia in the fetus. Direct effects of hypoxia on cerebral arteries account for the remaining fraction, although the vascular endothelium contributes relatively little to hypoxic vasodilatation in the immature cerebral circulation. In contrast to acute hypoxia, fetal cerebral blood flow tends to normalize during acclimatization to chronic hypoxia even though cardiac output is depressed. However, uncompensated chronic hypoxia in the fetus can produce significant changes in brain structure and function, alteration of respiratory drive and fluid balance, and increased incidence of intracranial hemorrhage and periventricular leukomalacia. At the level of the fetal cerebral arteries, chronic hypoxia increases protein content and depresses norepinephrine release, contractility, and receptor densities associated with contraction but also attenuates endothelial vasodilator capacity and decreases the ability of ATP-sensitive and calcium-sensitive potassium channels to promote vasorelaxation. Overall, fetal cerebrovascular adaptations to chronic hypoxia appear prioritized to conserve energy while preserving basic contractility. Many gaps remain in our understanding of how the effects of acute and chronic hypoxia are mediated in fetal cerebral arteries, but studies of adult cerebral arteries have produced many powerful pharmacological and molecular tools that are simply awaiting application in studies of fetal cerebral artery responses to hypoxia.
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Affiliation(s)
- William Pearce
- Center for Perinatal Biology, Loma Linda Univ. School of Medicine, Loma Linda, CA 92350, USA.
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Abstract
Placental insufficiency is a process leading to progressive deterioration in placental function and a decrease in transplacental transfer of oxygen and nutrients to the fetus. The resulting fetal hypoxemia is the major stimulus involved in the reduction in fetal growth as an attempt to reduce metabolic demands by the growing fetus. Fetal growth restriction (FGR) is the second cause of perinatal death after prematurity and can complicate up to 6% of all pregnancies. It is becoming apparent that its occurrence has major impacts on the fetus and placenta with consequences on the cardiovascular, metabolic and neurological development up to adulthood. We are just starting to unveil some of the basic mechanisms involved in this complex adaptation that may lead to reprogramming of fetal organs development mostly the heart, pancreas, lungs and brain. It is becoming clear that future research is needed to develop strategies to improve antenatal detection of FGR, in addition to reduce the risk of abnormal neurodevelopment during childhood, and onset of common diseases in adulthood following pregnancies complicated with placental insufficiency.
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Affiliation(s)
- Robert Gagnon
- Departments of Obstetrics, Gynecology and Physiology, University of Western Ontario, St. Joseph's Health Care London, 268 Grosvenor Street, London, Ont., Canada N6A 4V2.
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Meini A, Benocci A, Frosini M, Sgaragli GP, Garcia JB, Pessina GP, Aldinucci C, Palmi M. Potentiation of intracellular Ca2+ mobilization by hypoxia-induced NO generation in rat brain striatal slices and human astrocytoma U-373 MG cells and its involvement in tissue damage. Eur J Neurosci 2003; 17:692-700. [PMID: 12603259 DOI: 10.1046/j.1460-9568.2003.02483.x] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
The relationship between nitric oxide (NO) and intracellular Ca2+ in hypoxic-ischemic brain damage is not known in detail. Here we used rat striatal slices perfused under low-oxygen and Ca2+-free conditions and cultured human astrocytoma cells incubated under similar conditions as models to study the dynamics of intracellular NO and Ca2+ in hypoxia-induced tissue damage. Exposure of rat striatal slices for 70 min to low oxygen tension elicited a delayed and sustained increase in the release of 45Ca2+. This was potentiated by the NO donors sodium nitroprusside (SNP) and spermine-NO and inhibited by N-omega-nitro-L-arginine methyl ester (L-NAME) or by the NO scavenger 2-phenyl-4,4,5,5 tetramethylimidazoline-1-oxyl-3-oxide (PTIO). A membrane-permeant form of heparin in combination with either ruthenium red (RR) or ryanodine (RY) also inhibited 45Ca2+ release. In human astrocytoma U-373 MG cells, hypoxia increased intracellular Ca2+ concentration ([Ca2+]i) by 67.2 +/- 13.1% compared to normoxic controls and this effect was inhibited by L-NAME, PTIO or heparin plus RR. In striatal tissue, hypoxia increased NO production and LDH release and both effects were antagonized by L-NAME. Although heparin plus RR or RY antagonized hypoxia-induced increase in LDH release they failed to counteract increased NO production. These data therefore indicate that NO contributes to hypoxic damage through increased intracellular Ca2+ mobilization from endoplasmic reticulum and suggest that the NO-Ca2+ signalling might be a potential therapeutic target in hypoxia-induced neuronal degeneration.
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Affiliation(s)
- Antonella Meini
- Istituto di Scienze Farmacologiche, Università di Siena, via A Moro 2, 53100 Siena, Italy
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Joseph V, Mamet J, Lee F, Dalmaz Y, Van Reeth O. Prenatal hypoxia impairs circadian synchronisation and response of the biological clock to light in adult rats. J Physiol 2002; 543:387-95. [PMID: 12181309 PMCID: PMC2290468 DOI: 10.1113/jphysiol.2002.022236] [Citation(s) in RCA: 33] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022] Open
Abstract
The aim of this study was to test the hypothesis that prenatal hypoxia in rats might lead to consistent changes in the entrainment of the circadian clock by light. Pregnant female rats were placed in a chamber provided with hypoxic gas (10 % O2--90 % N2) at gestational day 5 and returned to normoxia before delivery. Once adult, rats born to hypoxic mothers had significant alterations in their circadian rhythm of locomotor activity (recorded in freely accessible running wheels). Under a regular 12/12 light/dark (LD) cycle, they showed a phase advance of their rhythm of activity (mean phase advance of 87 min) and were less active than control rats. After an abrupt 6 h phase delay in the LD cycle, rats from the prenatal hypoxic group (PNH) took significantly more time to resynchronise to the new LD cycle compared to controls (+53 %; 6.0 +/- 1.5 vs. 9.2 +/- 0.5 days respectively). Under constant darkness, PNH and control rats had a similar period of activity (24.27 +/- 0.20 vs. 24.40 +/- 0.13) but the response of PNH rats to a light pulse in the early subjective night was less marked than that of control rats (101 +/- 9 vs. 158 +/- 13 min). When submitted to acute restraint stress, PNH rats had a prolonged secretion of corticosterone compared to controls. These results indicate that prenatal hypoxia is a factor that has long lasting consequences for the functional output of the biological clock and the hormonal response to stress.
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Affiliation(s)
- Vincent Joseph
- Centre d'Etudes des Rythmes Biologiques, Université Libre de Bruxelles, Hôpital Erasme, 808 Route de Lennik, 1070 Bruxelles, Belgium.
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Pryor EC, Zhang J, Massmann GA, Figueroa JP. Prolonged mild fetal hypoxia up-regulates type I nitric oxide synthase expression in discrete areas of the late-gestation fetal sheep brain. Am J Obstet Gynecol 2002; 187:164-70. [PMID: 12114905 DOI: 10.1067/mob.2002.122403] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
OBJECTIVE Our purpose was to study the effects of prolonged mild hypoxemia on type I nitric oxide synthase (NOS) messenger RNA, protein, and enzymatic activity in the fetal sheep brain. STUDY DESIGN Pregnant sheep were randomly allocated to receive maternal nitrogen (n = 8) or compressed air (controls, n = 5) to reduce fetal brachial artery PO(2) by 25% for 5 days. Type I NOS mRNA (determined by ribonuclease protection assay) protein (determined by Western blot) and enzymatic activity (determined by citrulline assay) were measured in the hippocampus, striatum, cerebellum, and frontal cortex. Data are presented as mean +/- SEM and were compared by means of one-way analysis of variance or two-sample t test. RESULTS The reduction in maternal inspired oxygen concentration decreased fetal PO(2) by 26% and oxygen content by 25% without an associated change in PCO(2) or pH. Fetal hypoxemia increased type I NOS mRNA by threefold in the striatum and by 2-fold in the frontal cortex and cerebellum, but it did not change mRNA expression in the hippocampus (P <.05). Type I NOS protein and catalytic activity increased only in the striatum (P <.05). CONCLUSION Prolonged mild hypoxemia has a differential effect on type I NOS mRNA in fetal sheep brain areas. Type I NOS protein and catalytic activity significantly increased only in the striatum. Our data suggest that fetal type I NOS gene expression is regulated at transcriptional, post-transcriptional, and translational levels.
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Affiliation(s)
- Elizabeth C Pryor
- Perinatal Research Laboratory, Department of Obstetrics and Gynecology, Wake Forest University School of Medicine, Winston-Salem, NC 27157, USA
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Sillau AH, McCullough RE, Dyckes R, White MM, Moore LG. Chronic hypoxia increases MCA contractile response to U-46619 by reducing NO production and/or activity. J Appl Physiol (1985) 2002; 92:1859-64. [PMID: 11960934 DOI: 10.1152/japplphysiol.00797.2001] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Chronic hypoxia alters contractile sensitivity of isolated arteries to alpha-adrenergic stimulation and other agonists. However, most studies have been performed in thoracic aortas or other large vessels making little contribution to vascular resistance in their respective circulations. To determine the effect of chronic hypoxia on the vasoconstrictor response in a small, resistance-sized vessel, we studied second and third generation middle cerebral arteries (MCA; approximately 75-microm internal diameter before mounting). MCA were isolated from normoxic (inspired oxygen = 125 Torr) and hypoxic (8 wk at 3,960 m; inspired oxygen = 90 Torr) guinea pigs, and their vasoconstrictor responses were determined to the thromboxane mimetic U-46619 by using dual-pipette video microscopy. Arteries from hypoxic animals had greater contractile sensitivity to U-46619 compared with those of the normoxic animals (-log EC50 = 7.86 +/- 0.11 vs. 7.62 +/- 0.06, respectively, P < 0.05). Addition of the nitric oxide (NO) inhibitor nitro-L-arginine (200 microM) to the vessel bath eliminated the differences in contractile sensitivity between the MCA from the normoxic and chronically hypoxic groups. Supplementation with L-arginine in the drinking water sufficient to raise plasma L-arginine levels 41% reduced MCA contractile sensitivity to U-46619 in the normoxic group (-log EC50 = 7.22 +/- 0.31, P < 0.05 compared with the nonsupplemented normoxic group) but not in the chronically hypoxic group. These results show that chronic hypoxia increases the sensitivity of the MCA to the vasoconstrictor U-46619, likely because of a reduction in NO production and/or activity.
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Affiliation(s)
- A Hugo Sillau
- Women's Health Research Center, University of Colorado Health Sciences Center, Denver 80262, USA
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Galleguillos M, Valenzuela MA, Riquelme R, Sanhueza E, Sánchez G, Figueroa JP, Llanos AJ. Nitric oxide synthase activity in brain tissues from llama fetuses submitted to hypoxemia. Comp Biochem Physiol A Mol Integr Physiol 2001; 129:605-14. [PMID: 11423330 DOI: 10.1016/s1095-6433(01)00299-9] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022]
Abstract
The fetal llama (Lama glama; a species adapted to live in chronic hypoxia in the highlands of the Andes) did not increase cerebral blood flow and reduce the brain oxygen uptake during hypoxemia. Although nitric oxide (NO) is a normal mediator in the regulation of vascular tone and synaptic transmission, NO overproduction by hypoxemia could produce neuronal damage. We hypothesized that nitric oxide synthase (NOS) activity is either maintained or reduced in the central nervous system of the llama fetuses submitted to chronic hypoxemia. Approximately 85% of the Ca(2+)-dependent NOS activity was soluble, at least 12% was associated with the mitochondrial fraction, and less than 5% remains associated with microsomes. To understand the role of NO in chronic hypoxemia, we determined the effect of 24-h hypoxemia on NOS activity in the central nervous system. No changes in activity or the subcellular distribution of NOS activity in brain tissues after hypoxemia were found. We proposed that the lack of changes in NOS activity in the llama under hypoxemia could be a cytoprotective mechanism inherent to the llama, against possible toxic effects of NO.
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Affiliation(s)
- M Galleguillos
- Departamento de Ciencias Biológicas Animales, Facultad de Ciencias Veterinarias y Pecuarias, Universidad de Chile, Santiago, Chile
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Thompson LP, Aguan K, Pinkas G, Weiner CP. Chronic hypoxia increases the NO contribution of acetylcholine vasodilation of the fetal guinea pig heart. Am J Physiol Regul Integr Comp Physiol 2000; 279:R1813-20. [PMID: 11049865 DOI: 10.1152/ajpregu.2000.279.5.r1813] [Citation(s) in RCA: 29] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
To investigate the effect of chronic hypoxia (HPX) on vasodilation of the fetal heart, we exposed pregnant guinea pigs to room air or 12% O(2) for 4, 7, or 10 days. We excised hearts from anesthetized fetuses (60 +/- 3 days; 65-day gestation = term) and measured changes in both the coronary artery pressure of the isolated constant-flow preparation and endothelial nitric oxide synthase (eNOS) mRNA of fetal ventricles. Dilator responses to cumulative addition (10(-9)-10(-5) M) of acetylcholine and sodium nitroprusside in prostaglandin F(2alpha) (5 x 10(-6) M)-constricted hearts were similar among normoxia (NMX), 4-, 7-, and 10-day HPX (control). Nitro-L-arginine (L-NA, 10(-4)M), a NOS inhibitor, inhibited maximal acetylcholine dilation of hearts exposed to 10-day HPX greater than NMX, 4-, and 7-day HPX. Hypoxia (after 7 and 10 days) increased eNOS mRNA of fetal ventricles compared with NMX and 4-day HPX. 4-Aminopyridine (3 mM), a voltage-dependent K(+)-channel inhibitor, inhibited acetylcholine- but not sodium nitroprusside-induced dilation of NMX and 10-day HPX hearts to a similar magnitude. Glibenclamide (10(-5) M), an ATP-sensitive K(+)-channel inhibitor, had no effect on vasodilation. We conclude that chronic HPX increases the contribution of NO but does not alter K(+)-channel activation in response to acetylcholine-stimulated coronary dilation. Thus increases in NO production via upregulation of eNOS gene expression may be an adaptive response to chronic HPX in the fetal coronary circulation.
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Affiliation(s)
- L P Thompson
- Department of Obstetrics, Gynecology and Reproductive Sciences, University of Maryland School of Medicine, Baltimore, Maryland 21158, USA
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