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Tournier A, Beacom M, Westgate JA, Bennet L, Garabedian C, Ugwumadu A, Gunn AJ, Lear CA. Physiological control of fetal heart rate variability during labour: Implications and controversies. J Physiol 2021; 600:431-450. [PMID: 34951476 DOI: 10.1113/jp282276] [Citation(s) in RCA: 12] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/18/2021] [Accepted: 11/25/2021] [Indexed: 11/08/2022] Open
Abstract
The interpretation of fetal heart rate (FHR) patterns is the only available method to continuously monitor fetal wellbeing during labour. One of the most important yet contentious aspects of the FHR pattern is changes in FHR variability (FHRV). Some clinical studies suggest that loss of FHRV during labour is a sign of fetal compromise so this is reflected in practice guidelines. Surprisingly, there is little systematic evidence to support this observation. In this review we methodically dissect the potential pathways controlling FHRV during labour-like hypoxaemia. Before labour, FHRV is controlled by the combined activity of the parasympathetic and sympathetic nervous systems, in part regulated by a complex interplay between fetal sleep state and behaviour. By contrast, preclinical studies using multiple autonomic blockades have now shown that sympathetic neural control of FHRV was potently suppressed between periods of labour-like hypoxaemia, and thus, that the parasympathetic system is the sole neural regulator of FHRV once FHR decelerations are present during labour. We further discuss the pattern of changes in FHRV during progressive fetal compromise and highlight potential biochemical, behavioural and clinical factors that may regulate parasympathetic-mediated FHRV during labour. Further studies are needed to investigate the regulators of parasympathetic activity to better understand the dynamic changes in FHRV and their true utility during labour. This article is protected by copyright. All rights reserved.
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Affiliation(s)
- Alexane Tournier
- Department of Obstetrics, Universite de Lille, CHU Lille, ULR 2694 - METRICS, Lille, F 59000, France
| | - Michael Beacom
- The Fetal Physiology and Neuroscience Group, Department of Physiology, The University of Auckland, Auckland, New Zealand
| | - Jenny A Westgate
- The Fetal Physiology and Neuroscience Group, Department of Physiology, The University of Auckland, Auckland, New Zealand
| | - Laura Bennet
- The Fetal Physiology and Neuroscience Group, Department of Physiology, The University of Auckland, Auckland, New Zealand
| | - Charles Garabedian
- Department of Obstetrics, Universite de Lille, CHU Lille, ULR 2694 - METRICS, Lille, F 59000, France
| | - Austin Ugwumadu
- Department of Obstetrics and Gynaecology, St George's Hospital, St George's University of London, London, SW17 0RE, UK
| | - Alistair J Gunn
- The Fetal Physiology and Neuroscience Group, Department of Physiology, The University of Auckland, Auckland, New Zealand
| | - Christopher A Lear
- The Fetal Physiology and Neuroscience Group, Department of Physiology, The University of Auckland, Auckland, New Zealand
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Abstract
Heart disease remains one of the greatest killers. In addition to genetics and traditional lifestyle risk factors, we now understand that adverse conditions during pregnancy can also increase susceptibility to cardiovascular disease in the offspring. Therefore, the mechanisms by which this occurs and possible preventative therapies are of significant contemporary interest to the cardiovascular community. A common suboptimal pregnancy condition is a sustained reduction in fetal oxygenation. Chronic fetal hypoxia results from any pregnancy with increased placental vascular resistance, such as in preeclampsia, placental infection, or maternal obesity. Chronic fetal hypoxia may also arise during pregnancy at high altitude or because of maternal respiratory disease. This article reviews the short- and long-term effects of hypoxia on the fetal cardiovascular system, and the importance of chronic fetal hypoxia in triggering a developmental origin of future heart disease in the adult progeny. The work summarizes evidence derived from human studies as well as from rodent, avian, and ovine models. There is a focus on the discovery of the molecular link between prenatal hypoxia, oxidative stress, and increased cardiovascular risk in adult offspring. Discussion of mitochondria-targeted antioxidant therapy offers potential targets for clinical intervention in human pregnancy complicated by chronic fetal hypoxia.
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Affiliation(s)
- Dino A Giussani
- Department of Physiology, Development, and Neuroscience; The Barcroft Centre; Cambridge Cardiovascular British Heart Foundation Centre for Research Excellence; and Cambridge Strategic Research Initiative in Reproduction, University of Cambridge, UK
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Jellyman JK, Fletcher AJW, Fowden AL, Giussani DA. Glucocorticoid Maturation of Fetal Cardiovascular Function. Trends Mol Med 2020; 26:170-184. [PMID: 31718939 DOI: 10.1016/j.molmed.2019.09.005] [Citation(s) in RCA: 12] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/16/2019] [Revised: 09/17/2019] [Accepted: 09/30/2019] [Indexed: 12/27/2022]
Abstract
The last decade has seen rapid advances in the understanding of the central role of glucocorticoids in preparing the fetus for life after birth. However, relative to other organ systems, maturation by glucocorticoids of the fetal cardiovascular system has been ignored. Here, we review the effects of glucocorticoids on fetal basal cardiovascular function and on the fetal cardiovascular defense responses to acute stress. This is important because glucocorticoid-driven maturational changes in fetal cardiovascular function under basal and stressful conditions are central to the successful transition from intra- to extrauterine life. The cost-benefit balance for the cardiovascular health of the preterm baby of antenatal glucocorticoid therapy administered to pregnant women threatened with preterm birth is also discussed.
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Affiliation(s)
- Juanita K Jellyman
- Department of Biological Sciences, California State Polytechnic University, Pomona, CA, USA.
| | | | - Abigail L Fowden
- Department of Physiology Development and Neuroscience, University of Cambridge, Cambridge, UK; Cambridge Cardiovascular Strategic Research Initiative, Cambridge, UK; Cambridge Strategic Research Initiative in Reproduction, Cambridge, UK
| | - Dino A Giussani
- Department of Physiology Development and Neuroscience, University of Cambridge, Cambridge, UK; Cambridge Cardiovascular Strategic Research Initiative, Cambridge, UK; Cambridge Strategic Research Initiative in Reproduction, Cambridge, UK.
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Morrison JL, Berry MJ, Botting KJ, Darby JRT, Frasch MG, Gatford KL, Giussani DA, Gray CL, Harding R, Herrera EA, Kemp MW, Lock MC, McMillen IC, Moss TJ, Musk GC, Oliver MH, Regnault TRH, Roberts CT, Soo JY, Tellam RL. Improving pregnancy outcomes in humans through studies in sheep. Am J Physiol Regul Integr Comp Physiol 2018; 315:R1123-R1153. [PMID: 30325659 DOI: 10.1152/ajpregu.00391.2017] [Citation(s) in RCA: 101] [Impact Index Per Article: 16.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/05/2023]
Abstract
Experimental studies that are relevant to human pregnancy rely on the selection of appropriate animal models as an important element in experimental design. Consideration of the strengths and weaknesses of any animal model of human disease is fundamental to effective and meaningful translation of preclinical research. Studies in sheep have made significant contributions to our understanding of the normal and abnormal development of the fetus. As a model of human pregnancy, studies in sheep have enabled scientists and clinicians to answer questions about the etiology and treatment of poor maternal, placental, and fetal health and to provide an evidence base for translation of interventions to the clinic. The aim of this review is to highlight the advances in perinatal human medicine that have been achieved following translation of research using the pregnant sheep and fetus.
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Affiliation(s)
- Janna L Morrison
- Early Origins of Adult Health Research Group, School of Pharmacy and Medical Sciences, University of South Australia, Adelaide, South Australia, Australia
| | - Mary J Berry
- Department of Paediatrics and Child Health, University of Otago , Wellington , New Zealand
| | - Kimberley J Botting
- Department of Physiology, Development, and Neuroscience, University of Cambridge , Cambridge , United Kingdom
| | - Jack R T Darby
- Early Origins of Adult Health Research Group, School of Pharmacy and Medical Sciences, University of South Australia, Adelaide, South Australia, Australia
| | - Martin G Frasch
- Department of Obstetrics and Gynecology, University of Washington , Seattle, Washington
| | - Kathryn L Gatford
- Robinson Research Institute and Adelaide Medical School, University of Adelaide , Adelaide, South Australia , Australia
| | - Dino A Giussani
- Department of Physiology, Development, and Neuroscience, University of Cambridge , Cambridge , United Kingdom
| | - Clint L Gray
- Department of Paediatrics and Child Health, University of Otago , Wellington , New Zealand
| | - Richard Harding
- Department of Anatomy and Developmental Biology, Monash University , Clayton, Victoria , Australia
| | - Emilio A Herrera
- Pathophysiology Program, Biomedical Sciences Institute (ICBM), Faculty of Medicine, University of Chile , Santiago , Chile
| | - Matthew W Kemp
- Division of Obstetrics and Gynecology, University of Western Australia , Perth, Western Australia , Australia
| | - Mitchell C Lock
- Early Origins of Adult Health Research Group, School of Pharmacy and Medical Sciences, University of South Australia, Adelaide, South Australia, Australia
| | - I Caroline McMillen
- Early Origins of Adult Health Research Group, School of Pharmacy and Medical Sciences, University of South Australia, Adelaide, South Australia, Australia
| | - Timothy J Moss
- The Ritchie Centre, Hudson Institute of Medical Research, Department of Obstetrics and Gynaecology, Monash University , Clayton, Victoria , Australia
| | - Gabrielle C Musk
- Animal Care Services, University of Western Australia , Perth, Western Australia , Australia
| | - Mark H Oliver
- Liggins Institute, University of Auckland , Auckland , New Zealand
| | - Timothy R H Regnault
- Department of Obstetrics and Gynecology and Department of Physiology and Pharmacology, Western University, and Children's Health Research Institute , London, Ontario , Canada
| | - Claire T Roberts
- Robinson Research Institute and Adelaide Medical School, University of Adelaide , Adelaide, South Australia , Australia
| | - Jia Yin Soo
- Early Origins of Adult Health Research Group, School of Pharmacy and Medical Sciences, University of South Australia, Adelaide, South Australia, Australia
| | - Ross L Tellam
- Early Origins of Adult Health Research Group, School of Pharmacy and Medical Sciences, University of South Australia, Adelaide, South Australia, Australia
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Llanos AJ, Riquelme RA, Herrera EA, Ebensperger G, Krause B, Reyes RV, Sanhueza EM, Pulgar VM, Behn C, Cabello G, Parer JT, Giussani DA, Blanco CE, Hanson MA. Evolving in thin air—Lessons from the llama fetus in the altiplano. Respir Physiol Neurobiol 2007; 158:298-306. [PMID: 17588504 DOI: 10.1016/j.resp.2007.04.012] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/31/2007] [Revised: 04/24/2007] [Accepted: 04/26/2007] [Indexed: 11/22/2022]
Abstract
Compared with lowland species, fetal life for mammalian species whose mothers live in high altitude is demanding. For instance, fetal llamas have to cope with the low fetal arterial PO2 of all species, but also the likely superimposition of hypoxia as a result of the decreased oxygen environment in which the mother lives in the Andean altiplano. When subjected to acute hypoxia the llama fetus responds with an intense peripheral vasoconstriction mediated by alpha-adrenergic mechanisms plus high plasma concentrations of catecholamines and neuropeptide Y (NPY). Endothelial factors such as NO and endothelin-1 also play a role in the regulation of local blood flows. Unlike fetuses of lowland species such as the sheep, the llama fetus shows a profound cerebral hypometabolic response to hypoxia, decreasing cerebral oxygen consumption, Na-K-ATPase activity and temperature, and resulting in an absence of seizures and apoptosis in neural cells. These strategies may have evolved to prevent hypoxic injury to the brain or other organs in the face of the persistent hypobaric hypoxia of life in the Andean altiplano.
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Affiliation(s)
- Aníbal J Llanos
- Laboratorio de Fisiología y Fisiopatología del Desarrollo, Programa de Fisiopatología, Instituto de Ciencias Biomédicas (ICBM), Facultad de Medicina, Universidad de Chile, Santiago, Chile.
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Bennet L, Booth L, Malpas SC, Quaedackers JS, Jensen E, Dean J, Gunn AJ. Acute systemic complications in the preterm fetus after asphyxia: role of cardiovascular and blood flow responses. Clin Exp Pharmacol Physiol 2006; 33:291-9. [PMID: 16620290 DOI: 10.1111/j.1440-1681.2006.04364.x] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
1. Poor perfusion of the kidneys and gut, and associated functional impairment, are major problems in the first days of life in very preterm infants. These complications can be associated with a substantial mortality and further problems such as reduced kidney growth and chronic renal problems in later childhood. 2. There is very little information, and consequently considerable debate, about how or even whether to improve perfusion of the vital organs of this most vulnerable group of babies. Current treatments simply do not consistently improve babies' perfusion generally or kidney and gut perfusion and function in particular. 3. In this review we critically examine clinical and experimental evidence that suggests that exposure to low oxygen levels before and during birth may be a significant contributor to impaired systemic perfusion, and highlight areas requiring further research. 4. This knowledge is essential to develop and refine ways of improving perfusion of the kidneys and other vital organs in premature babies.
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Affiliation(s)
- L Bennet
- Department of Physiology, Faculty of Medicine and Health Sciences, The University of Auckland, Auckland, New Zealand.
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Mellor DJ, Diesch TJ, Gunn AJ, Bennet L. The importance of ‘awareness’ for understanding fetal pain. ACTA ACUST UNITED AC 2005; 49:455-71. [PMID: 16269314 DOI: 10.1016/j.brainresrev.2005.01.006] [Citation(s) in RCA: 129] [Impact Index Per Article: 6.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/13/2004] [Revised: 11/17/2004] [Accepted: 01/12/2005] [Indexed: 11/29/2022]
Abstract
Our understanding of when the fetus can experience pain has been largely shaped by neuroanatomy. However, completion of the cortical nociceptive connections just after mid-gestation is only one part of the story. In addition to critically reviewing evidence for whether the fetus is ever awake or aware, and thus able to truly experience pain, we examine the role of endogenous neuro-inhibitors, such as adenosine and pregnanolone, produced within the feto-placental unit that contribute to fetal sleep states, and thus mediate suppression of fetal awareness. The uncritical view that the nature of presumed fetal pain perception can be assessed by reference to the prematurely born infant is challenged. Rigorously controlled studies of invasive procedures and analgesia in the fetus are required to clarify the impact of fetal nociception on postnatal pain sensitivity and neural development, and the potential benefits or harm of using analgesia in this unique setting.
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Affiliation(s)
- David J Mellor
- Riddet Centre and Institute of Food, Nutrition and Human Health, College of Sciences, Massey University, Palmerston North, New Zealand.
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Sanhueza EM, Riquelme RA, Herrera EA, Giussani DA, Blanco CE, Hanson MA, Llanos AJ. Vasodilator tone in the llama fetus: the role of nitric oxide during normoxemia and hypoxemia. Am J Physiol Regul Integr Comp Physiol 2005; 289:R776-83. [PMID: 15905225 DOI: 10.1152/ajpregu.00071.2005] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
The fetal llama responds to hypoxemia, with a marked peripheral vasoconstriction but, unlike the sheep, with little or no increase in cerebral blood flow. We tested the hypothesis that the role of nitric oxide (NO) may be increased during hypoxemia in this species, to counterbalance a strong vasoconstrictor effect. Ten fetal llamas were operated under general anesthesia. Mean arterial pressure (MAP), heart rate, cardiac output, total vascular resistance, blood flows, and vascular resistances in cerebral, carotid and femoral vascular beds were determined. Two groups were studied, one with nitric oxide synthase (NOS) blocker NG-nitro-l-arginine methyl ester (l-NAME), and the other with 0.9% NaCl (control group), during normoxemia, hypoxemia, and recovery. During normoxemia, l-NAME produced an increase in fetal MAP and a rapid bradycardia. Cerebral, carotid, and femoral vascular resistance increased and blood flow decreased to carotid and femoral beds, while cerebral blood flow did not change significantly. However, during hypoxemia cerebral and carotid vascular resistance fell by 44% from its value in normoxemia after l-NAME, although femoral vascular resistance progressively increased and remained high during recovery. We conclude that in the llama fetus: 1) NO has an important role in maintaining a vasodilator tone during both normoxemia and hypoxemia in cerebral and femoral vascular beds and 2) during hypoxemia, NOS blockade unmasked the action of other vasodilator agents that contribute, with nitric oxide, to preserving blood flow and oxygen delivery to the tissues.
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Affiliation(s)
- Emilia M Sanhueza
- Programa de Fisiopatología, Instituto de Ciencias Biomédicas, Facultad de Medicina, Universidad de Chile, Casilla 16038, Santiago 9, Chile.
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Thakor AS, Bloomfield MR, Patterson M, Giussani DA. Calcitonin gene-related peptide antagonism attenuates the haemodynamic and glycaemic responses to acute hypoxaemia in the late gestation sheep fetus. J Physiol 2005; 566:587-97. [PMID: 15860534 PMCID: PMC1464744 DOI: 10.1113/jphysiol.2005.085431] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/18/2005] [Accepted: 04/27/2005] [Indexed: 12/14/2022] Open
Abstract
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.
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Affiliation(s)
- A S Thakor
- Department of Physiology, University of Cambridge, Downing Street, Cambridge CB2 3EG, UK
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Quaedackers JS, Roelfsema V, Heineman E, Gunn AJ, Bennet L. The role of the sympathetic nervous system in postasphyxial intestinal hypoperfusion in the pre-term sheep fetus. J Physiol 2004; 557:1033-44. [PMID: 15073276 PMCID: PMC1665158 DOI: 10.1113/jphysiol.2004.062554] [Citation(s) in RCA: 38] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022] Open
Abstract
Asphyxia in utero in pre-term fetuses is associated with evolving hypoperfusion of the gut after the insult. We examined the role of the sympathetic nervous system (SNS) in mediating this secondary hypoperfusion. Gut blood flow changes were also assessed during postasphyxial seizures. Preterm fetal sheep at 70% of gestation (103-104 days, term is 147 days) underwent sham asphyxia or asphyxia induced by 25 min of complete cord occlusion and fetuses were studied for 3 days afterwards. Phentolamine (10 mg bolus plus 10 mg h(-1)i.v.) or saline was infused for 8 h starting 15 min after the end of asphyxia or sham asphyxia. Phentolamine blocked the fall in superior mesenteric artery blood flow (SMABF) after asphyxia and there was a significant decrease in MAP for the first 3 h of infusion (33 +/- 1.6 mmHg versus vehicle 36.7 +/- 0.8 mmHg, P < 0.005). During seizures SMABF fell significantly (8.3 +/- 2.3 versus 11.4 +/- 2.7 ml min(-1), P < 0.005), and SMABF was more than 10% below baseline for 13.0 +/- 1.7 min per seizure (versus seizure duration of 78.1 +/- 7.2 s). Phentolamine was associated with earlier onset of seizures (5.0 +/- 0.4 versus 7.1 +/- 0.7 h, P < 0.05), but no change in amplitude or duration, and prevented the fall in SMABF. In conclusion, the present study confirms the hypothesis that postasphyxial hypoperfusion of the gut is strongly mediated by the SNS. The data highlight the importance of sympathetic activity in the initial elevation of blood pressure after asphyxia and are consistent with a role for the mesenteric system as a key resistance bed that helps to maintain perfusion in other, more vulnerable systems.
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Affiliation(s)
- Josine S Quaedackers
- Department of Anatomy, The University of Auckland, Private Bag 92019 Auckland, New Zealand
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Llanos AJ, Riquelme RA, Sanhueza EM, Hanson MA, Blanco CE, Parer JT, Herrera EA, Pulgar VM, Reyes RV, Cabello G, Giussani DA. The fetal llama versus the fetal sheep: different strategies to withstand hypoxia. High Alt Med Biol 2003; 4:193-202. [PMID: 12855051 DOI: 10.1089/152702903322022794] [Citation(s) in RCA: 47] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022] Open
Abstract
The pregnant llama (Lama glama) has walked for millions of years through the thin oxygen trail of the Andean altiplano. We hypothesize that a pool of genes has been selected in the llama that express efficient mechanisms to withstand this low-oxygen milieu. The llama fetus responds to acute hypoxia with an intense peripheral vasoconstriction that is not affected by bilateral section of the carotid sinus nerves. Moreover, the increase in fetal plasma concentrations of vasoconstrictor hormones, such as catecholamines, neuropeptide Y, and vasopressin, is much greater in the llama than in the sheep fetus. Furthermore, treatment of fetal llamas with an alpha-adrenergic antagonist abolished the peripheral vasoconstriction and resulted in fetal cardiovascular collapse and death during acute hypoxia, suggesting an indispensable upregulation of alpha-adrenergic mechanisms in this high altitude species. Local endothelial factors such as nitric oxide (NO) also play a key role in the regulation of fetal adrenal blood flow and in the adrenal secretion of catecholamines and cortisol. Interestingly, in contrast to the human or sheep fetus, the llama fetus showed a small increase in brain blood flow during acute hypoxia, with no increase in oxygen extraction across the brain, and thereby a decrease in brain oxygen consumption. These results suggest that the llama fetus responds to acute hypoxia with hypometabolism. How this reduction in metabolism is produced and how the cells are preserved during this condition remain to be elucidated.
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Affiliation(s)
- Aníbal J Llanos
- Laboratorio de Fisiología y Fisiopatología del Desarrollo, Programa de Fisiopatología, Instituto de Ciencias Biomédicas, Facultad de Medicina, Universidad de Chile, Santiago, Chile.
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