title: Sustained sympathetic nervous system support of arterial blood pressure during repeated brief umbilical cord occlusions in near-term fetal sheep.
abstract: Sympathetic nervous system (SNS)-mediated peripheral vasoconstriction plays a key role in initial maintenance of blood pressure during rapid-onset asphyxia in the mammalian fetus, but it is attenuated after the first few minutes. It is unclear whether the SNS response is sustained during the brief, but frequently repeated, episodes of asphyxia characteristic of labor. In the present study, 14 fetal sheep at 0.85 of gestation received either chemical sympathectomy with 6-hydroxydopamine (6-OHDA; n = 7) or sham injection (control; n = 7), followed 4-5 days later by repeated 2-min episodes of complete umbilical cord occlusion every 5 min for up to 4 h or until mean arterial blood pressure (MAP) fell to <20 mmHg for two successive occlusions. In controls, umbilical cord occlusions were associated with a rapid initial fall in fetal heart rate (FHR) and femoral blood flow (FBF), with initial hypertension, followed by progressive development of hypotension during ongoing occlusions. Sympathectomy was associated with attenuation of the initial rise in MAP during umbilical cord occlusion, and after the onset of hypotension, a markedly more rapid fall of MAP to the nadir, with a correspondingly slower fall in FBF (P < 0.05). In contrast, MAP and FHR between successive occlusions were higher after sympathectomy (P < 0.05). There was no significant difference in the number of occlusions before terminal hypotension (6-OHDA; 16.1 ± 2.2 vs. control; 18.7 ± 2.3). These data show that SNS activity provides ongoing support for fetal MAP during prolonged exposure to brief repeated asphyxia.
authors.affiliation: Department of Physiology, University of Auckland, Auckland, New Zealand; and.
authors.forename: Robert
authors.initials: R
authors.lastname: Galinsky
authors.affiliation: Department of Physiology, University of Auckland, Auckland, New Zealand; and.
authors.forename: Ellen C
authors.initials: EC
authors.lastname: Jensen
authors.affiliation: Department of Physiology, University of Auckland, Auckland, New Zealand; and.
authors.forename: Laura
authors.initials: L
authors.lastname: Bennet
authors.affiliation: Department of Physiology, University of Auckland, Auckland, New Zealand; and.
authors.forename: Clinton J
authors.initials: CJ
authors.lastname: Mitchell
authors.affiliation: Department of Physiology, University of Auckland, Auckland, New Zealand; and.
authors.forename: Eleanor R
authors.initials: ER
authors.lastname: Gunn
authors.affiliation: Department of Physiology, University of Auckland, Auckland, New Zealand; and.
authors.forename: Guido
authors.initials: G
authors.lastname: Wassink
authors.affiliation: Department of Physiology, University of Auckland, Auckland, New Zealand; and The Liggins Institute, University of Auckland, Auckland, New Zealand.
authors.forename: Mhoyra
authors.initials: M
authors.lastname: Fraser
authors.affiliation: Department of Physiology, University of Auckland, Auckland, New Zealand; and.
authors.forename: Jennifer A
authors.initials: JA
authors.lastname: Westgate
authors.affiliation: Department of Physiology, University of Auckland, Auckland, New Zealand; and aj.gunn@auckland.ac.nz.
authors.forename: Alistair J
authors.initials: AJ
authors.lastname: Gunn
mesh_terms: D000818:Animals; D001237:Asphyxia / Q000503:physiopathology; D001794:Blood Pressure / Q000502:physiology*; D005260:Female; D005333:Fetus / Q000502:physiology*; D006339:Heart Rate / Q000502:physiology; D023421:Models, Animal; D016627:Oxidopamine / Q000494:pharmacology; D011247:Pregnancy; D012039:Regional Blood Flow / Q000502:physiology; D012756:Sheep; D013563:Sympathectomy, Chemical / Q000379:methods; D013564:Sympathetic Nervous System / Q000187:drug effects / Q000502:physiology*; D013565:Sympatholytics / Q000494:pharmacology; D014469:Umbilical Arteries / Q000503:physiopathology*; D014470:Umbilical Cord / Q000098:blood supply*; D014661:Vasoconstriction / Q000502:physiology*
chemical_list: D013565:Sympatholytics; D016627:Oxidopamine
keywords: fetal sheep; repeated asphyxia; sympathetic nervous system