title: Influence of sympathetic tone on heart rate during vagal stimulation and nitroprusside induced hypotension in ovine fetus.
abstract: OBJECTIVE
  To characterize effects of sympathetic tone on fetal heart rate (FHR) reflex responses and FHR variability in late gestation.
  
  
  METHODS
  Changes in FHR and autonomic tones were studied (i) after electrical vagal stimulation and (ii) during nitroprusside-induced hypotension, in seven late gestation ovine fetus in control condition (ctrl), after dobutamine (beta1-activation) and atenolol (beta1-blockade). Results are expressed as mean +/- SEM.
  
  
  RESULTS
  (i) Minimal FHR after vagal stimulation was not influenced by atenolol or dobutamine but dobutamine accelerated FHR normalization. (ii) During nitroprusside induced hypotension atenolol inhibited the initial increases in FHR and FHR variability (measured by SD and LFnu) but not the bradycardia occurring below a mean arterial pressure of 38 +/- 2 mmHg. Dobutamine did not abolish the depressor reflex. During hypotension the positive chronotropic effect of sympathetic tone increased from 15 +/- 2 to 42 +/- 7 bpm then decreased at a rate of -7.6 +/- 1.5 bpm mmHg(-1), vagal negative chronotropic influence steadily increased at a rate of 1.9 +/- 0.4 bpm mmHg(-1). Changes in FHR variability were not correlated with vagal or sympathetic chronotropic effects.
  
  
  CONCLUSIONS
  beta1-stimulation does not affect sinus-node response to vagal stimulation but improves the speed of FHR normalization. FHR response to hypotension depends on an initial increase in both sympathetic and parasympathetic chronotropic effects that is associated with a sympathetic dependent increase in FHR variability and is followed by a withdrawal of sympathetic tone.
authors.affiliation: Department of Pediatrics, CHU, Rennes, France.
authors.forename: Théophile
authors.initials: T
authors.lastname: Gaillot
authors.forename: Alain
authors.initials: A
authors.lastname: Beuchée
authors.forename: Sophie
authors.initials: S
authors.lastname: Jaillard
authors.forename: Laurent
authors.initials: L
authors.lastname: Storme
authors.forename: Anne Monique
authors.initials: AM
authors.lastname: Nuyt
authors.forename: François
authors.initials: F
authors.lastname: Carré
authors.forename: Patrick
authors.initials: P
authors.lastname: Pladys
mesh_terms: D000318:Adrenergic beta-Agonists / Q000494:pharmacology; D000319:Adrenergic beta-Antagonists / Q000494:pharmacology; D000818:Animals; D000959:Antihypertensive Agents / Q000494:pharmacology*; D001262:Atenolol / Q000494:pharmacology; D001784:Blood Gas Analysis; D001794:Blood Pressure / Q000502:physiology; D001919:Bradycardia / Q000139:chemically induced / Q000378:metabolism; D004280:Dobutamine / Q000494:pharmacology; D004558:Electric Stimulation; D005260:Female; D005333:Fetus / Q000502:physiology*; D006340:Heart Rate, Fetal / Q000502:physiology*; D007022:Hypotension / Q000139:chemically induced / Q000503:physiopathology*; D009599:Nitroprusside / Q000494:pharmacology*; D011247:Pregnancy; D012756:Sheep; D013564:Sympathetic Nervous System / Q000502:physiology*; D014630:Vagus Nerve / Q000502:physiology*
chemical_list: D000318:Adrenergic beta-Agonists; D000319:Adrenergic beta-Antagonists; D000959:Antihypertensive Agents; D009599:Nitroprusside; D004280:Dobutamine; D001262:Atenolol