title: Hypoxia-hypotension decreases pressor responsiveness to exogenous catecholamines after severe traumatic brain injury in rats.
abstract: OBJECTIVE
  To quantify the phenylephrine pressor responsiveness after severe brain injury combined with hypoxia-hypotension, and to study the respective roles of brain injury and hypoxia-hypotension in the observed alteration.
  
  
  METHODS
  Randomized study.
  
  
  METHODS
  Accredited animal laboratory.
  
  
  METHODS
  Adult Sprague Dawley rats.
  
  
  METHODS
  Anesthetized animals were assigned to control, brain injury, hypoxia-hypotension, and brain injury combined with hypoxia-hypotension groups. Brain injury was induced with an impact-acceleration device. During the 15-min hypoxia-hypotension, arterial oxygen pressure was decreased to 40 torr (5.3 kPa) and mean arterial pressure to 30 mm Hg. Thirty-six of the 53 included rats were alive at the end of hypoxia-hypotension (nine animals per group). In an additional group (Hypo, n = 8), mean arterial pressure was lowered to the level observed in brain injury combined with hypoxia-hypotension with pentobarbital infusion. Sixty minutes after injuries (T60), animals received 0.1, 1, and 10 microg/kg phenylephrine in a random order. Pressor responsiveness to phenylephrine was defined as maximal postinjection minus preinjection mean arterial pressure.
  
  
  RESULTS
  During hypoxia-hypotension, mortality was higher and residual restored blood volume was lower (p <.01) in the animals with brain injury and hypoxia-hypotension compared with hypoxia-hypotension alone. At T60, mean arterial pressure (mm Hg) was lower (p <.01) in the brain injury group (83 +/- 22) compared with controls (110 +/- 10) and in brain injury combined with hypoxia-hypotension (76 +/- 18) compared with controls and hypoxia-hypotension (107 +/- 14). Pressor responsiveness (mm Hg) to 1 and 10 microg/kg phenylephrine was less (p <.05) in brain injury combined with hypoxia-hypotension (15 +/- 6 and 44 +/- 8) and hypoxia-hypotension (15 +/- 3 and 44 +/- 8) compared with controls (26 +/- 2 and 57 +/- 11). No significant difference was observed for phenylephrine pressor responsiveness between controls and the Hypo group (25 +/- 5 and 66 +/- 7).
  
  
  CONCLUSIONS
  Combination of brain injury and hypoxia-hypotension induces a severe hemodynamic alteration associated with a decreased pressor responsiveness to phenylephrine. Transient hypoxia-hypotension is responsible for the depressed alpha-1 adrenergic reactivity.
authors.affiliation: Laboratoire de Physiologie (upress EA 2704), Université Paris-Sud, Faculté de médecine de Bicêtre, Le Kremlin Bicêtre, France. sabine.holtzer@bjn.ap-hop-paris.fr
authors.forename: S
authors.initials: S
authors.lastname: Holtzer
authors.forename: B
authors.initials: B
authors.lastname: Vigué
authors.forename: C
authors.initials: C
authors.lastname: Ract
authors.forename: K
authors.initials: K
authors.lastname: Samii
authors.forename: P
authors.initials: P
authors.lastname: Escourrou
mesh_terms: D000316:Adrenergic alpha-Agonists / Q000494:pharmacology* / Q000627:therapeutic use; D000818:Animals; D001786:Blood Glucose; D001930:Brain Injuries / Q000150:complications / Q000188:drug therapy*; D006439:Hemodynamics / Q000187:drug effects; D007022:Hypotension / Q000150:complications / Q000188:drug therapy*; D002534:Hypoxia, Brain / Q000150:complications / Q000188:drug therapy*; D007427:Intracranial Pressure; D008297:Male; D010656:Phenylephrine / Q000494:pharmacology* / Q000627:therapeutic use; D011311:Pressoreceptors / Q000187:drug effects*; D051381:Rats; D017207:Rats, Sprague-Dawley
chemical_list: D000316:Adrenergic alpha-Agonists; D001786:Blood Glucose; D010656:Phenylephrine