title: Bradycardia and hypotension associated with severe hemorrhage are reversed by morphine given centrally or peripherally in anesthetized rats.
abstract: BACKGROUND
  Severe simple hemorrhage (blood loss in the absence of tissue damage and nociception) leads to a reflex bradycardia and hypotension. Earlier studies showed that this reflex can be attenuated by prior administration of morphine. However, some patients may receive morphine, e.g., for analgesia after they have suffered severe hemorrhage. The aim of this study was to determine whether an established bradycardia and hypotension could be reversed by morphine.
  
  
  METHODS
  Four groups of male Wistar rats (236-258 g) were anesthetized with alphadolone/alphaxalone (16-19 mg x hg x h(-1) intravenously). All groups received a hemorrhage of 40% total blood volume (BV) at 2% BV x min(-1). After the loss of 27% BV, bradycardia and hypotension were established equally in groups I and II and III and IV. Groups I (n=8) and III (n=10) received 0.9% saline (20 microL intracerebroventricularly or 1 mL x kg(-1) intravenously, respectively), whereas groups II (n=10) and IV (n=10) received morphine (10 microg intracerebroventricularly or 0.5 mg x kg(-1) intravenously, respectively).
  
  
  RESULTS
  In groups I and III, heart rate and mean arterial blood pressure continued to fall, whereas the bradycardia was completely reversed and the hypotension partly reversed in groups II and IV after treatment with morphine.
  
  
  CONCLUSIONS
  Morphine, administered centrally or peripherally, can reverse the bradycardia and markedly can attenuate the hypotension associated with severe hemorrhage. However, any benefit may be more apparent than real because other studies suggest that mortality may be increased.
authors.affiliation: North Western Injury Research Centre, University of Manchester, United Kingdom.
authors.forename: M
authors.initials: M
authors.lastname: Ohnishi
authors.forename: E
authors.initials: E
authors.lastname: Kirkman
authors.forename: A
authors.initials: A
authors.lastname: Hiraide
authors.forename: R A
authors.initials: RA
authors.lastname: Little
mesh_terms: D000136:Acid-Base Equilibrium; D000701:Analgesics, Opioid / Q000008:administration & dosage*; D000758:Anesthesia; D000818:Animals; D001158:Arteries; D001919:Bradycardia / Q000188:drug therapy* / Q000209:etiology; D002245:Carbon Dioxide / Q000097:blood; D006339:Heart Rate; D006470:Hemorrhage / Q000150:complications*; D007022:Hypotension / Q000188:drug therapy* / Q000209:etiology; D007275:Injections, Intravenous; D007276:Injections, Intraventricular; D008297:Male; D009020:Morphine / Q000008:administration & dosage*; D010100:Oxygen / Q000097:blood; D051381:Rats; D017208:Rats, Wistar; D013997:Time Factors
chemical_list: D000701:Analgesics, Opioid; D002245:Carbon Dioxide; D009020:Morphine; D010100:Oxygen