title: Effects of dexmedetomidine on cardiorespiratory regulation in spontaneously breathing newborn rats.
abstract: BACKGROUND
  Dexmedetomidine, a selective α2-adrenoceptor agonist, is a new sedative agent.
  
  
  OBJECTIVE
  To examine the dexmedetomidine-associated changes in cardiorespiratory indices in spontaneously breathing newborn rats.
  
  
  METHODS
  An abdominal catheter to administer drugs and subcutaneous electrodes to record electrocardiographic data were inserted into 2- to 4-day-old rats under isoflurane anesthesia; the rats were then placed in individual chambers. After recovery from the anesthesia, the rats received intraperitoneal administrations of normal saline (NS, vehicle), dexmedetomidine (50 μg·kg(-1)), or dexmedetomidine (50 μg·kg(-1)) followed 5 min later with NS or the selective α2-adrenoceptor antagonist atipamezole (1 mg·kg(-1)) (n = 10 in each group). Cardiorespiratory indices were recorded for each animal throughout the experiment.
  
  
  RESULTS
  Dexmedetomidine administration significantly decreased heart rate (HR) and minute ventilation (V'E) (P < 0.05) compared with control, whereas NS administration did not. The decrease in HR and V'E after dexmedetomidine administration was significantly less in rats that received atipamezole (P < 0.05) than in those that received NS after dexmedetomidine administration. The dexmedetomidine-associated V'E depression was attributed to a significant decrease in respiratory frequency (fR) but not tidal volume (VT ). The change in fR was reversed by atipamezole administration, which itself induced no significant changes in HR and fR.
  
  
  CONCLUSIONS
  In spontaneously breathing immature rats, dexmedetomidine administration significantly reduced HR and V'E. Because atipamezole fully reversed decreases in fR and therefore V'E, dexmedetomidine-related respiratory suppression occurs predominantly through α2-adrenoceptor-related suppression of fR.
authors.affiliation: Department of Physiology, Nippon Dental University, School of Life Dentistry at Tokyo, Chiyoda-ku, Japan.
authors.forename: Junko
authors.initials: J
authors.lastname: Tamiya
authors.forename: Ryoji
authors.initials: R
authors.lastname: Ide
authors.forename: Masayuki
authors.initials: M
authors.lastname: Takahashi
authors.forename: Chikako
authors.initials: C
authors.lastname: Saiki
mesh_terms: D000317:Adrenergic alpha-Antagonists / Q000494:pharmacology; D000769:Anesthesia, Inhalation; D018685:Anesthetics, Inhalation; D000818:Animals; D000831:Animals, Newborn; D020927:Dexmedetomidine / Q000494:pharmacology*; D004562:Electrocardiography; D005260:Female; D006339:Heart Rate / Q000187:drug effects; D006439:Hemodynamics / Q000187:drug effects*; D006993:Hypnotics and Sedatives / Q000494:pharmacology*; D007093:Imidazoles / Q000494:pharmacology; D007530:Isoflurane; D011247:Pregnancy; D051381:Rats; D017208:Rats, Wistar; D015656:Respiratory Mechanics / Q000187:drug effects*; D013990:Tidal Volume / Q000187:drug effects
chemical_list: D000317:Adrenergic alpha-Antagonists; D018685:Anesthetics, Inhalation; D006993:Hypnotics and Sedatives; D007093:Imidazoles; C050701:atipamezole; D020927:Dexmedetomidine; D007530:Isoflurane
keywords: atipamezole; breathing pattern; dexmedetomidine; heart rate; immature; α2-adrenoceptor