title: [Respiratory effects of beta-endorphin in chronic hypoxic rats].
abstract: OBJECTIVE
  To assess the role of beta-EP in the physiological and pathophysiological process of respiratory regulation in chronic hypoxic rats.
  
  
  METHODS
  The chronic hypoxic rat model was established by intravenous injections of papain 6 times, once a week. The concentration of beta-endorphin in medulla, pons, hypothalamus, central gray and plasma of chronic hypoxic rats were measured by radioimmunoassay. All animals were pretreated with sodium pentobartital (35 mg/kg) before experiment. 102 rats were randomly divided into three groups. Group 1 (n = 36). The respiratory rate (RR) and tidal volume (VT) were measured after intravenous injection of naloxone (NLX, 2 mg/kg), beta-EP (40 micrograms/kg, 160 micrograms/kg) or normal saline, Group 2 (n = 48). By the intracerebroventricular administration of NLX and beta-EP to the models, RR, VT and PaCO2 were observed after microinjection 5, 15, 30, 45, 60 min. Group 3 (n = 18). The respiratory effects of beta-EP after directly into the nucleus tractus solitari of the anaesthetised rats were investigated.
  
  
  RESULTS
  The beta-EP contents in medulla, pons, hypothalamus, central gray and plasma of chronic hypoxic rats were significantly increased compared with control subjects (P < 0.01). It suggested that the pathophysiology of chronic hypoxic process infleuced the contents of beta-EP in the CNS and plasma in rats. Intracerebroventricular microinjection of beta-EP in normal rats, resulted in a significant decrease in RR (P < 0.05). No significant difference in RR and VT was observved after intravenous injection of naloxone (2 mg/kg) and beta-EP (40 micrograms/kg, 160 micrograms/kg) in treatment group compared with the control group (P > 0.05), Intracerebroventricular microinjection of NLX in chronic hypoxic rats, resulted in a marked increase in RR (P < 0.05) and central hypercapnic-sensitivity (t = 2.76, P < 0.05), Intracerebroventriculalr microinjection of beta-EP in chronic hypoxic models, resulted in severe respiratory depression after injection 15, 30, 45, 60 min (RR t = 3.41, 6.54, 6.97, 7.87, P < 0.01; VT t = 3.07, 7.27, 6.14, 6.08).
  
  
  CONCLUSIONS
  These results indicate the beta-endorphin may be involved in central respiratory control of chronic hypoxic rats.
authors.affiliation: Department of Respiratory Diseases, Changhai Hospital, Shanghai 200433.
authors.forename: X
authors.initials: X
authors.lastname: Xu
authors.forename: Q
authors.initials: Q
authors.lastname: Li
authors.forename: X
authors.initials: X
authors.lastname: Sun
mesh_terms: D000818:Animals; D002908:Chronic Disease; D004195:Disease Models, Animal; D000860:Hypoxia / Q000503:physiopathology*; D008297:Male; D009270:Naloxone / Q000494:pharmacology; D009292:Narcotic Antagonists / Q000494:pharmacology; D010100:Oxygen / Q000378:metabolism*; D051381:Rats; D017207:Rats, Sprague-Dawley; D012119:Respiration / Q000187:drug effects*; D001615:beta-Endorphin / Q000494:pharmacology*
chemical_list: D009292:Narcotic Antagonists; D009270:Naloxone; D001615:beta-Endorphin; D010100:Oxygen