title: Epinephrine dose-response of the isolated working heart in O2-exposed rats.
abstract: BACKGROUND
  Heart energy efficiency, which is affected by catecholamines, has previously been shown to decline in rats with prolonged normobaric O2 exposure.
  
  
  OBJECTIVE
  Oxygen exposure affects dose response of the heart to catecholamines.
  
  
  METHODS
  Epinephrine dose-response (10(-10) - 5 x 10(-6) mol.L-1) was measured in the isolated working heart excised from control rats breathing air, and rats exposed to normobaric 100% oxygen for either 24 h or 49 h. The variables measured were input (oxygen consumption (VO2) and output power, cardiac contractility (Emax and maximal dP/dT), coronary resistance, heart frequency (fH) and left ventricular pressure. Variable (Y*) dose response to epinephrine concentration (C) was fitted to the equation: Y* = Ymax/(1 + (C/C50)n), Ymax--maximal Y*, C50--C for half Ymax and n--an empirical power.
  
  
  RESULTS
  Oxygen exposure of the intact rat had little influence on baseline cardiac variables, but did affect sensitivity to catecholamines. A general effect of the O2 exposure was a left shift of the dose-response curve for example, C50 was reduced by 72, 41 and 43 x 10-8 mol.L-1 for VO2, fH and Emax, respectively, after the 24 h exposure.
  
  
  CONCLUSIONS
  There was a pronounced change in the dose-response in hearts from 24 h O2-exposed rats, a change partially reversed in hearts from 49 h O2-exposed rats. The high dose, which had a stimulatory effect on hearts from control rats, failed to stimulate hearts from hyperoxic rats.
authors.affiliation: Israel Naval Medical Institute, Haifa, Israel.
authors.forename: R
authors.initials: R
authors.lastname: Arieli
authors.forename: S A
authors.initials: SA
authors.lastname: Ben-Haim
authors.forename: A
authors.initials: A
authors.lastname: Bomzon
authors.forename: G
authors.initials: G
authors.lastname: Hayam
authors.forename: N
authors.initials: N
authors.lastname: Zamir
mesh_terms: D000316:Adrenergic alpha-Agonists / Q000494:pharmacology*; D000318:Adrenergic beta-Agonists / Q000494:pharmacology*; D000818:Animals; D004305:Dose-Response Relationship, Drug; D004734:Energy Metabolism / Q000187:drug effects*; D004837:Epinephrine / Q000494:pharmacology*; D006321:Heart / Q000187:drug effects* / Q000502:physiology*; D006439:Hemodynamics; D066298:In Vitro Techniques; D008297:Male; D010101:Oxygen Consumption / Q000187:drug effects; D051381:Rats; D017207:Rats, Sprague-Dawley
chemical_list: D000316:Adrenergic alpha-Agonists; D000318:Adrenergic beta-Agonists; D004837:Epinephrine