title: Heart rate reduction with ivabradine improves energy metabolism and mechanical function of isolated ischaemic rabbit heart.
abstract: OBJECTIVE
  The anti-anginal agent ivabradine slows heart rate (HR) by selectively inhibiting the I(f) current in the sinus node. We report an ex vivo study to evaluate the anti-ischaemic effect of ivabradine in terms of modulation of cardiac energy metabolism.
  
  
  RESULTS
  A Langendorff-perfused rabbit heart model was subjected to low-flow ischaemia and reperfusion. Cardiac metabolism was studied by measuring cardiac high-energy phosphate contents via HPLC, mitochondrial respiration was analysed polarographically, and cardiac redox potentials by HPLC. Cardiac function was determined in terms of the recovery of developed pressure during reperfusion and release of creatine kinase (CK) (spectrophotometrically) and noradrenaline (HPLC) after reperfusion. Four concentrations of ivabradine (0.3, 1, 3, and 6 microM) were tested on aerobically perfused hearts to select the most effective without causing changes in mechanical parameters. This proved to be 3 microM, which was therefore the concentration selected for the ischaemia-reperfusion experiments. Ivabradine concentration-dependently reduced HR with a maximal effect of 41 +/- 4% at 3 microM (P < 0.001 vs. vehicle), without a negative inotropic effect. This concentration protected the heart against ischaemia-reperfusion damage by reducing the rise in diastolic pressure (from 66 +/- 3 with vehicle to 39 +/- 4 mmHg, P < 0.01) and improving developed pressure after 30 min reperfusion (39 +/- 3 vs. 18 +/- 3 mmHg with vehicle, P < 0.01). Ivabradine reduced both CK and noradrenaline release by 47% (both P < 0.05 vs. vehicle) and improved mitochondrial respiratory control index (from 6.9 +/- 0.3 to 11.9 +/- 1.3, P < 0.001). It preserved cardiac energy metabolism (ATP, from 3.7 +/- 0.3 to 11.0 +/- 0.6 microM/g dry weight, P < 0.001) and redox state (NADPH/NADP(+), from 2.5 +/- 0.5 to 4.2 +/- 0.5, P < 0.001). There was a significant correlation between HR reduction in the ivabradine-treated hearts and cardiac creatine phosphate (r = 0.574, P = 0.02) and ATP levels (ATP, r = 0.674, P = 0.0042) at the end of ischaemia. These benefits were no longer detectable during pacing.
  
  
  CONCLUSIONS
  HR reduction by ivabradine confers a marked anti-ischaemic benefit. It significantly reduces cardiac energy consumption, preserves redox potentials during ischaemia, and enhances recovery at reperfusion.
authors.affiliation: Department of Cardiology, University of Ferrara, Corso Giovecca, 203, 44100 Ferrara, Italy.
authors.forename: Claudio
authors.initials: C
authors.lastname: Ceconi
authors.forename: Anna
authors.initials: A
authors.lastname: Cargnoni
authors.forename: Gloria
authors.initials: G
authors.lastname: Francolini
authors.forename: Giovanni
authors.initials: G
authors.lastname: Parinello
authors.forename: Roberto
authors.initials: R
authors.lastname: Ferrari
mesh_terms: D000255:Adenosine Triphosphate / Q000378:metabolism; D000818:Animals; D001552:Benzazepines / Q000494:pharmacology*; D003402:Creatine Kinase / Q000378:metabolism; D054815:Cyclic Nucleotide-Gated Cation Channels / Q000037:antagonists & inhibitors*; D004734:Energy Metabolism / Q000187:drug effects*; D006321:Heart / Q000187:drug effects* / Q000502:physiology; D006339:Heart Rate / Q000187:drug effects*; D000077550:Ivabradine; D008297:Male; D017202:Myocardial Ischemia / Q000188:drug therapy* / Q000503:physiopathology; D015428:Myocardial Reperfusion Injury / Q000517:prevention & control; D009638:Norepinephrine / Q000378:metabolism; D011817:Rabbits
chemical_list: D001552:Benzazepines; D054815:Cyclic Nucleotide-Gated Cation Channels; D000077550:Ivabradine; D000255:Adenosine Triphosphate; D003402:Creatine Kinase; D009638:Norepinephrine