title: Reduced oxygen supply explains the negative force-frequency relation and the positive inotropic effect of adenosine in buffer-perfused hearts.
abstract: In isolated rat hearts perfused with HEPES and red blood cell-enriched buffers, we examined changes in left ventricular pressure induced by increases in heart rate or infusion of adenosine to investigate whether the negative force-frequency relation and the positive inotropic effect of adenosine are related to an inadequate oxygen supply provided by crystalloid perfusates. Hearts perfused with HEPES buffer at a constant flow demonstrated a negative force-frequency relation, whereas hearts perfused with red blood cell-enriched buffer exhibited a positive force-frequency relation. In contrast, HEPES buffer-perfused hearts showed a concentration-dependent increase in left ventricular systolic pressure [EC50 = 7.0 +/- 1.2 nM, maximal effect (Emax) = 104 +/- 2 and 84 +/- 2 mmHg at 0.1 microM and baseline, respectively] in response to adenosine, whereas hearts perfused with red blood cell-enriched buffer showed no change in left ventricular pressure. The positive inotropic effect of adenosine correlated with the simultaneous reduction in heart rate (r = 0.67, P < 0.01; EC50 = 3.8 +/- 1.4 nM, baseline 228 +/- 21 beats/min to a minimum of 183 +/- 22 beats/min at 0.1 microM) and was abolished in isolated hearts paced to suppress the adenosine-induced bradycardia. In conclusion, these results indicate that the negative force-frequency relation and the positive inotropic effect of adenosine in the isolated rat heart are related to myocardial hypoxia, rather than functional peculiarities of the rat heart.
authors.affiliation: Department of Internal Medicine, School of Medicine, State University of Campinas, Campinas SP, Brazil.
authors.forename: Rodrigo M
authors.initials: RM
authors.lastname: Marin
authors.forename: Kleber G
authors.initials: KG
authors.lastname: Franchini
mesh_terms: D000241:Adenosine / Q000037:antagonists & inhibitors / Q000494:pharmacology*; D000818:Animals; D002021:Buffers; D009202:Cardiomyopathies / Q000503:physiopathology*; D002316:Cardiotonic Agents / Q000037:antagonists & inhibitors / Q000494:pharmacology*; D004912:Erythrocytes; D006339:Heart Rate / Q000187:drug effects; D000860:Hypoxia / Q000503:physiopathology*; D066298:In Vitro Techniques; D008297:Male; D009200:Myocardial Contraction / Q000187:drug effects*; D010477:Perfusion; D051381:Rats; D017208:Rats, Wistar
chemical_list: D002021:Buffers; D002316:Cardiotonic Agents; D000241:Adenosine