title: Adenosine potentiates coronary flow and inhibits oxygen consumption during isoprenaline infusion in isolated perfused guinea pig hearts.
abstract: It has been shown that adenosine, a potent coronary vasodilator, is released during cardiac sympathetic stimulation and that infusion of adenosine reduces the increase in myocardial contractile force elicited by catecholamines. The purpose of our study was: 1) to examine if adenosine also attenuates the rise in O2 consumption (MVO2) induced by infusing isoprenaline; and 2) to determine whether such a fall in MVO2 occurs primarily because of a relative decrease in tissue O2 extraction or a change in coronary flow. We isolated guinea pig hearts, perfused the vasculature at constant pressure and measured coronary flow, inflow and outflow pO2, and isovolumetric left ventricular pressure (PLV) and its derivative (dP/dt). Before, during and after infusing isoprenaline, we infused adenosine at increasing rates; but both drugs were infused at rates which did not maximally increase flow. We observed that adenosine reduced the increases in PLV and +dP/dt due to isoprenaline from 52 to 24% and from 81 to 55%. Moreover, linear regression analysis showed that the rise in MVO2 by isoprenaline was antagonised as a function of adenosine. This relative fall in MVO2 resulted primarily because of a decrease in O2 extraction since coronary flow was enhanced as a function of adenosine. Thus, although adenosine enhances the increase in flow due to isoprenaline overall it attenuates tissue O2 extraction and MVO2. Our study suggests that during sympathetic cardiac stimulation, endogenously released adenosine may not only produce vasodilatation and enhance the delivery of O2, but may also attenuate cardiac muscle work and the extraction of O2 with a net inhibition of MVO2.
mesh_terms: D000241:Adenosine / Q000494:pharmacology*; D000818:Animals; D003326:Coronary Circulation / Q000187:drug effects*; D005260:Female; D006168:Guinea Pigs; D006321:Heart / Q000187:drug effects; D066298:In Vitro Techniques; D007545:Isoproterenol / Q000494:pharmacology*; D008297:Male; D009206:Myocardium / Q000378:metabolism; D010101:Oxygen Consumption / Q000187:drug effects*; D010477:Perfusion
chemical_list: D000241:Adenosine; D007545:Isoproterenol