The adenosine hypothesis revisited: relationship between purine release and coronary flow in isolated rat heart

We evaluated the adenosine hypothesis through a new approach, based on the study of the relationship between coronary flow or resistance and purine release, which is an accurate index of myocardial adenosine release. Isolated rat hearts were perfused at different work loads, in hypoxic conditions and after a short period of global ischaemia. When the results of all experiments were considered together, purine release was significantly but weakly related to coronary flow and coronary resistance (r=0.416 v coronary flow, r=0.378 v the reciprocal of coronary resistance, (p<0.01). Closer relationships were obtained within the three subgroups: the correlation coefficients increased to 0.819 and 0.835 (p<0.001) in the hearts perfused at different work loads with normal oxygen supply, to 0.701 and 0.757 (p<0.02 and p<0.01) in the hypoxic hearts, and to 0.897 and 0.978 (p<0.02 and p<0.01) in the hearts recovering from ischaemia. The relationships between purine release and coronary flow or resistance were significantly different in the three subgroups (p<0.001): at any value of purine release coronary resistance was highest during hypoxia and lowest after ischaemia, while the opposite was true for coronary flow. We suggest that the adenosine hypothesis is converted into a “weaker” statement: adenosine is involved in the adjustment between heart performance and coronary resistance but other factors contribute to the regulation of coronary flow, and/or affect the response to adenosine.