Time-dependent response of coronary flow to prolonged adenosine infusion: doubling of peak reactive hyperaemic flow.

In 11 anaesthetised, Open chest dogs the time course and degree of the coronary vasodilating response to intracoronary adenosine infusion was assessed. Continuous adenosine infusion, at a rate of 2.5 to 13.5 mumol . min-1, produced rapid (15 to 30s) vasodilation of the same degree as that evoked by a 30 s period of ischaemia (reactive peak hyperaemia), a finding reported previously by others. However, continuing the infusion led to further coronary vasodilation, reaching a maximum 20 to 45 min from the beginning of the infusion and remaining constant for up to 2 h, independently of further increases in the dose. This late response produced, on average, vasodilatation twice as great as that observed during reactive hyperaemia and was not associated with any haemodynamic change or with the opening of arterio-venous shunts. The results: 1) suggest the existence of a double, time-dependent response of coronary receptor(s) to adenosine; 2) demonstrate, in the presence of a prolonged vasodilating stimulus, a possible increase in coronary blood flow to a degree far beyond that of post-ischaemic reactive peak flow, which is generally considered to be the maximal value of coronary blood flow that can be achieved.