Phasic release of adenosine during steady state metabolic stimulation in the isolated guinea pig heart.

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Abstract
If adenosine is the major factor responsible for myocardial metabolic vasodilation, its release should be sustained as long as oxygen consumption and coronary flow are augmented. To see if adenosine meets this criterion, we examined the time course of its release during norepinephrine infusion in isolated, non-working guinea pig hearts (n = 8). During an 11-minute infusion period (steady state perfusate concentration = 6 X 10(-8) M), the coronary effluent was collected over 30-second intervals for measurements of coronary flow (ml/min per g), and adenosine and inosine release (pmol/min per g). Myocardial oxygen consumption (MVO2 = microliter O2/min per g) was measured at 1, 4, 6.5, and 11 minutes. Control values of coronary flow, myocardial oxygen consumption, and adenosine and inosine release were 7.5 +/- 0.4, 85 +/- 5, 22 +/- 5, and 431 +/- 39, respectively. During norepinephrine infusion, coronary flow, myocardial oxygen consumption, and adenosine release attained maximal levels within one minute (inosine within 2 minutes). These values were 10.6 +/- 0.4, 125 +/- 9, 849 +/- 110, and 2595 +/- 581, respectively. Thereafter, coronary flow and myocardial oxygen consumption values were sustained. In contrast, adenosine and inosine release significantly declined to nadirs by 9.5 minutes. Thereafter, steady state levels were maintained at 117 +/- 24 and 960 +/- 294, respectively.(ABSTRACT TRUNCATED AT 250 WORDS)