Tracer adenosine: a novel myocardial flow marker.

UNLABELLED Local myocardial blood flow measurements are of great importance in experimental and clinical settings. However, a lack of ideal markers is evident. Adenosine is suggested to be a potential candidate because of its high uptake and rapid intracellular sequestration. We specifically tested the hypothesis that the local deposition density of labeled adenosine within the heart reflects local myocardial blood flow. METHODS Tracer microspheres, the recognized standard for local blood flow measurements, were injected and compared with simultaneously injected labeled adenosine ((3)H/(14)C) in tracer concentration into the left atrium of anesthetized Beagle dogs (n = 7). Myocardial deposition densities were assessed through beta-scintillation and gamma-counting measurements in samples (100-128 per heart) of an average wet mass of 487 +/- 54 mg. To challenge local myocardial blood flow distribution, alprostadil was infused into the left circumflex artery in 3 experiments. In 2 other experiments, erythro-9-hydroxy-nonyl-adenine (EHNA) was infused to inhibit degradation of injected adenosine to inosine. RESULTS Tracer adenosine and microspheres did not exert significant local or systemic hemodynamic effects. Both were almost completely extracted from blood within 2 min and locally retained in the tissue. Deposition densities of tracer microspheres and labeled adenosine correlated closely in each experiment, independently of the respective protocol (control, EHNA, or alprostadil), over a wide range of local myocardial blood flows (0.23-12.9 mL min(-1) g(-1)). The mean correlation coefficient (n = 293) was r = 0.93 (r(2) = 0.86; P < 0.0001), indicating that the deposition density of (3)H-adenosine could explain local blood flow as measured with the tracer microsphere technique with 86% probability. CONCLUSION Adenosine appears to be a reliable marker of local blood flow in dog myocardium.