Effects of reduced coronary flow on thallium-201 accumulation and release in an in vitro rat heart preparation.

To study the relation between myocardial thallium-201 (TI-201) uptake, TI-201 release, and reduced coronary flow, isolated Langendorff rat hearts (n = 8) were perfused for 3 hours at constant flows ranging from physiologic (12 ml/min) to severely ischemic (1.5 ml/min); thallium activity was monitored with a scintillation probe. Each heart was perfused for 1 hour with thallium buffer, followed by 2 hours with thallium-free buffer at the same flow rate. Accumulation curves for all 4 flows were monoexponential. However, release curves during the 2 hours of washout with thallium-free buffer demonstrated a biexponential configuration. The early fast release component decreased with reductions in coronary flow, and the later slow release component did not vary significantly with flow. These data show that thallium clearance has at least 2 components: a rapid (possibly extracellular) component related to coronary flow and a slow (possibly intracellular) component independent of coronary flow. These findings should be useful in providing a better understanding of thallium redistribution observed clinically.