Myocardial kinetics and organ distribution of thallium-201 in two different age groups of rats.

Effects of aging were investigated on kinetics and distribution of 201 thallium (201TI) in isolated myocardial tissue and other organs of rats after injection in vivo of this radionuclide. Older rats showed a trend toward lesser organ uptake, but this was statistically significant only in kidneys, fat, and fur. Experimental outflow curves for 201TI from isolated myocardial wall segments revealed a sustained higher level of 201TI in the older rats throughout the outflow. Further analysis of the washout kinetics with a three-compartment model (extracellular, intracellular, and subcellular) showed a significant reduction of extracellular compartment and increase of subcellular compartment in older rats. The extracellular to overall intracellular ratio also decreased significantly in the older rats. The changes found for 201TI in extracellular and subcellular myocardial compartments in older rats at rest are also similar to those seen in myocardium of young rats after exercise. It is concluded that, although aging has effects on distribution of 201TI in myocardium, such effects are not likely to impair the quality of myocardial scintigraphy in older patient