Variables of myocardial backdiffusion, determined with 17-iodo-131 heptadecanoic acid in the normal dog heart.

Under normal and ischemic conditions backdiffusion of radiolabeled non-esterified fatty acids (NEFA) has been demonstrated. In the fasted normal canine heart the extraction fraction (EF) during interventions with glucose or lactate loading, vasodilation, and metabolic level augmentation was determined, and compared with the control EF. Backdiffusion alterations were deduced from the EF changes. After iv injection of 17-iodo-131 heptadecanoic acid (IHDA), 11 blood samples were drawn from aorta and coronary sinus in a time period of 60 minutes. In the control and vasodilation group the EF slowly decreased from 40 to 10%. In contrast, the EF in the noradrenaline group was constant. During glucose and lactate infusion the EF became negative within 10 min and remained negative. These results suggest that during physiological circumstances backdiffusion is determined by the metabolic level of the heart and its substrate availability.