Free fatty acid content of myocardial interstitial spaces of dog.

Morphological and biochemical observations from our laboratory have shown the presence of lipids in the cardiac interstitial spaces of the dog. The present study was designed to assess the importance of free fatty acids (FFA) in these lipids using FFA or sucrose tracers in 14 anesthetized fasting open-chest mongrel dogs. Endogenous FFA and labeled tracers were measured in arterial and coronary sinus plasma; they were also determined in lymph collected from cardiac efferent lymphatic trunks. [14C] sucrose was infused at a constant rate in the femoral vein of 5 dogs. The concentration of the tracer in the lymph was 90% of the arterial concentration after 60 min of infusion. On the other hand, when [1-14C] palmitate was infused at the same rate in 7 dogs, the ratio of lymph to arterial tracer concentration was only 20% (60 min) and 25% (120 min), even though the myocardial extraction and oxidation of the tracer were stable. This ratio tended to reach a plateau (greater than or equal to 90%) only 24 hr after a bolus injection of the tracer. This tracer study shows the presence of a pool of myocardial fatty acids with a relatively slow turnover rate that may constitute an important reservoir of FFA.