A SANDWICH ENZYME-LINKED-IMMUNOSORBENT-ASSAY FOR THE DETERMINATION OF RAT-HEART FATTY ACID-BINDING PROTEIN USING THE STREPTAVIDIN-BIOTIN SYSTEM - APPLICATION TO TISSUE AND EFFLUENT SAMPLES FROM NORMOXIC RAT-HEART PERFUSION

An enzyme linked immuno-sorbent assay (ELISA) of the sandwich type for the determination of heart-type fatty acid-binding protein (H-FABP(c)) was developed, making use of the streptavidin-biotin system. The assay turned out to be virtually disturbance insensitive and showed a detection limit for H-FABP(c) of 0.2-mu-g/1 with an intra- and inter-assay variation of 5% and 14%, respectively. The H-FABP(c) content of adult rat heart muscle was found to be 0.740 +/- 0.120 mg/g wet weight. The H-FABP(c) content of a number of skeletal muscles varied from 0.013 to 0.303 mg/g wet weight and was related to the content of type I muscle fibers of these tissues, suggesting a role for H-FABP(c) in intracellular fatty acid metabolism. The assay was further applied to study the release of H-FABP(c) from isolated rat heart during normoxic Langendorff perfusion, as compared to that of lactate dehydrogenase (LDH), into fluid derived from the right ventricular cavity (Q(rv)) and that from the interstitial space (Q(i)). Total release of H-FABP(c) per 15 min amounted to 0.015 +/- 0.010% but that of LDH to 0.080 +/- 0.040% of their total tissue content. Furthermore, for both H-FABP(c) and LDH 80% was released into Q(i), which only accounted for 1-2% of total flow. These findings suggest that during normoxic perfusion of rat heart H-FABP(c), and LDH are released from different cellular compartments and that the bulk amount of released intracellular proteins is transported via the lymph instead of being directly released into the bloodstream.