The two radioiodinated fatty acid analogs 15-(para-131 I-phenylpentadecanoic acid (pPPA) and 15-(ortho-131I-phenyl)-pentadecanoic acid (oPPA) are isomers with individually different routes in lipid metabolism but with near equal transport kinetics into tissue.
Methods: Normal adult male Wistar rats (n = 79) and those with liver cell damage from adriamycin treatment (n = 84) received 1.48- 1.85 MBq 131I-pPPA or 131I-oPPA (specific activity, 33.3-46.3 GBq/microM) into the jugular vein. At 1, 2, 3, 5, 7, 10 and 20 min, livers of up to five animals per group were examined for total tracer uptake and tracer incorporation into various lipid fractions.
Results: Uptake of both isomers into the total liver plateaued at about 2 min; the ratio oPPA/pPPA in normal liver averaged 2.63 and was significantly higher than the average ratio of 1.50 after adriamycin treatment. This fall in ratio was mainly due to an increase of pPPA uptake. Significant differences of the respective ratios were found in the plateau for the phospholipids (9.7 versus 3.0), cholesterol (2.4 versus 0.7) and triglycerides (2.0 versus 0.4).
Conclusion: The dual-tracer technique with pPPA and oPPA promises to be clinically useful for the diagnosis of liver disease by imaging the ratios of tracer uptake in the total liver and by in vitro analysis of the uptake ratio in serum triglycerides.