A simple mathematical model for the receptor based radiopharmaceuticals

In order to estimate the hepatic binding protein (HBP) content of normal liver, Tc-99m-galactosyl-neoglycoalbumin (NGA) was administered intravenously to rabbits at different loading doses: 0.1 mg/Kg, 0.5 mg/Kg, 1 mg/Kg and 2 mg/Kg. A saturation effect was observed on the NGA uptake curves followed with a gamma camera (ROI over the whole liver). However, even at the highest injected dose, the maximum NGA uptake in liver still exceeded 80 % of the injected dose. These results indicate that the mechanism of uptake of NGA in the rabbit liver was not a simple receptor binding, but a more complex mechanism. With a simple mathematical model, it was possible to explain these results by taking into account receptor recycling. (Authors)