Tissue distribution of 131I-labelled epidermal growth factor in the pig visualized by dynamic scintigraphy

We visualized the metabolism of intravenously injected 131I-labelled epidermal growth factor in the pig using dynamic scintigraphy combined with repetitive samplings of blood, urine and bile. The labelled peptide was recognized in the samples by means of immunoprecipitation and high pressure liquid chromatography. The plasma elimination was extremely rapid, and it was described with a triexponential equation, C(t) = A*e -alpha*t+B*e-beta*t+C*e-gamma*t. The first two exponentials denoted the distribution phase, and the third the elimination phase. T1/2 alpha ranged from 0.4-0.7 min, T1/2 beta from 2.0-2.2 min and T1/2 gamma from 53.3-97.6 min. Concomitant with the rapidly declining plasma concentration, the gamma camera visualized the uptake by the liver and the kidneys. The liver was the principal organ for clearance and degradation of the labelled peptide, but only 0.12-0.30% of the injected dose was excreted into the bile. The renal uptake and the urinary excretion accounted for 6.6-13.0 and 2.5-4.9% of the given dose, respectively.