Synthesis of bioactive 131I-labeled epidermal growth factor and its distribution in rat tissues

Radioactive monoiodotyrosyl epidermal growth factor has been synthesized and purified by means of preparative gel electrophoresis. The labeled product retains full biological activity, as compared to that of the native epidermal growth factor. In more extensively iodinated derivatives the biological activity decreases as a function of the degree of iodination. The purified 131I-labeled epidermal growth factor has been injected intraperitoneally in the rat and its distribution in some peripheral tissues such as liver, spleen, cornea, lung, heart, epidermis, skeletal muscle, kidney, brain, pancreas, intestine and testis, followed as a function of time. Only two tissues concentrate 131I-labeled epidermal growth factor with respect to the blood: the epidermis (about + 300%) and the epithelial cells of the cornea (about + 800%). The addition in vitro of native epidermal growth factor is able either to inhibit the binding of the labeled growth factor to the target tissues, or to discharge it after binding in a way which suggests a competition for the specific receptor sites.