RESUMO
Objective To study the characteristics of the binding of 125 I-VIP with VIP receptor in H22 hepatocarcinoma cells in mice and in vitro. Methods VIP was radio-labelled with carrier free 125 I with the chloramine T method and purified with sephadex G-50 column chromatography. Experiments of saturation binding and competition binding were carried to study the characteristics of the binding between 125 IVIP and the VIP receptors in the H22 cells in vitro. Experiments of dynamic biodistribution and competion distribution were performed to verify the characteristics of the binding between 125 I-VIP and VIP receptors in mice with H22 hepatocarcarcinoma. Results The labelling rate of 125 I to VIP was 73.8%. The specific radioactivity of 125 I-VIP was 18.2 TBq/mmol and the radiochemical purity was 98%. The binding of 125 I-VIP with VIP receptors in H22 cells was inhibited by non-labelled VIP in a dose-dependent manner. Two classes of specific high affinity binding sites for VIP expression in H22 cells were detected with scatchard analysis. The Kd was 1.74 nmol/L and 28.63 nmol/L and Bmax was 0.27 pmol/10 6 cells and 5.57 pmol/10 6 cells for high and low affinity binding sites respectively. Radioactivity accumulation was higher in the carcinoma tissue than in the muscles of the mice bearing H22 hepatocarcinoma in each phase (P
