High-performance liquid chromatographic analysis of 'specifically bound' label after [125I]angiotensin II binding to...

The combined hypothalamus-thalamus-septum and anteroventral third ventricular region (HTSA) of the rat was examined for [125I]angiotensin II ([125I]AII) binding using two protocols: one that preserved synaptosomal structure and a second that did not. Although maximum binding (Bmax) and dissociation constants (Kd) were similar in both preparations, high-performance liquid chromatographic analyses revealed that [125I]AII made up the majority of specifically bound label in the synaptosome preserved preparation while [125I]tyrosine ([125I]Tyr) represented most of the specifically bound label in the disrupted preparation. These results indicate that [125I]Tyr accumulation occurred subsequent to binding and degradation of [125I]AII and are consistent with the notion that rapid internalization of the receptor-[125I]AII complex occurs in those preparations where the synaptosomal structure remains intact.