Characterization of angiotensin binding in the African Green monkey

The observation that there are differences in the characteristics and distribution of angiotensin receptors in the central nervous system of mammalian species led to the analysis of angiotensin binding in a primate model, the African Green monkey. Initial studies using [ 125 I]angiotensin II ([ 125 I]AII) as the radioligand showed binding in peripheral tissues but little binding in the central nervous system. Conversely, binding studies using [ 125 I]AIII as the radioligand indicated more central nervous binding with diminished peripheral binding. Specific binding of [ 125 I]AIII is evident throughout the brain with high binding in the circumventricular organs, striatum, caudate nucleus, olfactory bulb and localized areas of the thalamus and cerebral cortex. This binding was found to posses many of the properties commonly associated with binding to membrane-bound receptors. The specifically bound radioligand extracted from incubations of [ 125 I]AIII and central nervous tissue appears to be a product of the metabolism of [ 125 I]AIII rather that the peptide itself. Binding of [ 125 I]AII does occur in peripheral tissues and to a limited extent in the cerebellum, but to a different receptor from that characterized using [ 125 I]AIII. These results are similar to those seen in the gerbil and raise questions concerning the utilization of the rat as the primary model for studying the biochemistry of the brain-angiotensin system in humans.