Hepatic Binding Sites for Angiotensin II in the Rat

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Abstract
1. 125I-labelled (Asn1, Val5)-angiotensin II (125I-labelled AII) incubated with purified rat liver membranes was degraded with time, as estimated by three techniques: binding to an excess of specific antibody, polyacrylamide-gel electrophoresis and rebinding to fresh membranes. Degradation was inhibited in the presence of an excess of β1–24-corticotrophin but still very marked. 2. 125I-labelled AII became bound to purified rat liver membranes. Association and dissociation rates were slow. Binding was competitively inhibited by (Asn1, Val5)-AII, (Asp1, Ile5)-AII and (Des, Asn1, Ile5)-AII. Apparent KD was approximately 0·1 nmol/l. 3. Bound hormone was also partly degraded independently of time. 4. Angiotensinases inhibitors had different effects on 125I-labelled AII binding. A clear increase was observed in the presence of β1–24-corticotrophin and phenylmethylsulphonylfluoride whereas binding was decreased in the presence of EDTA or 8-hydroxyquinoline. 5. These results demonstrate the presence of high-affinity binding sites for AII and of angiotensinases in hepatic membranes.

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