Angiotensin II-Like Material Extracted from the Rat Brain Is Distinct from Authentic Angiotensin II

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Abstract
Specific radioimmunoassay and radioreceptor assay for angiotensin II (A II) were used for the possible identification of this peptide in the rat brain. An A II-like material (A II-LM) was detected with both assays applied to acidic extracts of various brain structures. The regional distribution of A II-LM was uneven, but absolute levels (in A II equivalents) could not be accurately determined, as they were highly dependent on the assay used. Partial purification of A II-LM by Sep-Pak C 18 chromatography and affinity chromatography using anti-A II antibodies bound to Ultrogel gave a compound coeluting with authentic A II in reverse-phase HPLC. However, gel filtration through Sephadex G-25 and TSK Spherogel 3000 SW as well as anion exchange HPLC demonstrated that A II-LM did not correspond to authentic A II. Partial characterization of A II-LM indicated that this compound was probably a peptide with an apparent molecular weight of 5,000-7,000 (instead of 1,046 for A II) and more polar but less positively charged than A II. Whether A II-LM is, in fact, the endogenous ligand of A II binding sites in brain remains an interesting hypothesis for further investigations.