The Globin Fragment LVV‐Hemorphin‐7 Is an Endogenous Ligand for the AT4 Receptor in the Brain

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Abstract
Angiotensin IV (Val‐Tyr‐Ile‐His‐Pro‐Phe) has been reported to interact with specific high‐affinity receptors to increase memory retrieval, enhance dopamine‐induced stereotypy behavior, and induce c‐fos expression in several brain nuclei. We have isolated a decapeptide (Leu‐Val‐Val‐Tyr‐Pro‐Trp‐Thr‐Gln‐Arg‐Phe) from sheep brain that binds with high affinity to the angiotensin IV receptor. The peptide was isolated using 125I‐angiotensin IV binding to bovine adrenal membranes to assay receptor binding activity. This peptide is identical to the amino acid sequence 30–39 of sheep βA‐ and βB‐globins and has previously been named LVV‐hemorphin‐7. Pharmacological studies demonstrated that LVV‐hemorphin‐7 and angiotensin IV were equipotent in competing for 125I‐angiotensin IV binding to sheep cerebellar membranes and displayed full cross‐displacement. Using in vitro receptor autoradiography, 125I‐LVV‐hemorphin‐7 binding to sheep brain sections was identical to 125I‐angiotensin IV binding in its pattern of distribution and binding specificity. This study reveals the presence of a globin fragment in the sheep brain that exhibits a high affinity for, and displays an identical receptor distribution with, the angiotensin IV receptor. This globin fragment, LVV‐hemorphin‐7, may therefore represent an endogenous ligand for the angiotensin IV receptor in the CNS.

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