Novel Opioid Peptide Amidorphin: Characterization and Distribution of Amidorphin‐Like Immunoreactivity in Bovine, Ovine, and Porcine Brain, Pituitary, and Adrenal Medulla

We have recently isolated from bovine adrenal medulla a novel C‐terminally amidated opioid peptide, amidorphin, which derives from proenkephalin A. Amidorphin revealed a widespread distribution in bovine, ovine, and porcine tissue. Particularly high concentrations of amidorphin immunoreactivity were detected in adrenal medulla, posterior pituitary, and striatum, similar to the major gene products of proenkephalin A. In the adrenal medulla of each species. authentic amidorphin was the predominant immunoreactive form. Pituitary and brain, however, contained predominantly putative N‐terminally shortened fragments of amidorphin of a slightly lower molecular weight and shorter retention times on HPLC. In addition, in ovine adrenal medulla, a putative high‐molecular‐weight form of amidorphin was detected. These findings are indicative of a tissue‐specific processing of the proenkephalin A precursor, leading predominantly to authentic amidorphin in the adrenal medulla and further processing to smaller C‐terminal fragments in the brain and pituitary.