Dermorphin-like immunoreactivity in guinea pig and rat stomach

Dermorphin is an opioid peptide containing one D-amino acid isolated from amphibian skin. We examined the presence of dermorphin-like immunoreactivity (DMP-IR) in mammalian brain and tissues using an antiserum developed in our own laboratory which works at a dilution of 1:120,000 for Radioimmunoassay (RIA) and can detect 2.1 pg of dermorphin. We were unable to find DMP-IR in guinea pig, rat and toad brain and rat and toad spinal cord either extracted with methanol or with HCl. The guinea pig and rat stomach contained significant amounts of DMP-IR (228.9 pg/mg protein and 97.5 pg/mg protein respectively) when extracted with HCl but not with methanol. The DMP-IR we detected in the stomach is not dermorphin per se. A single peak of DMP-IR was found on Sephadex G-25 gel filtration. When re-chromatographed on reverse phase HPLC, this peak of DMP-IR gave rise to three peaks of DMP-IR.