Distribution of met-enkephalin-Arg6-Phe7 in various tissues of rats and guinea pigs.

A specific and sensitive radioimmunoassay coupled with gel filtration and HPLC was used to demonstrate the presence and to measure MEAP content in stomach, doudenum, ileum, myenteric plexus, colon, heart, lung, pancreas, liver, adrenal and superior cervical sympathetic ganglia of rat and guinea pig. The highest content was found in various parts of intestine, lung and superior cervical sympathetic ganglia, pancreas and liver were practically devoid of immunoreactivity. In these tissues we found that the distribution of MEAP is not parallel to that of metenkephalin (ME). Our assay excludes interferences by high molecular weight MEAP-like peptides, the cardioexcitatory tetrapeptide (Phe-Met-Arg-Phe NH2) and the correspondent acid Phe-Met-Arg-Phe.