Distribution of Met5-enkephalin-Arg6, Phe7 in rat spinal cord.

The distribution of Met5-enkephalin-Arg6, Phe7 (YGGFMRF) in rat spinal cord was determined by a specific RIA and compared with that of Met5-enkephalin. The concentration of YGGFMRF on a per mg protein basis was highest in sacral cord and successively decreased in more rostral segments. A similar rostro-caudal distribution was observed for Met5-enkephalin. Regional microdissection revealed the dorsal grey matter to be highest in YGGFMRF content followed by ventral gray, ventral white and dorsal white matter; a similar pattern was observed for Met5-enkephalin. The ratio of Met5-enkephalin: YGGFMRF concentration was 5.4 +/- 0.15 (S.E.M.) on average in all regions measured, indicating a very close quantitative relationship between the two molecules. Our data suggest that YGGFMRF may act as a precursor of or cotransmitter with Met5-enkephalin in spinal cord tissue.