Met5-enkephalin- and Met5-enkephalin-Arg6-Gly7-Leu8-immunoreactive nerve fibers in the pig female reproductive system.

The localization of Met5-enkephalin (ME) immunoreactivity in the female genital organs of the rat, guinea pig and pig was studied by indirect immunofluorescence method. In the rat and guinea pig, no ME immunoreactivity was observed in the uterus, fallopian tube or ovary. In the pig uterus and fallopian tube ME-immunoreactive nerve fibers were observed in muscular and submucose layers as well as around the blood vessels. In the pig ovary, ME immunoreactivity was localized in nerve fibers in medullary and cortical parts of the organ. Met5-enkephalin-Arg6-Gly7-Leu8 (MEAGL) immunoreactivity was also studied in the pig uterus, where its distribution was similar to that of ME. The present results suggest that the pig genital organs receive innervation by nerve fibers containing proenkephalin A-derived peptides, which may have a role in modulation of neurotransmission in these organs.