Met-enkephalin-like immunoreactivity (MELI) and enkephalinase activity (EKA) in cord blood and newborns in the first hours of life.

Recently, the presence and the concomitant release with catecholamines of metenkephalin and other pro-enkephalin A deriving peptides have been demonstrated in the adrenal medulla of various mammals and man. As high amounts of catecholamines are released in the newborn at delivery, probably following the stress of parturition, a similar release of met-enkephalin and other pro-enkephalin A deriving peptides from the newborn chromaffin tissue may be hypothesized. In the present study we investigate the occurrence of met-enkephalin-like immunoreactivity and enkephalinase (quite a specific enkephalin degrading enzyme) in cord and newborn plasma at different hours after birth. Our results show the presence of high met-enkephalin-like immunoreactivity levels in cord and newborn plasma with respect to normal adult values. On the contrary, cord blood enkephalinase activity was lower than in adult subjects and further decreased during the first hours of life. A positive correlation was found between the two parameters. These data seem to indicate a release of met-enkephalin-like peptides from the newborns' sympathoadrenal tissue following the stress of delivery and in the first hours of life.