Kyotorphin and D-kyotorphin stimulate Met-enkephalin release from rat striatum in vitro.

The release of immunoreactive Met-enkephalin (I-ME) from the rat striatum was studied in vitro using a batch technique. A basal release of the order of 2-3% of total I-ME tissue content per 10 min was found. Both dipeptides kyotorphin and D-kyotorphin produced equipotently dose-dependent I-ME release, with 0.5 mM maximal concentration causing 2-3-fold stimulation of release. This release was calcium-dependent. In concentrations up to 1 mM both dipeptides did not change the basal release of [3H]noradrenaline, [3H]GABA, [3H]D-aspartate and immunoreactive beta-endorphin from various brain structures. The results support a role of kyotorphin as a specific I-ME-releasing factor in the rat brain.