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 oe 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 varioys brain structures. The results support a role of kyotorphin as a specific I-ME-releasing factor in the rat brain.
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