Synthetic MIF analogues. Part II: Dopa potentiation and fluphenazine antagonism.

A comparison is described between the activity of the melanocyte-stimulating hormone release inhibiting factor (MIF) and those of five synthetic tripeptide analogues of MIF. The comparison was based upon the ability of the compounds to potentiate the behavioral effects of L-dopa in mide and to antagonize fluphenazine-induced catalepsy in rats. Three of the tripeptides potentiated L-dopa in a manner similar to that of MIF. All of the synthetic analogues antagonized fluphenazine after a single dose although their potency and their duration of action differed. MIF was active in the latter test only following chronic administration. The possible mechanism of action and the potential clinical applicability of the tripeptides are briefly discussed.