Potentiation of levodopa effect by intravenous L-prolyl-L-leucyl-glycine amide in man.

L-prolyl-L-leucyl-glycine amide (P.L.G.) has melanocyte-stimulating-hormone-inhibitory hormone (M.I.F.) activity. When injected intravenously as a bolus of 200 mg, it greatly potentiated the effect of an oral levodopa dose upon motor performance objectively measured by a battery of tests. This amelioration in motility was accompanied by improvement in intellectual functioning.