Inhibition of MSH Release in Frogs by Direct Application of L-Prolyl-L-leucylglycinamide to the Pituitary 1

Summary

Ten nanograms of L-prolyl-L-leucylglycinamide (PLG), when applied directly to the pituitary, resulted in lightening of a frog whose skin was previously darkened by destruction of the hypothalamus. As much as 10 mg of PLG was inactive when injected into the dorsal lymph sac or aortic trunk. Incubation of PLG for 10 min in frog serum caused significant inactivation of the material. This inactivation may partially account for the poor MIF activity observed after systemic injection of PLG. The newly modified assay described here is particularly recommended for future studies with MIF because of its simplicity.