High Quality Content by WIKIPEDIA articles! Melanocyte-inhibiting factor (also known as Pro-Leu-Gly-NH2, Melanostatin, MSH release-inhibiting hormone or MIF-1) is an endogenous peptide fragment derived from cleavage of the hormone oxytocin, but having generally different actions in the body. MIF-1 produces multiple effects, both blocking the effects of opioid receptor activation, while at the same time acting as a positive allosteric modulator of the D2 and D4 dopamine receptor subtypes, as well as inhibiting release of other neuropeptides such as alpha-MSH, and potentiating melatonin activity.