Melanocyte-stimulating hormone--mimetic action of the phenothiazines.

We have compared the melanophore-stimulating action of four phenothiazines, trifluoperazine, perphenazine, chlorpromazine, and prochlorperazine, with alpha-MSH on the skin of the lizard Anolis carolinensis, using a new rate method of bioassay. The dose-response curves for the phenothiazines were parallel to that of alpha-MSH, and when given together alpha-MSH and chlorpromazine were additive. The phenothiazines may therefore stimulate melanosome dispersion in the lizard skin by the same mechanism as alpha-MSH; a MSH-mimetic action of phenothiazines may similarly explain their pigmentary action in man. The pigmentary potency of the phenothiazines corresponded with their therapeutic potency in man; this is in keeping with a neuro-regulatory role for MSH peptides and suggests a possible therapeutic use for them.