The Lightening Effect of Actinomycin D on the Skin of Amphiuma tridactylum. ∗

Summary

A lightening of the skin of amphiuma was observed within 4 to 6 hours after injection of actinomycin D in doses of 5 and 10 μg/g body weight. This effect was associated with the aggregation of melanin-granules in both the epidermal and dermal melanophores and was spontaneously reversible within 8-12 hours after it was first observed. However, the administration of synthetic β-MSH reversed this effect within 2 hours. Cycloheximide, an inhibitor of protein synthesis did not produce paling of skin in amphiuma. Melatonin which has been known as a potent lightening agent in frog did not produce such an effect in amphiuma. The possibility that actinomycm D produced paling of the skin by blocking the secretion of MSH by the pituitary and that in vivo the mechanism of synthesis of this hormone may be different from other poly-peptides has been discussed.