[Nle4, D-Phe7]-alpha-MSH: a superpotent melanotropin with prolonged action on vertebrate chromatophores

The in vitro and in vivo responses of integumental chromatophores to alpha-MSH and a related analogue, [Nle4, D-Phe7] -alpha-MSH, were studied in a number of vertebrate species: the teleost, Lebistes reticulatus; the amphibians, Rana pipiens, R. catesbeiana, Xenopus laevis, Bufo alvarius, and B. cognatus; the lizard, Anolis carolinensis; the rattlesnake, Crotalus atrox. The alpha-melanotropin analogue was a superpotent agonist in the in vitro frog (R. pipiens, R. catesbeiana) and lizard (A. carolinensis) skin bioassays. In all species studied, the analogue exhibited ultraprolonged melanotropic activity, both in vitro and in vivo. This melanotropin and related analogues should prove useful in the study of numerous physiological processes, particularly when prolonged melanotropic activity is desired.