Des-acetyl MSH and gamma-MSH act as partial agonists to alpha-MSH on the Anolis melanophore

The biological activities of alpha-MSH des-acetyl MSH, gamma-MSH and LPH37-58 were compared using the Anolis rate method of bioassay. Dose-response data showed LPH37-58 to be equipotent with alpha-MSH, but des-acetyl MSH and gamma-MSH were found to be much less active. The effect of LPH37-58 was additive to that of alpha-MSH, indicating that LPH37-58 is a full agonist of alpha-MSH. The lower potency peptides des-acetyl MSH and gamma-MSH reduced the effect of alpha-MSH and are, therefore, partial agonists of alpha-MSH. The action of MSH peptides in vivo may be modulated by interaction with agonists.