The involvement of melanotrophins in physiological colour change in the dogfish Scyliorhinus canicula.

Desacetylated alpha-, beta-, and gamma-MSH purified from the neurointermediate lobe of the pituitary gland of the dogfish Squalus acanthias were all equipotent in turning partially hypophysectomized dogfish, Scyliorhinus canicula, dark. However, each possessed less than 2% of the melanotrophic activity of either acetylated mammalian alpha-MSH or synthetic acetylated Squ. acanthias alpha-MSH. These results suggest that acetylation is much more important than amidation in determining melanotrophic potency in vivo in the dogfish. Intravenous administration into grey-adapted dogfish of an antibody capable of binding the alpha-MSH-like peptides present in the blood was very effective at inducing pallor. In contrast, a gamma-MSH antibody had no effect on the melanophores of Scy. canicula. Overall the results suggest that it is alpha-melanotrophins that regulate physiological colour change in the dogfish Scy. canicula.