Thyroid stimulating and pigmentary effects of synthetic peptides related to α-MSH and ACTH

Abstract

Seven synthetic peptides related to α-MSH and ACTH and eleven stereoisomeric fragments of α-MSH (sequence 6–10) were tested for their thyroid stimulating effects. This TSH-like activity was determined by following 131I release in mice injected with 131I and treated with thyroxine. N-α-acetyl-β-corticotropin-(1–24)-tetracosapeptide and β-corticotropin-(1–24)-tetracosapeptide hydrazide had the highest MSH activity and elicited the greatest effects on the blood levels of 131I. The α-MSH-(7–13)-heptapeptide which had a moderate MSH activity, also caused a significant stimulation of 131I release in mice. On the other hand, β-corticotropin-(11–24)-tetradecapeptide, which had virtually no MSH activity, possessed some TSH-like activity. D-His-D-Phe-D-Arg-D-Trp-Gly and the analogous L-pentapeptide, which were essentially free of MSH activity, had no effect on the thyroid at doses up to 100 μg. per mouse. Seven MSH-ACTH stereoisomers, which individually assayed up to 1,200 MSH U/mg., similarly had no effect on the thyroid, but L-His-D-Phe-L-Arg-L-Trp-Gly and three stereoisomers which had a low but definite MSH activity, did exert some TSH-like effects. These studies reveal that, although some relationship between MSH and TSH-like activity can be observed among peptides of the MSH-ACTH group, there is no definite correlation between these activities.