Ki: 0.21 nM (human MC1 receptor)

ACTH (1-17) is a potent agonist at the hMC1R. ACTH (1-17) shows high affinity for the hMC1R with a K _i value of 0.21±0.03 nM which is slightly higher than that of 0.13±0.005 nM for alpha-MSH. ACTH (1-17) induces a slight and not significant increase in growth hormone secretion even when micromolar concentrations of the peptide are employed in rat pituitary cultures.

Inhibition of DNA labeling is noted when the ACTH (1-17) is administered at 2 hr after the beginning of the daily dark span when nocturnal animals become active. When administered at this circadian stage, the larger dose in particular is associated with an inhibition of DNA labeling lasting for 24 hr. The inhibitory effect is much shorter when the same dose is injected 4 hr earlier.