Mammalian neuromuscular development accelerated with early but slowed with late gestational administration of ACTH Peptide

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Abstract
The neuropeptide ACTH 4–10, a nonsteroidogenic fragment of adrenocorticotropic hormone, has two distinct and opposite effects on developing nerve and muscle. Muscle is positively influenced by ACTH during the first part of gestation (G days 3–12) before innervation occurs. Subsequent effects on innervation are largely depressive and exerted only during G13–21. Treatment during G3–12 increases twitch amplitude, rise time and speed of contraction of directly and indirectly stimulated extensor digitorum longus (EDL) muscle of two wk old rats. Treatment during G13–21 slows contractions of indirectly stimulated EDL, whereas treatment throughout gestation (G3–G21) shows little effect. Thus, ACTH first accelerates muscle development then modulates this development through neuronal depression.