Steroid responses to ACTH-like polypeptides.

Abstract

ABSTRACT The intravenous administration in 6 hr of 75 U of purified porcine ACTH, or of commercial ACTH or of 0.75 mg of a synthetic ACTH-like polypeptide representing, from the N-terminus, amino acid residues 1-24, 1-23, or 1-20 of this hormone produced comparable increases in plasma 11-(OH) corticosteroids. Hence, full corticotropin activity as reflected by increases in plasma corticosteroids was manifested by synthetic molecules about ½ the size of the natural product. Moreover, 0.25 mg of the polypeptide composed of 24 amino acid residues proved to be equal to 75 U of purified porcine ACTH in raising plasma steroids during a prolonged 6-hr intravenous infusion, establishing that ACTH and the shorter synthetic molecule are at least equipotent on a molar basis. A synthetic MSH-type molecule, representing the first 13 amino acid residues of ACTH, did not have this property in man. The 0.75 mg dosage of the polypeptide representing amino acid residues 1–24 yielded the same increase in plasma 11-(OH) corti...