[Levels of ACTH and endogenous-digitalis-like substances in human blood]

Simultaneous determination of immunoreactive ACTH and immunoreactive digitalis like substances (DLS) in 71 plasma specimens of 44 persons proved that in spite of a great range of ACTH concentrations in the followed individuals (1.7-271 nmol/l) there is not a major correlation between DLS and ACTH or a significant difference in plasma DLS concentrations in the groups of persons with suppressed, normal or increased ACTH concentrations. Acute increase of ACTH plasma concentrations after synthetic ACTH application or a suppression of plasma ACTH by dexamethasone were not accompanied by corresponding changes of immunoreactive DLS. Thus it follows from this investigation that in spite of its biological digitalis like activity and interference of synthetic ACTH 1-24 high concentrations with digoxin enzymoimmunoassay in vitro, ACTH in concentrations found in human plasma is not responsible for endogenous immunoreactive DLS levels in plasma.