Immunoreactive ACTH in cerebrospinal fluid

A previous report of the presence of ACTH in cerebrospinal fluid (1) prompted an investigation of its concentration in the CSF of patients with nonendocrine disease and of the mechanism by which it enters this fluid. The mean immunoreactive ACTH concentration in 22 patients was 98 pg/ml which slightly, but not significantly, exceeded the mean concentration in simultaneously obtained plasma specimens (74 pg/ml). However, there was no correlation (r = 0.2) between the concentrations of individual pairs of ACTH values obtained from plasma and CSF. The transport of ACTH between the blood and CSF compartments was investigated in man and the cat. After 48 hr administration of exogenous ACTH in man, when the plasma concentration was very high, the CSF ACTH concentration remained low. During infusion of labeled ACTH in cats, a steadystate plasma/CSF radioactivity ratio was obtained after 4-6 hr, at which time the concentration of radioactivity attributable to labelled ACTH was 100 times higher in plasma than in CSF. These findings indicate that the blood-CSF barrier is relatively impermeable to ACTH in man and the cat. The relatively high CSF ACTH concentrations found in patients with non-endocrine disease suggests that some or most of the ACTH present in CSF may enter by a mechanism which by-passes the blood-CSF barrier.