A rostral-caudal concentration gradient in cerebrospinal fluid adrenocorticotropin

In two separate experiments, cerebrospinal fluid (CSF) adrenocorticotropin immunoreactive (ACTH-IR) concentrations in the rhesus monkey followed a significant rostral-caudal gradient. In the first study, CSF was sampled from an indwelling catheter in awake animals. The mean ACTH-IR concentration in the cisternal region was 12.3 pg/ml, as compared to 8.56 pg/ml in the lumbar region. In the second study, CSF was sampled in a different group of monkeys by percutaneous puncture at the cisterna magna and at L5-L6. In this study, the mean ACTH-IR concentration in samples collected from the cistern was also greater than the concentration from L5-L6. In addition, a significant correlation within subjects was found between samples collected from the two sites (r = 0.86). These results demonstrate that the site of CSF sampling is a variable in determining CSF ACTH-IR concentrations and suggest that lumbar CSF ACTH-IR concentrations in humans may be interpreted as indexes of ACTH changes at higher levels in the central nervous system.