RELATIONSHIP BETWEEN ADRENOCORTICOTROPIN BIOACTIVITY IN BLOOD AND CEREBROSPINAL-FLUID OF RHESUS-MONKEYS

ACTH levels, measured by a cytochemical bioassay, were determined in the plasma and CSF of adult female rhesus monkeys which were ovariectomized and receiving estrogen replacement therapy. In control monkeys, ACTH bioactivity was found in both CSF (10.2 .+-. 1.8 ng/l) and plasma (186 .+-. 51 ng/l) in samples taken at 14.00 h (lights on: 07.00-19.00 h). Dexamethasone treatment (0.2 mg/kg) twice daily for 4 days suppressed plasma ACTH levelz (52.8 .+-. 25.2 ng/l) but had no effect on CSF levels (7.6 .+-. 2.7 ng/l). Raising plasma ACTH, either by daily injections of a long-acting preparation of ACTH(1-24) for 6 days or by bilateral adrenalectomy (and subsequently withdrawing cortisol replacement therapy) also resulted in no detectable changes in ACTH levels in the CSF. A regression analysis between ACTH in the plasma and CSF from samples taken throughout the experiments showed no correlation. Measurement of ACTH by radioimmunoassay, whilst satisfactory for determination of this peptide in plasma, could not identify authentic ACTH in the CSF. Apparently, bioactive ACTH does not enter the CSF in detectable quantities from either the peripheral vascular compartment or from the animal''s own pituitary gland; reducing ACTH secretion from the pituitary also evidently has no effect on levels of ACTH in the CSF. This is in marked contrast to other pituitary peptide hormones, including prolactin, which is secreted together with ACTH during stress but which, unlike ACTH, enters the CSF relatively easily.