Diurnal Patterns for Cortisol, Cortisone and Agouti-Related Protein in Human Cerebrospinal Fluid and Blood.
Level 4 - case-series / case-control
Small descriptive physiological study in a single group of healthy individuals
PubMed 31838496 · doi:10.1210/clinem/dgz274
What was done
This was a secondary physiological analysis using stored cerebrospinal fluid (CSF) and plasma samples from 8 healthy subjects who served as controls in a sleep study. CSF was sampled every 2 hours for 36 hours via an indwelling lumbar catheter alongside concurrent 2-hour plasma sampling to characterize diurnal rhythms of cortisol, cortisone, and agouti-related protein (AgRP).
What was found
CSF cortisol and cortisone showed a diurnal rhythm that followed the plasma rhythm by a 2-hour lag, with peak concentrations at 0900h and nadir at 0100h. The ratio of active cortisol to inactive cortisone in the CSF was 48% higher at peak compared to nadir. Plasma AgRP exhibited a diurnal rhythm out of phase with cortisol, whereas CSF AgRP demonstrated a less distinct rhythm that oscillated in phase with cortisol.
Why it matters
These findings provide direct human evidence that central nervous system glucocorticoids undergo daily rhythmic fluctuations linked to systemic circulation and central appetite-regulating peptides.
Limits
The study is limited by an extremely small sample size (n = 8) and secondary use of sleep study control samples. The abstract omits exact concentration values, variance metrics, and statistical significance levels, and direct metabolic or behavioral consequences of these rhythms were not tested.
Cited by
- supports In the human circadian rhythm, cortisol levels are naturally at their lowest around 2:00 AM and peak at 8:00 AM.