A pilot study of the phase angle between cortisol and melatonin in major depression - a potential biomarker?

INTRODUCTION: Hypothalamic-pituitary-adrenal (HPA) axis and melatonin rhythm alterations have been independently reported in major depression (MDD) as well as in insomnia. In this pilot study, we link cortisol and melatonin rhythms and propose that the phase angle between cortisol acrophase (CA) and dim-light melatonin onset (20 pg/ml) (DLMO-20) may yield a useful state specific biomarker for MDD. METHODS: Six healthy (HC) and six depressed (MDD) psychotropic free subjects were admitted to the General Clinical Research Center. Blood was sampled for cortisol and melatonin from 1600h to 1000h, under dim lights (<20lux) and constant routine. Time for DLMO-20 and peak cortisol concentration was determined for each subject. Phase angle was computed as the difference in time between CA and DLMO-20. RESULTS: Phase angle was significantly increased in MDD's versus HC's (13.40+/-1.61h. versus 11.61+/-1.66h, p=0.026). Using ROC analysis, a phase angle greater than 13.57h distinguished MDD's from HC's (sensitivity=0.83, specificity=1.0). Mean nocturnal melatonin (1600-1000h) was significantly decreased in MDD's versus HC's (22.67+/-9.08 pg/ml versus 47.82+/-14.76 pg/ml, p=0.015). CONCLUSIONS: The phase angle between CA and DLMO-20 appears to distinguish HC's from MDD's and may be a useful biomarker to aid biologic assessment as well as treatment. Lower nocturnal melatonin in MDD's highlights its importance in MDD's pathophysiology. Additional study with larger sample size is needed to confirm the results of this pilot study. The mechanism for this phase angle difference and decreased melatonin, itself, requires further study.

The acute effects of a mineralocorticoid receptor (MR) agonist on nocturnal hypothalamic-adrenal-pituitary (HPA) axis activity in healthy controls.

INTRODUCTION: Both glucocorticoid and mineralocorticoid receptors (GRs and MRs) help modulate cortisol feedback on the hypothalamic-adrenal-pituitary (HPA) axis. In brain, MRs inhibit the HPA axis and are thought to be fully occupied. Thus, prior studies of the effects of an MR agonist on HPA axis activity have first used metyrapone to inhibit cortisol production and to consequently deplete the receptors. Herein, we propose that an MR agonist may inhibit the HPA axis without first "unloading" receptors of endogenous cortisol. METHODS: Healthy subjects were admitted to the General Clinical Research Center. Blood was sampled for cortisol and adrenocorticotropic hormone (ACTH) from 16:00 to 24:00 h, when greatest MR activity is expected, on two consecutive nights. The first night established a baseline and the second night established response. On the second afternoon, all subjects were given 0.5mg fludrocortisone. Mean cortisol and ACTH were computed from 16:00 to 24:00 h. RESULTS: Fludrocortisone acutely decreased mean cortisol (p=0.003; effect size (ES) 1.65) and mean ACTH (p=0.000, ES 4.46). Additionally, post hoc analysis showed that fludrocortisone tended to decrease the cortisol/ACTH ratio (p=0.0686, ES 0.92) across the same time period. CONCLUSIONS: Fludrocortisone significantly inhibits nocturnal HPA axis activity without first depleting MR receptors with metyrapone. This suggests that brain MRs are not fully occupied by endogenous cortisol and can be further activated by an agonist. The decrease in cortisol/ACTH ratio suggests a possible role on adrenal sensitivity as well. The ability to lower nocturnal HPA axis activity has interesting implications in disorders of HPA axis excess, such as insomnia, depression and healthy aging.

Aging and the role of the HPA axis and rhythm in sleep and memory-consolidation.

Changes in the hypothalamo-pituitary-adrenal (HPA) axis and its rhythm with aging have interesting implications for sleep. Herein, the authors review sleep and HPA changes associated with normal aging and point out the similarities in how they change over time. The authors also discuss the effects of sleep on declarative memory consolidation, in particular. This focused review suggests that some of the declarative memory dysfunction with normal aging, and possibly procedural memory dysfunction, may be partially reversible by instituting methods to augment slow-wave sleep (SWS). Also, agents that decrease nocturnal corticotropin-releasing hormone and the cortisol nadir and enhance SWS may offer potential ways to manipulate the HPA axis/rhythm and improve sleep and memory. In this regard, the authors propose that drugs that act directly on the HPA axis (e.g., mineralocorticoid agonists) may be potentially quite useful for improving both sleep and declarative memory consolidation during sleep.

On the interactions of the hypothalamic-pituitary-adrenal (HPA) axis and sleep: normal HPA axis activity and circadian rhythm, exemplary sleep disorders.

The hypothalamic-pituitary-adrenal (HPA) axis plays important roles in maintaining alertness and modulating sleep. Dysfunction of this axis at any level (CRH receptor, glucocorticoid receptor, or mineralocorticoid receptor) can disrupt sleep. Herein, we review normal sleep, normal HPA axis physiology and circadian rhythm, the effects of the HPA axis on sleep, as well as the effects of sleep on the HPA axis. We also discuss the potential role of CRH in circadian-dependent alerting, aside from its role in the stress response. Two clinically relevant sleep disorders with likely HPA axis dysfunction, insomnia and obstructive sleep apnea, are discussed. In insomnia, we discuss how HPA axis hyperactivity may be partially causal to the clinical syndrome. In obstructive sleep apnea, we discuss how HPA axis hyperactivity may be a consequence of the disorder and contribute to secondary pathology such as insulin resistance, hypertension, depression, and insomnia. Mechanisms by which cortisol can affect slow wave sleep are discussed, as is the role the HPA axis plays in secondary effects of primary sleep disorders.

Human cutaneous vascular responses to whole-body tilting, Gz centrifugation, and LBNP.

We hypothesized that gravitational stimuli elicit cardiovascular responses in the following order with gravitational stress equalized at the level of the feet, from lowest to highest response: short-(SAC) and long-arm centrifugation (LAC), tilt, and lower body negative pressure (LBNP). Up to 15 healthy subjects underwent graded application of the four stimuli. Laser-Doppler flowmetry measured regional skin blood flow. At 0.6 G(z) (60 mmHg LBNP), tilt and LBNP similarly reduced leg skin blood flow to approximately 36% of supine baseline levels. Flow increased back toward baseline levels at 80-100 mmHg LBNP yet remained stable during 0.8-1.0 G(z) tilt. Centrifugation usually produced less leg vasoconstriction than tilt or LBNP. Surprisingly, SAC and LAC did not differ significantly. Thigh responses were less definitive than leg responses. No gravitational vasoconstriction occurred in the neck. All conditions except SAC increased heart rate, according to our hypothesized order. LBNP may be a more effective and practical means of simulating cardiovascular effects of gravity than centrifugation.