Abstract and Introduction
Abstract
Context: Night-shift work causes circadian misalignment, predicts the development of metabolic diseases, and complicates the interpretation of hormone measurements.
Objective: To investigate endogenous circadian rhythms, dissociated from behavioral and environmental confounds, in adrenal and gonadal steroids after simulated shift work.
Methods: Fourteen healthy adults (ages 25.8 ± 3.2 years) were randomized to 3 days of night or day (control) shift work followed by a constant routine protocol designed to experimentally unveil rhythms driven endogenously by the central circadian pacemaker. Blood was sampled every 3 hours for 24 hours during the constant routine to concurrently obtain 16 Δ4 steroid profiles by mass spectrometry. Cosinor analyses of these profiles provided mesor (mean abundance), amplitude (oscillation magnitude), and acrophase (peak timing).
Results: Night-shift work marginally increased cortisol by 1 µg/dL (P = 0.039), and inactive/weak derivatives cortisone (P = 0.003) and 18-hydroxycortisol (P < 0.001), but did not alter the mesor of potent androgens testosterone and 11-ketotestosterone. Adrenal-derived steroids, including 11-ketotestosterone (P < 0.01), showed robust circadian rhythmicity after either day- or night-shift work. In contrast, testosterone and progesterone showed no circadian pattern after both shift work conditions. Night-shift work did not alter the amplitude or acrophase of any of the steroid profiles.
Conclusion: Experimental circadian misalignment had minimal effects on steroidogenesis. Adrenal steroids, but not gonadal hormones, showed endogenous circadian regulation robust to prior shift schedule. This dichotomy may predispose night-shift workers to metabolic ill health. Furthermore, adrenal steroids, including cortisol and the main adrenal androgen 11-ketostosterone, should always be evaluated during the biological morning whereas assessment of gonadal steroids, particularly testosterone, is dependent on the shift-work schedule.
Introduction
Sleep loss increases cortisol (a key catabolic signal) and decreases testosterone (a major anabolic hormone), thereby imbalancing the hormonal signaling of whole-body metabolism.[1–4] This dysregulation would be expected to cause metabolic dysfunction, and experimental studies do in fact show that sleep loss induces insulin resistance, a major factor in the development of type 2 diabetes mellitus.[3,4] Furthermore, we recently demonstrated that fixing cortisol and testosterone to prevent imbalance during sleep loss muted the development of insulin resistance.[3–5] This suggests that cortisol and testosterone signaling are important mechanisms by which sleep loss induces insulin resistance.
Both cortisol and testosterone also exhibit well-established temporal profiles that vary systematically across the 24-hour day. Alterations in signaling of these and other hormones could help explain why experimentally shifting the timing of behavioral rhythms relative to endogenous circadian rhythmicity (ie, circadian misalignment) induces insulin resistance, even in the absence of sleep loss.[3,6] And it may ultimately explain why night-shift work, which induces circadian misalignment, is associated with the future development of common metabolic disorders such as obesity and type 2 diabetes mellitus.[3,7] This is because the induction of insulin resistance is widely recognized as underpinning the development of type 2 diabetes mellitus, and controlled experimental trials show that 1 to 4 nights of in-laboratory simulated shift work, even in the absence of sleep loss, induces insulin resistance.[3]
Although cortisol and testosterone are the main metabolically active hormones secreted from the adrenal gland and testis, respectively, a set of 11-oxygenated androgens of predominately adrenal origin have been recently implicated in the signaling of many physiological and pathophysiological processes that impact metabolic health. These processes occur across the human lifespan and in both sexes and include, for example, polycystic ovarian disease in younger women and castration-resistant prostate cancer in older men.[8,9] Understanding the signaling characteristics of cortisol, testosterone, and these other hormones is a prerequisite to properly identify and interpret the clinical and regulatory implications of such hormone abnormalities.[10]
The signaling and action of many hormones, including cortisol and testosterone, depends on their underlying pulsatile and diurnal (ie, 24-hour) rhythms.[11–13] Randomized controlled trials show that better mimicking the diurnal rhythmicity of cortisol further optimized weight, blood pressure and glucose metabolism,[14] and replicating both pulsatile and diurnal rhythmicity further improved working memory and caused subtle differences in the neural processing of emotional input assessed by functional magnetic resonance imaging and psychological face expression recognition tasks.[15]
The 24-hour patterns observed in these hormones could be driven centrally by the central circadian pacemaker in the suprachiasmatic nuclei of the hypothalamus and/or by external environmental or behavioral factors that have a diurnal pattern. Identifying the underlying 24-hour patterns of these hormones as driven specifically by the central circadian pacemaker, free of external influences, requires the use of the constant routine protocol as the gold standard method to remove or uniformly distribute external influences so that only the endogenous rhythm is expressed.[16,17] The endogenous circadian rhythm of cortisol was established decades ago using the constant routine method,[18,19] and one of these studies also showed that circadian misalignment did not alter the timing of the cortisol rhythm.[19] However, the underlying endogenous rhythm of testosterone remains unknown because a constant routine has not been utilized to assess it, and the diurnal rhythms observed in prior studies may have been driven by external influences, including cycles of light/dark, sleep/wake, feeding/fasting, and activity/rest.[20–22] Prior studies examining the diurnal rhythm of 11-oxygenated androgens also did not remove the influence of these external confounds by utilizing a constant routine protocol.[10] Accordingly, the aim of this study was to determine the very nature of the underlying 24-hour pattern of secretion of clinically relevant androgenic hormones as driven by the central circadian pacemaker, and the effect of circadian misalignment on these endogenous rhythms.
We therefore conducted an in-laboratory study where healthy young men and women were assigned to 3 days of either a simulated day-shift (ie, control condition) or night-shift (ie, experimental condition) schedule at random. Following the 3 days of shift work, blood was collected every 3 hours through an intravenous catheter during a 24-hour constant routine protocol, in which subjects remained semirecumbent and awake, in a controlled environment with fixed ambient temperature and dim light, and ate identical small snacks regularly every hour. The blood samples were used for later simultaneous extraction and concurrent measurement of 16 Δ4 steroids that comprise the mineralocorticoid, glucocorticoid, and androgen pathways—including cortisol, testosterone, and certain 11-oxygenated androgens—using liquid chromatography triple quadrupole tandem mass spectrometry.[23]
J Endo Soc. 2022;6(12) © 2022 Endocrine Society
