Abstract
Cortisol is often measured as a marker for stress. Therefore, a profound validation of the time-lag between the stressor and the increase and peak in cortisol levels is needed. No study measured both the urinary and salivary cortisol time-lag after a psychological stressor. In this study, we used a frequent sampling study design to (1) describe the urinary and salivary cortisol pattern during a control day; and (2) characterize the induced excretion pattern of urinary and salivary cortisol after a psychological stressor in six zoo-housed bonobos. Liquid chromatography-tandem mass spectrometry was used to analyze 71 urine and 162 saliva samples collected on a control and a test day. We found that the time-lag between the stressor and the maximal cortisol concentration was similar in urine and saliva (160 min after the stressor). However, salivary cortisol after the stressor did show a faster and steeper increase than urinary cortisol. We also show inter-individual variation in the baseline and stress levels of cortisol, which should be considered in future cortisol studies. Our research highlights the importance of validation studies to confirm relevant sampling windows for cortisol sampling in order to obtain biologically meaningful results.
Highlights
Cortisol is often measured as a marker for stress
One physiological response to a stressor is the activation of the hypothalamus–pituitary–adrenal (HPA) axis, which is a cascade of events, mediated by an integrated network of neuroanatomical structures and peripheral organs leading to physiological changes that help to restore homeostasis
A peak occurred around 12:00 h (Fig. 1, solid line)
Summary
Cortisol is often measured as a marker for stress. a profound validation of the time-lag between the stressor and the increase and peak in cortisol levels is needed. The GC’s in circulation are transported to target tissues, where they bind to receptors in the brain, liver, kidneys and other tissues This results in an array of effects, including the release of additional energy for necessary physiological functions to respond to the stressor. Cortisol levels in blood represent a short-term stress response[4], which allows for measuring the effect of a specific event on the activation of the HPA-axis. Urinary cortisol has been stated to reflect the longer lasting effect of a certain stressful event, since it represents the pooled cortisol values over minutes to hours, depending on the s pecies[13,31,32], while salivary cortisol concentrations reliably represent circulating cortisol levels with a short time-lag of several m inutes[5,31,33,34]. Frequent sampling of urine and saliva after such a stressor could provide a profound characterization of the time-lag of both cortisol responses, allowing for a comparison between them
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