Abstract

Background: Acute psychological stress activates the hypothalamic-pituitaryadrenal axis and the autonomic nervous system together, and both are routinely treated as interchangeable indices of a single stress response. Whether the two systems actually covary within individuals is less certain. Objective: This study quantified endocrine and autonomic reactivity to a standardised laboratory stressor and tested whether the magnitude of the cortisol response predicts the magnitude of the autonomic response. Methods: Ninety-six healthy adults underwent a standardised social-evaluative stress protocol. Salivary cortisol and five-minute electrocardiographic epochs were obtained at six time points from ten minutes before to forty-five minutes after onset. Heart rate, root mean square of successive differences and low-to-high frequency ratio were derived. Reactivity was summarised by area under the curve with respect to increase, and analysed by repeated-measures analysis of variance. Results: All measures changed significantly over time. Autonomic measures peaked during the stressor whereas cortisol peaked twenty minutes after it, and autonomic effect sizes exceeded endocrine ones. Autonomic indices correlated strongly with one another, yet cortisol reactivity was only weakly related to autonomic reactivity. Cortisol responders and non-responders showed near-identical autonomic responses. Conclusion: Endocrine and autonomic stress reactivity are temporally and quantitatively dissociated, and neither substitutes for the other.

Keywords: Acute psychological stress, Salivary cortisol, Hypothalamic-pituitary-adrenal axis, Heart rate variability, Autonomic nervous system, Area under the curve, Stress reactivity