Exercise intensity and its impact on relationships between salivary immunoglobulin A, saliva flow rate and plasma cortisol concentration

Introduction Salivary secretory immunoglobulin A (sIgA), saliva flow rate and plasma cortisol concentrations have been shown to be influenced by exercise, particularly the intensity exercise is performed at, and circadian variation. The autonomic nervous system partly regulates salivary secretion, but it is not yet known whether cortisol also explains some variation in salivary parameters. Methods Twelve moderately trained male individuals (V̇ O2peak legs: 46.2±6.8 mL·kg−1·min−1) performed three 45-min constant load exercise trials in the morning: arm cranking exercise at 60%V̇ O2peak arms; moderate cycling at 60%V̇ O2peak legs; and easy cycling at 60%V̇ O2peak arms. Timed saliva samples and blood samples for plasma cortisol concentration determination were obtained before, post, 2 h post, and 4 h post-exercise. Saliva was collected in an additional resting trial at the same time points. Results At each time point for each exercise trial, negative correlations between cortisol and saliva flow rate (explaining 25±17% of the variance, R2=0.002–0.46) and positive correlations between cortisol and sIgA concentration (explaining 8±8% of the variance R2=0.002–0.24) were found. Saliva flow rate increased over time, whereas sIgA concentration and cortisol decreased over time for all trials (P<0.05), there was no effect of time for sIgA secretion rate (P=0.16). Conclusion These results show a relationship between cortisol and saliva flow rate, which directly impacts on the concentration of salivary analytes. This study further confirms circadian variations in salivary parameters which must be acknowledged when standardising salivary data collection.