Direct Potentiometric Method for Human Stress Determination

Stress was firstly defined in 19351, as a reaction of humans to external stimuli. In the modern way of life and every day actions, the term stress is very common and has a significant influence on human reactions, health, work ability and mood. There is also a direct connection between stress and depression in humans2. Apart from adults, recent studies show that preschool children are also under stress, and some helping support strategies could reduce it3. Thus, it appears that quantification of stress is a challenging issue, not only in humans, but also in animals4. Stress response is inducing the sympathetic nervous system and hypothalamic-pituitary-adrenal system, where hormone regulation is included (norepinephrine and cortisol). Invasive techniques measure hormone levels in the blood as an indicator of stress, but these levels are very low and hard to measure, and response time is too long and delayed by 20–30 minutes in response to loading stress. The use of salivary biomarkers has gained increased popularity over the past decade in psychological and biomedical research. While the measurement of free cortisol in saliva has proven to be in correlation with stress5, salivary amylase activity has appeared as a new highlight in stress measurement6. When secretion of the salivary amylase is stimulated by direct innervations, its response is very quick, generally within one to a few minutes, a markedly quicker response than that induced by hormonal regulation7,8. Salivary glands amplify the low levels of norepinephrine and give a faster and more sensitive response to the psychological stress than cortisol. To date, there are no international standard measurement methods for human salivary amylase activity. Salivary amylase has a high activity, ranging from several thousands to hundred thousand units per litre9. According to literature, in human and animal science, amylase activity rises remarkably under autonomic system activation10, such as response to a) physical stressors like exercise11,12, exposure to a high-pressure chamber13, running14, bicycle exercise15, sky diving or cold exposure16; and b) psychological stress7 or relaxation interventions17. While it seems clear that alpha-amylase levels rise following physical stress, the response to psychological stressors appears to be more inconsistent. This might be due to the psychological nature of the stressors employed or other methodological details5. Furthermore, concerning medical aspects, salivary amylase activity has also been employed as a marker for schizophrenia, since several researches indicate that the autonomic nervous system dysfunctions in patients with schizophrenia18; in patients with chronic relapsing pancreatitis, the activity of the salivary amylase was significantly lowered19 and recently, there have been attempts to suggest salivary amyDirect Potentiometric Method for Human Stress Determination