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Stress and the Role of Alpha-Amylase

Publié le 1 février, 2008 | Pas de commentaires
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Stress contributes to the development of various physical and psychological illnesses. While the effects of cortisol on stress have been thoroughly studied, the role of the enzyme alpha-amylase has only recently been investigated. The latest research suggests that alpha-amylase is linked to our emotions and our health.

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Stress is on everyone’s mind. While a certain level of stress is healthy and perhaps necessary, high levels of persistent and intense stress can lead to a host of negative outcomes affecting behavioral, social, health, and psychological functioning1. Many consider stress to be a disease that can make us mentally and physically sick. Moreover, it is estimated that the economic toll of stress costs the American government more than $200 billion dollars annually in terms of lost productivity and health costs2. In order to combat stress-related symptoms and diseases, it is important to understand the systems involved in the stress response and to be informed about relevant techniques measuring their activation.

One of the most widely accepted definitions of stress is given by Richard Lazarus, a professor at the University of California, and his former student, Susan Folkman3. They consider stress to be a dynamic relationship between an individual and his or her environment perceived by the person as demanding or exceeding his or her resources. The body then reacts to the stressor by exhibiting a stress response. A stressor can be physical in nature (such as getting into a car accident) or something more psychological, like realizing one’s financial trouble. When an individual experiences a stressor, two primary bodily systems are activated: the autonomic nervous system (ANS) and the hypothalamic pituitary adrenal system (HPA axis). When an individual experiences stress, the brain triggers the secretion of a cascade of stress hormones regulated by the HPA axis4-5. One of those hormones is cortisol. Atypical cortisol concentrations and patterns have been linked to various outcomes including high levels of aggression, impaired memory and the degradation of the immune system1.

The other influential system involved in the stress response is the ANS, which has been largely neglected by stress research4-5. Activation of the ANS occurs almost immediately following the experience of a stressor to help prepare the body to cope with the situation. The ANS is comprised of two systems with opposing roles: the sympathetic nervous system (SNS) and the parasympathetic nervous system (PNS). When an organism is aroused or stressed, the SNS is activated and the hormones adrenaline and noradrenaline are released. These hormones prepare the body to deal with the challenge by eliciting bodily reactions such as: dilating the pupils, accelerating the heartbeat and inhibiting digestion. Once the stressful situation is over, the PNS is activated and returns the systems of the body back to normal4-5.

Adrenaline and noradrenaline are the hormones released when the SNS is activated and, as such, are a direct reflection of SNS activity. They prepare the body to engage with or flee from the stressor, and for that reason, have been of interest to researchers for several years. However, they can only be sampled through blood and urine. Fortunately, research has found a non-invasive, more convenient way to measure the activity of the SNS by sampling alpha-amylase, an enzyme found in saliva that has been thoroughly studied in oral biology. Its primary function is the digestion of carbohydrates and starches, although it has also been identified as the first line of immune defense because it helps clear bacteria from the mouth6. While alpha-amylase is not a direct byproduct of the SNS, several well-conducted studies have linked the two7. For example, alpha-amylase concentrations have been shown to rise during physical and psychological stress, whereas blocking noradrenaline and adrenaline receptors in the brain inhibits increases in alpha-amylase. Additionally, baseline levels and stress-related increases of alpha-amylase are correlated with noradrenaline levels. Even though these studies do not necessarily allow causal interpretations regarding the relationship between alpha-amylase and level of stress, alpha-amylase is considered to be a reliable non-invasive marker of SNS activation.

Similarities and differences in stress markers

A certain level of stress is necessary in order to accomplish various life-sustaining tasks and, therefore, a certain level of cortisol and alpha-amylase must be present in the body at all times. This baseline level varies according to the time of day. Cortisol peaks just after awakening (to prepare the body to get ready for the day), and gradually declines throughout the day, whereas alpha-amylase appears to do the reverse8. The pattern displayed by alpha-amylase is similar to other markers of the SNS (such as heart rate), demonstrating its lowest levels in the morning and gradually increasing throughout the course of the day.

Cortisol and alpha-amylase can also be measured in a reactive manner. Stress researchers can expose individuals to a potentially stressful situation and measure their reactions to it. Although both cortisol and alpha-amylase concentrations typically peak in response to stress, they do so at different points in time9. Whereas cortisol typically peaks approximately 10 minutes after being exposed to the stressor and then gradually returns to baseline, alpha-amylase has a near immediate increase in response to a stressor, and returns to baseline approximately 10 minutes after exposure. This pattern of response is consistent with the faster reactivity of the SNS compared to the HPA axis. While reactivity of alpha-amylase is not reliably found in humans until approximately adolescence, baseline levels can provide valuable information concerning other aspects of functioning, including sociability and cognitive development, early in life.

Alpha-amylase and associated measures

In addition to acting as a measure of the stress response, alpha-amylase has been linked to several other emotional, behavioral and health-related issues. Douglas Granger and his colleagues have conducted several studies examining alpha-amylase in children. In one study, preschoolers were asked to participate in a series of tasks designed to elicit a mild stress reaction, including a delay of gratification task and a disappointing experience. They found that while there was no reactivity of alpha-amylase in response to a stressor, children’s baseline levels of alpha-amylase were linked to child-teacher relationships: higher levels of alpha-amylase were related to more distant relationships10. Furthermore, alpha-amylase was associated with the functioning of the children’s immune system. Granger and colleagues conducted another study in which they had 8 and 9 year olds listen to an argument supposedly occurring in an adjacent room in an attempt to elicit a stress response. They found that girls who demonstrated higher post-stress alpha-amylase levels displayed more health and social problems, while boys revealed higher rates of aggression and heightened cognitive problems10. These findings are groundbreaking, but it must be noted that they are all correlational in nature. Regardless of the direction of association, the patterns observed are robust and the authors propose the findings suggest that social relationships and health are significant in the individual differences seen in levels of alpha-amylase.

Where do we go from here?

Stress has long been the object of study, but we are only beginning to understand its complexities. Through new techniques, researchers are now able to measure the response of the primary stress systems in a convenient, non-invasive manner, thus allowing research in this area to progress more rapidly. Stress research is important as the findings can be used to improve our quality of life. By gaining a thorough understanding of the systems governing stress response, we can develop intervention techniques designed to target over-activation of these systems, decrease stress, and improve health. The recent findings concerning alpha-amylase is a solid starting point for much needed future research.

References

1. Cicchetti, Dante and Donald Cohen. “Perspectives on Developmental Psychopathology”. Theory and Methods. Eds. Dante Cicchetti and Donald Cohen. New York: Wiley, 1995. 3-20.
2. McEwen, Bruce and Elizabeth Norton Lasley. The End of Stress as We Know It. Washington, D.C.: Joseph Henry Press, 2002.
3. Lazarus, Richard S. and Susan Folkman. Stress, Appraisal, and Coping. New York: Springer, 1984.
4. Sapolsky, Robert M. “Neuroendocrinology of the Stress Response”. Behavioral Endocrinology. Eds. M. Becker and D. Crews. Cambridge, MA: The MIT Press, 1992. 287-324.
5. Sapolsky, Robert M. “Neurochemistry: Taming Stress”. Scientific American 289 (2003): 88-98.
6. Marcotte, Harold and Marc C. Lavoie. “Oral Microbial Ecology and the Role of Salivary Immunoglobulin.” Microbiology and Molecular Biology Reviews 62 (1998): 71-109.
7. Chatterton, Robert T., Kirsten M. Vogelsong, Yu-cai Lu, A.B. Ellman, Gerald A. Hudgens “Salivary Alpha-Amylase as a Measure of Endogenous Adrenergic Activity.” Clinical Physiology 16 (1996): 433-448.
8. Nater, Urs, M., Nicolas Rohleder, Wolff Schlotz, Ulrike Ehlert, and Clemens Kirschbaum. “Determinants of the Diurnal Course of Salivary Alpha-Amylase.” Psychoneuroendocrinology 32 (2007): 392-401.
9. Gordis, Elana, B., Douglas A. Granger, Elizabeth J. Susman, and Penelope K. Trickett. “Asymmetry Between Salivary Cortisol and Alpha-Amylase Reactivity to stress: Relation to Aggressive Behavior in Adolescents.” Psychoneuroendocrinology 31 (2006): 976-987.
10. Granger, Douglas A., Katie T. Kivlighan, Blair Clancy, Mona El-Sheikh, Jacquelyn Mize, Jared A. Lisonbee, Joseph A. Buckhalt, Laura R. Stroud, Kathryn Handwerger and Eve B. Schwartz. “Integrating the Measurement of Salivary Alpha-Amylase Into Studies of Child Health, Development, and Social Relationships.” Journal of Social and Personal Relationships 23.2 (2006): 267-290.

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