Invited viewpoint
α-Amylase as a reliable and convenient measure of sympathetic activity: don’t start salivating just yet!

https://doi.org/10.1016/j.psyneuen.2010.12.019Get rights and content

Summary

Recent years have seen a growing interest in salivary α-amylase (sAA) as a non-invasive marker for sympathetic nervous system (SNS) activity. Saliva offers many advantages as a biomarker fluid and sAA is one of its most plentiful components. sAA is a digestive enzyme that breaks down starch, which provides a simple means of quantification by measuring its enzymatic activity. This commentary will address a number of common misconceptions and methodological issues that surround the use of sAA as a marker of SNS activity and limit its utility in biobehavioral research.

The usefulness of sAA as an SNS marker is undermined by the fact that the parasympathetic nerves also play a significant role in sAA release. Local parasympathetic nerves regulate sAA activity via: (1) α-amylase release from glands that are solely or mainly parasympathetically innervated; (2) via synergistic sympathetic–parasympathetic effects on protein secretion (known as ‘augmented secretion’); and (3) via effects on salivary flow rate. Regarding methodology, we discuss why it is problematic: (1) to ignore the contribution of salivary flow rate; (2) to use absorbent materials for saliva collection, and; (3) to stimulate saliva secretion by chewing. While these methodological problems can be addressed by using standardized and timed collection of unstimulated saliva, the physiological regulation of sAA secretion presents less resolvable issues. We conclude that at present there is insufficient support for the use and interpretation of sAA activity as a valid and reliable measure of SNS activity.

Section snippets

Is sAA activity determined by sympathetic activity?

Most psychophysiologists are aware that measuring sympathetic activity is a knotty issue: activation of the SNS does not occur in the generalized manner that is sometimes assumed and the various measures of SNS activation do not correlate well (Grassi and Esler, 1999, Folkow, 2000). The latter also applies to sAA: stress studies show that changes in sAA activity do not, or only modestly, correlate with changes in other SNS markers, such as cardiac pre-ejection period, skin conductance, and

Not all salivary glands respond the same

Most sAA literature refers to “saliva” without acknowledgement that this fluid is a complex mixture derived from many different glands and different cell types within glands. In short, saliva is produced by three pairs of major glands; the parotid glands, the submandibular glands and the sublingual glands. In addition there are numerous minor glands in the submucosa underlying the lip, cheeks and palate with a substantial contribution to salivary protein content (Humphrey and Williamson, 2001).

Ignoring the contribution of salivary flow rate

Probably one of the major causes of confusion in sAA research is that researchers do not consider secretion rate. Indeed, of the sAA studies published in Psychoneuroendocrinology only one attempted to quantify the possible confounding effects of flow rate. This omission is most likely inherited from cortisol research, in which, due to the nature of this analyte, flow rate does not play a significant role. In contrast to cortisol, sAA is synthesized in the acinar cells (i.e., the main secretory

Conclusion

While biopsychology boasts a strong tradition of endocrine, immune, and cardiovascular research, scholars of this field rarely had training in oral biology. It is likely that with such training many would have made different choices with regard to methods and the interpretation of sAA data. Currently most researchers adhere to a methodology that was validated for cortisol research. For example, among the sAA studies published in Psychoneuroendocrinology to date, virtually none controlled for

Role of the funding sources

The authors received no funding in support of this work.

Conflict of interest

The authors have no conflicts of interests to declare.

Acknowledgements

We are grateful to Prof. Robert Dantzer for his invitation to submit this commentary, and thank Dr. Rose-Marie Bluthé for her editorial support.

References (29)

  • L. Strazdins et al.

    Impact of saliva collection methods on sIgA and cortisol assays and acceptability to participants

    J. Immunol. Methods

    (2005)
  • B. Asking

    Sympathetic stimulation of amylase secretion during a parasympathetic background activity in the rat parotid gland

    Acta Physiol. Scand.

    (1985)
  • G.G. Berntson et al.

    Cardiac autonomic balance versus cardiac regulatory capacity

    Psychophysiology

    (2008)
  • J.A. Bosch et al.

    Psychological stress as a determinant of protein levels and salivary-induced aggregation of Streptococcus gordonii in human whole saliva

    Psychosom. Med.

    (1996)
  • Cited by (0)

    View full text