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