Acute stress responses in salivary alpha-amylase predict increases of plasma norepinephrine

Current biobehavioral research increasingly employs salivary alpha-amylase (sAA) as a surrogate marker for sympathetic nervous system (SNS) activity. While different lines of evidence point to the validity of this assumption, the literature is inconsistent with regard to associations of sAA with well-established SNS indicators, such as plasma norepinephrine (NE) or epinephrine (E). Small samples as well as application of different stress paradigms might be responsible. This study therefore set out to examine the relation between stress-induced sAA activity with NE and E by exposing a larger and less constrained sample to an effective stress protocol. Sixty-six healthy participants (mean age 24.30±4.24 yrs), including n=40 women, n=26 men, n=18 oral contraceptive (OC) users, and n=15 habitual smokers, were recruited and subjected to the Trier Social Stress Test (TSST). Saliva and blood samples were taken at four time points throughout the experiment for later analysis of sAA activity and NE/E concentration, respectively. As expected, sAA, NE, and E showed significant increases in response to the acute stress induction (all p<0.001). Regression analyses (controlling for age, BMI, sex, smoking and OC) revealed that stress responses in sAA significantly predicted stress responses in NE (r=0.326; p=0.025). Interestingly, stress responses in E predicted NE to a lesser extend (β=0.265; p=0.064). E responses showed no association with sAA (β=0.265; p=0.064). Higher sAA levels were found in habitual smokers (F=4.27; p=0.043) and in individuals with lower BMI (F=2.81; p=0.099). In conclusion, current data clearly show an association between stress responses of sAA and plasma NE. This relationship is stronger than the association of norepinephrine and epinephrine responses, thus placing the predictive power of sAA well within the expected range for different SNS markers.