Salivary alpha-amylase: a potential surrogate marker for sympathetic activity
GM Russell & SL Lightman
Stress responsiveness is mediated through sympathetic and hypothalamic-pituitary-adrenal axis activation. The gold standard investigation is the plasma catecholamine and cortisol response to the insulin tolerance test (ITT). This is invasive, and the use of salivary surrogates for stress responses would be a great advance.
Demonstrate whether salivary alpha-amylase is a potential surrogate marker for sympathetic activity in response to ITT.
Local ethics committee approval was obtained. Fourteen healthy male volunteers underwent a double-blinded randomised controlled trial receiving either placebo or ITT. Intravenous soluble actrapid insulin (0.15 units/kg) or similar volume of normal saline was given. Venous blood samples were taken every 15 minutes for plasma glucose and catecholamines and every 30 minutes for cortisol. Saliva was collected using Salivettes every 30 minutes for salivary cortisol and 15 minutes for salivary alpha-amylase.
Adequate hypoglycaemia was achieved by all subjects on the ITT arm. Statistically significant rises in stress hormones were seen for ITT in comparison to placebo (% rise Vs Control: serum cortisol=58% v −13%; salivary cortisol=448% v −37%, adrenaline=2606% v 10%, noradrenaline=84% v −2%, salivary alpha amylase=290% v 19%). The log percentage peak rise for salivary alpha amylase was correlated with noradrenaline only (r=0.76, P=0.002). Log-transformed serum and salivary cortisol percentage peak rises were significantly correlated (r=0.68, P=0.008).
Salivary alpha-amylase is significantly correlated with noradrenaline only. If future studies confirm a causal relationship, salivary alpha-amylase may be a useful surrogate marker of noradrenergic activity. Serum and salivary cortisol was also significantly correlated. Salivary samples may potentially allow easy, stress free, non-invasive measures of both autonomic and HPA stress responses.