Salivary alpha amylase not chromogranin A reflects sympathetic activity: exercise responses in elite male wheelchair athletes with or without cervical spinal cord injury

Background: Salivary alpha-amylase (sAA) and chromogranin A (sCgA) have both been suggested as non-invasive markers for sympathetic nervous system (SNS) activity. A complete cervical spinal cord injury leading to tetraplegia is accompanied with sympathetic dysfunction; the aim of this study was to establish the exercise response of these markers in this in vivo model. Methods: Twenty-six elite male wheelchair athletes (C6-C7 tetraplegia: N=8, T6-L1 paraplegia: N=10 and non spinal cord injured controls: N=8) performed treadmill exercise to exhaustion. Saliva and blood samples were taken pre, post, and 30 min post exercise and analysed for sAA, sCgA and plasma adrenaline concentration, respectively. Results: In all three subgroups, sAA and sCgA were elevated post exercise (P<0.05). Whilst sCgA was not different between subgroups, a group x time interaction for sAA explained the reduced post exercise sAA activity in tetraplegia (162±127 vs 313±99 (paraplegia) and 328±131 U∙mL-1 (controls), P=0.005). The post exercise increase in adrenaline was not apparent in tetraplegia (P=0.74). A significant correlation was found between adrenaline and sAA (r=0.60, P=0.01), but not between adrenaline and sCgA (r=0.06, P=0.79). Conclusions: The blunted post-exercise rise in sAA and adrenaline in tetraplegia implies that both reflect SNS activity to some degree. It is questionable whether sCgA should be used as a marker for SNS activity, both due to the exercise response which is not different between the subgroups and its non-significant relationship with adrenaline.