The relationship between interleukin-6 in saliva, venous and capillary plasma, at rest and in response to exercise.
IL-6 plays a mechanistic role in conditions such as metabolic syndrome, chronic fatigue syndrome and clinical depression and also plays a major role in inflammatory and immune responses to exercise. The purpose of this study was to investigate the levels of resting and post exercise IL-6 when measured in venous plasma, saliva and capillary plasma. Five male and five females completed 2 separate exercise trials, both of which involved standardized exercise sessions on a cycle ergometer. Venous blood and saliva samples were taken immediately before and after Trial A, venous and capillary blood samples were taken immediately before and after Trial B. IL-6 values were obtained using a high-sensitivity enzyme-linked immunosorbent assay (ELISA). In Trial A venous plasma IL-6 increased significantly from 0.4±0.14pg/ml to 0.99±0.29pg/ml (P<0.01) while there was no increase in salivary IL-6. Venous plasma and salivary IL-6 responses were not correlated at rest, post exercise or when expressed as an exercise induced change. In Trial B venous and capillary plasma IL-6 increased significantly (venous: 0.22±0.18 to 0.74±0.28pg/ml (P⩽0.01); capillary: 0.37±0.22 to 1.08±0.30pg/ml (P<0.01). Venous and capillary plasma responses did not correlate at rest (r=0.59, P=0.07) but did correlate post exercise (r=0.79, P⩾0.001) and when expressed as an exercise induced change (r=0.71, P=0.02). Saliva does not appear to reflect systemic IL-6 responses, either at rest or in response to exercise. Conversely, capillary plasma responses are reflective of systemic IL-6 responses to exercise.