Effect of prolonged, submaximal exercise and carbohydrate ingestion on monocyte intracellular cytokine production in humans

1. The present study was undertaken to examine the effect of exercise and carbohydrate (CHO) ingestion on intracellular monocyte cytokine production. Subjects performed 2 h of cycling at 70% peak pulmonary O-2 uptake ((V) over dot (O2,peak)) while ingesting either an 8% CHO beverage or a sweet placebo. Whole blood was incubated with (stimulated) or without (spontaneous) lipopolysaccharide (LPS) and surface stained for monocyte surface antigens. The cells were permeabilised, stained for intracellular cytokines and analysed using flow cytometry. 2. Exercise had no effect on the number of monocytes spontaneously producing cytokines, but the number of stimulated IL-1 alpha-, TNF-alpha- and IL-6-positive monocytes were elevated (P < 0.01) immediately post-exercise and 2 h post-exercise. These stimulated cells produced less (P < 0.05) TNF-alpha immediately post-exercise, and less (P < 0.05) TNF- and IL-1 alpha 2 h post-exercise. There was a small, but significant increase (P < 0.05) in the plasma IL-6 concentration immediately post-exercise. 3. Exercise resulted in an elevation (P < 0.01) in the plasma adrenaline concentration in the placebo trial, and ingestion of CHO attenuated this increase. CHO ingestion had no effect on monocyte cytokine production, plasma IL-B or circulating leukocyte numbers. 4. These data suggest that circulating monocytes are not the origin of increased levels of plasma IL-6 during exercise: prolonged cycling exercise increased the number of monocytes producing cytokines upon stimulation, but these cells produced less cytokines post-exercise. In addition, attenuation of plasma adrenaline levels had no effect on plasma IL-6 or monocyte cytokine production.