Heat stress, cytokines, and the immune response to exercise

To examine the effect of exercise and heat stress on cytokine production, seven males (77 +/- 2 kg; VO(2peak) = 4.7 +/- 0.4 L min(-1)) completed two (15 degrees C; CON or 35 degrees C; HEAT) 90 min cycling trials at 70% VO(2peak). Blood samples were collected throughout and analysed for spontaneous, and LPS-stimulated intracellular monocyte cytokine production, plasma cytokine levels, and circulating stress hormone concentration. Plasma epinephrine, norepinephrine, and cortisol concentration were elevated (P < .05) as a result of exercise in CON. HEAT increased (P < .05) epinephrine and norepinephrine levels, however, cortisol concentration was not different between the two trials. Exercise had no effect on the concentration of circulating monocytes spontaneously producing IL-6, TNF-alpha or IL-1alpha, however, there was a decrease in the amount of TNF-alpha per cell post-compared with pre-exercise. HEAT had no effect on spontaneous intracellular cytokine production. Circulating levels of both IL-6 and TNF-alpha were elevated in HEAT, but not in CON. Upon stimulation with LPS, the concentration of monocytes positive for IL-6, TNF-alpha, and IL-1alpha production was elevated (P < .01) post- and 2 h post-compared with pre-exercise. Stimulated cells, however, produced less (P < .05) TNF-alpha post-exercise and less (P < .05) TNF-alpha and IL-6 2 h post-exercise. HEAT resulted in an increase (P < .05) in the concentration of stimulated cells positive for TNF-alpha and IL-1alpha, however, did not affect the amount of cytokine produced by stimulated monocytes. These results demonstrate that exercise decreases the amount of cytokine produced by LPS-stimulated monocytes, possibly due to elevated levels of circulating stress hormones. Heat stress did not, however, augment the suppression in the amount of cytokine produced by circulating monocytes upon stimulation, despite elevated catecholamines.

Effect of adrenergic blockade on lymphocyte cytokine production at rest and during exercise

To examine the effect of exercise and adrenergic blockade on lymphocyte cytokine production, six men ingested either a placebo (control) or an alpha- (prazosin hydrochloride) and beta-adrenoceptor antagonist (timolol malate) capsule (blockade, or BLK) 2 h before performing 19 +/- 1 min of supine bicycle exercise at 78 +/- 3% peak pulmonary uptake. Blood was collected before and after exercise, stimulated with phorbol 12-myristate 13-acetate and ionomycin, and surface stained for T (CD3(+)) and natural killer [NK (CD3(-)CD56(+))] lymphocyte surface antigens. Cells were permeabilized, stained for the intracellular cytokines interleukin (IL)-2 and interferon (IFN)-gamma, and analyzed using flow cytometry. BLK had no effect on the resting concentration of stimulated cytokine-positive T and NK lymphocytes or the amount of cytokine they were producing. Exercise resulted in an increase (P < 0.05) in the concentration of stimulated T and NK lymphocytes producing cytokines in the circulation, but these cells produced less (P < 0.05) cytokine post- compared with preexercise. BLK attenuated (P < 0.05) the elevation in the concentration of lymphocytes producing cytokines during exercise; however, BLK did not affect the amount of IL-2 and IFN-gamma produced. These results suggest that adrenergic stimulation contributes to the exercise-induced increase in the concentration of lymphocytes in the circulation; however, it does not appear to be responsible for the exercise-induced suppression in cytokine production.

Carbohydrate ingestion attenuates the increase in plasma interleukin-6, but not skeletal muscle interleukin-6 mRNA, during exercise in humans

1. The present study was undertaken to examine the effects of exercise and carbohydrate (CHO) ingestion on interleukin-6 (IL-6) gene expression in skeletal muscle and plasma IL-6 concentration. 2. Seven moderately trained men completed 60 min of exercise at a workload corresponding to each individual's lactate threshold on four randomised occasions. Two trials were conducted on a bicycle ergometer (Cyc) and two on a running treadmill (Run) either with (CHO) or without (Con) the ingestion of a CHO beverage throughout the exercise. Muscle biopsies were obtained from the vastus lateralis before and immediately after exercise and IL-6 gene expression in these samples was determined using real-time PCR. In addition, venous blood samples were collected at rest, and after 30 min during and at the cessation of exercise. These samples were analysed for plasma IL-6. 3. Irrespective of exercise mode or CHO ingestion, exercise resulted in a 21 +/- 4-fold increase (P < 0.01; main exercise effect) in IL-6 mRNA expression. In contrast, while the mode of exercise did not affect the exercise-induced increase in plasma IL-6, CHO ingestion blunted (P < 0.01) this response. 4. These data demonstrate that CHO ingestion attenuates the plasma IL-6 concentration during both cycling and running exercise. However, because IL-6 mRNA expression was unaffected by CHO ingestion, it is likely that the ingestion of CHO during exercise attenuates IL-6 production by tissues other than skeletal muscle.

Circulating monocytes are not the source of elevations in plasma IL-6 and TNF-alpha levels after prolonged running

The present study was undertaken to examine the effect of prolonged running on monocyte intracellular cytokine production and plasma cytokine concentration. Blood samples were collected 1 h before, immediately after, 2 h after, and 24 h after a competitive marathon run. There was no change in the number of cells spontaneously producing tumor necrosis factor (TNF)-alpha; however, there was a decrease in the number of cells producing interleukin (IL)-1alpha and IL-6 (P < 0.01) postexercise. In contrast, there was an increase in the number of monocytes that responded to lipopolysaccharide stimulation by producing IL-1alpha, TNF-alpha, and IL-6 (P < 0.01) immediately and 2 h postexercise; however, these cells contained less cytokine (P < 0.05). Plasma IL-6, TNF-alpha, epinephrine, norepinephrine, and cortisol concentrations were markedly increased (P < 0.01) postexercise. These data demonstrate that circulating monocytes are not the source of elevated levels of plasma IL-6 and TNF-alpha after prolonged running. In addition, it is likely that stress hormones result in a decrease in the amount of cytokine produced by LPS-stimulated cells postexercise.

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

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 O2 uptake (VO2,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. Exercise had no effect on the number of monocytes spontaneously producing cytokines, but the number of stimulated IL-1alpha-, 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-alpha and IL-1alpha 2 h post-exercise. There was a small, but significant increase (P < 0.05) in the plasma IL-6 concentration immediately post-exercise. 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-6 or circulating leukocyte numbers. 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.

Effect of temperature on muscle metabolism during submaximal exercise in humans

To study the effect of temperature on muscle metabolism during submaximal exercise, six endurance-trained men had one thigh warmed and the other cooled for 40 min prior to exercise using water-perfused cuffs. One cuff was perfused with water at 50-55 degrees C (HL) with the other being perfused with water at 0 degree C (CL). With the cuffs still in position, subjects performed cycling exercise for 20 min at a work load corresponding to 70% VO2,peak (where VO2,peak is peak pulmonary oxygen uptake) in comfortable ambient conditions (20-22 degrees C). Muscle biopsies were obtained prior to and following exercise and forearm venous blood was collected prior to and throughout the exercise period. Muscle temperature (Tmus) was not different prior to treatment, but treatment resulted in a large difference in pre-exercise Tmus (difference = 6.9 +/- 0.9 degrees C; P < 0.01). Although this difference was reduced following exercise; it was nonetheless significant (difference = 0.4 +/- 0.1 degree C; P < 0.05). Intramuscular [ATP] was not affected by either exercise or muscle temperature. [Phosphocreatine] decreased (P < 0.01) and [creatine] increased (P < 0.01) with exercise but were not different when comparing HL with CL. Muscle lactate concentration was not different prior to treatment nor following exercise when comparing HL with CL. Muscle glycogen concentration was not different when comparing the trials before treatment, but the post-exercise value was lower (P < 0.05) in HL compared with CL. Thus, net muscle glycogen use was greater during exercise with heating (208 +/- 23 vs. 118 +/- 22 mmol kg-1 for HL and CL, respectively; P < 0.05). These data demonstrate that muscle glycogen use is augmented by increases in intramuscular temperature despite no differences in high energy phosphagen metabolism being observed when comparing treatments. This suggests that the increase in carbohydrate utilization occurred as a direct effect of an elevated muscle temperature and was not secondary to allosteric activation of enzymes mediated by a reduced ATP content.

Effect of epinephrine on muscle glycogenolysis during exercise in trained men

To test the hypothesis that an elevation in circulating epinephrine increases intramuscular glycogen utilization, six endurance-trained men performed two 40-min cycling trials at 71 +/- 2% of peak oxygen uptake in 20-22 degrees C conditions. On the first occasion, subjects were infused with saline throughout exercise (Con). One week later, after determination of plasma epinephrine levels in Con, subjects performed the second trial (Epi) with an epinephrine infusion, which resulted in a twofold higher (P < 0.01) plasma epinephrine concentration in Epi compared with Con. Although oxygen uptake was not different when the two trials were compared, respiratory exchange ratio was higher throughout exercise in Epi compared with Con (0.93 +/- 0.01 vs. 0.89 +/- 0.01; P < 0.05). Muscle glycogen concentration was not different when the trials were compared preexercise, but the postexercise value was lower (P < 0.01) in Epi compared with Con. Thus net muscle glycogen utilization was greater during exercise with epinephrine infusion (224 +/- 37 vs. 303 +/- 30 mmol/kg for Con and Epi, respectively; P < 0.01). In addition, both muscle and plasma lactate and plasma glucose concentrations were higher (P < 0.05) in Epi compared with Con. These data indicate that intramuscular glycogen utilization, glycolysis, and carbohydrate oxidation are augmented by elevated epinephrine during submaximal exercise in trained men.