Search Results

This study investigated the effect of a high and low dose of caffeine on antigen-stimulated natural killer (NK) cell (CD3⁻CD56⁺) activation after prolonged, strenuous cycling, as assessed by the early-activation molecule CD69. In a randomized crossover design, 12 healthy male endurance-trained cyclists cycled for 90 min at 70% VO_2peak 60 min after ingesting either 0 (PLA), 2 (2CAF), or 6 (6CAF) mg/kg body mass of caffeine. Whole blood was stimulated with Pediacel (5 in 1) vaccine. A high dose of caffeine (6CAF) increased the number of CD3⁻CD56⁺ cells in the circulation immediately postexercise compared with PLA (p < .05). For both 2CAF and 6CAF, the geometric mean fluorescence intensity (GMFI) of CD69⁺ expression on unstimulated CD3⁻CD56⁺ cells was significantly higher than with PLA (both p < .05). When cells were stimulated with antigen, the GMFI of CD69 expression remained significantly higher with 2CAF than with PLA 1 hr postexercise (p < .05). Although not achieving statistical significance, 6CAF also followed a similar trend when stimulated (p = .09). There were no differences in GMFI of CD69 expression between 2CAF and 6CAF. These results suggest that a high (6 mg/kg) dose of caffeine was associated with the recruitment of NK cells into the circulation and that both a high and low (2 mg/kg) dose of caffeine increased unstimulated and antigen-stimulated NK-cell activation 1 hr after high-intensity exercise. Furthermore, there does not appear to be a dose-dependent effect of caffeine on NK-cell activation 1 hr after prolonged intensive cycling.

This study investigated the effect of caffeine ingestion on neutrophil oxidative burst responses to prolonged cycling. In a two part study, 19 endurance trained male cyclists (Part A – 11; Part B – 8) performed 90 min of exercise at 70% VO_2max 1 h after ingesting 6 mg/kg body mass of caffeine (CAF) or placebo (PLA). CAF ingestion had no effect on the PMA-stimulated oxidative burst response (Part A), yet it attenuated the exercise-induced decline in f-MLP stimulated response that occurred with PLA (Part B). CAF ingestion significantly increased serum caffeine concentration and plasma adrenaline concentration following exercise. In addition, circulating lymphocyte count was increased following CAF ingestion whereas there was no effect on neutrophil number. Therefore, although CAF ingestion was associated with an increase in adrenaline, this was not associated with an expected decrease in neutrophil function. This suggests that in the present study, CAF ingestion influenced neutrophil function via alternative mechanisms.

The purpose of this study was to examine the effects of a probiotic supplement during 4 mo of spring training in men and women engaged in endurance-based physical activities on incidence of upper respiratory tract infections (URTI) and mucosal immune markers. Sixty-six highly active individuals were randomized to probiotic (n = 33) or placebo (n = 33) groups and, under double-blind procedures, received probiotic (PRO: Lactobacillus salivarius, 2 × 10₁₀ bacterium colony-forming units) or placebo (PLA) daily for 16 wk. Resting blood and saliva samples were collected at baseline and after 8 and 16 wk. Weekly training and illness logs were kept. Fifty-four subjects completed the study (n = 27 PRO, n = 27 PLA). The proportion of subjects on PRO who experienced 1 or more wk with URTI symptoms was not different from that of those on PLA (PRO .58, PLA .59; p = .947). The number of URTI episodes was similar in the 2 groups (PRO 1.6 ± 0.3, PLA 1.4 ± 0.3; p = .710). Severity and duration of symptoms were not significantly different between treatments. Blood leukocyte, neutrophil, monocyte, and lymphocyte counts; saliva IgA; and lysozyme concentrations did not change over the course of the study and were not different on PRO compared with PLA. Regular ingestion of L. salivarius does not appear to be beneficial in reducing the frequency of URTI in an athletic cohort and does not affect blood leukocyte counts or levels of salivary antimicrobial proteins during a spring period of training and competition.

Recent studies have shown that neutrophils can utilize glutamine and that glutamine supplementation can improve neutrophil function in postoperative and burn patients. The present study investigated the influence of oral glutamine supplementation on stimulated neutrophil degranulation and oxidative burst activity following prolonged exercise. Subjects, 7 well-trained men, reported to the laboratory following an overnight fast and cycled for 2 hrs at 60% ${\text{VO}}_{\mathrm{2max}}$ on two occasions a week apart. They were randomly assigned to either a glutamine or placebo treatment. For both trials, subjects consumed a sugar-free lemon drink at 15-min intervals until 90 minutes, then a lemon flavored glutamine drink (GLN) or sugar-free lemon drink (PLA) was consumed at 15-min intervals for the remaining exercise and the 2-hr recovery period. Venous blood samples were taken pre-, during, and postexercise. Glutamine supplementation had no effect on the magnitude of postexercise leukocytosis, the plasma elastase concentration following exercise (which increased in both trials), or the plasma elastase release in response to bacterial stimulation (which fell in both trials). Neutrophil function assessed by oxidative burst activity of isolated cells did not change following exercise in either trial. These findings therefore suggest that the fall in plasma glutamine concentration does not account for the decrease in neutrophil function (degranulation response) following prolonged exercise.

We examined the effects of a low-carbohydrate (CHO) diet on the plasma glutamine and circulating leukocyte responses to prolonged strenuous exercise. Twelve untrained male subjects cycled for 60 min at 70% of maximal oxygen uptake on two separate occasions, 3 days apart. All subjects performed the first exercise task after a normal diet: they completed the second exercise task after 3 days on either a high-CHO diet (75±8% CHO, n = 6) or a low-CHO diet (7±4% CHO, n = 6). The low-CHO diet was associated with a larger rise in plasma cortisol during exercise, a greater fall in the plasma glutamine concentration during recovery, and a larger neutrophilia during the postexercise period. Exercise on the high-CHO diet did not affect levels of plasma glutamine and circulating leukocytes. We conclude that CHO availability can influence the plasma glutamine andcirculaling leukocyte responses during recovery from intense prolonged exercise.

Ingesting carbohydrate (CHO) beverages during heavy exercise is associated with smaller shifts in numbers of circulating neutrophils and attenuated changes in neutrophil functional responses. The influence of dietary CHO availability on these responses has not been determined. Therefore, the present study investigated the influence of pre-exercise CHO status on circulating neutrophil and lipopolysaccharide (LPS)-stimulated neutrophil degranulation responses to prolonged cycling. Twelve trained male cyclists performed a glycogen-lowering bout of cycling and were randomly assigned to follow a diet ensuring either greater than 70% (HIGH) or less than 10% (LOW) of daily energy intake from CHO for the next 3 days. On day 4, subjects performed an exercise test that comprised cycling for 1 hour at 60% W_max immediately followed by a time-trial (TT) ensuring an energy expenditure equivalent to cycling for 30 min at 80% W_max. Subjects repeated the protocol after 7 days, this time following the second diet. The order of the trials was counterbalanced. At TT completion, the HIGH compared with the LOW trial was associated with higher plasma glucose concentration, lower plasma cortisol concentration, and lower circulating neutrophil count. LPS-stimulated neutrophil degranulation per cell fell similarly on both trials. These findings suggest that pre-exercise CHO status influences neutrophil trafficking but not function in response to prolonged cycling.

Ingesting carbohydrate (CHO) beverages during heavy exercise is associated with smaller changes in the plasma concentrations of several cytokines. The influence of dietary CHO availability on these responses has not been determined. Therefore, the present study investigated the influence of pre-exercise CHO status on plasma interleukin (IL)-6, IL-10, and IL-1 receptor antagonist (IL-1ra) responses to prolonged cycling. Seven trained male cyclists performed a glycogen-lowering bout of cycling and were randomly assigned to follow a diet ensuring either greater than 70% (HIGH) or less than 10% (LOW) of daily energy intake from CHO for the next 3 days. On day 4 subjects performed an exercise test that comprised cycling for 1 hour at 60% W_max immediately followed by a time-trial (TT) ensuring an energy expenditure equivalent to cycling for 30 min at 80% W_max. Subjects repeated the protocol after 7 days, this time following the second diet. The order of the trials was counterbalanced. At 1 and 2 hours post-TT, plasma concentrations of IL-6 and IL-10 were 2-fold greater on the LOW trial than on the HIGH trial, and peak plasma concentrations of TL-1ra were 9-fold greater on the LOW trial than on the HIGH trial. These findings suggest that pre-exercise CHO status can influence the plasma cytokine response to prolonged cycling.