Sven Asp

Pro- and anti-inflammatory cytokine balance in strenuous exercise in humans

1 The present study investigates to what extent and by which time course prolonged strenuous exercise influences the plasma concentration of pro‐inflammatory and inflammation responsive cytokines as well as cytokine inhibitors and anti‐inflammatory cytokines. 2 Ten male subjects (median age 27.5 years, range 24–37) completed the Copenhagen Marathon 1997 (median running time 3:26 (h:min), range 2:40–4:20). Blood samples were obtained before, immediately after and then every 30 min in a 4 h post‐exercise recovery period. 3 The plasma concentrations of tumour necrosis factor (TNF)α, interleukin (IL)‐1β, IL‐6, IL‐1ra, sTNF‐r1, sTNF‐r2 and IL‐10 were measured by enzyme‐linked immunosorbent assay (ELISA). The highest concentration of IL‐6 was found immediately after the race, whereas IL‐1ra peaked 1 h post exercise (128‐fold and 39‐fold increase, respectively, as compared with the pre‐exercise values). The plasma level of IL‐1β, TNFα, sTNF‐r1 and sTNF‐r2 peaked in the first hour after the exercise (2.1‐, 2.3‐, 2.7‐ and 1.6‐fold, respectively). The plasma level of IL‐10 showed a 27‐fold increase immediately post exercise. 4 In conclusion, strenuous exercise induces an increase in the pro‐inflammatory cytokines TNFα and IL‐1β and a dramatic increase in the inflammation responsive cytokine IL‐6. This is balanced by the release of cytokine inhibitors (IL‐1ra, sTNF‐r1 and sTNF‐r2) and the anti‐inflammatory cytokine IL‐10. The study suggests that cytokine inhibitors and anti‐inflammatory cytokines restrict the magnitude and duration of the inflammatory response to exercise.

Evidence that interleukin‐6 is produced in human skeletal muscle during prolonged running

1 This study was performed to test the hypothesis that inflammatory cytokines are produced in skeletal muscle in response to prolonged intense exercise. Muscle biopsies and blood samples were collected from runners before, immediately after, and 2 h after a marathon race. 2 The concentration of interleukin (IL)‐6 protein in plasma increased from 1.5 ± 0.7 to 94.4 ± 12.6 pg ml−1 immediately post‐exercise and to 22.1 ± 3.8 pg ml−1 2 h post‐exercise. IL‐1 receptor antagonist (IL‐1ra) protein in plasma increased from 123 ± 23 to 2795 ± 551 pg ml−1, and increased further to 4119 ± 527 pg ml−1 2 h post‐exercise. 3 The comparative polymerase chain reaction technique was used to evaluate mRNA for IL‐6, IL‐1ra, IL‐1β and tumour necrosis factor (TNF)‐α in skeletal muscle and blood mononuclear cells (BMNC) (n= 8). Before exercise, mRNA for IL‐6 could not be detected either in muscle or in BMNC, and was only detectable in muscle biopsies (5 out of 8) after exercise. Increased amounts of mRNA for IL‐1ra were found in two muscle biopsies and five BMNC samples, and increased amounts of IL‐1β mRNA were found in one muscle and four BMNC samples after exercise. TNF‐α mRNA was not detected in any samples. 4 This study suggests that exercise‐induced destruction of muscle fibres in skeletal muscles may trigger local production of IL‐6, which stimulates the production of IL‐1ra from circulating BMNC.

Muscle contractions induce interleukin-6 mRNA production in rat skeletal muscles

1 The present study explored the hypothesis that interleukin‐6 (IL‐6) might be locally produced in response to skeletal muscle contractions and whether the production might reflect the type of muscle contraction performed. Rats were anaesthetized and the calf muscles of one limb were stimulated electrically for concentric or eccentric contractions (4 × 10 contractions with 1 min of rest between the 4 series, 100 Hz). The contralateral muscles served as unstimulated controls. The mRNA levels for IL‐6, the glucose transport protein GLUT‐4 and β‐actin in the rat muscles (white and red gastrocnemius and soleus) were quantified by quantitative competitive RT‐PCR. 2 The IL‐6 mRNA level, measured 30 min after the stimulation, increased after both eccentric and concentric contractions and there were no significant differences in IL‐6 mRNA levels between the different muscle fibre types. No significant increase in IL‐6 mRNA level was seen in the unstimulated contralateral muscle fibres. 3 No increase in GLUT‐4 mRNA level was detected, indicating that the increase in IL‐6 mRNA level was not due to general changes in transcription. 4 We conclude that IL‐6 is locally produced after muscle contraction, with no significant differences between different muscle fibre types. This local production of IL‐6 is not due to general changes in transcription, since no changes in the level of GLUT‐4 mRNA were found. The fact that increased IL‐6 mRNA levels were seen after both concentric and eccentric contractions indicates that the production of IL‐6 is not solely due to muscle damage, seen primarily after eccentric exercise.

Chemokines are elevated in plasma after strenuous exercise in humans

Abstract During the last few years much attention has been paid to the chemokines. Chemokine receptors are necessary to render a target permissive for infection by the human immunodeficiency virus (HIV) and high concentrations of chemokines have been shown to protect against the progression of HIV disease towards death. In the present study, we investigated the capability of strenuous exercise to induce elevated plasma concentrations of the chemokines interleukin (IL)-8, macrophage inflammatory protein (MIP)-1α and MIP-1β. Eight male athletes completed the Copenhagen Marathon 1997. Blood was sampled before, immediately after the run and every 30 min during a 4 h recovery period. Plasma chemokine concentrations were measured using enzyme-linked immunosorbent assays. The IL-8, MIP-1α and MIP-1β concentrations all peaked 0.5 h after the run when they were 6.7-fold, 3.5-fold and 4.1-fold increased, respectively. The elevated concentrations of chemokines in plasma after exercise could have implications for HIV-infected individuals; a possibility that needs further investigation.

Marathon running transiently increases c-Jun NH2-terminal kinase and p38γ activities in human skeletal muscle

1 We examined the pattern of activation and deactivation of the stress‐activated protein kinase signalling molecules c‐Jun NH2‐terminal kinase (JNK) and p38 kinase in skeletal muscle in response to prolonged strenuous running exercise in human subjects. 2 Male subjects (n= 14; age 32 ± 2 years; VO2,max 60 ± 2 ml kg−1 min−1) completed a 42.2 km marathon (mean race time 3 h 35 min). Muscle biopsies were obtained 10 days prior to the marathon, immediately following the race, and 1, 3 and 5 days after the race. The activation of JNK and p38, including both p38α and p38γ, was measured with immune complex assays. The phosphorylation state of p38 (α and γ) and the upstream regulators of JNK and p38, mitogen‐activated protein kinase kinase 4 (MKK4) and mitogen‐activated protein kinase kinase 6 (MKK6), were assessed using phosphospecific antibodies. 3 JNK activity increased 7‐fold over basal level immediately post‐exercise, but decreased back to basal levels 1, 3 and 5 days after the exercise. p38γ phosphorylation (4‐fold) and activity (1.5‐fold) increased immediately post‐exercise and returned to basal levels at 1, 3 and 5 days following exercise. In contrast, p38α phosphorylation and activity did not change over the time course studied. MKK4 and MKK6 phosphorylation increased and decreased in a trend similar to that observed with JNK activity and p38γ phosphorylation. Prolonged running exercise did not affect JNK, p38α, or p38γ protein expression in the days following the race. 4 This study demonstrates that both JNK and p38 intracellular signalling cascades are robustly, yet transiently increased following prolonged running exercise. The differential activation of the p38 isoforms with exercise in human skeletal muscle indicates that these proteins may have distinct functions in vivo.

Eccentric exercise decreases glucose transporter GLUT4 protein in human skeletal muscle.

1. Eccentric exercise causes impaired postexercise glycogen resynthesis. To study whether changes in muscle concentration of the glucose transporter (GLUT4) protein might be involved, seven healthy young men performed one‐legged eccentric exercise by resisting knee flexion enforced by a motor‐driven device. 2. The GLUT4 protein concentration in the exercised and in the control thigh was unchanged immediately after exercise. On days 1 and 2 after exercise, the GLUT4 protein concentration in the exercised muscle was 68 +/‐ 10 and 64 +/‐ 10% (means +/‐ S.E.M.; P < 0.05), respectively, of the concentration in the control muscle, and had returned to control values on days 4 and 7. 3. The muscle glycogen concentration decreased from 404 +/‐ 44 to 336 +/‐ 44 mmol (kg dry wt)‐1 (P < 0.05) during exercise. The glycogen concentration remained significantly lower than in the control thigh on days 1 and 2 after exercise but on days 4 and 7 no differences were found. 4. Although no cause‐effect relationship was established, these findings may suggest that decreased muscle concentrations of GLUT4 protein, and, hence, a decreased rate of glucose transport into muscle cells, may be involved in the sustained low glycogen concentration seen after eccentric exercise.

Eccentric exercise decreases maximal insulin action in humans: muscle and systemic effects.

1. Unaccustomed eccentric exercise decreases whole‐body insulin action in humans. To study the effects of one‐legged eccentric exercise on insulin action in muscle and systemically, the euglycaemic clamp technique combined with arterial and bilateral femoral venous catheterization was used. Seven subjects participated in two euglycaemic clamps, performed in random order. One clamp was preceded 2 days earlier by one‐legged eccentric exercise (post‐eccentric exercise clamp (PEC)) and one was without the prior exercise (control clamp (CC)). 2. During PEC the maximal insulin‐stimulated glucose uptake over the eccentric thigh was marginally lower when compared with the control thigh, (11.9%, 64.6 +/‐ 10.3 vs. 73.3 +/‐ 10.2 mumol kg‐1 min‐1, P = 0.08), whereas no inter‐thigh difference was observed at a submaximal insulin concentration. The glycogen concentration was lower in the eccentric thigh for all three clamp steps used (P < 0.05). The glucose transporter GLUT4 protein content was on average 39% lower (P < 0.05) in the eccentric thigh in the basal state, whereas the maximal activity of glycogen synthase was identical in the two thighs for all clamp steps. 3. The glucose infusion rate (GIR) necessary to maintain euglycaemia during maximal insulin stimulation was lower during PEC compared with CC (15.7%, 81.3 +/‐ 3.2 vs. 96.4 +/‐ 8.8 mumol kg‐1 min‐1, P < 0.05). 4. Our data show that 2 days after unaccustomed eccentric exercise, muscle and whole‐body insulin action is impaired at maximal but not submaximal concentrations. The local effect cannot account for the whole‐body effect, suggesting the release of a factor which decreases insulin responsiveness systemically.

Exercise metabolism in human skeletal muscle exposed to prior eccentric exercise

1 The effects of unaccustomed eccentric exercise on exercise metabolism during a subsequent bout of graded concentric exercise were investigated in seven healthy male subjects. Arterial and bilateral femoral venous catheters were inserted 2 days after eccentric exercise of one thigh (eccentric thigh) and blood samples were taken before and during graded two‐legged concentric knee‐extensor exercise. Muscle biopsies were obtained from the eccentric and control vastus lateralis before (rest) and after (post) the concentric exercise bout. 2 Maximal knee‐extensor concentric exercise capacity was decreased by an average of 23 % (P < 0.05) in the eccentric compared with the control thigh. 3 The resting muscle glycogen content was lower in the eccentric thigh than in the control thigh (402 ± 30 mmol (kg dry wt)−1vs. 515 ± 26 mmol (kg dry wt)−1, means ± s.e.m., P < 0.05), and following the two‐legged concentric exercise this difference substantially increased (190 ± 46 mmol (kg dry wt)−1vs. 379 ± 58 mmol (kg dry wt)−1, P < 0.05) despite identical power and duration of exercise with the two thighs. 4 There was no measurable difference in glucose uptake between the eccentric and control thigh before or during the graded two‐legged concentric exercise. Lactate release was higher from the eccentric thigh at rest and, just before termination of the exercise bout, release of lactate decreased from this thigh (suggesting decreased glycogenolysis), whereas no decrease was found from the contralateral control thigh. Lower glycerol release from the eccentric thigh during the first, lighter part of the exercise (P < 0.05) suggested impaired triacylglycerol breakdown. 5 At rest, sarcolemmal GLUT4 glucose transporter content and glucose transport were similar in the two thighs, and concentric exercise increased sarcolemmal GLUT4 content and glucose transport capacity similarly in the two thighs. 6 It is concluded that in muscle exposed to prior eccentric contractions, exercise at a given power output requires a higher relative workload than in undamaged muscle. This increases utilization of the decreased muscle glycogen stores, contributing to decreased endurance.

Competitive sustained exercise in humans, lymphokine activated killer cell activity, and glutamine – an intervention study

This study examined whether oral glutamine supplementation abolishes some of the exercise-induced changes in lymphocyte functions following long-term intense exercise. A group of 16 marathon runners participating in The Copenhagen Marathon 1996 were placed randomly in either a placebo (n = 7) or a glutamine receiving group (n = 9). Each subject received four doses of either placebo or glutamine (100 mg · kg−1) administered at 0, 30, 60, and 90-min post-race. In the placebo group the plasma glutamine concentrations were lower than pre-race values during the post-exercise period [mean 647 (SEM 32) compared to 470 (SEM 22) μmol · l−1 90-min post-race, P < 0.05] whereas glutamine supplementation maintained the plasma glutamine concentration (at ∼750 μmol · l−1). Glutamine supplementation in vivo had no effect on the lymphokine activated killer (LAK) cell activity, the proliferative responses or the exercise-induced changes in concentrations or percentages of any of the leucocyte subpopulations examined. Glutamine addition in in vitro studies enhanced the proliferative response in both groups. These data would suggest that decreased plasma glutamine concentrations post-exercise are not responsible for exercise-induced decrease in LAK activity and that the influence of glutamine in vitro is not dependent on the plasma glutamine concentration at the time of sampling.

Effect of prior eccentric contractions on lactate/H+ transport in rat skeletal muscle

The effect of prior eccentric contractions on skeletal muscle lactate/H+transport was investigated in rats. Lactate transport was measured in sarcolemmal giant vesicles obtained from soleus and red (RG) and white gastrocnemii (WG) muscles 2 days after intense eccentric contractions (ECC) and from the corresponding contralateral control (CON) muscles. The physiochemical buffer capacity was determined in the three muscle types from both ECC and CON legs. Furthermore, the effect of prior eccentric contractions on release and muscle content of lactate and H+ during and after supramaximal stimulation was examined using the perfused rat hindlimb preparation. The lactate transport rate was lower ( P < 0.05) in vesicles obtained from ECC-WG (29%) and ECC-RG (13%) than in vesicles from the CON muscles. The physiochemical buffer capacity was reduced ( P < 0.05) in ECC-WG (13%) and ECC-RG (9%) compared with the corresponding CON muscles. There were only marginal effects on the soleus muscle. Muscle lactate concentrations and release of lactate during recovery from intense isometric contractions were lower ( P< 0.05) in ECC than in CON hindlimbs, indicating decreased anaerobic glycogenolysis. In conclusion, the sarcolemmal lactate/H+ transport capacity and the physiochemical buffer capacity were reduced in prior eccentrically stimulated WG and RG in rats, suggesting that muscle pH regulation may be impaired after unaccustomed eccentric exercise. In addition, the data indicate that the glycogenolytic potential is decreased in muscles exposed to prior eccentric contractions.The effect of prior eccentric contractions on skeletal muscle lactate/H+ transport was investigated in rats. Lactate transport was measured in sarcolemmal giant vesicles obtained from soleus and red (RG) and white gastrocnemii (WG) muscles 2 days after intense eccentric contractions (ECC) and from the corresponding contralateral control (CON) muscles. The physiochemical buffer capacity was determined in the three muscle types from both ECC and CON legs. Furthermore, the effect of prior eccentric contractions on release and muscle content of lactate and H+ during and after supramaximal stimulation was examined using the perfused rat hindlimb preparation. The lactate transport rate was lower (P < 0.05) in vesicles obtained from ECC-WG (29%) and ECC-RG (13%) than in vesicles from the CON muscles. The physiochemical buffer capacity was reduced (P < 0.05) in ECC-WG (13%) and ECC-RG (9%) compared with the corresponding CON muscles. There were only marginal effects on the soleus muscle. Muscle lactate concentrations and release of lactate during recovery from intense isometric contractions were lower (P < 0.05) in ECC than in CON hindlimbs, indicating decreased anaerobic glycogenolysis. In conclusion, the sarcolemmal lactate/H+ transport capacity and the physiochemical buffer capacity were reduced in prior eccentrically stimulated WG and RG in rats, suggesting that muscle pH regulation may be impaired after unaccustomed eccentric exercise. In addition, the data indicate that the glycogenolytic potential is decreased in muscles exposed to prior eccentric contractions.