Skeletal muscle growth in young rats is inhibited by chronic exposure to IL-6 but preserved by concurrent voluntary endurance exercise.

Childhood diseases are often accompanied by chronic inflammation, which is thought to negatively impact growth. Interleukin-6 (IL-6) is typically cited as an indicator of inflammation and is linked to impaired growth. This study was designed to isolate and identify potential effects of chronic IL-6 exposure on skeletal muscle growth during development. A second aim was to determine if endurance exercise, thought to antagonize chronic inflammation, would interact with any effects of IL-6. The muscles of one leg of rapidly growing rats were exposed to IL-6 or vehicle for 14 days. Subgroups of IL-6-infused rats were provided access to running wheels. Local IL-6 infusion resulted in approximately 13% muscle growth deficit (myofibrillar protein levels). Exercise (>4,000 m/day) prevented this deficit. IL-6 infusion increased mRNA for suppressor of cytokine signaling-3 (SOCS3) and tumor necrosis factor-alpha (TNF-alpha), and this was not prevented by exercise. IL-6 infusion increased the mRNAs for atrogin, insulin-like growth factor-I (IGF-I), and IGF binding protein-4 (IGFBP4), and these effects were mitigated by exercise. Exercise stimulated an increase in total RNA ( approximately 19%) only in the IL-6-infused muscle, suggesting that a compensatory increase in translational capacity was required to maintain muscle growth. This study indicates that IL-6 exposure during periods of rapid growth in young animals can retard growth possibly via interactions with key growth factors. Relatively high volumes of endurance-type exercise do not exacerbate the negative effects of IL-6 and in fact were found to be beneficial in protecting muscle growth.

Effect of prior hyperglycemia on IL-6 responses to exercise in children with type 1 diabetes.

The proinflammatory cytokine interleukin-6 (IL-6) may modulate the onset and progression of complications of diabetes. As this cytokine increases after exercise, and many other exercise responses are altered by prior glycemic fluctuations, we hypothesized that prior hyperglycemia might exacerbate the IL-6 response to exercise. Twenty children with type 1 diabetes (12 boys/8 girls, age 12-15 yr) performed 29 exercise studies (30-min intermittent cycling at approximately 80% peak O2 uptake). Children were divided into four groups based on highest morning glycemic reading [blood glucose (BG) < 150, BG 151-200, BG 201-300, or BG > 300 mg/dl]. All exercise studies were performed in the late morning, after hyperglycemia had been corrected and steady-state conditions (plasma glucose < 120 mg/dl, basal insulin infusion) had been maintained for > or = 90 min. Blood samples for IL-6, growth factors, and counterregulatory hormones were drawn at pre-, end-, and 30 min postexercise time points. At all time points, circulating IL-6 was lowest in BG < 150 and progressively higher in the other three groups. The exercise-induced increment also followed a similar dose-response pattern (BG < 150, 0.6 +/- 0.2 ng/ml; BG 151-200, 1.2 +/- 0.8 ng/ml; BG 201-300, 2.1 +/- 1.1 ng/ml; BG > 300, 3.2 +/- 1.4 ng/ml). Other measured variables (growth hormone, IGF-I, glucagon, epinephrine, cortisol) were not influenced by prior hyperglycemia. Recent prior hyperglycemia markedly influenced baseline and exercise-induced levels of IL-6 in a group of peripubertal children with type 1 diabetes. While exercise is widely encouraged and indeed often considered part of diabetic management, our data underscore the necessity to completely understand all adaptive mechanisms associated with physical activity, particularly in the context of the developing diabetic child.