Examination of the Myokine Response in Pregnant and Non-pregnant Women Following an Acute Bout of Moderate-Intensity Walking

1. Plasma interleukin (IL)-6 concentration is increased with exercise and it has been demonstrated that contracting muscles can produce IL-The question addressed in the present study was whether the IL-6 production by contracting skeletal muscle is of such a magnitude that it can account for the IL-6 accumulating in the blood. 2. This was studied in six healthy males, who performed one-legged dynamic knee extensor exercise for 5 h at 25 W, which represented 40% of peak power output (Wmax). Arterial-femoral venous (a-fv) differences over the exercising and the resting leg were obtained before and every hour during the exercise. Leg blood flow was measured in parallel by the ultrasound Doppler technique. IL-6 was measured by enzyme-linked immunosorbent assay (ELISA). 3. Arterial plasma concentrations for IL-6 increased 19-fold compared to rest. The a-fv difference for IL-6 over the exercising leg followed the same pattern as did the net IL-6 release. Over the resting leg, there was no significant a-fv difference or net IL-6 release. The work was produced by 2.5 kg of active muscle, which means that during the last 2 h of exercise, the median IL-6 production was 6.8 ng min-1 (kg active muscle)-1 (range, 3.96-9.69 ng min-1 kg-1). 4. The net IL-6 release from the muscle over the last 2 h of exercise was 17-fold higher than the elevation in arterial IL-6 concentration and at 5 h of exercise the net release during 1 min was half of the IL-6 content in the plasma. This indicates a very high turnover of IL-6 during muscular exercise. We suggest that IL-6 produced by skeletal contracting muscle contributes to the maintenance of glucose homeostasis during prolonged exercise.

Persistent systemic inflammation, a typical feature of inflammatory rheumatic diseases, is associated with a high cardiovascular risk and predisposes to metabolic disorders and muscle wasting. These disorders can lead to disability and decreased physical activity, exacerbating inflammation and the development of a network of chronic diseases, thus establishing a 'vicious cycle' of chronic inflammation. During the past two decades, advances in research have shed light on the role of exercise as a therapy for rheumatic diseases. One of the most important of these advances is the discovery that skeletal muscle communicates with other organs by secreting proteins called myokines. Some myokines are thought to induce anti-inflammatory responses with each bout of exercise and mediate long-term exercise-induced improvements in cardiovascular risk factors, having an indirect anti-inflammatory effect. Therefore, contrary to fears that physical activity might aggravate inflammatory pathways, exercise is now believed to be a potential treatment for patients with rheumatic diseases. In this Review, we discuss how exercise disrupts the vicious cycle of chronic inflammation directly, after each bout of exercise, and indirectly, by improving comorbidities and cardiovascular risk factors. We also discuss the mechanisms by which some myokines have anti-inflammatory functions in inflammatory rheumatic diseases.

Skeletal muscle is the largest organ in the body. Skeletal muscles are primarily characterized by their mechanical activity required for posture, movement, and breathing, which depends on muscle fiber contractions. However, skeletal muscle is not just a component in our locomotor system. Recent evidence has identified skeletal muscle as a secretory organ. We have suggested that cytokines and other peptides that are produced, expressed, and released by muscle fibers and exert either autocrine, paracrine, or endocrine effects should be classified as "myokines." The muscle secretome consists of several hundred secreted peptides. This finding provides a conceptual basis and a whole new paradigm for understanding how muscles communicate with other organs such as adipose tissue, liver, pancreas, bones, and brain. In addition, several myokines exert their effects within the muscle itself. Many proteins produced by skeletal muscle are dependent upon contraction. Therefore, it is likely that myokines may contribute in the mediation of the health benefits of exercise. © 2013 American Physiological Society.