[Paracrine and endocrine functions of muscles].

BACKGROUND: Myokines discharged from working muscles are intensively researched in view of rising importance of preventive and secondary preventive effects of the autocrine, paracrine and endocrine functions.

OBJECTIVES: Recording of the current state of knowledge on the paracrine and endocrine effects of myokines and evaluation of training measures to optimize myokine concentration.

METHOD: A selective database-driven literature search was carried out on myostatin, interleukin-6 (IL-6), interleukin-15 (IL-15), irisin, cathepsin B, brain-derived neurotrophic factor (BDNF), meteorin-like and kynurenine for the period 2011 until June 2021. The paracrine and endocrine effects of the myokines are analyzed. Their release after acute physical stress and training is described.

RESULTS: IL-6 and IL-15 act in lipid metabolism and carbohydrate metabolism, IL-6 also in the brain and immune system. Irisin produces a conversion of white to brown adipose tissue ("browning"), so does meteorin-like. Cathepsin B has a central effect. Kynurenine acts indirectly via kynurenic acid in the brain. The secretion of myokines depends on the intensity of physical stress and is modified by training. Prevention of vascular and neurologic diseases, cognitive enhancement and increased immunological function can be reached by setting free myokines during physical activity. Therapeutical use by technologically modified myokines is proposed in metabolic and neurological diseases, immobilization and sarcopenia.

CONCLUSIONS: The current research situation on myokines gives reason to recommend regular muscular activity in addition to the previously evidence-based benefits of sport in order to achieve preventive and therapeutic effects.