Wikipedia
Myonectin (CTRP15) is a myokine, described in 2012 by Seldin, et al.
It is a novel nutrient-responsive myokine secreted by skeletal muscle to regulate whole-body fatty acid metabolism. Myonectin is a member of the C1q/TNF-related protein (CTRP) family. This important, biologically active molecule is released into circulation by muscular contraction, and is roughly equivalent to insulin in its potency.
Seldin and his colleagues have written: "Myonectin is expressed and secreted predominantly by skeletal muscle.... (Our) results suggest that myonectin is a nutrient-responsive metabolic regulator secreted by skeletal muscle in response to changes in cellular energy state resulting from glucose or fatty acid fluxes. Many metabolically relevant secreted proteins (e.g. adiponectin, leptin, resistin, and RBP) and the signaling pathways they regulate in tissues are known to be dysregulated in the condition of obesity. The reduction in expression and circulating levels of myonectin in the obese state may represent yet another component of the complex metabolic circuitry dysregulated by excess caloric intake. Although exercise has long been known to have profound positive impacts on systemic insulin sensitivity and energy balance, the underlying mechanisms remain incompletely understood. That voluntary exercise dramatically increases the expression and circulating levels of myonectin to promote fatty acid uptake into cells may underlie one of the beneficial effects of physical exercise."
It was shown to be identical to erythroferrone, a hormone produced in erythroblasts that is involved in iron metabolism.