RETN and Obesity: Several hormones and cytokines—with the most commonly researched being leptin, adiponectin, ghrelin, resistin, tumor necrosis factor (TNF)-α, interleukin (IL)-6, IL-10, IL-1β, MCP-1, plasminogen activator inhibitor (PAI)-1 and proteins of the renin–angiotensin system (RAS)—are released inappropriately in obesity and have been implicated in the development of endothelial dysfunction [14,15,16].