Adipokines
Leptin is a critical regulator of energy storage through appetite/satiety control: when energy stores are adequate, leptin signals to the hypothalamus to reduce appetite drive, thus reducing food intake. As in other species, leptin is secreted from equine adipocytes in proportion to body fat mass. Indeed, animals with increased body fat (without disease) have higher plasma and adipose tissue expression of leptin (Staub et al., 2019; Buff et al., 2002).
Adiponectin is produced almost exclusively by adipocytes (Fang & Judd, 2011) and it acts primarily on muscle and liver to increase insulin sensitivity and reduce inflammation. In most species, including horses, there is an inverse relationship between fat mass and plasma adiponectin (Kearns et al., 2006).
Resistin is also an adipose-specific protein, whose transcription is induced during differentiation of adipocytes. In rodents, it has been shown to decrease gluconeogenesis in the liver (Banerjee et al., 2004). Numerous human studies have failed to demonstrate a reliable association between resistin levels, obesity and/or insulin dysregulation. In contrast, resistin may be a marker of inflammation (Banerjee and Lazar, 2003), consistent with findings in horses (Fuentes-Romero et al., 2021).