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).