Steroid hormones
Adipose is crucial for the action and metabolism of steroid hormones, particularly glucocorticoids and sex steroids. Furthermore, glucocorticoids are essential in differentiation of mature adipocytes. Adipose tissue in humans and horses contains high levels of glucocorticoid receptor (GR) and also the metabolizing enzyme 11β-hydroxysteroid dehydrogenase type 1 (HSD1,) which metabolises inactive cortisone into active cortisol and thus potentiates activation of GR (Morgan et al., 2018). Horses predominantly metabolise their cortisol through the carbonyl reductase 1 pathway which is very active in adipose tissue and produces a metabolite which impacts glucose homeostasis (Morgan et al., 2017). Less is known about sex steroid metabolism and receptors in equine adipose tissue, though sexually dimorphic patterns of adipose distribution are noted (such as the large nuchal crest adipose depots in stallions) suggesting androgens may impact adipose deposition.