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.