Leptin as a Metabolic and Energy Homeostatic Hormone in Dairy Animals: A Review

Leptin, a 16-kDa protein secreted from white adipocytes is involved in the regulation of feed intake, energy expenditure and whole-body energy balance in animals. The gene encoding leptin identified by positional cloning and in the mutation leading to the profound obese phenotype of the ob/ob mouse. Exogenous administration of leptin to ob/ob mice significantly improved the reproductive and endocrine status, reduced feed intake and weight loss. The expression and secretion of leptin is highly correlated with body fat mass and adipocyte size. Cortisol and insulin are the potent stimulators of leptin expression, which is attenuated by β-adrenergic agonists, cAMP and thiazolidinediones. Leptin circulates mainly in bound form with serum, which may regulate its half life and biological activity. Many of leptin's effects on feed intake and energy expenditure are thought to be mediated centrally via neurotransmitters such as neuropeptide Y. Its peripheral effects include the regulation of insulin secretion by pancreatic beta cells and its action, besides energy metabolism in adipocytes and skeletal muscle. Leptin is thought to be a metabolic signal, which regulates effect of nutrition on reproductive functions. Leptin also plays a major role in haematopoiesis and in the anorexia accompanying an acute cytokine challenge. The profound effects of leptin on regulating energy balance make it a prime candidate for drug therapies for animals. However, the role of the leptin axis appears to be complex as leptin interacts with pathways in the central nervous system and through direct peripheral mechanisms. In this review, various aspects like the tissues in which leptin is synthesized, the mechanisms, which mediate leptin synthesis, the structure of leptin and understanding the role of leptin in the periphery etc., have been dealt with.