Effect of leptin on metabolic hormones, energy metabolites, immunity and reproduction in farm animals -A review

Leptin is a 16 kDa protein hormone and it is synthesized primarily by white adipose tissue. It was discovered in 1994 and has been shown to be a potential regulator (inhibitor) of feed intake and could influence the hypothalamo-pituitary-gonadal axis. Effects of leptin on the immune system such as enhanced cytokine production have also been documented. Leptin also involved in regulation of feeding behaviour, energy balance and fertility. The expression and secretion of leptin is highly correlated with body fat mass and adipocyte size. Plasma leptin positively correlated to glucose and insulin and negatively correlated to growth hormone, cortisol and NEFA levels. Cortisol and insulin are potent stimulators of leptin. Leptin circulates specifically bound to serum, which may regulate its half life and biological activity. Its peripheral effects include the regulation of insulin action secretion by pancreatic beta cells and its action, besides energy metabolism in adipocytes and skeletal muscle. Leptin is thought to be a metabolic signal that regulates effects of nutrition on reproductive functions. Leptin also plays a major role in haematopoiesis. There is growing interest in the role of leptin especially in the high-producing, early lactation dairy cow, as drastic changes in energy balance and endocrine physiology combined with immunosuppression and increases the incidence of reproductive and metabolic disorders. In this review, various aspects of leptin like synthesis, structure and it's role on metabolic hormone, energy metabolites, immunity and reproduction have been dealt with.