Submitted to: Australasian Pig Science Association Meeting
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: November 29, 1999
Publication Date: N/A
Interpretive Summary: Leptin is a small hormone produced by the adipose tissue that is secreted into the bloodstream. This hormone has actions on feeding behavior, metabolism, reproduction and immunology. Review of the literature indicates that leptin may function as a regulator of overall energy balance in the normal pig. It is a signal synthesized in the peripheral energy stores (adipose tissue) in increasing quantity as the energy stores increase in volume. This signal is secreted by the adipose tissue and acts at the peripheral tissues and in the central nervous system to produce a reduction in feed/energy intake as a counterbalance. Leptin may have effects in the periphery as well as the central nervous system as receptors are present on many tissues. Thus, leptin has been demonstrated to alter nutrient partitioning through metabolic actions on muscle and adipose tissue. The onset of puberty and subsequent fertility mandate a positive energy balance for reproduction. Data suggests that leptin may contribute to the overall signal for the onset of puberty through actions both in the central nervous system and at the ovary. In addition, leptin can promote development of the immune system. Starving animals have depressed immune systems and low serum leptin levels. Leptin administration stimulates macrophage and T cell growth and activity. The potential application of leptin to swine will be dependent upon acquiring the knowledge necessary to affect these biological processes in such a manner as to improve production efficiency of the pig.
Technical Abstract: Investigations into the actions of leptin have revealed numerous functions for this protein in regulating feed intake, metabolism, reproduction and immune function. Leptin is a secretory protein produced by adipocytes. The complete sequence of the pig leptin gene has been characterized. Leptin mRNA level in swine adipose tissue varies in proportion to changes in serum leptin, suggesting primarily transcriptional regulation. The leptin protein has been reported to induce anywhere from a 5-90% reduction in feed intake depending on route of administration, dosage and ancillary treatments. The effect of leptin on regulating feeding behavior has led to the hypothesis that leptin is a regulator of overall energy balance in the normal animal. Animals deficient in leptin are infertile. Treatment of either male or female ob/ob mice reverses the sterility. In normal mice, leptin administration results in an early onset of puberty. It has been hypothesized that leptin functions as a permissive afferent signal integrating information from energy stores. Interpretation of this signal influences reproductive function, resulting in synchronization of endocrine and behavioral components of reproductive activity during times of energy imbalance. The structure of leptin suggests that it is a member of the family of cytokine molecules. Mice deficient (ob/ob) or resistant (db/db) to leptin have reduced T-cell function and deficient hemopoietic activity. Leptin produces a T-cell pro-inflammatory response. The future application of leptin to swine will be dependent upon its use to affect feeding behavior, metabolism reproduction and immune function in such a manner as to improve the production efficiency of the pig based upon current research.