Submitted to: Comparative Biochemistry and Physiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/16/2004
Publication Date: 2/16/2004
Citation: McMurtry, J.P., Ashwell, C.M., Brocht, D.M., Caperna, T.J. 2004. Plasma clearance and tissue distribution of radiolabeled leptin in the chicken. Comparative Biochemistry and Physiology. Part A 138:27-32. Interpretive Summary: The factors regulating appetite or feed intake are many and complex. Depending on the species, optimum feed intake is a problem in the poultry industry. In turkey poults, under-consumption in the neonatal period can lead to morbidity and mortality. Conversely, for the broiler breeder candidate hen, over-consumption is the norm, and results in adverse conditions associated with obesity. Why these conditions exist and how to properly control them is crucial from a management standpoint. Leptin, a hormone produced by the liver and fat cells, has been shown to be a potentially important component of feed intake regulation and energy balance. This study was conducted to elucidate potential target tissues for leptin action as well as to determine whether plasma binding proteins are present in the chicken. Results of these experiments demonstrated that many peripheral tissues, such as the lung and testis are target tissues for leptin. This strongly suggests that leptin is not only important as a component for regulation of feed intake by the central nervous system, but may have important functions in peripheral tissues. In addition, it was shown that unlike the situation in mammals, plasma proteins that bind leptin are not present in birds. This is a significant finding in that it indicates that leptin is metabolized very rapidly in birds. This information will be of interest to other scientists.
Technical Abstract: Leptin is an adipose and liver tissue-derived secreted protein in chickens that has been implicated in the regulation of food intake and whole-body energy balance. In this study, the metabolic clearance and tissue uptake of leptin were examined in the chicken. Four-week old broiler males were infused with I-125-labeled mouse leptin. Chromatography of radiolabeled leptin in plasma produced two peaks, one at 16 kDa (free leptin) and a free iodine peak. No leptin binding protein in blood was detected. Leptin was cleared with a half-life estimate of 23 minutes. In order to investigate the tissue distribution and uptake of radiolabeled leptin, multiple tissues were removed from infused birds at 15 and 240 min post-infusion, and TCA-precipitable radioactivity was determined. The amounts of radioactivity at 15 min post-infusion in the tissues in rank order were: kidney, testis, lung, spleen, heart, liver, small and large intestine, gizzard, pancreas, bursa, leg and breast muscle, fat, and brain. A slightly different pattern of distribution was observed at 240 min post-infusion. We conclude from these studies that unlike mammals, no circulating leptin binding protein is present in chickens. Leptin is metabolized and cleared very rapidly from blood by the kidney.