Submitted to: Comparative Biochemistry and Physiology
Publication Type: Peer reviewed journal
Publication Acceptance Date: 2/10/2004
Publication Date: 2/10/2004
Citation: Ramsay, T.G., Bush, J.A., McMurtry, J.P., Thivierge, M.C., Davis, T.A. 2004. Peripheral leptin administration alters hormone and metabolite levels in the young pig. Comparative Biochemistry and Physiology, Part A. 138:17-25. Interpretive Summary: Leptin is a hormone produced by adipose tissue that can affect feeding behavior, animal health and reproduction. Studies in pigs have demonstrated that leptin can reduce feed intake when injected directly to the brain. The present study was conducted to determine if peripheral leptin administration can alter feed intake, hormone secretion and metabolism. Pigs were given a single injection of recombinant porcine leptin in the peripheral blood stream with subsequent blood sampling from the jugular vein during the next 24 hours. Feed intake was reduced by treatment with leptin at the two highest dosages (500 ug/kg body weight [bwt] and 200 ug/kg bwt) provided. Blood sugar was depressed, most likely due to the reduction in feed intake. Blood free fatty acids were elevated, again most likely due to the reduction in feed intake. The lowest leptin dose tested (100 ug/kg bwt) increase blood leptin levels but had no effect on feed intake or any other parameter measured. The middle dosage of leptin tested (200 ug/kg bwt) stimulated a pulsatile increase in blood growth hormone levels. The data from this study indicates that pig leptin can affect feeding behavior, stimulate growth hormone secretion and shift energy metabolism following administration to the peripheral bloodstream. The ability for a single injection of leptin to produce significant changes in hormone and metabolite levels suggests that this hormone, produced by the fat cell, has a role in regulation of peripheral metabolism in the pig.
Technical Abstract: The present study was conducted to determine if peripheral leptin administration can alter GH secretion or feed intake in the young pigs. Six, 6 kg female pigs were fed twice daily at 0800 (3%) and 1500 h (3%) a diet containing 24% crude protein prior to the study. Animals were fasted overnight and randomly chosen to receive porcine recombinant leptin or saline injections. The dose of leptin given per pig was initially 500 µg/kg body weight (BW) (L500) in 0.2% BSA as a bolus injection into the carotid artery. Blood samples were obtained from the jugular vein over a 24-h period. Feed was presented to each pig at 1h following leptin injection with subsequent re-weighing of food every 2h. Three days later in a cross-over design, the experiment was repeated with a leptin dose of 100 µg/kg BW (L100) or saline. Three days following this experiment, the experimental protocol was repeated with a leptin dose at 200 µg/kg BW (L200) or saline. Leptin reduced intake in pigs treated with L500 and L200 (P<0.05), but did not affect pigs treated with L100 (P>0.05). Blood glucose was depressed in pigs treated with L500 or L200 (P<0.05). Plasma non-esterified fatty acid (NEFA) remained elevated following feed presentation in pigs treated with L500 or L200(P<0.05). Plasma insulin levels were elevated by feeding in control animals, while insulin levels were depressed in pigs treated with L500 or L200 (P<0.05). In all experiments, leptin injection elevated plasma leptin levels (P < 0.05). Plasma growth hormone (GH) was significantly elevated in pigs treated with L200 (P<0.05) with three peaks apparent at 5, 8, and 13 h post injection. The ability for a single injection of leptin to produce significant changes in hormone and metabolite levels suggests that this peptide has a role in regulation of peripheral metabolism.