Submitted to: Journal of Animal Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/9/2004
Publication Date: 12/1/2004
Citation: Ramsay, T.G., Richards, M.P. 2004. Hormonal regulation of leptin and leptin receptor expression in porcine subcutaneous adipose tissue. Journal of Animal Science. v 82:3486-3492. Interpretive Summary: Leptin is a hormone produced by pig adipose tissue that can affect feeding behavior, animal health and reproduction. Studies in pigs have demonstrated that leptin can reduce feed intake. This experiment was designed to determine if the production and release of porcine leptin is a regulated phenomenon. Secondly, this study attempted to determine whether expression of leptin and its receptor can be manipulated by hormonal mechanisms in market size animals. The data demonstrate that leptin secretion can be stimulated, as well as inhibited. Secondly, expression of the leptin gene and the leptin receptor gene are also responsive in market weight animals. These results suggest the potential to manipulate the efficiency of feeding behavior in finishing animals, at a time when changes in body composition can be critical for improving profitability .
Technical Abstract: The present study was performed to examine the response of the leptin gene to hormonal stimuli in porcine adipose tissue from finishing pigs. Ten Yorkshire gilts (approximately 150 kg BW) were used in this study. Dorsal subcutaneous adipose tissue samples were acquired and adipose tissue explants (approximately 100 mg) were prepared using sterile technique. Tissue slices were then transferred to 12 well tissue culture plates containing 1 mL of media 199 with 25 mM Hepes, 0.5 % BSA, pH 7.4 and various hormone supplements of interest. Triplicate tissue slices were incubated with either basal medium or hormone supplemented media in a tissue culture incubator at 37ºC with 95% air/5% CO2. Following 24 h of incubation, tissue samples from these incubations were blotted and transferred to microfuge tubes with subsequent freezing in liquid nitrogen and storage at -80ºC prior to analysis for gene expression by RT-PCR and subsequent quantification of transcripts by capillary electrophoresis with laser-induced fluorescence detection . Media from these incubations was collected in microfuge vials and stored at -20ºC prior to analysis for leptin content by RIA. Dexamethasone (1 uM) reduced leptin secretion by 25% (p < 0.05), while the combination of insulin and dexamethasone stimulated leptin secretion into the medium by 60% (p < 0.05). Porcine growth hormone (GH) inhibited leptin secretion by 33% (p < 0.05). Neither triiodothyronine (T310 nM) or IGF-1 (250 ng/mL medium) had an effect on leptin secretion from adipose tissue slices (p > 0.05). Dexamethasone produced a 35% increase in leptin mRNA expression relative to insulin (p < 0.05). Incubation of tissue cultures with GH, T3 or leptin for 24 h had no effect on leptin mRNA expression (p > 0.05). Dexamethasone induced a 34% decrease in total leptin receptor expression, relative to insulin treated adipose tissue slices, following 24 h of incubation. Porcine GH, T3 and leptin had no effect on total leptin receptor expression (p> 0.05). These data suggest that leptin secretion is a regulated phenomenon and that post-translational processing may be significant. Alternatively transport and exocytosis of leptin containing vesicles in the pig adipocyte may be quite complicated to account for the differences in observed gene expression and protein secretion.