| Four experiments were conducted both in vivo and in vitro to investigate dietary energy and oil source on ob gene, long form leptin receptor gene (Ob-Rl), insulin-like growth factor-1 (IGF-1) and peroxisome proliferator-activated receptorγ (PPARγ) genes in swine adipose tissues. In experiment 1, 36, 42 d crossbred weaned piglets (Landrace×Large White) (15.0±0.29 kg BW) were randomly allotted to six treatments with replicates of six pens with one pig per pen. Every two treatments ate one of three dietary energy level including 13.4, 15.1 and 16.7 MJ/kg diets. One of the two treatments was ad libitum, the other was restricted feeding. Body weight and feed intake were weighed every week to calculate growth performance and plasma samples collected to assess plasma growth factors and hormone levels on d 14 and 28. Results indicated that comparing to ad libitum, restricted feeding decreased pigs performance including average daily gain (P < 0.01) and feed: gain (P < 0.01), and dietary energy level had no effect on pigs performance. Restricted feeding increased plasma leptin (P < 0.01) and NPY (P < 0.01) concentrations, and plasma leptin (P < 0.01) and NPY (P < 0.01) concentrations maintained at a higher level when fed 15.1 MJ/kg diet. In experiment 2, 14, 49 d crossbred piglets (Landrace X Large White) (20.0±0.3 kg BW) were allotted to two oil source dietary treatments, one is fish oil another is soybean oil. Pigs were randomly allotted to two treatments with replicates of seven pens with one pig per pen. Body weight and feed intake were weighed every week to calculate growth performance. To assess plasma growth factors and hormone levels, plasma samples were obtained from one pig per pen on d 7, 14 and 21. Oil source only affected daily gain (P = 0.05), feed intake (P = 0.01) and feed: gain (P = 0.01) in first week. Fish oil had lower performance but increased plasma IGF-1 level (P < 0.01) in first week. On d 28 three ad libitum treatments in experiment 1 and d 21 in experiment 2, all the pigs were sacrificed to obtain dorsal subcutaneous, abdominal subcutaneous and visceral adipose tissue samples. Real time-PCR was used to determine ob, Ob-Rl, IGF-1 and PPARγ genes expression. In ad libitum treatments of experiment 1, dorsal adipose tissue ob gene, Ob-Rl and IGF-1 mRNA expression were increased by feeding the diet containing 15.1 MJ/kg DE compared with the diets containing 13.4 and 16.7 MJ/kg DE. There was no difference in ob gene expression in abdominal and visceral adipose tissue due to the different energy level. PPARγ mRNA abundance increased with dietary energy level enhanced. In experiment 2, fish oil rich in n-3 PUFA decreased ob gene expression in adipose tissues compared with soybean oil rich in n-6 PUFA (P < 0.01). Both ob, Ob-Rl and IGF-1 mRNA were expressed more in abdominal tissues, than in dorsal tissues with the lowest level found in visceral adipose tissue. In an in vitro experiment, primary adipose tissues were cultured with serum-free DMEM containing 40 μmol/L EPA, DHA, LA and leptin 1×10-7mol/L. At 0, 1/4.1/2, 1, 2, 4, 8, 12, 18 and 24 h, 0.2 mL culture supernatant fluid was obtained per treatment to determined leptin levels using RIA analysis. At 24 h, adipose tissues were collected and total RNA isolated. Ob, Ob-Rl, IGF-1 and PPARγ mRNA abundance were measured by Real-time PCR. Results indicated that leptin pool might exist inadipose tissues and ob gene expression is insulin and PPARy independent. Different oil source relative to dietary energy level effectively changed ob gene expression in fat depots and its expression appeared to differ regionally in our studies. This suggests that leptin is not a precise homeostatic energy balance control system but that individual fat depots also have different unique physiological functions. Nutrient substances involving PUFAs and energy level may play a role to some extent in changing the physiological functions of leptin different individual fat depots. Regulation of nutrition might provide a means for altering specific body fat depots, which can provide some clue to controlling obesity in adolescents.
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