论文部分内容阅读
We hypothesized that specific dietary or ruminally produced fatty acids would differentially affect adipogenic and lipogenic gene expression and fatty acid biosynthesis in intramuscular (i.m.) and subcutaneous (s.c.) adipose tissues.Several studies were conducted to test this hypothesis.Study 1∶28 Angus crossbred steers were assigned randomly to three groups of 9 or 10 steers and fed a basal diet without additional fat (control), with 3% palm oil (rich in palmitic acid), or with 3% soybean oil (rich in polyunsaturated fatty acids), for 10 wk, top-dressed daily.Subcutaneous adipocyte mean volume, glucose and acetate incorporation into total lipids in vitro, and glucose-6-phosphate dehydrogenase (G6PDH) and NADP-malate dehydrogenase (NADP-MDH) activities were greater in palm oil-fed steers than in soybeansupplemented cattle.These data indicate that palmitic and/or oleic acid in the palm oil promoted lipogenesis.Study 2: arginine (50 g/d), alanine (100 g/d), with and without trans-10, cis-12 CLA (100 g/d) were infused into the abomasum of 24 steers.NADP-MDH activity was higher in steers infused with arginine than in steers infused with arginine + CLA by d 28.SCD1 gene expression was lower, and GPR43 gene expression was higher, in s.c.adipose tissue of steers infused with alanine + CLA than in steers infused with arginine (± CLA).Study 3: i.m.and s.c.adipose tissues were collected from the longissimus thoracis muscle of 12 Angus steers at 12, 14, and 16 mo of age and adipose tissue explants were incubated for 48 h with 40 μM linolenic (ALA), oleic, stearic, trans-vaccenic acid (TVA), or 18∶2 trans-10, cis-12 CLA for 48 h.All fatty acids except CLA and stearic acid increased acetate incorporation into lipids in i.m.adipose tissue, and CLA depressed lipogenesis in s.c.adipose tissue, but none of the fatty acids affected gene expression.Study 4: bovine semimembranosus satellite cells (BSC) and s.c.preadipocytes were isolated from crossbred steers and cultured for a 3-d proliferation period.After proliferation, BSC and preadipocytes were treated for 3 d with 100 μM oleic acid, 10 μg/mL insulin, 1 μg/mL pioglitazone, and 1 μg/mL dexasmethasone.Subsequently the differentiating myoblasts and adipocytes were cultured with 5 mM arginine and/or 40 μM trans-10, cis12 CLA for 4 d.Finally, myoblasts and adipocytes were single-or co-cultured for 2 h singly or in combination.Arginine stimulated SCD1 gene expression, whereas CLA depressed SCD1 gene expression in adipocytes and myoblasts.Co-culture of adipocyes and myoblasts increased C/EBPβ and PPARγ gene expression in differentiated myoblasts and increased GPR43 gene expression in adipocytes.Collectively, these studies have demonstrated that fatty acids have specific effects on i.m.and s.c.lipogenesis and adipogenesis.