Department of Animal Science, Texas A&M University, College Station, TX.
J Anim Sci. 2018 Apr 3;96(3):921-929. doi: 10.1093/jas/sky017.
We hypothesized that abomasal infusion of glucose would promote de novo fatty acid biosynthesis from glucose in vitro in bovine intramuscular (i.m.) and subcutaneous (s.c.) adipose tissues to a greater extent than ruminal infusion of acetate, propionate, or glucose. Angus crossbred steers (n = 24), 22 mo of age, were fitted with ruminal cannulas, and steers were adapted to another corn/sorghum finishing diet over a 2-wk period while recovering from the placement of the cannulas. After the adaptation period, the steers were fed the second finishing diet at 130% of their voluntary intake and were infused with isocaloric amounts (3.76 Mcal/d) of glucose, propionate, or acetate for 35 d. Glucose was infused either into the rumen or into the abomasum, whereas propionate and acetate were infused into the rumen. Acetate infusion decreased DM and DE intakes (P < 0.05). The 5th to 8th longissimus muscle section was removed immediately and transported to the laboratory within 10 min post-exsanguination in 38 °C, oxygenated Krebs Henseleit buffer containing 5 mM glucose and 5 mM acetate. Intramuscular and s.c. adipose tissues were dissected from the muscle and incubated in vitro in 5 mM glucose plus 5 mM acetate (containing [U-14C]glucose or [1-14C]acetate). Lipid content was lower (P = 0.04) in i.m. adipose tissue of the acetate-infused steers than in the other treatment groups, and i.m. adipocytes from acetate-infused steers were smaller (P = 0.01) than those from propionate-infused steers. The rate of incorporation of acetate into glyceride-fatty acids (GFA) in i.m. and s.c. adipose tissues was greater (P < 0.03) in steers receiving ruminal or abomasal infusions of glucose than in adipose tissues from steers infused with acetate. The greatest rates of GFA synthesis were observed in s.c. adipose tissue from steers infused ruminally with propionate or abomasally infused with glucose (P < 0.001). In i.m. and s.c. adipose tissues, the proportion of acetyl units from acetate incorporated into GFA was greater in steers receiving glucose infusion in the rumen or abomasum than in steers receiving acetate or propionate infusion (P < 0.05). Contrary to our hypothesis, abomasal glucose infusion did not promote greater fatty acid biosynthesis from glucose in i.m. adipose tissue than ruminal glucose infusion. However, glucose infusion caused the greatest production of acetyl units from acetate in i.m. and s.c. adipose tissues.
我们假设，与瘤胃输注乙酸盐、丙酸盐或葡萄糖相比，向牛肌肉内（i.m.）和皮下（s.c.）脂肪组织的网胃输注葡萄糖会促进葡萄糖从头合成脂肪酸。安格斯杂交阉牛（n = 24），22 月龄，安装瘤胃插管，在适应另一种玉米/高粱育肥日粮的同时，在插管放置后恢复 2 周。适应期后，以 130%的自由采食量给牛饲喂第二育肥日粮，并连续 35 天输注等热量（3.76 Mcal/d）的葡萄糖、丙酸盐或乙酸盐。葡萄糖或通过瘤胃输注，或通过网胃输注，而丙酸盐和乙酸盐则通过瘤胃输注。乙酸盐输注降低了 DM 和 DE 摄入量（P < 0.05）。第 5 至 8 节最长肌段在放血后立即取出，在 38°C 下，在含有 5 mM 葡萄糖和 5 mM 乙酸盐的有氧 Krebs Henseleit 缓冲液中，在 10 分钟内运送到实验室。从肌肉中分离出肌肉内和皮下脂肪组织，并在含有 [U-14C]葡萄糖或 [1-14C]乙酸盐的 5 mM 葡萄糖加 5 mM 乙酸盐（含有 5 mM 葡萄糖加 5 mM 乙酸盐）中进行体外孵育。乙酸盐输注的牛的肌肉内脂肪组织中的脂质含量较低（P = 0.04），并且来自乙酸盐输注的牛的肌肉内脂肪细胞较小（P = 0.01），小于来自丙酸盐输注的牛的脂肪细胞。肌肉内和皮下脂肪组织中乙酸盐掺入甘油三酯脂肪酸（GFA）的速度在接受瘤胃或网胃葡萄糖输注的牛中大于接受乙酸盐输注的牛（P < 0.03）。在接受瘤胃内丙酸盐输注或网胃内葡萄糖输注的牛的皮下脂肪组织中观察到最大的 GFA 合成率（P < 0.001）。在肌肉内和皮下脂肪组织中，从乙酸盐掺入 GFA 的乙酰基单位比例在接受瘤胃或网胃葡萄糖输注的牛中大于接受乙酸盐或丙酸盐输注的牛（P < 0.05）。与我们的假设相反，与瘤胃葡萄糖输注相比，网胃葡萄糖输注并没有促进肌肉内葡萄糖向脂肪酸的生物合成。然而，葡萄糖输注导致肌肉内和皮下脂肪组织中乙酸盐产生的乙酰基单位最多。
