Kristensen N B, Harmon D L
Department of Animal Nutrition and Physiology, Danish Institute of Agricultural Sciences, Denmark.
J Anim Sci. 2004 Dec;82(12):3549-59. doi: 10.2527/2004.82123549x.
Four steers fitted with a ruminal cannula and chronic indwelling catheters in the mesenteric artery, mesenteric vein, hepatic portal vein, hepatic vein, and the right ruminal vein were used to study the absorption and metabolism of VFA from bicarbonate buffers incubated in the temporarily emptied and washed reticulorumen. Portal and hepatic vein blood flows were determined by infusion of p-aminohippurate into the mesenteric vein, and portal VFA fluxes were calibrated by infusion of isovalerate into the ruminal vein. The steers were subjected to four experimental treatments in a Latin square design with four periods within 1 d. The treatments were Control (bicarbonate buffer) and VFA buffers containing 4, 12, or 36 mmol butyrate/kg of buffer, respectively. The acetate content of the buffers was decreased with increasing butyrate to balance the acidity. The butyrate absorption from the rumen was 39, 111, and 300 +/- 4 mmol/h for the three VFA buffers, respectively. The ruminal absorption rates of propionate (260 +/- 12 mmol/h), isobutyrate (11.4 +/- 0.7 mmol/h), and valerate (17.3 +/- 0.7 mmol/h) were not affected by VFA buffers. The portal recovery of butyrate and valerate absorbed from the rumen increased (P < 0.01) with increasing butyrate absorption and reached 52 to 54 +/- 4% with the greatest butyrate absorption. The liver responded to the increased butyrate absorption with a decreasing fractional extraction of propionate and butyrate, and with the greatest butyrate absorption, the splanchnic flux was 22 +/- 1% and 18 +/- 1% of the absorbed propionate and butyrate, respectively. The increased propionate and butyrate release to peripheral tissues was followed by increased (P < 0.05) arterial concentrations of propionate (0.08 +/- 0.01 mmol/kg) and butyrate (0.07 +/- 0.01 mmol/kg). Arterial insulin concentration increased (P = 0.01) with incubation of VFA buffers compared with Control and was numerically greatest with the greatest level of butyrate absorption. We conclude that the capacity to metabolize butyrate by the ruminal epithelium and liver is limited. If butyrate absorption exceeds the metabolic capacity, it affects rumen epithelial and hepatic nutrient metabolism and affects the nutrient supply of peripheral tissues.
选用4头装有瘤胃瘘管以及在肠系膜动脉、肠系膜静脉、肝门静脉、肝静脉和右瘤胃静脉中留置慢性导管的阉牛，研究在暂时排空并冲洗的网胃-瘤胃中孵育的碳酸氢盐缓冲液中挥发性脂肪酸（VFA）的吸收和代谢。通过向肠系膜静脉输注对氨基马尿酸来测定门静脉和肝静脉血流量，并通过向瘤胃静脉输注异戊酸来校准门静脉VFA通量。阉牛按拉丁方设计接受4种实验处理，1天内分4个时间段进行。处理分别为对照（碳酸氢盐缓冲液）和分别含有4、12或36 mmol丁酸/kg缓冲液的VFA缓冲液。随着丁酸含量增加，缓冲液中乙酸含量降低以平衡酸度。三种VFA缓冲液的瘤胃丁酸吸收率分别为39、111和300±4 mmol/h。丙酸（260±12 mmol/h）、异丁酸（11.4±0.7 mmol/h）和戊酸（17.3±0.7 mmol/h）的瘤胃吸收率不受VFA缓冲液影响。瘤胃吸收的丁酸和戊酸的门静脉回收率随丁酸吸收增加而升高（P<0.01），在丁酸吸收量最大时达到52%至54%±4%。肝脏对增加的丁酸吸收的反应是丙酸和丁酸的分数提取率降低，在丁酸吸收量最大时，内脏通量分别为吸收的丙酸和丁酸的22%±1%和18%±1%。向外周组织释放的丙酸和丁酸增加后，动脉血中丙酸（0.08±0.01 mmol/kg）和丁酸（0.07±0.01 mmol/kg）的浓度升高（P<0.05）。与对照相比，孵育VFA缓冲液后动脉胰岛素浓度升高（P=0.01），且在丁酸吸收水平最高时数值最大。我们得出结论，瘤胃上皮和肝脏代谢丁酸的能力是有限的。如果丁酸吸收超过代谢能力，会影响瘤胃上皮和肝脏的营养代谢，并影响外周组织的营养供应。
