Southorn B G, Kelly J M, McBride B W
Department of Animal and Poultry Science, University of Guelph, ON, Canada.
J Nutr. 1992 Dec;122(12):2398-407. doi: 10.1093/jn/122.12.2398.
We conducted two experiments to evaluate the flooding dose method for measuring intestinal and liver protein synthesis in sheep. Experiment 1 showed that large doses of phenylalanine did not cause marked metabolic disturbances. Experiment 2 examined the effectiveness of flooding with phenylalanine and the time dependency of the protein synthesis calculation. Rams were injected with 1.2 MBq L-[ring 2,6-3H]phenylalanine/kg body wt and slaughtered 20, 40 or 60 min later. Plasma specific radioactivity reached a plateau within 2.5 min and did not change significantly (P > 0.05) throughout the experiment. Tissue intracellular free pool specific radioactivity also remained constant from 20 to 60 min postinfusion. Flooding conditions were achieved in the intracellular free pool of intestinal tissues (specific radioactivity 70-96% of plasma specific radioactivity), although liver flooding was less successful (57-67%). Protein synthesis rates measured after 20 min were significantly (P < 0.05) higher in the liver, jejunum and ileum than those measured at 60 min. Protein synthesis rates also tended to decline with time in the duodenum and colon (P > 0.05). There were no significant differences (P > 0.05) between protein synthesis rates calculated using the intracellular specific radioactivity vs. plasma specific radioactivity in the duodenum, ileum or colon. Therefore, this method represents an improvement over continuous infusion methods for measurements of protein synthesis in visceral tissues.
我们进行了两项实验，以评估用于测量绵羊肠道和肝脏蛋白质合成的冲击剂量法。实验1表明，大剂量苯丙氨酸不会引起明显的代谢紊乱。实验2研究了苯丙氨酸冲击的有效性以及蛋白质合成计算的时间依赖性。给公羊注射1.2 MBq L-[环2,6-3H]苯丙氨酸/千克体重，并在20、40或60分钟后宰杀。血浆比放射性在2.5分钟内达到平稳状态，并且在整个实验过程中没有显著变化（P>0.05）。输注后20至60分钟，组织细胞内游离池比放射性也保持恒定。肠道组织的细胞内游离池中达到了冲击条件（比放射性为血浆比放射性的70-96%），尽管肝脏的冲击效果较差（57-67%）。20分钟后测得的肝脏、空肠和回肠中的蛋白质合成率显著高于60分钟时测得的（P<0.05）。十二指肠和结肠中的蛋白质合成率也随时间趋于下降（P>0.05）。在十二指肠、回肠或结肠中，使用细胞内比放射性与血浆比放射性计算的蛋白质合成率之间没有显著差异（P>0.05）。因此，该方法相对于连续输注法在测量内脏组织蛋白质合成方面有改进。
