Protein intake regulation by the liver

我们之前已经证明，大鼠通过不同的机制调节蛋白质和能量的摄入。在本研究中，我们通过低蛋白和高蛋白饮食的自我选择方法，研究了成年大鼠（PCA）和未（对照）门静脉吻合时肝脏参与蛋白质摄入调节的情况。1. 饲喂酪蛋白的PCA大鼠食量正常，生长正常，蛋白质摄入量约为对照组的60%。2. 当使用低质量蛋白（面筋）时，PCA大鼠的蛋白质摄入量仅为对照组的20%，并且生长不佳。这一结果与正常大鼠相反，正常大鼠在膳食蛋白质质量下降的情况下，通过增加蛋白质摄入量来保持正常生长。PCA大鼠没有增加蛋白质的摄入，可能是因为它们无法处理过量的膳食氮。3. 给予酪蛋白饮食的饥饿PCA大鼠将蛋白质摄入量增加到与对照组相同的水平。4. 然而，麸质摄入量的增加很小，PCA大鼠摄入的麸质量仅为对照组的25%。5. 尿素对PCA大鼠的蛋白质和能量摄入没有影响。6. 相反，饲粮中添加铵降低了能量摄取量，但没有降低蛋白质摄取量。7. 通过补充支链氨基酸，PCA大鼠的蛋白质摄入量略有增加，但比对照组少得多。由此可见，肝脏通过调节氮代谢来影响蛋白质的摄入。

We previously demonstrated that the rat regulated the intake of protein as well as energy by different mechanisms. In the present study we investigated the participation of the liver in the regulation of protein intake using adult rats with (PCA) or without (control) portacaval anastomosis by the self-selection method of low and high protein diets. 1. PCA rats given casein diet consumed normal amount of food and grew normally, but protein intake was about 60% of control. 2. When low quality protein (gluten) was used, the protein intake of PCA rats was only 20% of control and did not grow well. This result is in contrast with that of normal rats which showed normal growth by increasing protein intake as dietary protein quality decreased. It seems that PCA rats did not increase protein intake probably because they could not handle excess dietary nitrogen. 3. Starved PCA rats given casein diet increased protein intake to the same level as control. 4. However, the increase in gluten intake was small and the amount of gluten consumed by PCA rats was only 25% of control. 5. Urea had no effect on the intake of protein as well as energy in PCA rats. 6. In contrast, energy intake but not protein intake decreased by ammonium supplementation. 7. Protein intake increased a little by the supplementation of branched-chain amino acids but was much less in PCA rats than control. It may be concluded that liver influenced protein intake by modifying nitrogen metabolism.