Protein intake regulation by the liver

我们以前证明，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，我们调查了参与调节蛋白质摄入量的肝脏成年大鼠（PCA）或（对照）门腔静脉吻合术的低蛋白和高蛋白饮食的自我选择方法。1.给予酪蛋白饲料的PCA大鼠摄食量正常，生长正常，但蛋白质摄入量约为对照组的60%。2.当使用低质量蛋白质（面筋）时，PCA大鼠的蛋白质摄入量仅为对照组的20%，并且生长不良。这一结果与正常大鼠的结果相反，正常大鼠在膳食蛋白质质量下降时通过增加蛋白质摄入而显示出正常生长。看来PCA大鼠没有增加蛋白质摄入量，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大鼠增加蛋白质摄入量至与对照组相同的水平。4.然而，面筋摄入量的增加很小，PCA大鼠消耗的面筋量仅为对照组的25%。5.尿素对PCA大鼠的蛋白质和能量摄入量没有影响。6.相反，能量摄入，但不是蛋白质摄入减少铵补充。7.蛋白质摄入量增加了一点支链氨基酸的补充，但在PCA大鼠远远低于对照组。因此，肝脏可能通过调节氮代谢来影响蛋白质摄入。

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.