Protein intake regulation by the liver

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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.