Abstract
It is well known that growth retardation of young rats fed a low casein diet is induced when added an essential amino acid mixture lacking histidine (histidine imbalance). Omission of an amino acid (or acids) from the imbalancing amino acid mixture lessened the imbalance phenomenon, especially in the case of lysine.
The lysine omission (-Lys) caused a little increase in free histidine concentration of blood samples from portal vein and heart, which was lowered by the histidine imbalanced diet. Activities of digestive enzymes of the -Lys group were elevated compared with those of the imbalanced group. Though the rate of histidine transport in small intestines was almost the same among the three tested groups, the coexistence of an imbalancing amino acid mixture with histidine in an infused to small intestines tended to reduce the rate of histidine transport, and the lysine omission from the mixture tended to restore it.
Possible contributions of digestive enzymes and intestinal transport of the first limiting amino acid to the amino acid imbalance were discussed.
