The Evaluation of Proteins in Hypoproteinemic Dogs

The relationships between nitrogen balance and absorbed nitrogen and ingested nitrogen in normal and hypoproteinemic dogs are described by the equations: NB = K (AN) − NEo NB = K′ (NI) − NEo where NB is nitrogen balance, AN is absorbed nitrogen, NI is ingested nitrogen, and NEo is the excretion of nitrogen on a protein-free diet. These are linear relationships, within experimental error, in the regions of negative and low positive nitrogen balance. K and K′ are functions of the retention of nitrogen by the animal and may be called biological values or nitrogen balance indexes of absorbed and ingested nitrogen respectively. The values for K, K′ and “net protein” value increase, while those for absorbed nitrogen at equilibrium and NEo decrease from normal in the hypoproteinemic dog. These constants are functions of, but not necessarily the fractions of, nitrogen retained in the body of the animal since values greater than unity have been obtained while feeding egg white to hypoproteinemic dogs. Continued feeding of egg white results in a decrease in the excretion of nitrogen on a protein-free diet (NEo). The data can be interpreted to mean that egg white spares body nitrogen. Regeneration of plasma protein increases in magnitude as the nitrogen balance increases on the positive side. Thus regeneration of tissue proteins in hypoproteinemic dogs as reflected in the increase of plasma proteins is a function of the nitrogen balance produced and therefore of K or K′.