Tissue components of the domestic fowl. 3. The non-protein nitrogen of plasma and erythrocytes

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Abstract
Non-protein nitrogen (NPN) was measured on blood or plasma deproteinized by trichloroacetic acid. Diffusates of blood which had been diluted and boiled at pH 6.4 gave the same values. Deproteinization by tungstate removed some diffusible NPN. "Ninhydrin N" was also measured on trichloroacetic acid filtrates. Erythrocyte NPN is 5 to 6 times that of plasma. The erythrocyte portion of the blood volume fluctuates with the physiological state and varies in relation to sex and nutrition; it therefore biases measurements of NPN made on whole blood. Significantly higher levels of whole blood NPN were found in the first of each of the following pairs: (a) starved and fed laying hens; (b) fed and starved non-laying hens; (c) fed non-laying and fed laying hens; (d) immature and non-laying hens. These differences are almost entirely due to differences in erythrocyte volume. Erythrocyte NPN concentrations were markedly higher in immature birds than in adults. Plasma NPN concentrations were significantly higher (a) in non-laying than in laying fed hens, (b) in immature than in non-laying hens. In a single experiment involving 6 hens a statistically significant correlation was found between their erythrocyte N concentrations and the number of eggs laid during the 6 days subsequent to blood sampling. Uric acid plasma levels were related to sex and to the physiological and nutritional states. In filtrates of erythrocytes and plasma of hens and cocks, qualitatively analyzed by high-voltage paper electrophoresis, 18 free 2-amino acids were detected with evidence of higher concentrations of some in the erythrocytes, namely arginine, aspartate, cystine-cysteine, glycine, histidine, leucine-isoleucine and lysine. A high concentration of taurine in the cells and the apparent absence from the blood of glutamine are noteworthy. 4-Aminobutyrate was found in cock plasma. The NPN of plasma and of erythrocytes was fractionated into "ninhydrin N" and "residual N". In immature birds the amounts of both the erythrocyte "ninhydrin" and "residual N" were at levels distinctly higher in mature animals. The erythrocyte" ninhydrin N" of non-layers was higher than that of layers, whereas the reverse held for the erythrocyte "residual N". The plasma "residual N" and the plasma NPN of non-layers was significantly higher than that of layers. The plasma "ninhydrin N" corresponds with values found by others for "amino acids.".