Effect of the Quality of Dietary Protein on Nitrogen Compounds in the Urine of Rats

Abstract

To learn in more detail the effect of dietary protein quality on the ratio of urinary N compounds of rats, the excretion rate of urea, allantoin, creatinine and their partition were determined when the rats of 4 ages (21-, 27-, 61- and 158-day-old) were fed each diet containing casein and wheat gluten at the 14% level. The nutritive value of both proteins was simultaneously compared using the usual methods for biological value, net protein utilization, net protein ratio and the ratio of creatinine N to total urinary N. In general, urea excretion increased with the decrease of protein quality and increased with protein intake or age, or both. Although allantoin excretion was more complex and less variable than urea excretion, that of the casein groups was consistently higher than that of gluten groups except in the case of the 158-day-old rats. In using the ratios between urinary N compounds to describe nutritive value of dietary protein, the values for (allantoin/urea) × protein intake were comparable to that of other criteria: biological value or net protein ratio, although the effect of age and dietary protein quality on allantoin excretion needs further investigation.