Abstract
Three experiments were conducted on incorporation of urea nitrogen into body proteins. The first was to study the distribution of 15N in organs after 15N-urea administration, the second to estimate how much urea could be utilized for protein synthesis, and the third to clarify a nutritional role of urea nitrogen. Rats fed on low protein (5% casein) diet were used. The results were as follows;
1) The retention rates of 15N in the whole body, as shown in a percentage of administered 15N, were 25.34% in LPD (rats fed on low protein diet) group and only 5.26% in SPD (rats fed on standard protein diet) group. Among the organs, the carcass protein had the largest part of 15N retention.
2) 15N incorporation into plasma protein increased in proportion to the amouut of administered 15N-urea between 10 and 30mg/100g B.W. However, the efficiency of 15N utilization in protein synthesis was depressed over the range of 30mg/100g B.W. and reached the maximum at 50mg/100g B.W.
3) Growth curve of weanling rats fed on low protein diet supplemented with urea rose significantly by 50% from that of weanling rats fed on control (without supplementation).
Thus, it is concluded that urea nitrogen can be utilized for the synthesis of body protein in rats fed on low protein diet, inducing an increase in body weight. The maximum level of urea N bioutility existed so that the amount of urea supplementation should be proper.
