Urea Degradation Rate Research Articles

The effects of dietary sucrose and the concentration of plasma urea and rumen ammonia on the degradation of urea in the gastrointestinal tract of cattle.

1. The rates of entry of urea into plasma, of urea degradation in the gastrointestinal tract, and the partition of that degradation between the rumen and post-ruminal tract were determined by use of [14C]urea and NaH14CO3 in Hereford steers receiving hay diets with or without sucrose. The concentrations of plasma urea and rumen ammonia were varied by infusions of urea into the rumen or abomasum. 2. For all diets, plasma urea concentration was related to urea entry rate, to degradation of urea in the whole gastrointestinal tract, and to its degradation in the post-ruminal tract, but the relationship with its degradation in the rumen was poor. 3. Degradation of urea in the rumen was related in a multiple regression in a curvilinear manner in three groups of diets (pasture-hay alone, pasture-hay--lucerne (Medicago sativa) mixtures, diets with sucrose), and negatively to rumen ammonia concentration for pasture-hay diets, and diets with sucrose. 4. Ruminal clearance of urea (rate of urea degradation per plasma urea concentration) was negatively related to the rumen ammonia concentration for steers given diets with sucrose, of pasture-hay with or without urea infusions. Provision of sucrose in the diet significantly increased clearance. 5. Enhanced urea degradation in the rumen associated with dietary sucrose supplements accounted for 0.4 of additional microbial N synthesis in the rumen. 6. The partition of transfer of urea to the rumen via saliva and through the rumen wall is discussed.

The nitrogen metabolism of sheep consuming Flinders grass (Iseilema spp.), Mitchell grass (Astrebla spp.) and mixed native pasture

Some aspects of nitrogen metabolism of sheep given Mitchell grass (Astrebla spp.), Flinders grass (Iseilema spp.) and mixed native pasture were investigated. All diets were of low nutritive value as demonstrated by negative nitrogen and energy balances in sheep on these diets. Studies of urea metabolism demonstrated a significant relationship between plasma urea concentration, the rate of irreversible loss of urea from plasma and the rate of urea degradation in the digestive tract. On average, 81% of the urea synthesized in the body was transferred to the digestive tract and degraded to ammonia and carbon dioxide. The proportion of urea degradation occurring intraruminally was estimated during an intravenous infusion of 14C urea by measuring the rate of appearance of 14CO2 in ruminal fluid, the proportion degraded post-ruminally being obtained by difference. Urea degraded in the rumen accounted for 7–13% of the total quantity degraded in the digestive tract, and the rate of urea transfer (0.55 ± 0.13 g nitrogen/day) was not related to the rate of urea synthesis in the body. The lower digestive tract was the major site of urea degradation in sheep given these low protein diets, and the rate of urea transfer to this part of the digestive tract was linearly related to the rate of urea synthesis in the body. The implications of these findings are discussed in relation to nitrogen conservation in sheep given low quality diets.

UREA DEGRADATION IN THE CAMEL

Following a single injection of 14C-urea, the kinetics of urea metabolism have been studied in two female Arabian camels (Camelus dromedarius) fed roughage diets containing 6.1 (diet A), 9.6 (diet B), and 13.6% (diet C) crude protein. In general, plasma urea concentration, urea pool size, urea entry rate and urinary urea excretion rate increased as the dietary nitrogen intake increased. The mean extents of urea degradation were approximately 86, 74 and 47% for diets A, B, and C, respectively, as calculated from the ratio of urea degradation rate to urea entry rate, or from the fraction of 14C-urea recovered in the urine. The following parameters were linearly related: urea entry rate and urea pool size, urea pool size and plasma urea concentration, percentage urea degraded and urea entry rate, and percentage urea degraded and crude protein intake.

Efficiency of utilization of urea nitrogen for albumin synthesis by chronically uraemic and normal man.

1. The relation between endogenous urea metabolism and albumin synthesis has been studied in ten patients with chronic renal failure and in four normal subjects, after single intravenous injections of [14-C]urea,[15-N]urea and 125-I-labelled albumin. 2. The rate of urea synthesis was determined from the dynamics of plasma [14-C]urea specific radioactivity and the rate of urea metabolism was estimated from the relative rates of urea synthesis and urea appearance in urine and body water. Deconvolution analysis of plasma [15N]albumin enrichmevt and 125-i-labelled albumin radioactivity yielded the cumulative incorporation of 15-N into total exchangeable albumin and enabled calculation of the absolute rate of urema nitrogen utilization for albumin synthesis. 3. Although the mean absolute rate of urea degradation in uraemic patients (3-7 mmol/h) was higher than in normal subjects (2-3 mmol/h) there was no significant positive correlation between urea degradation and plasma urea concentration. 4. In uraemic subjects, there was a significant positive correlation between urea synthetic rate and urea degration rate. 5. The rate of utilization of urea nitrogen for albumin synthesis was low, but was very much higher in uraemic subjects (mean 83-8 mumol/h) compared with normal subjects (mean 6-4 mumol/h), as was the provision by urea of the nitrogen required for albumin synthesis in uraemic subjects (2-37%) compared with normal subjects (0-13%). 6. The efficiency of utilization of urea nitrogen for albumin synthesis was higher in the uraemic patients (1-3%) than the normal subjects (0-2%), and was higher in those patients with chronic renal failure who received a 30 g protein diet than those on 70 g of protein. A significant negative correlation was noted between efficiency of urea nitrogen utilization and the rate of synthesis of albumin. 7. These studies suggest the presence of a mechanism for the conservation of urea nitrogen in chronic renal failure which is unrelated to the extent of urea degradation, and which can only be partly explained by the higher proportion of intraluminal gut nitrogen derived from urea.

Action of Urea on Tobacco Mosaic Virus: II. The Bonds Between Protein Subunits

The rate of urea degradation is not uniform over the tobacco mosaic virus (TMV) rod, as might be expected since the protein subunits appear to be chemically identical. Only two stable intermediates are formed; the four components with sedimentation constants, S(40) (20), about 80, 120, 140, and 165 correspond to the two intermediates with and without RNA tails. Analysis of the reaction kinetics for the disappearance of whole virus and of the first intermediate was made in terms of a new hypothesis concerning protein bonding.