Nitrogen Excretion

Mammals and birds adapt to prolonged fasting by mobilizing fat stores and minimizing protein loss. This strategy ends with an increase in protein utilization associated with behavioural changes promoting food foraging. Using the Zucker rat as a model, we have investigated the effect of severe obesity on this pattern of protein loss during long-term fasting. Two interactions between the initial adiposity and protein utilization were found. First, protein conservation was more effective in obese than in lean rats: fatty rats had a three times lower daily nitrogen excretion and proportion of energy expenditure deriving from proteins, and a lower daily protein loss in various muscles. This phase of protein sparing is moreover nine times longer in the fatty rats. Second, obese animals did not show the late increase in nitrogen excretion that occurred in their lean littermates. Total body protein loss during starvation was larger in fatty rats (57% versus 29%) and, accordingly, total protein loss was greater in their muscles. At the end of the experiment, lean and obese rats had lost 98% and 82%, respectively, of their initial lipid reserves, and fatty rats still had an obese body composition. These results support the hypothesis that in severely obese humans and animals a lethal cumulative protein loss is reached long before the exhaustion of fat stores, while the phase of protein conservation is still continuing. In contrast, in lean rats, survival of fasting seems to depend on the availability of lipid fuels. The data also suggest that accumulation of too much fat in wild animals is detrimental for survival, because it eliminates the late phase of increase in nitrogen excretion that is linked to a food foraging behaviour anticipating a lethal depletion of body reserves.

Nile tilapia weighing 8.29–11.02 g were fed a practical diet at seven ration levels (starvation, 0.5, 1, 2, 3, 4% body weight per day and satiation) twice a day at 30 °C. Feed consumption, apparent digestibility, nitrogenous excretion and growth were determined directly, and heat production was calculated by difference of energy budget. The relationship between specific growth rate in

The functions of the various gut regions of Oikopleura dioica (oesophagus, left and right gastric lobes, vertical intestine, mid-intestine and rectum) were investigated by means of histochemical, histoenzymatic and immunohistochemical techniques at light and electron microscopes. Ciliary food progression is evidenced by the presence of ATPases on cilia, along the entire gut, with the exception of the cardiac valve, a passive device controlling food direction. Absorptive processes (alkaline phosphatase), active transport (ATPases) and nitrogen excretion (D-amino acid oxidase) occur along the entire gut, in both ciliated microvillar and globular cells. The latter, typical of the left gastric lobe and rectum, are also involved in endocytotic processes (exogenous peroxidase as tracer) and intracellular digestion (α-amylase, aminopeptidase M, acid phosphatase, 5′-nucleotidase, non-specific esterase). The giant cells of the gastric band participate in extracellular digestion; they contain secretory granules positive to various hydrolytic enzymes, the activity of which is also recognisable in faecal pellets inside the intestinal lumen. Lipid storage occurs mainly in the right gastric lobe and vertical intestine, whereas protein storage takes place in the rectal granular cells. Epithelial transport and possible osmoregulation occur along the entire gut, especially at the level of diffuse baso-lateral interdigitations, which increase the plasmalemma surface enormously, are often associated with mitochondria and possess numerous ATPase pumps. Data extend previous histological observations and hypotheses on the physiological role of the various gut regions. The remarkable and specific location of enzymatic activities and nutrient storage are in agreement with the high capacity of O. dioica to process a great quantity of food very rapidly and efficiently.

Few investigations have studied protein metabolism in children and adolescent athletes which makes difficult the assessment of daily recommended dietary protein allowances in this population. The problematic in paediatric competitors is the determination of additional protein needs resulting from intensive physical training. The aim of this investigation was to determine protein requirement in 14-year-old male adolescent soccer players. Healthy male adolescent soccer players (N = 11, 13.8 +/- 0.1 year) participated in a short term repeated nitrogen balance study. Diets were designed to provide proteins at three levels: 1.4, 1.2 and 1.0 g protein per kg body weight (BW). Nutrient and energy intakes were assessed from 4 day food records corresponding to 4 day training periods during 3 weeks. Urine was collected during four consecutive days and analysed for nitrogen. The nitrogen balances were calculated from mean daily protein intake, mean urinary nitrogen excretion and estimated faec...

During the past few decades, considerable attention has been given to the impact of nutrition on kidney disease. Although most dietary attempts to treat chronic renal failure (CRF) and to decrease uremia recommend a protein restriction, another dietetic approach, based on dietary fibers (DF), can lead to the same urea- lowering effect by increasing urea-nitrogen (N) excretion in stool with

Urine excretion is a substantial factor in the amount of manure that needs to be managed, and urinary N can contribute to ammonia volatilization. Development and validation of prediction equations focusing on dietary factors to decrease urine and urinary nutrient excretion will provide information for managing urine and feces separately or for other future technologies. The objective of this study was to develop equations for prediction of urine excretion and excretion of urinary N, Na, and K and to evaluate both new and previously published prediction equations for estimation of urine and urinary nutrient excretion from lactating dairy cows. Data sets from metabolism studies conducted at Washington State University were compiled and evaluated for excretion of minerals. Urine excretion averaged 24.1 kg/d and urinary nitrogen excretion ranged from 63 to 499 g/d in the calibration data set. Regression equations were developed to predict urine excretion, urinary N excretion, and urinar...

Teleost fish have been shown to excrete a variety of nitrogenous substances among which are ammonia, urea, and creatine. Previous reports show values for excretion of near­ shore or bottom fish but not of pelagic species. Two species of anchovy and jack mackerel were placed in chambers and their nitro­ genous excretion products were measured. Ammonia, urea, and creatine accounted for 82% of the total nitrogen excreted by Engraulis mordax and the identified fraction was 83% ammonia, 16% urea, and 1% creatine.

A three-year study was carried out to assess the effect of different grass-legume mixtures on the N excretion of grazing Sardinian sheep in early-mid lactation (January-May). Replicate groups rotationally grazed plots of three grass-legume mixtures consisting of common grass (Lolium rigidum, Gaudin) and different legumes, namely: Medicago polymorpha (burr medic, treatment BM), Trifolium subterraneum (subclover, treatment SC) and Hedysarum coronarium (sulla, treatment SU). Herbage dry matter intake and faecal dry matter excretion were estimated by the n-alkane method in three sheep per replicate group on three or two occasions per year. The N content in herbage and faeces was measured in freeze-dried samples collected on the same occasions. N excretion in urine was estimated by difference, assuming no changes in body N while N utilisation efficiency (NUE) was calculated as the ratio between the yield of N in milk and N intake (NI). In years 1 and 3, corresponding to a higher proporti...