Nitrogenous End Products Research Articles

An L-arginine-dependent mechanism mediates Kupffer cell inhibition of hepatocyte protein synthesis in vitro.

The hepatic failure associated with severe sepsis is characterized by specific, progressive, and often irreversible defects in hepatocellular metabolism (1). Although the etiologic microbe can often be identified, the direct causes and mechanisms of the hepatocellular dysfunction are poorly understood. We have hypothesized that Kupffer cells (KC), which interact with ambient septic stimuli, respond by providing signals to adjacent hepatocytes (HC) in sepsis . Furthermore, we have provided evidence (2, 3) that KC activated by LPS from Gram-negative bacteria can induce profound changes in the function of neighboring HC in coculture. In our model, coculture of either KC (2) or peritoneal macrophages (Mphi)(3) with HC normally promotes HC protein synthesis ([(3)H]leucine incorporation). The addition of LPS or killed Escherichia colt' to such cocultures induces a profound decrease in HC protein synthesis, as well as qualitative changes ([(35)S]methionine, SDS-gel electrophoresis) in protein synthesis without inducing HC death (2, 3) . In this report we show that the inhibition in protein synthesis is mediated via an L-arginine-dependent mechanism. The metabolism of L-arginine by activated Mphi to substances with cytostatic and even lethal effects on target cells is a relatively recent discovery. After the description by Stuehr and Marletta (4, 5) that LPS- triggered Mphi produced nitrite/nitrate (NO(2)(-)/NO(3)(-)), Hibbs et al. (6, 7) and Iyengar et al. (8) demonstrated that L-arginine was the substrate for the formation of both these nitrogen end products and citrulline. A role for the arginine-dependent mechanism in Mphi tumor cytotoxicity (6, 7) and microbiostatic activity (9) has been suggested. However, the in vivo functions of this novel Mphi mechanism have not yet been defined, but it is possible that there are both physiologic as well as pathologic roles. Our in vitro results raise the possibility that some metabolic responses to microbial invasion maybe partially mediated by the L-arginine-dependent mechanism. What other metabolic responses are affected and the possible pathologic consequences remain to be studied.

Carbohydrate, fat, and protein metabolism in muscle and in the whole body after mixed meal ingestion

The effect of ingesting a meal containing 3,275 kJ (47.3% carbohydrate, two-thirds of which was in the form of simple sugars, 39.4% fat, and 13.2% protein) on the oxidation of carbohydrate fat and protein (or amino acids) was assessed by indirect calorimetry and measurement of the rate of excretion of nitrogenous end products in urine and changes in the plasma urea concentration. Simultaneously, an assessment was made of substrate metabolism in forearm muscle by measuring forearm blood flow and concentration of metabolites in arterialized and deep venous blood. The mean resting energy expenditure during the first four hours after food ingestion was 15% higher than in the preprandial period ( P < .01). The extra energy dissipated during this time is equivalent to 5.3% of the energy provided in the meal. Carbohydrate oxidation increased by 111% ( P < .01), protein oxidation increased by 40% ( P < .05), and fat oxidation decreased by 21% ( P < .05). The concentration of glucose and amino acids and their uptake by muscle increased after food ingestion, while the reverse occurred with nonesterified fatty acids (NEFA). In the early postprandial period there was a marked suppression in the uptake of NEFA by muscle and a tendency toward decreased rather than increased release of glycolytic products (lactate + pyruvate + alanine), despite an up to sevenfold increase in the uptake of glucose. Fructose, which accounted for about 30% of the carbohydrate in the diet, was not taken up by muscle to any significant extent. It is estimated that during the first four hours after the meal muscle accounted for the uptake of 20% to 25% of the carbohydrate provided in the meal. This was associated with a small and nonsignificant change in the oxygen uptake by muscle. The data suggest that: (1) the increased uptake of glucose by muscle in the postprandial period does not necessarily increase the release of glycolytic products or increase the activity of the glucose-alanine and Cori cycles between muscle and liver; (2) triglyceride may become a more important energy source for muscle than circulating NEFA, especially in the early postprandial period; (3) muscle is not a major site of dietary-induced thermogenesis (zero to four hours); and (4) it is likely that nonmuscular tissues took up more carbohydrate (including fructose) than skeletal muscle during the first four hours after ingestion of this meal (even if it is assumed that as little as 50% of the dietary carbohydrate had been absorbed by four hours).

Adaptations of the reed frog Hyperolius viridiflavus (Amphibia, Anura, Hyperoliidae) to its arid environment : III. Aspects of nitrogen metabolism and osmoregulation in the reed frog, Hyperolius viridiflavus taeniatus, with special reference to the role of iridophores.

Reed frogs of the superspecies Hyperolius viridiflavus occur throughout the seasonally very dry and hot African savannas. Despite their small size (300-700 mg), estivating reed frogs do not avoid stressful conditions above ground by burrowing into the soil, but endure the inhospitable climate relatively unprotected, clinging to mostly dry grass stems. They must have efficient mechanisms to enable them to survive e.g. very high temperatures, low relative humidities, and high solar radiation loads. Mechanisms must also have developed to prevent poisoning by the nitrogenous wastes that inevitably result from protein and nucleotide turnover. In contrast to fossorial amphibians, estivating reed frogs do not become torpid. Reduction in metabolism is therefore rather limited so that nitrogenous wastes accumulate faster in these frogs than in fossorial amphibians. This severely aggravates the osmotic problems caused by dehydration. During dry periods total plasma osmolarity greatly increases, mainly due to urea accumulation. Of the total urea accumulated over 42 days of experimental water deprivation, 30% was produced during the first 7 days. In the next 7 days rise in plasma urea content was negligible. This strong initial increase of urea is seen as a byproduct of elevated amino acid catabolism following the onset of dry conditions. The rise in total plasma osmolarity due to urea accumulation, however, is not totally disadvantageous, but enables fast rehydration when water is available for very short periods only. Voiding of urine and feces ceases once evaporative water loss exceeds 10% of body weight. Therefore, during continuous water deprivation, nitrogenous end products are not excreted. After 42 days of water deprivation, bladder fluid was substantially depleted, and urea concentration in the remaining urine (up to 447 mM) was never greater than in plasma fluid. Feces voided at the end of the dry period after water uptake contained only small amounts of nitrogenous end products. DSF (dry season frogs) seemed no to be uricotelic. Instead, up to 35% of the total nitrogenous wastes produced over 42 days of water deprivation were deposited in an osmotically inert and nontoxic form in iridophore crystals. The increase in skin purine content averaged 150 μg/mg dry weight. If urea had been the only nitrogenous waste product during an estimation period of 42 days, lethal limits of total osmolarity (about 700 mOsm) would have been reached 10-14 days earlier. Thus iridophores are not only involved in colour change and in reducing heat load by radiation remission, but are also important in osmoregulation during dry periods. The selective advantages of deposition of guanine rather than uric acid are discussed.

In situ measurement of respiratory metabolism and nitrogen fluxes at the interface of oyster beds

Nitrogen and oxygen fluxes were measured in situ during monthly dark enclosure experiments on oyster beds. The incubations were performed on undisturbed sediment with its endofauna, on 10 oysters Crassostrea gigas isolated from the substratum, and on 10 oysters associated with the sediment, to assess the impact of oyster farming on the environment. Ammonia was released by the sediment following a seasonal pattern, s ammonia excretion increased in spring (3.21 pm01 g-' h-') and autumn (2.5 to 6.7 pm01 g-' h-'), compared to low winter values (0.28 pm01 g-' h-'), in accordance with changes in temperature and oxygen consumption (0.14 and 1.3 mg O2 g-' h-' in winter and summer respectively). Some nitrate production was observed, suggesting occasional nitrification. Primary amine exchanges were rather erratic, whereas urea seems to play an important role seasonally as a nitrogenous end-product, in relation to a lower condition index at the end of the winter A sirnp!e budge? sf sediment-water exchanges, calculated on a m-' basis (e. g. 2 kg oysters m-'), indicates that over the year the oysters' contribution to the fluxes averages 37 and 40 % for ammonia and urea release respectively, and 26 O/ O for oxygen uptake. However, the actual contribution of oysters to the exchanges at the water-sediment interface rarely fits the expected values from potential estimates. Oxygen consumption, ammonia release and nitrate absorption of the association of oysters with sediment are mainly depressed, except durlng winter and early spring when respiration is stimulated.

Adaptations of the reed frogHyperolius viridiflavus (Amphibia, Anura, Hyperoliidae) to its arid environment

Ofall amphibians living in arid habitats, reed frogs (belonging to the super species Hyperolius viridiflavus) are the most peculiar. Froglets are able to tolerate dry periods of up to 35 days or longer immediately after metamorphosis, in climatically exposed positions. They face similar problems to estivating juveniles, i.e. enduranee of long periods of high temperature and low RH with rather limited energy and water reserves. In addition, they must have had to develop meehanisms to prevent poisoning by nitrogenous wastes that rapidly accumulate during dry periods as a metabolie consequenee of maintaining a non-torpid state. During dry periods, plasma osmolarity of H. v. taeniatus froglets strongly increased, mainly through urea accumulation. Urea accumulation was also observed during metamorphic climax. During postmetamorphic growth, chromatophores develop with the density and morphology typical of the adult pigmentary pattern. The dermal iridophore layer, which is still incomplete at this time, is fully developed within 4-8 days after metamorphosis, irrespective of maintenance conditions. These iridophores mainly contain the purines guanine and hypoxanthine. The ability of these purines to reflect light provides an excellent basis for the role of iridophores in temperature regulation. In individuals experiencing dehydration stress, the initial rate of purine synthesis is doubled in eomparison to specimens continuously maintained under wet season conditions. This increase in synthesis rate leads to a rapid increase in the thiekness of the iridophore layer, thereby effectively reducing radiation absorption. Thus, the danger of overheating is diminished during periods of water shortage when evaporative cooling must be avoided. After the development of an iridophore layer of sufficient thickness for effective radiation reflectance, synthesis of iridophore pigments does not cease. Rather, this pathway is further used during the remaining dry season for solving osmotic problems eaused by accumulation of nitrogenous wastes. During prolonged water deprivation, in spite of reduced metabolic rates, purine pigments are produced at the same rate as in wet season conditions. This leads to a higher relative proportion of nitrogen end products being stored in skin pigments under dry season conditions. At the end of an experimental dry season lasting 35 days, up to 38% of the accrued nitrogen is stored in the form of osmotically inactive purines in thc skin. Thus the osmotic problems caused by evaporative water loss and urea production are greatly reduced.

Phosphamidon induced alterations in the nitrogen metabolic profiles of penaeid prawn,Penaeus indicus during acute and chronic exposure

Changes in the nitrogen metabolic profdes of midgut gland, muscle and gill tissues were studied, following the exposure ofPenaeus indicus to acute (2 day) and chronic (10, 20 and 30 day) exposure to sublethal concentration (0–2 ppm) of phosphamidon. The proteolytic activity of phosphamidon exposed prawn tissues was significantly elevated. All the phosphamidon exposed prawn tissues showed efficient mechanisms of ammonia detoxification in the chronically exposed prawns when compared to acutely exposed prawns. The survivability of these prawns in the polluted habitats might be due to the operation of compensatory adaptive mechanisms in the metabolic profdes such as increased biosynthesis of different kinds of proteins and also the detoxification and transformation of ammonia, the toxic nitrogenous end product of aquatic organisms.

Renal excretion of nitrogenous compounds in vertebrates.

The renal excretion of nitrogenous compounds plays an important role not only in the elimination of nitrogen end-products but also in regulating the acid-base and osmotic balance of body fluids. The major nitrogenous compounds excreted by the vertebrate kidney are ammonia, urea and uric acid. The present review addresses the renal excretion of these compounds and, in addition, the amino acid taurine. The functions of excretion; the mechanisms of excretion including renal metabolism, renal handling (secretion, reabsorption, and filtration), and transepithelial transport processes; and the factors regulating these mechanisms are discussed. Renal nitrogen excretion among the vertebrate classes from fish to mammals is compared.

Lactate, alanine and glutamine metabolism in isolated canine pup liver cells

The metabolism of lactate, alanine and glutamine was studied in isolated canine liver cells. Lactate proved a better gluconeogenic precursor than alanine and glutamine. Glucose was synthesized at similar rates from both amino acids and ureogenesis from glutamine was double that from alanine. As in isolated rat liver cells, glucose and urea represented the main carbon and nitrogenous end-products of lactate, alanine and glutamine metabolism. Taken with the known levels of hepatic uptake of glutamine and alanine, these findings suggest that in the fasted dog, unlike in the fasted rat, glutamine and not alanine is the main transporter of nitrogen and carbon from muscle to liver for urea synthesis and gluconeogenesis.

Nitrogen metabolism in goldfish, Carassius auratus (L.). Pathway of aerobic and anaerobic glutamate oxidation in goldfish liver and muscle mitochondria

1. 1. Intact mitochondria isolated from lateral red muscle and liver of goldfish were under aerobic and anaerobic conditions incubated with glutamate, ADP and phosphate. In order to evaluate the route of glutamate oxidation, the accumulation of alanine, ammonia and aspartate was measured. 2. 2. In liver mitochondria, glutamate is exclusively oxidized via glutamate dehydrogenase, resulting in the accumulation of ammonia as the only nitrogenous end-product. This process proves to be completely blocked by anoxia. 3. 3. In red muscle mitochondria glutamate is oxidized via glutamate-oxaloacetate transaminase, resulting in the accumulation of aspartate. This process is not fully blocked by anoxia. 4. 4. These results indicate that in goldfish liver aerobic ammonia production takes place via glutamate dehydrogenase, while in muscle both aerobically and anaerobically to be produced via the purine nucleotide cycle.

Methionine Requirement of Weanling Large White × Landrace Pigs as Determined by Plasma Urea Concentration, Nitrogen Retention and Some Urinary Nitrogenous Components

The methionine requirements of weanling Large White × Landrace pigs fed a 20% protein cassava flour-soybean meal diet were evaluated using nitrogen balance, plasma urea concentration, urinary nitrogenous end products and the index—(allantoin/urinary urea) × protein intake (A/U × Ip). Sensitivities of the response criteria to sex differences in methionine requirements were compared. Allantoin excretion consistently and significantly (P < 0.05) increased with increasing methionine levels to a maximum of 0.55% total methionine. Maximum nitrogen retention was observed in diets containing 0.55, 0.47 and 0.55% total methionine for castrated males, females and the pooled data for both sexes, respectively. Minimum urea concentration in plasma was obtained with the diets containing 0.55% methionine. The index, + A/U × Ip, showed that the diet was better utilized when it contained 0.63, 0.55 and 0.63% total methionine in castrates, females and combination of the two sexes, respectively.pigs methionine requirements nitrogen balance urea

Nitrogen Excretion by Turkey Vultures

-The proportions of nitrogen (N), as urate-N (76.1%), NH3-N (16.4%), and urea-N (7.5%) in the urine of fasted Turkey Vultures, are similar to those found in the urine of domestic chickens and ducks, the only other birds for which comparable data are available. Vultures show an adaptive increase in the percentage of urinary N excreted as urate (up to 86.8%) and a decrease in NH3-N (down to 8.9%) and urea-N (down to 4.3%) in the period after feeding on meat. These alterations in the proportions of nitrogenous wastes increase the efficiency of N excretion; fed birds excrete 4.8 times more N per milliliter of urinary water than fasted birds. The efficiency of N excretion during the 1.5-h period after feeding is comparable to that of the most efficient mammalian excretory systems. The elimination of urate (i.e., uric acid or any other urate compound) as the major nitrogenous excretory compound of birds generally is considered to be an adaptation for water conservation. Needham (1938) described the benefits of urate as a nitrogenous end product in cleidoic eggs; the potential osmotic advantage of urate excretion to adult birds is discussed in most current avian physiology texts (e.g., Sykes 1971, Shoemaker 1972, Sturkie 1976). The low solubility of urate in water (Peters and van Slyke 1946) and its ability to form colloids (Young and Dreyer 1933) might cause less osmotic water to be lost in urate excretion than might occur with osmotically active nitrogenous wastes. The advantages of urate excretion might be evident in two ways in species adapted to either water shortage or high demands for nitrogen (N) excretion relative to water availability: (1) by excretion of a consistently high proportion of urate or (2) by transient increases in the proportion of N excreted as urate, in response to either decreased water availability or high N intake. Regarding the first of these possibilities, previous studies of the proportions of nitrogenous excretory compounds have used only domestic chickens and ducks (e.g., Table II, Shoemaker 1972). While urate accounted for the largest proportion of the waste N in all studies, the percentages of urate-N ranged from 60 to 87% in chickens (see reviews by Sykes 1971, Shoemaker 1972). The only study on ducks (Stewart et al. 1968) reported a low proportion of urateN (54-57%), and it is tempting to speculate that this is a reflection of an abundant water supply with little selective pressure to conserve water. Studies of wild species with different drinking and feeding habits, and from different habitats, are needed to determine whether patterns of nitrogen excretion show long-range evolutionary adaptations. McNabb and McNabb (1975a) found no evidence of adaptive changes in the proportion of urate-N excreted by chickens when water availability was reduced to the minimum required for weight maintenance. While water was limited, chickens ate less high protein food rather than increase urate-N excretion. Moreover, studies such as that of Teekell et al. (1968) show no increase in the proportion of excreted urate over the range of 0-14% dietary protein. In contrast, Sykes (1971) presented data which suggest that fed chickens excrete a higher proportion of urate than fasted chickens. However, he gave only mean values from unpublished work, without statistical analysis, and as he did not indicate if water was available, these data cannot be evaluated adequately. Our objective was to investigate nitrogen excretion in a carnivorous species, the Turkey Vulture (Cathartes aura). Vultures feed on carrion which may be far from water. Thus, when feeding under natural conditions, they consume much nitrogen but are limited to that water available in the food. We compared the proportions of urinary N

Susceptibility of urea and uric acid levels to neurohormone influence in the freshwater pulmonate, lymnaea acuminata

Effects of pooled ganglionic extract on the urea and uric acid levels from blood, hepatopancreas, mantle and kidney of the pulmonate L. acuminata have been analysed. Blood urea and mantle uric acid were significantly (P<0.005 and P<0.05 respectively) increased following injection with pleuroparietalpedal-visceral (PPPV Complex) ganglia homogenate within 2 hrs. On the contrary hepatopancreas urea and kidney uric acid levels were significantly (P<0.00) lowered. Cerebral ganglia homogenate and boiled extract of PPPV complex did not provoke any significant change in urea and uric acid levels. It is advocated that (a) neurohormone(s) which is (are) heat-labile and originate from the PPPV complex, influence(s) the nitrogen end-products in these snails.

Studies on enzymes of nitrogen metabolism, and nitrogen end products in the developing chick ( Gallus domesticus) embryo

1. 1. A total of 450 fertilized eggs were used to study the concentrations of uric acid, urea and ammonia in allantoic and amniotic fluids, and some enzymes of nitrogen metabolism in the liver and kidney during the development of the chick embryo from the 5th to 21st day of incubation. 2. 2. Concentrations of the compounds studied were higher in allantoic fluid. The molar concentration of allantoic uric acid increased steadily with time. The pattern of urea and ammonia in both allantoic and amniotic fluids were the same. 3. 3. Arginase (E.C.3.5.3.1) activity in both embryonic kidney and definitive kidney was higher than that in the liver. The specific activity of arginase (μmole urea formed/hr per g wet wt kidney) dropped during development. 4. 4. Little arginine synthetase activity (argininosuccinate synthetase, E.C.6.3.4.5; and argininosuccinate lyase, E.C.4.3.2.1) was found in kidney, but non in the liver. 5. The complete urea cycle function was absent in both the liver and the kidney of the chick embryo.

Rates of nitrogen excretion by species of Mytilus (Bivalvia: Mollusca)

Although the nitrogenous excretory products of a number of marine bivalve molluscs have been identified (Hammen, Miller &amp; Geer, 1966; Hammen, 1968; Emerson, 1969; Allen &amp; Garrett, 1971; Bayne, 1973 a) and average values for rates of nitrogen excretion recorded for some species (Lum &amp; Hammen, 1964; Hammen et al. 1966; Bayne, 1973a), there is little information available on the ways in which environmental factors may affect either the balance between the various nitrogenous end-products, or their rates of excretion. The most thorough investigations have dealt with the effects of reduced salinity, which causes an increase in the rates of excretion of ammonia by Macoma inconspicua (Emerson, 1969), Mya arenaria (Allen &amp; Garrett, 1971) and Mytilus edulis (Bayne, 1975). Dilution of the medium is also known to accelerate the loss of amino acids from the body, as part of the mechanism of volume regulation (Pierce &amp; Greenberg, 1972, 1973). There is some evidence of altered rates of excretion during starvation (Hammen, 1968; Emerson, 1969; Bayne, 1973 a, b) and differences in excretion rate due to differences in animal size have been documented for Donax vittatus by Ansell &amp; Sivadas (1973) and for Mytilus californianus by Bayne, Bayne, Carefoot &amp; Thompson (1976 a, b).

Nutrition of Glossina morsitans: Metabolism of U- 14C glucose during pregnancy

A Glossina morsitans female can synthesize alanine, aspartic acid, cystine, glutamic acid, glycine, proline, and serine, and also lipids, from d-[U- 14C] glucose during pregnancy and utilize these products for nourishment of the growing intra-uterine larva. The third instar larva shortly after formation of the puparium can also synthesize these nutrients from glucose and is thus similar to the adult female fly in this respect. It is possible that some glucose taken up by the larva via the maternal uterine glands is converted to the above nutrients. Although the specific nutritional requirements of the growing larva are largely provided by its female parent, the larva has active synthetic systems for the regulation and maintenance of its inherent metabolic steady state. This is reflected in the synthesis of large amounts of glutamic acid in the larva whereas in the adult the emphasis appears to be on the synthesis of proline. Most of the injected glucose and its synthetic products are utilized to provide energy for biosynthetic activity. Uric acid is the main nitrogenous end product of catabolism of non-essential amino acids. A small proportion of such amino acids and glucose are also excreted. Embryonic development which lasts for about 4 days following ovulation is sustained by nutrients within the egg. Following eclosion, the first instar larva begins to feed upon uterine gland secretions. This instar lasts for about 1 day. Ecdysis to the second instar, which lasts for 1 to 2 days, is associated with a three- to fourfold increase in the rate of nutrient uptake. Most rapid feeding begins when the third instar develops. These results are discussed in terms of larval growth in relation to feeding by the adult female parent.

Studies on nitrogen catabolism in Panagrellus redivivus, Goodey, 1945 (Nematoda: Cephalobidae)

1. 1. The activities of ornithine-urea cycle, amino acid and purine deaminating and purine degradating enzymes were measured in whole nematode homogenates, and radiocarbon incorporation from urea-cycle intermediates into urea determined. 2. 2. Evidence for a functional urea cycle of low activity was obtained; purine degradation was shown to be insignificant. 3. 3. The significance of these studies is discussed in relation to the nitrogenous end-products excreted by Panagrellus redivivus.

Plasma protein binding of thiopental in patients with impaired renal or hepatic function.

Binding of thiopental to proteins in plasma from healthy, cirrhotic, and uremic subjects was studied using equilibrium dialysis. In plasma from healthy volunteers 28.0 plus or minus 0.9 per cent of thiopental was unbound. In plasma from patients with hepatic disease 53.0 plus or minus 2.1 per cent was unbound, while in patients with renal disease 55.7 plus or minus 1.5 per cent remained unbound. The decreased binding in uremia could not be explained completely by competitive displacement by nitrogenous end products or by hypoalbuminemia, although hypoalbuminemia may account for the decreased binding in cirrhotic patients.

A Glutaminase in the Body Wall of Terrestrial Isopods

THE ability of some terrestrial invertebrates to discharge their nitrogen endproduct in the form of gaseous ammonia seems to violate “Needham's rule” which states that owing to the toxicity of ammonia the ammonotelism of aquatic animals has been replaced by ureocotelism and uricotelism in terrestrial groups. Both gastropods1 and isopods2 execrete some or most of their N-endproducts as gaseous ammonia. This method would seem to preserve ammonotelism, the “cheapest” way of excreting nitrogen, without its negative corollary, the loss of large amounts of body fluid.

Main excretory end-products of protein and purine metabolism in lizards and snakes

1. Uric acid is the main nitrogenous constituent of the urinary excreta of a group of lizards and snakes forming 54.55% to 67.51% of the total excretory nitrogen. 2. Excretion of the insoluble uric acid as a main nitrogenous end product helps these animals for water conservation as they live under xerophilous conditions of low water intake. 3. Allantoin is present in the urinary concretions of lizards and absent from that of snakes. 4. Uric acid represents the end product of protein metabolism, and in lizards, allantoin should be a accepted as representing the line of purine metabolism.

Creatininemia versus uremia. The relative significance of blood urea nitrogen and serum creatinine concentrations in azotemia.

Excerpt The terms uremia and azotemia are applied to acute or chronic conditions in which the blood concentration of nitrogenous end products rises. The terms are otherwise poorly defined. Nitrogen...