Nitrogenous End Products Research Articles

Degradation of oxytetracycline by ferrate(VI): Treatment optimization, UHPLC-MS/MS and toxicological studies of the degradation products, and impact of urea and creatinine on the removal

The degradation of oxytetracycline (OTC) by ferrate(VI) for its application in wastewater treatment was investigated. The degradation conditions such as pH, reaction time, and molar ratio of ferrate(VI) to OTC were optimized by central composite design and response surface methodology. The most efficient, 90 % removal of OTC was obtained at pH 3, molar ratio ferrate(VI)/OTC of 3, and reaction time of 60 s. In the first step, demethylation, deamidation, and hydroxylation derivatives of OTC were formed. The end-products of the OTC degradation were hydroxyaliphatic amines and phenolic compounds formed from ring scission in the tetracene moiety of OTC. The end-products were not toxic to both bacteria (MARA and Microtox®) and protozoa (Spirotox) tests. Urea and creatinine are the major nitrogenous end-products of human metabolism occurring in municipal wastewater. Therefore, the impact of creatinine and urea on removal of OTC was also investigated. The presence of creatinine at investigated molar ratios of 1:1 and 1:2 did not affect the removal of OTC by ferrate(VI). The removal of OTC was 90 % after 60 s. However, after 60 s, in the presence of urea at molar ratio OTC/urea 1:1, removal efficiency was reduced from 90 to 80 %, whereas, at higher molar ratio of 1:2, the efficiency was 90 %. It may be explained by the formation of urea radicals that may facilitate the degradation of OTC by ferrate(VI) and its degradation products. The urea radicals may also induce formation of more reactive ferrate(V) or ferrate(IV) species. The ferrate was also applied to remove OTC from treated wastewater. Overall study results have shown thatferrate(VI) has a good potential for use in removal of tetracycline antibiotics from wastewater.

Microbiomes and Planctomycete diversity in large-scale aquaria habitats.

In commercial large-scale aquaria, controlling levels of nitrogenous compounds is essential for macrofauna health. Naturally occurring bacteria are capable of transforming toxic nitrogen species into their more benign counterparts and play important roles in maintaining aquaria health. Nitrification, the microbially-mediated transformation of ammonium and nitrite to nitrate, is a common and encouraged process for management of both commercial and home aquaria. A potentially competing microbial process that transforms ammonium and nitrite to dinitrogen gas (anaerobic ammonium oxidation [anammox]) is mediated by some bacteria within the phylum Planctomycetes. Anammox has been harnessed for nitrogen removal during wastewater treatment, as the nitrogenous end product is released into the atmosphere rather than in aqueous discharge. Whether anammox bacteria could be similarly utilized in commercial aquaria is an open question. As a first step in assessing the viability of this practice, we (i) characterized microbial communities from water and sand filtration systems for four habitats at the Tennessee Aquarium and (ii) examined the abundance and anammox potential of Planctomycetes using culture-independent approaches. 16S rRNA gene amplicon sequencing revealed distinct, yet stable, microbial communities and the presence of Planctomycetes (~1–15% of library reads) in all sampled habitats. Preliminary metagenomic analyses identified the genetic potential for multiple complete nitrogen metabolism pathways. However, no known genes diagnostic for the anammox reaction were found in this survey. To better understand the diversity of this group of bacteria in these systems, a targeted Planctomycete-specific 16S rRNA gene-based PCR approach was used. This effort recovered amplicons that share <95% 16S rRNA gene sequence identity to previously characterized Planctomycetes, suggesting novel strains within this phylum reside within aquaria.

Age- and sex-specific reference intervals for blood urea nitrogen in Chinese general population

Blood urea nitrogen (BUN) is a nitrogenous end product of protein metabolism. This study aims to explore the age- and sex-specific distribution of BUN among healthy Chinese adults. A total of 24,006 BUN values from healthy adults (14,148 males and 9858 females) were included in the cross-sectional study. Males had a higher median BUN value compared to females (4.6 mmol/L vs. 4.1 mmol/L). BUN values showed a positive correlation with body mass index (BMI), cholesterol, and blood sugar (P < 0.0001). However, eGFR showed a negative correlation with the BUN reference value (P < 0.0001) in both sexes. Multiple linear regression analysis confirmed that the positive associations of BUN levels and age were statistically significant after adjusting confounding factors (P < 0.001). Thus, the serum BUN values increased by 0.21 mmol/L for males and 0.282 mmol/L for females per 10 years. The BUN values corresponding to the 1st, 2.5th, 50th, 97.5th, and 99th percentiles for any specific age in both sex were also calculated. These results indicate that the serum BUN reference value is significantly affected by age and gender, and thus, its interpretation is age- and sex-dependent.

Big particles, best nutrition? Absorption and excretion of protein by Anastrepha obliqua larvae (Diptera: Tephritidae).

For purposes of mass-rearing fruit flies, nutrient intake through artificial diets is a challenge, artificial food content and processing should promote sufficient absorption and availability to ensure fly fitness. Bulking agents play an essential role in creating a quality diet, but its physical characteristics, such as particle size, may establish a better microenvironment for feeding and development. Currently, there is a lack of information about protein metabolism in mass-reared fruit flies. Therefore, we evaluated whether the particle size of the bulking agent affects the absorption and excretion of the proteins, as well as their effect on the life-history traits of Anastrepha obliqua. We determined the protein content of hemolymph and feces, as well as the presence of nitrogen end-products as indicators of their level of absorption in a diet elaborated with coarse and fine corn cob particles as a bulking agent. The bromatological composition showed that coarse particles increased the bioavailability and content of crude, digestible, and soluble protein for the diet and hemolymph protein of larvae alike. We found an inverse relationship between the protein content of the hemolymph and feces of the larvae. Ammonium was determined to be a product of the catabolism of proteins. Also, A. obliqua improved its development (yield and pupal weight) and fitness (adult emergence and flight ability) when larvae were reared on a coarse particle diet. In conclusion, a diet elaborated with a coarse bulking agent features increased protein bioavailability and nutritional quality, which, in turn, increases the life-history traits of A. obliqua.

Plant-Dominant Low-Protein Diet for Conservative Management of Chronic Kidney Disease.

Chronic kidney disease (CKD) affects >10% of the adult population. Each year, approximately 120,000 Americans develop end-stage kidney disease and initiate dialysis, which is costly and associated with functional impairments, worse health-related quality of life, and high early-mortality rates, exceeding 20% in the first year. Recent declarations by the World Kidney Day and the U.S. Government Executive Order seek to implement strategies that reduce the burden of kidney failure by slowing CKD progression and controlling uremia without dialysis. Pragmatic dietary interventions may have a role in improving CKD outcomes and preventing or delaying dialysis initiation. Evidence suggests that a patient-centered plant-dominant low-protein diet (PLADO) of 0.6–0.8 g/kg/day composed of >50% plant-based sources, administered by dietitians trained in non-dialysis CKD care, is promising and consistent with the precision nutrition. The scientific premise of the PLADO stems from the observations that high protein diets with high meat intake not only result in higher cardiovascular disease risk but also higher CKD incidence and faster CKD progression due to increased intraglomerular pressure and glomerular hyperfiltration. Meat intake increases production of nitrogenous end-products, worsens uremia, and may increase the risk of constipation with resulting hyperkalemia from the typical low fiber intake. A plant-dominant, fiber-rich, low-protein diet may lead to favorable alterations in the gut microbiome, which can modulate uremic toxin generation and slow CKD progression, along with reducing cardiovascular risk. PLADO is a heart-healthy, safe, flexible, and feasible diet that could be the centerpiece of a conservative and preservative CKD-management strategy that challenges the prevailing dialysis-centered paradigm.

Nitrate assimilation pathway in higher plants: critical role in nitrogen signalling and utilization

The process of nitrate assimilation is a very crucial pathway for the sustainable growth and productivity of higher plants. This process is catalysed by two enzymes, nitrate reductase and nitrite reductase. Both the enzymes differ from each other with respect to their structural organisation, subcellular location, catalytic efficiencies and regulatory mechanisms. Nitrate reductase catalyses the rate limiting step of nitrate assimilation process. The genes and proteins of this enzyme have been isolated and characterised from many higher plants. The additional role of NR in the production of nitric oxide has been also reported in last several years. The reduced ammonium is assimilated into carbon skeleton, ?-ketoglutarate, by the concerted action of glutamine synthetase and glutamate synthase. Glutamine and glutamate are the transportable forms of nitrogen among various tissues and metabolic processes. The rate of nitrate assimilation is regulated by the rate of uptake of nitrate by nitrate transporters, availability of carbon skeleton, accumulation of nitrogenous end products, light and the rate of photosynthesis. The partitioning of metabolites and resources between carbon and nitrogen metabolism is an important factor for the growth and yield of plants. During the last several decades excess use of nitrogen fertiliser has caused environmental pollution. Efforts have been made to increase the nitrogen use efficiency of plants to reduce the cost on fertiliser and nitrate pollution, increase the productivity and protein content of several commonly used crops. This review discusses the process of nitrate assimilation and its interaction with the carbon metabolism.

Abstract IA06: Changes in the composition and activity of the colonic microbiome that may explain the extreme risk of colon cancer in Alaskan Native People

Abstract Alaska Native People (AN) suffer the highest recorded incidence of CRC globally (100:100,000) and thus have the greatest risk of dying from this disease. Diet drives genetic susceptibility risk factors, and there is convincing evidence that high consumption rates of red and processed meats and fat increase risk, while a diet rich in fiber suppresses risk. We have shown that the high risk of colon cancer in African Americans (~65:100,000) is suppressed by increasing the consumption of high-fiber foods, in part driven by the health-promoting and antineoplastic influence of colonic microbiome cometabolites (e.g., short chain fatty acids [SCFA] and butyrate) and the suppression of inflammatory and procarcinogenic cometabolites (e.g., conjugated bile acids, nitrogenous end products). This study aimed to determine if dietary-microbiome metabolism explains the extreme risk of colon cancer in AN. 20 adults living in Anchorage and 9 in Barrow (age range 40-65 years) were prospectively recruited and dietary data were recorded. This cohort was compared to 25 native Africans who consume a high-fiber diet (&amp;gt;50g/day) and have an extremely low risk of colon cancer (&amp;lt;5:100,000). Meta-taxonomic analysis of stool was performed by 16s rRNA sequencing and by 1H NMR (nuclear magnetic spectroscopy) for analysis of the metabolome. Results confirmed the AN diet was rich in protein and fat, but low in fiber-rich foods. Measurements of the microbiome composition showed clear separation between AN and Africans on PCA and MDS plots (p=0.0001). The microbiotas were dominated at the genus level by Blautia, Bacteroides, and Lachnospiraceae, which characterize Western populations (enterotype I) while the Africans overexpressed Prevotella, Ruminococcus, and Succinovibria, organisms that play a key role in fiber breakdown and butyrogenesis (enterotype II). The fecal metabolome showed clear separation on OPLS-DA cross-validated scores plot (p=4x10-11) driven in part by higher levels of SCFA and butyrate in Africans. Subgroup analysis showed that these differences were exaggerated in the Barrow cohort. In conclusion, these findings are consistent with our hypothesis that the extreme risk of colon cancer in AN is related to insufficient intake of fiber-rich foods and that fiber supplementation of their current diet may reduce the development of cancer. Citation Format: Stephen O'Keefe, Annette Wilson, Kathryn Koller, Christie Flanagan, Flora Sapp, Gretchen Day, Peter Holck, Barbara Methe, Alison Morris, Jia Li, James Kinross, Timothy Thomas. Changes in the composition and activity of the colonic microbiome that may explain the extreme risk of colon cancer in Alaskan Native People [abstract]. In: Proceedings of the Tenth AACR Conference on the Science of Cancer Health Disparities in Racial/Ethnic Minorities and the Medically Underserved; 2017 Sep 25-28; Atlanta, GA. Philadelphia (PA): AACR; Cancer Epidemiol Biomarkers Prev 2018;27(7 Suppl):Abstract nr IA06.

Improving sewage sludge composting by addition of spent mushroom substrate and sucrose

The effects of spent mushroom substrate (SMS) and sucrose (S) amendment on emissions of nitrogenous gas (mainly NH3 and N2O) and end products quality of sewage sludge (SS) composting were evaluated. Five treatments were composted for 20 days in laboratory-scale using SS with different dosages of SMS and S, without additive amended treatment used as control. The results indicated that SMS amendments especially combination with S promoted dehydrogenase activity, CO2 production, organic matter degradation and humification in the composting, and maturity indices of composting also showed that the 30%SMS+2%S treatment could be much more appropriate to improve the composting process, such as total Kjeldahl nitrogen, nitrification index, humic acids/fulvic acids ratio and germination index, while the emissions of NH3 and N2O were reduced by 34.1% and 86.2%, respectively. These results shown that the moderate addition of SMS and S could improve the compost maturity and reduce nitrogenous gas emission.

Environmental factors affecting the presence of Acidimicrobiaceae and ammonium removal under iron-reducing conditions in soil environments

The oxidation of ammonium (NH4+) under iron reducing conditions, also referred to as Feammox, has been described in recent years by several investigators. The environmental characteristics in which the Feammox process occurs need to be understood in order to determine its contribution to the nitrogen cycle. In this study, through extensive field sampling at various locations in the US (mostly New Jersey) and South China, soil chemical analyses, serial incubation experiments, analysis of microbial communities, and using canonical correspondence analyses, it was determined that the soil pH, as well as its Fe(III) and NH4+ concentration were the most important factors controlling the distribution of Acidimicrobiaceae, which have been linked to the Feammox reaction. Under the conditions that favored the presence of Feammox bacteria and their oxidation of NH4+ under iron reducing conditions, denitrification bacteria were also abundant. However, the presence of known nitrous oxide (N2O) reducers was limited under these conditions, implying that at locations where the Feammox process is active, conditions might favor a higher N2O:N2 ratio for the nitrogen (N) end products. To determine the effect of dissolved oxygen (DO) on NH4+ oxidation under iron reducing conditions, incubations were conducted at two different DO levels. In incubations with DO < 0.02 mg/L, and when NH4+ oxidation was noticeable, the proportion of Acidimicrobiaceae with respect to total bacteria increased, while the proportion of other known NH4+ oxidizing bacteria (aerobic ammonia-oxidizing bacteria and anammox bacteria) decreased. In incubations of the same soil but with DO = 0.8–1.0 mg/L the opposite trend was observed, indicating that Feammox favored very low or no DO in these incubations.

Protein- and diabetes-induced glomerular hyperfiltration: role of glucagon, vasopressin, and urea.

A single protein-rich meal (or an infusion of amino acids) is known to increase the glomerular filtration rate (GFR) for a few hours, a phenomenon known as "hyperfiltration." It is important to understand the factors that initiate this upregulation because it becomes maladaptive in the long term. Several mediators and paracrine factors have been shown to participate in this upregulation, but they are not directly triggered by protein intake. Here, we explain how a rise in glucagon and in vasopressin secretion, directly induced by protein ingestion, might be the initial factors triggering the hepatic and renal events leading to an increase in the GFR. Their effects include metabolic actions in the liver and stimulation of sodium chloride reabsorption in the thick ascending limb. Glucagon is not only a glucoregulatory hormone. It is also important for the excretion of nitrogen end products by stimulating both urea synthesis in the liver (along with gluconeogenesis from amino acids) and urea excretion by the kidney. Vasopressin allows the concentration of nitrogenous end products (urea, ammonia, etc.) and other protein-associated wastes in a hyperosmotic urine, thus allowing a very significant water economy characteristic of all terrestrial mammals. No hyperfiltration occurs in the absence of one or the other hormone. Experimental results suggest that the combined actions of these two hormones, along with the complex intrarenal handling of urea, lead to alter the composition of the tubular fluid at the macula densa and to reduce the intensity of the signal activating the tubuloglomerular feedback control of GFR, thus allowing GFR to raise. Altogether, glucagon, vasopressin, and urea contribute to set up the best compromise between efficient urea excretion and water economy.

Effect of Environmental acidic pH on Oxygen Consumption in Different stages of Fish, Cyprinus carpio(L)

The data in table 1 and 2 showed changes in the total respiration and unit oxygen consumption of the developmental stages of fresh water fish during short-term exposure and acclimation to sub lethal acidic (pH 5.5) media. The oxygen consumption of fry significantly depleted in all the days of exposure to sub lethal acidic pH 5.5 starting from first day to fourteen days of exposure. The rate of total oxygen consumption depletion was higher in second day followed by fourth and sixth day with a gradual decreased trend was observed in the depletion up to fourteenth day of exposure. Similarly it is also observed significant decrease of total oxygen consumption and also rate of oxygen consumption of fingerling on exposure to sub lethal acidic pH in all the days of exposure, i.e., first day to fourteenth day when compared to control. The unit oxygen consumption of fry and fingerling on exposure to sub lethal pH media exhibited significant depletion when compared to control. The rate of depletion was more in the initial days of exposure and it was reduced gradually in 12 th and 14 th days of exposure. Further, the animal excretion was highly depleted in acclimated fry to sub lethal acidic media when compared to control. Similarly, excretory pattern of the fingerling also showed significant reduction on acclimation to sub lethal acidic medium over control. The tissue ammonia levels were also significantly depleted in both fry and fingerlings on acclimation to sub lethal acidic medium when compared to control (table 3). But the rate of depletion was more in fingerlings than to fry stage. It is concluded that the acclimation processes to sub lethal acidic medium induced compensatory changes in nitrogenous end products metabolism of fry and fingerlings while providing positive survival capacity under acidic stress conditions.

Physiological adaptations to prolonged fasting in the overwintering striped skunk (Mephitis mephitis)

Wintertime physiology of captive striped skunks (Mephitis mephitis) in response to cold ambient temperature (Ta) and fasting was investigated with body temperature (Tb) and activity recordings and analyses of hematology, plasma biochemistry and tissue fatty acids (FA). After 105days of food deprivation, the skunks were in phase II of fasting indicated by the elevated plasma nonesterified FA and glycerol but no accumulation of nitrogen end products. Shorter-chain saturated and monounsaturated FA together with C18–20 n−3 polyunsaturated FA were preferentially mobilized. Individual amino acids responded to fasting in a complex manner, while essential and nonessential amino acid sums remained stable. Increases in hemoglobin and hematocrit suggested dehydration. The activity levels were lower in mid-January–early March, and the activity bouts were mostly displayed between 17:00–23:00h. Daily torpor was observed in two females with 29 and 46 bouts. The deepest torpor (Tb<31°C) occurred between dawn and early afternoon and lasted for 3.3±0.18h. The average minimum Tb was 29.2±0.15°C and the lowest recorded Tb was 25.8°C. There was significant relation between the average 24-h Tb and Ta. Increases in wintertime Ta, as predicted by climate change scenarios, could influence torpor patterns in the species.

Water and Kidney Physiology

Vasopressin plays a crucial role in the ability of the kidney to concentrate urine. In the last 3 to 4 years, a renewed interest in vasopressin has emerged, because of availability of selective, orally active antagonists of the different vasopressin receptors and of an immunoassay for the measurement of copeptin, a surrogate marker of vasopressin. All solutes are not concentrated equally in the urine. The concentration of urea and of other nitrogenous end-products accounts for most of the solute-free water reabsorbed by the kidney. The concentration of these wastes represents a burden for the kidney because it operates at the expense of a less efficient excretion of several solutes and induces a significant hyperfiltration and increased metabolic demand. These consequences of vasopressin action may participate in kidney disease progression.

EXCRETORY NITROGEN METABOLISM AND GLUCONEOGENESIS DURING DEVELOPMENT OF HIGHER VERTEBRATES

ABSTRACT The concept of nitrogen “excretion” by mammalian and avian embryos is examined in light of contemporary knowledge of hepatic metabolism. The origin of “waste” nitrogen and the hepatic pathways for its conversion to either urea or uric acid for excretion are described. The probable evolution of these pathways among the higher tetrapod vertebrates and the impact of the selective advantage of uricoteley on the radiation of the archosaurs are considered. The intimate connection of hepatic gluconeogenesis with nitrogenous end product formation in birds and mammals is examined. Finally, the development of the capacities for gluconeogenesis and for either ureogenesis or urieogenesis in the perinate is discussed relative to the problem of development in a cleidoic egg.

Uric acid biosensor based on chemiluminescence detection using a nano-micro hybrid matrix

Uric acid (UA) is a nitrogenous end product of the purine catabolism in humans. Excessive production of UA may lead to hyperuricemia, gout, and kidney disorders. The study aims at developing an indirect enzymatic UA biosensing assay based on H2O2 detection. The UA biosensing assay was prepared by loading pentacene in peroxalate nanoparticles and Uricase co-immobilized in alginate microspheres. These biosensing formulations were characterized using DLS, optical microscopy, SEM, TEM, and CLSM. Nanoparticles embedded in alginate microspheres formed were used for H2O2 and UA sensing. The dye loaded nanoparticles and co-encapsulated microspheres were formed with size ranges from 520 nm and 60 μm, respectively. Uricase loading using atomization evaluated using Bradford assay was found to be greater than 98% in all tested concentrations. Sensing studies for H2O2 and UA were carried out using fluorescence spectroscopy. H2O2 could be detected in a linear range of 0–6 μM with a regression coefficient of 0.979 and in a range of 6–50 μM with a regression coefficient of 0.984. The limit of detection for each of the range was found to be 1 and 3 μM, respectively. UA sensing showed regression constant 0.977 and 0.949 in range of 0–0.1 mg/ml and 0.015–0.04 mg/ml, respectively. Thus chemiluminescent alginate microspheres containing peroxalate nanoparticles co-immobilized with uricase can be used as diagnostic markers for detection of UA.

Plasma Citrulline Concentration as a Marker for Disease Activity in Patients With Crohn’s Disease

Citrulline is a nitrogen end product produced from the intermediary metabolism of glutamine through the enzymatically mediated urea cycle, almost exclusively in the enterocytes of small intestinal epithelium, with some synthesis in colonocytes. Intestinal dysfunction resulting from intestinal diseases or injuries affects intermediary metabolism, which includes citrulline synthesis. We sought to determine whether plasma citrulline was a biomarker for disease activity in patients with Crohn's disease with the hypothesis that citrulline concentration would be reduced during active disease. A total of 81 outpatients aged 18 to 65 years (mean, 40.6±15.4 y) with a known history of Crohn's disease were studied prospectively. Patients with prior small intestinal resection, or renal or hepatic insufficiency were excluded. Crohn's disease activity was measured by Harvey-Bradshaw Index (HBI) and was correlated to the plasma citrulline concentration measured simultaneously (ion chromatography). Spearman correlation coefficients were used to assess for an association between the 2 variables. Subgroup analyses of patients with isolated small intestinal disease and endoscopically or radiologic verified disease activity were also performed. Twenty-two patients had isolated colonic disease and 59 had small intestinal involvement. Twenty-six of these patients had concurrent endoscopy and/or computed tomography or magnetic resonance imaging. On the basis of HBI scores, 32 patients had active disease (HBI ≥5) and 49 patients had inactive disease. The mean HBI scores were 4.8±5.5. The mean plasma citrulline concentration was normal, although was below normal in some patients. However, it failed to distinguish between active and inactive patients based on the HBI (active 27.8±8.8 μmol/L, inactive 27.8±11.1 μmol/L, P=0.991). There was no significant linear association between the ranks of citrulline and ranks of HBI (rs=0.012, P=0.915). Of the 59 patients with isolated small intestinal disease, there was no association between plasma citrulline concentration and the HBI (Spearman correlation coefficient, 0.073; P=0.583). There was no difference in plasma citrulline concentrations among those with confirmed inflammation by imaging or endoscopy (confirmed, 26.2±11.8; negative, 28.0±10.0; independent t test P=0.583). Plasma citrulline concentration was not a marker of disease activity in patients with Crohn's disease. However, all patients studied were outpatients and it is possible that plasma citrulline concentration may be depressed only in patients with more severe disease or extensive small bowel involvement. In addition, plasma citrulline may be increased in the postabsorptional state, and for the most part, our patients were nonfasting. More studies are needed to further elucidate the role of citrulline as a marker of disease activity in patients with Crohn's disease. The possibility also exists that citrulline may be a better marker in patients with previous resection, and this group will require specific evaluation.

Increased uric acid levels in drug-naïve subjects with bipolar disorder during a first manic episode

Recent evidence suggests that purinergic system dysfunction may play a role in the pathophysiology and therapeutics of bipolar disorder (BPD). Uric acid is a key nitrogenous end product of purine metabolism. In addition to being a potential marker of treatment response, high levels of uric acid may represent a state marker during mania. In this study, we assessed the presence of purinergic dysfunction in 20 treatment-naïve first episode patients with BPD who were experiencing a manic episode. Patients were matched with 24 healthy controls. We found that acutely manic patients had significantly higher levels of plasma uric acid (4.85 ± 1.60 mg/dL) compared to healthy controls (2.96 ± 0.63 mg/dL, p < 0.001; F = 28.1). No association between uric acid levels with severity of manic symptoms was observed. These results support the role of purinergic system dysfunction in BPD early in the course of illness, and suggest that this phenomenon is not the result of chronicity or medication exposure. Overall, our findings suggest a novel mechanism in the pathophysiology of BPD.

Quantitative determination of urea concentrations in cell culture medium

Urea is the major nitrogenous end product of protein metabolism in mammals. Here, we describe a quantitative, sensitive method for urea determination using a modified Jung reagent. This assay is specific for urea and is unaffected by ammonia, a common interferent in tissue and cell cultures. We demonstrate that this convenient colorimetric microplate-based, room temperature assay can be applied to determine urea synthesis in cell culture.

The regulatory role of glucocorticoid and mineralocorticoid receptors in pulsatile urea excretion of the gulf toadfish,Opsanus beta

Gulf toadfish, Opsanus beta, are one among a group of unusual teleosts that excrete urea as their predominant nitrogen end product in response to stressful conditions. Under conditions of crowding or confinement, fasted toadfish excrete the majority of their nitrogen waste in large pulses of urea (>90% of total nitrogen) lasting up to 3 h. An earlier study demonstrated that cortisol has an inhibitory influence on urea pulse size. The present study tested the hypothesis that cortisol mediates changes in urea pulse size in ureotelic toadfish through the glucocorticoid receptor (GR) and not the mineralocorticoid receptor (MR). In vivo pharmacological investigations were used to manipulate the corticosteroid system in crowded toadfish, including experimentally lowering plasma cortisol levels by the injection of metyrapone, blocking cortisol receptors through exposure to either RU-486 (GR antagonist) and spironolactone (MR antagonist), or through exogenous infusion of the tetrapod mineralocorticoid aldosterone (tetrapod MR agonist). The data demonstrate that lowering the activity of cortisol, either by inhibiting its synthesis or by blocking its receptor, resulted in a two- to threefold increase in pulse size with no accompanying change in pulse frequency. Treatment with spironolactone elicited a minor ( approximately 1.5-fold) reduction in pulse size, as did aldosterone treatment, suggesting that the anti-mineralocorticoid spironolactone has an agonistic effect in a piscine system. In summary, the evidence suggests that urea transport mechanisms in pulsing toadfish are upregulated in response to low cortisol, mediated primarily by GRs, and to a lesser extent MRs.

Measurement of the rate of protein turnover and synthesis in the marsupial Honey possum (Tarsipes rostratus)

Rates of protein turnover and synthesis were measured in wild-caught Honey possums (Tarsipes rostratus) in the southwest of Western Australia and compared between males and females with and without pouch young. Possums were injected with 50 microg of (15)N-glycine and ammonia collected within 24 h was used as the nitrogen end-product in a single-injection protocol. The overall mean rate of protein synthesis measured was 7.7+/-0.5 g kg(-0.75) day(-1), which falls within the range of values reported for other marsupial species. Whole body rates of nitrogen flux and protein synthesis did not vary significantly between males and females with and without young, but females with pouch young showed significantly lower rates of protein synthesis when expressed in relation to metabolic body size. This difference was no longer apparent, however, if the mass of the females was corrected for the estimated mass of the young in the pouch averaging 9.3+/-1.6 g kg(-0.75) day(-1) and suggesting that the young should not be considered as part of the metabolic body pool. Whole body rates of protein degradation were significantly reduced in females carrying pouch young, suggesting that protein may be being diverted from the pool to milk production. Calculations indicate that the daily fraction of the female's nitrogen synthesis rate that needs to be diverted to pouch young to sustain their growth is less than 5%, and may not be detectable with the current methodology.