Some aspects of ammonia toxicity in animal cells

Ammonia Toxicity and Associated Protein Oxidation: A Single-Cell Surface Enhanced Raman Spectroscopy Study

Ammonia (NH3) is a commonly used industrial chemical to which exposure at high concentrations can result in severe skin damage. Moreover, high levels of ammonia in the human body can lead to hyperammonemia conditions and enhanced cancer metabolism. In this work, the toxicity mechanism of NH3 has been studied against human dermal fibroblast (HDF) cells using surface-enhanced Raman spectroscopy (SERS). For this purpose, gold nanoparticles of size 50 nm have been prepared and used as probes for Raman signal enhancement, after being internalized inside HDF cells. Following the exposure to ammonia, HDF cells showed a significant variation in the protein ternary structure's signals, demonstrating their denaturation and oxidation process, together with early signs of apoptosis. Meaningful changes were observed especially in the Raman vibrations of sulfur-containing amino acids (cysteine and methionine) together with aromatic residues. Fluorescence microscopy revealed the formation of reactive oxygen and nitrogen species in cells, which confirmed their stressed condition and to whom the causes of protein degradation can be attributed. These findings can provide new insights into the mechanism of ammonia toxicity and protein oxidation at a single-cell level, demonstrating the high potential of the SERS technique in investigating the cellular response to toxic compounds.

Instantaneous Inactivation of Herpes Simplex Virus by Silicon Nitride Bioceramics

Hydrolytic reactions taking place at the surface of a silicon nitride (Si3N4) bioceramic were found to induce instantaneous inactivation of Human herpesvirus 1 (HHV-1, also known as Herpes simplex virus 1 or HSV-1). Si3N4 is a non-oxide ceramic compound with strong antibacterial and antiviral properties that has been proven safe for human cells. HSV-1 is a double-stranded DNA virus that infects a variety of host tissues through a lytic and latent cycle. Real-time reverse transcription (RT)-polymerase chain reaction (PCR) tests of HSV-1 DNA after instantaneous contact with Si3N4 showed that ammonia and its nitrogen radical byproducts, produced upon Si3N4 hydrolysis, directly reacted with viral proteins and fragmented the virus DNA, irreversibly damaging its structure. A comparison carried out upon testing HSV-1 against ZrO2 particles under identical experimental conditions showed a significantly weaker (but not null) antiviral effect, which was attributed to oxygen radical influence. The results of this study extend the effectiveness of Si3N4's antiviral properties beyond their previously proven efficacy against a large variety of single-stranded enveloped and non-enveloped RNA viruses. Possible applications include the development of antiviral creams or gels and oral rinses to exploit an extremely efficient, localized, and instantaneous viral reduction by means of a safe and more effective alternative to conventional antiviral creams. Upon incorporating a minor fraction of micrometric Si3N4 particles into polymeric matrices, antiherpetic devices could be fabricated, which would effectively impede viral reactivation and enable high local effectiveness for extended periods of time.

Habitat-dependent prokaryotic microbial community, potential keystone species, and network complexity in a subtropical estuary

Microbes (e.g., bacteria and archaea) are indispensable components for the key biological processes of estuarine ecosystems and three main habitats (sediment, particle, and water) are harboring diverse estuarine microbes. However, we still know little about how the microbial community structures, potential keystone species, and network properties change among these three habitats in estuarine ecosystems. In this study, we collected size-fractioned water and sediment samples from the Pearl River Estuary to reveal their microbial diversity, community structures, network properties, and potential keystone taxa. We found that the sediment microbial community was remarkably more diverse than particle-attached (PA) and free-living (FL) communities, whereas its ecological network was less complex in terms of node distance and connectivity. TOC was determined as the main driver of sediment community, while the PA and FL communities were predominantly shaped by NO₂^-, non-ionic ammonia (NH) and pH. Among the bulk water, there were no significant differences between PA and FL communities in diversity, community structure, and network complexity. However, the PA community was more susceptible to metal elements, suggesting their higher level of involvement in physiological metabolism. Potential keystone taxa among community networks were taxonomically divergent in three habitats. Specifically, Synechococcales (Cyanobacteria) and Actinomarinales (Actinobacteria) exclusively served as the module-hubs in FL network, while members from phylum Proteobacteria and Bacteroidetes were the module-hubs and connectors in PA network. Potential keystone taxa in sediment network were more diverse and covered 9 phyla, including the only archaeal lineage Bathyarchaeia (Crenarchaeota). Overall, our study provided more detailed information about estuarine microbial communities in three habitats, especially the potential keystone species, which provided new perspectives on evaluating further effects of anthropogenic disturbances on estuarine microbes and facilitated the environment monitoring based on microbial community.

The Influence of Rotational Length, along with Pre- and Post-Grazing Measures on Nutritional Composition of Pasture during Winter and Spring on New Zealand Dairy Farms

The quality of ryegrass−clover pasture was investigated between August (winter: start of calving) and November (spring: end of breeding) on pasture-based dairy farms (>85% of total feed from pasture) that had short (n = 2, Farms A and B; winter ~30 days, spring ~20−25 days) or long (n = 2, Farms C and D; winter ~35 days, spring ~25−30 days) grazing rotations to determine whether quality was affected by grazing rotation length (RT). Weekly assessments of pasture growth and herbage quality were made using a standardised electronic rising plate meter, and near-infrared spectroscopy, respectively. Data were subjected to repeated measure mixed model analysis, in which herbage quality was the outcome variable. The highest pre-grazing dry matter (PGDM) and height, post-grazing dry matter (DM) and height, and number of live leaves per tiller (leaf regrowth stage, LS) were present in late spring. Neutral detergent fibre (NDF), acid detergent fibre (ADF), metabolisable energy (ME), and organic matter digestibility (OMD) were positively correlated to each other (r2 ≥ 0.8) whilst ADF and lipid, and ADF and OMD were negatively correlated (r2 ≥ −0.8; p < 0.01). Metabolisable energy content was negatively correlated with ADF and NDF (r2 = −0.7, −0.8, respectively), and was inversely related to PGDM. Metabolisable energy was higher (p < 0.05) in farms with shorter (overall mean: 11.2 MJ/kg DM) than longer (10.9 MJ/kg DM) RT. Crude protein was also inversely related to PGDM and was higher with shorter (23.2% DM) than longer (18.3% DM; p < 0.05) RT. Pre-grazing DM affected the amount of pasture that was grazed and, hence, the amount of DM remaining after grazing (post-grazing DM or residual), so that PGDM was correlated with post-grazing height and residual DM (r2 = 0.88 and 0.51, respectively; both p < 0.001). In conclusion, RT, LS, and PGDM during winter and spring influenced the herbage quality, therefore, better management of pastures may enhance the productivity of dairy cows.

Oxidative Stress and Assisted Reproduction: A Comprehensive Review of Its Pathophysiological Role and Strategies for Optimizing Embryo Culture Environment

Oxidative stress (OS) due to an imbalance between reactive oxygen species (ROS) and antioxidants has been established as an important factor that can negatively affect the outcomes of assisted reproductive techniques (ARTs). Excess ROS exert their pathological effects through damage to cellular lipids, organelles, and DNA, alteration of enzymatic function, and apoptosis. ROS can be produced intracellularly, from immature sperm, oocytes, and embryos. Additionally, several external factors may induce high ROS production in the ART setup, including atmospheric oxygen, CO2 incubators, consumables, visible light, temperature, humidity, volatile organic compounds, and culture media additives. Pathological amounts of ROS can also be generated during the cryopreservation-thawing process of gametes or embryos. Generally, these factors can act at any stage during ART, from gamete preparation to embryo development, till the blastocyst stage. In this review, we discuss the in vitro conditions and environmental factors responsible for the induction of OS in an ART setting. In addition, we describe the effects of OS on gametes and embryos. Furthermore, we highlight strategies to ameliorate the impact of OS during the whole human embryo culture period, from gametes to blastocyst stage.

Antimicrobial Efficacy of Un-Ionized Ammonia (NH3) against Salmonella Typhimurium in Buffered Solutions with Variable pH, NH3 Concentrations, and Urease-Producing Bacteria

The presence of Salmonella in poultry litter, when used as a biological soil amendment, presents a risk for the preharvest contamination of fresh produce. Poultry litter is rich in organic nitrogen, and previous studies have suggested that ammonia (NH₃) in poultry litter may affect the survival of Salmonella. Salmonella enterica serovar Typhimurium was inoculated into buffer solutions to characterize the pH dependency, minimum antimicrobial concentration, and efficacy of NH₃ production. In solutions with 0.4 M total ammonia nitrogen (TAN) at various pH levels (5, 7, 8, and 9), significant inactivation of Salmonella only occurred at pH 9. Salmonella was reduced by ∼8 log CFU/mL within 12 to 18 h at 0.09, 0.18, 0.26, and 0.35 M NH₃. The minimum antimicrobial concentration tested was 0.04 M NH₃, resulting in an ∼7 log CFU/mL reduction after 24 h. Solutions with urea (1% and 2%) and urease enzymes rapidly produced NH₃, which significantly reduced Salmonella within 12 h. The urease-producing bacterium Corynebacterium urealyticum showed no antagonistic effects against Salmonella in solution. Conversely, with 1% urea added, C. urealyticum rapidly produced NH₃ in solution and significantly reduced Salmonella within 12 h. Salmonella inactivation data were nonlinear and fitted to Weibull models (Weibull, Weibull with tailing effects, and double Weibull) to describe their inactivation kinetics. These results suggest that high NH₃ levels in poultry litter may reduce the risk of contamination in this biological soil amendment. This study will guide future research on the influence of ammonia on the survival and persistence of Salmonella in poultry litter.

IMPORTANCE Poultry litter is a widely used biological soil amendment in the production of fresh produce. However, poultry litter may contain human pathogens, such as Salmonella, which introduces the risk of preharvest produce contamination in agricultural fields. Ammonia in poultry litter, produced through bacterial degradation of urea, may be detrimental to the survival of Salmonella; however, these effects are not fully understood. This study utilized aqueous buffer solutions to demonstrate that the antimicrobial efficacy of ammonia against Salmonella is dependent on alkaline pH levels, where increasing concentrations of ammonia led to more rapid inactivation. Inactivation was also demonstrated in the presence of urea and urease or urease-producing Corynebacterium urealyticum. These findings suggest that high levels of ammonia in poultry litter may reduce the risk of contamination in biological soil amendments and will guide further studies on the survival and persistence of Salmonella in poultry litter.

Effects of water activity, ammonia and Corynebacterium urealyticum on the survival of Salmonella Typhimurium in sterile poultry litter

AIMS

This study examined the effects of water activity (a_w ), ammonia and Corynebacterium urealyticum on the survival of Salmonella Typhimurium in sterile poultry litter.

METHODS AND RESULTS

Sterile poultry litter inoculated with S. Typhimurium was adjusted to pH 9.0, various a_w levels (0.84, 0.92 and 0.96), and total ammonia nitrogen levels were increased either by the addition of ammonium sulphate or C. urealyticum inoculation with 1% urea added. All litter treatments were incubated at 30°C and sampled daily for five days. Similar results were observed at each a_w level in both experiments. At 0.84 and 0.92 a_w , S. Typhimurium populations in litter fell below 1 log CFU g^-1 within 5 days, with no significant differences between the controls and increased ammonia treatments. At 0.96 a_w , Salmonella populations treated with increased ammonia levels were significantly lower than control treatments on days 1-5.

CONCLUSIONS

This study showed that C. urealyticum can produce ammonia in litter at higher a_w levels with sufficient available urea and that the antimicrobial efficacy of ammonia is dependent on high a_w (~0.96) in litter.

SIGNIFICANCE AND IMPACT OF THE STUDY

These results provide insights into the production of ammonia in litter, its antimicrobial efficacy in litter and the importance of a_w in this interaction.

Reusable nano-BG-FET for point-of-care estimation of ammonia and urea in human urine

A back-gate-field-effect-transistor (BG-FET) has been developed to selectively detect ammonia and urea. The BG-FET was prepared on a p-type Si substrate with an n-type channel of CdS-TiO₂ nanocomposite and poly-methyl methacrylate film as dielectric layer. The reusability of the sensor was ensured by putting it as a cover to a chamber where samples were detected. The BG-FET showed an increase in drain current with the increase in ammonia release from chamber because higher numbers of charge carriers were created when ammonia adsorped on CdS-TiO₂ nanostructures. Control experiments suggested that the variation in current-to-voltage response of BG-FET could also be calibrated to measure the activity of a host of other hazardous gases. The lowest concentration of ammonia detected was ∼0.85 ppm with a response time of 30 s at a gate voltage of 0.5 V or less, which were superior than available field effect transistors ammonia sensors. Addition of urease in urine liberated ammonia equivalent to urea content in urine, which could be detected by the proposed BGFET. The urea-urease enzyme catalysis reaction made the sensor specific in detecting the biomarker. The accuracy, sensitivity, and reusability of the device was found to be suitable to develop a point-of-care testing device for ammonia and urea detection.

Effects of low dietary cation-anion difference induced by ruminal ammonium chloride infusion on performance, serum, and urine metabolites of lactating dairy cows

Objective

The objective of the present study was to determine ammonium chloride tolerance of lactating dairy cows, by examining effects of negative dietary cation anion difference (DCAD) induced by ruminal ammonium chloride infusion on performance, serum and urine minerals, serum metabolites and enzymes of lactating dairy cows.

Methods

Four primiparous lactating Chinese Holstein cows fitted with ruminal cannulas were infused with increasing amounts (0, 150, 300, or 450 g/d) of ammonium chloride in a crossover design. The DCAD of the base diet was 279 mEq/kg dry matter (DM) using the DCAD formula (Na + K – Cl – S)/kg of DM. Ammonium chloride infusion added the equivalent of 0, 128, 330, and 536 mEq/kg DM of Cl in treatments. According to the different dry matter intakes (DMI), the resulting actual DCAD of the four treatments was 279, 151, −51, and −257 mEq/kg DM, respectively.

Results

DMI decreased linearly as DCAD decreased. Yields of milk, 4% fat-corrected milk, energy-corrected milk, milk fat, and milk protein decreased linearly as DCAD decreased. Concentrations of milk protein and milk urea nitrogen increased linearly with decreasing DCAD. Concentration of Cl− in serum increased linearly and concentration of PO43- in serum increased quadratically as DCAD decreased. Urine pH decreased linearly and calculated urine volume increased linearly with decreasing DCAD. Linear increases in daily urinary excretion of Cl⁻, Ca²⁺, PO₄³⁻, urea N, and ammonium were observed as DCAD decreased. Activities of alanine aminotransferase, aspartate aminotransferase, and γ-glutamyl transferase in serum and urea N concentration in serum increased linearly as DCAD decreased.

Conclusion

In conclusion, negative DCAD induced by ruminal ammonium chloride infusion resulted in a metabolic acidosis, had a negative influence on performance, and increased serum enzymes indicating potential liver and kidney damage in lactating dairy cows. Daily ammonium chloride intake by lactating dairy cows should not exceed 300 g, and 150 g/d per cow may be better.

Characterizing steady states of genome-scale metabolic networks in continuous cell cultures

In the continuous mode of cell culture, a constant flow carrying fresh media replaces culture fluid, cells, nutrients and secreted metabolites. Here we present a model for continuous cell culture coupling intra-cellular metabolism to extracellular variables describing the state of the bioreactor, taking into account the growth capacity of the cell and the impact of toxic byproduct accumulation. We provide a method to determine the steady states of this system that is tractable for metabolic networks of arbitrary complexity. We demonstrate our approach in a toy model first, and then in a genome-scale metabolic network of the Chinese hamster ovary cell line, obtaining results that are in qualitative agreement with experimental observations. We derive a number of consequences from the model that are independent of parameter values. The ratio between cell density and dilution rate is an ideal control parameter to fix a steady state with desired metabolic properties. This conclusion is robust even in the presence of multi-stability, which is explained in our model by a negative feedback loop due to toxic byproduct accumulation. A complex landscape of steady states emerges from our simulations, including multiple metabolic switches, which also explain why cell-line and media benchmarks carried out in batch culture cannot be extrapolated to perfusion. On the other hand, we predict invariance laws between continuous cell cultures with different parameters. A practical consequence is that the chemostat is an ideal experimental model for large-scale high-density perfusion cultures, where the complex landscape of metabolic transitions is faithfully reproduced.

Diet selection of sheep: sodium bicarbonate, but not the offering of hay, modifies the effect of urea on diet selection

The hypotheses tested were that the expected preference of sheep for a food with adequate rumen degradable protein (RDP) supplemented with urea would be reduced both by the addition of a buffer (sodium bicarbonate (SB)) and by offering ad libitum access to hay. A control food (C), calculated to be adequate in its ratio of effective RDP to fermentable metabolizable energy (fME), was formulated. Other foods were made by adding 12·5 (U1) or 25 (U2) g urea per kg fresh matter (FM) to C and 20 g SB per kg FM to C, U1and U2. The acid buffering capacity (ABC) of each food was measured in vitro. The experiment consisted of two successive periods, each of 4 weeks. Ninety-eight female, Texel ✕ Greyface sheep were randomly allocated to 14 groups each with seven animals. Groups 1 to 6 were offered one of: C, U2, C + SB, U2+ SB, C with hay or U2with hay throughout the experiment. Groups 7 to 10 were offered the choices of C v. U1or C v. U2, either with or without hay in a change-over design; animals that received hay during period 1 (groups 8 and 10) did not do so during period 2 and vice versa (groups 7 and 9). Groups 11 to 14 (no. = 7) were offered the choices of C v. U1or C v. U2, either with or without SB supplemented to both foods, in a change-over design. Adding either urea, or SB, or both to C had no effects on intake or live-weight gain when offered alone. Both supplements significantly (P 0·001) increased the ABC of food C. Throughout the experiment hay consumption was very low (overall mean: 23 (s.e. 2·5) g hay per sheep day). Offering hay caused no change in the preference for the urea-supplemented foods. Sheep offered the choices C v. U1or C v. U2, with neither hay nor SB, selected 0.466 (s.e. 0·036) and 0.588 (s.e. 0·025) kg/kg total food intake (TFI) of U1and U2respectively. The proportions of the urea-supplemented foods were significantly reduced (P 0.01) by SB supplementation: to 0.348 (s.e.0·045) and 0·406 (s.e.0·059) kg/kg TFI of U1and U2respectively. The effect of SB addition on the diet selection of sheep could be due to its buffering properties. When SB is added to both foods the need for urea to be used as a buffer is reduced with a consequent decrease in the proportion selected as the urea-supplemented food. Effects of diet on buffering may override other diet selection objectives, such as the avoidance of an excess intake of RDP.

Direct-fed microbials containing lactate-producing bacteria influence ruminal fermentation but not lactate utilization in steers fed a high-concentrate diet

Direct-fed microbials (DFM) have been shown to improve gain and growth efficiency and also modulate ruminal fermentation. In Exp. 1,72 beef steers were used to compare a lactate-producing bacterial (LAB) DFM consisting primarily of Lactobacillus acidophilus and Enterococcus faecium,and a lactate-producing and lactate-utilizing (LAB/LU) DFM consisting primarily of L. acidophilus and Propionibacterium both fed at 10(9) cfu/d. Steers were fed a corn-based finishing diet for 153 d and then slaughtered for collection of carcass characteristics. In Exp. 2, 12 ruminally cannulated steers were fed acorn-based finishing diet and treated with 10(9) cfu/d of LAB DFM. Rumen fluid was sampled on d 14 and 28 over a 12-h period. Steers were ruminally dosed with a 2-L solution of neutralized DL-lactate (0.56 M)and Cr-EDTA (13.22 M) 3 h postfeeding on d 15 and 29. Ruminal samples were collected at 10- and 20-minintervals for the first and second hour postdosing. No differences (P ≥ 0.14) between control (CON) and LAB for DMI, ADG, growth efficiency, or carcass characteristics were observed. Dry matter intake was greater (P = 0.04) for LAB/LU than LAB from d 0 to 28 but did not differ (P ≥ 0.29) thereafter. Average daily gain was greater (P = 0.04) and efficiency tended(P = 0.06) to be greater for LAB than LAB/LU over the entire 153 d. In Exp. 2, total VFA concentration and molar proportions of butyrate were unaffected(P ≥ 0.24). Molar proportions of acetate exhibited a DFM by hour interaction (P = 0.04); however, on average, molar proportion of acetate was 4.4% greater for DFM. Conversely, DFM did not affect the molar proportion of propionate (P = 0.39). On average,molar proportions of propionate tended to increase(P = 0.07), and acetate tended to decrease (P = 0.07)across days. Mean daily ruminal pH was similar for CON on d 14 and 28, whereas mean pH increased from d 14 to 28 for DFM (DFM × day; P = 0.08).Minimum pH remained unchanged for CON over time but increased from d 14 to 2 for DFM (DFM × day;P = 0.10). Maximum pH decreased from d 14 to 28 in CON but increased over time with DFM (DFM × day;P = 0.05). DL- and L-lactate utilization were unaffected by DFM (P ≥ 0.33) or day (P ≥ 0.50). Although the LAB DFM did not impact growth performance, itd id modulate ruminal fermentation, as evidenced by shifts in ruminal VFA profile and pH; however, DFM did not appear to influence ruminal lactate utilization.

Effects of different levels of urea supplementation on nutrient intake and growth performance in growing camels fed roughage based complete pellet diets

The utilization of urea in camels has beneficial and negative effects. The aims of this study were to investigate the effects of different levels of urea supplementation on nutrients intake, digestibility, growth performance, feed efficiency and economics in growing camels fed roughage based complete pellet diets. In the present study, eighteen growing camels with an average live body weight of 306.17 ± 2.05 kg were randomly assigned in three treatments: T1 = roughage complete pellet diet without urea, T2 = T1 plus 1% urea, and T3 = T1 plus 2% urea. The results showed that the urea supplementation significantly affected average daily feed and nutrient intake of dry matter (DM), organic matter (OM), crude protein (CP), neutral detergent fiber (NDF), and acid detergent fiber (ADF) (P < 0.05). On the contrary, the average daily intake of nitrogen free extract (NFE) and water were not influenced by increasing urea supplementation (P > 0.05). Similarly, digestion coefficient of DM, CP, ether extract (EE), crude fiber (CF) and ADF was influenced by increasing urea level (P < 0.05), while the digestion coefficient of OM, NFE and NDF was not affected by increasing urea level (P > 0.05). The intake of digestive nutrients was similar among all treatment groups. Total body live weight gain and average daily gain were significantly higher in urea supplemented groups (P < 0.05) than in the control group. The supplementation of urea at 1% in low quality roughage complete pellet diets significantly improved (P < 0.05) the feed efficiency. In conclusion, these results indicated that the incorporation of urea at 1% in roughage based complete pellet diets could positively improve nutrients intake, digestibility, growth performance and feed conversion efficiency of growing camels.

Air Quality in Alternative Housing Systems may have an Impact on Laying Hen Welfare. Part II-Ammonia

The EU ban on conventional barren cages for laying hens from 2012 has improved many aspects of laying hen welfare. The new housing systems allow for the expression of highly-motivated behaviors. However, the systems available for intensive large-scale egg production (e.g., aviaries, floor housing systems, furnished cages) may cause other welfare challenges. We have reviewed the literature regarding the health, behavior, production characteristics, and welfare of laying hens when exposed to ammonia in their housing environment. Concentrations of ammonia gas are commonly high in aviaries and floor housing systems in which manure is not regularly removed, whereas they are usually lower in furnished cages. High levels are found during the cold season when ventilation flow is often reduced. Ammonia is a pungent gas, and behavioral studies indicate chickens are averse to the gas. High concentrations of gaseous ammonia can have adverse health effects and, when very high, even influence production performance. The most profound effects seen are the occurrence of lesions in the respiratory tract and keratoconjunctivitis. There is also evidence that high ammonia concentrations predispose poultry to respiratory disease and secondary infections. We conclude that there are animal welfare challenges related to high ammonia levels, and that immediate actions are needed. Development of improved systems and management routines for manure removal and ventilation will be important for the reduction of ammonia levels and hence will contribute to safeguarding hen welfare.

Monoamine oxidases as sources of oxidants in the heart

Oxidative stress can be generated at several sites within the mitochondria. Among these, monoamine oxidase (MAO) has been described as a prominent source. MAOs are mitochondrial flavoenzymes responsible for the oxidative deamination of catecholamines, serotonin and biogenic amines, and during this process they generate H2O2 and aldehyde intermediates. The role of MAO in cardiovascular pathophysiology has only recently gathered some attention since it has been demonstrated that both H2O2 and aldehydes may target mitochondrial function and consequently affect function and viability of the myocardium. In the present review, we will discuss the role of MAO in catecholamine and serotonin clearance and cycling in relation to cardiac structure and function. The relevant contribution of each MAO isoform (MAO-A or -B) will be discussed in relation to mitochondrial dysfunction and myocardial injury. Finally, we will examine both beneficial effects of their pharmacological or genetic inhibition along with potential adverse effects observed at baseline in MAO knockout mice, as well as the deleterious effects following their over-expression specifically at cardiomyocyte level. This article is part of a Special Issue entitled "Redox Signalling in the Cardiovascular System".

Resposta de vacas leiteiras à substituição parcial de farelo de soja por ureia encapsulada

Avaliou-se a substituição parcial de farelo de soja na dieta-controle por ureia encapsulada ou por ureia, ambos acrescidos de polpa cítrica. Dezoito vacas foram alocadas a uma sequência de três tratamentos, em seis quadrados latinos 3x3, com períodos de 21 dias. O teor de proteína bruta nas dietas foi 15,5%, cerca de 1,5% oriundo de nitrogênio não proteico (NNP). O uso de NNP reduziu o consumo diário de matéria seca em 0,8kg (P=0,04), sem influenciar a produção de leite (31,5kg, P=0,98). A conversão do alimento em leite foi menor na dieta-controle (P<0,09). As fontes de NNP aumentaram o teor de N-ureico no plasma (NUP) duas horas após a alimentação da manhã (P=0,06). A frequência de NUP acima de 22,0mg/dL foi maior com ureia (P<0,01), similarmente ao observado para o teor e a secreção diária de N-ureico no leite (P<0,01). A substituição de farelo de soja por NNP e polpa cítrica melhorou a eficiência alimentar, sem afetar o balanço de nitrogênio.

NTPDase and acetylcholinesterase activities in silver catfish, Rhamdia quelen (Quoy & Gaimard, 1824) (Heptapteridae) exposed to interaction of oxygen and ammonia levels

The effects of various levels of oxygen saturation and ammonia concentration on NTPDase (ecto-nucleoside triphosphate diphosphohydrolase, E.C. 3.6.1.5) and acetylcholinesterase (AChE, E.C. 3.1.1.7) activities in whole brain of teleost fish (Rhamdia quelen) were investigated. The fish were exposed to one of two different dissolved oxygen levels, including high oxygen (6.5 mg.L-1) or low oxygen (3.5 mg.L-1), and one of two different ammonia levels, including high ammonia (0.1 mg.L-1) or low ammonia (0.03 mg.L-1) levels. The four experimental groups included the following (A) control, or high dissolved oxygen plus low NH3; (B) low dissolved oxygen plus low NH3; (C) high dissolved oxygen plus high NH3; (D) low dissolved oxygen plus high NH3. We found that enzyme activities were altered after 24 h exposure in groups C and D. ATP and ADP hydrolysis in whole brain of fish was enhanced in group D after 24 h exposure by 100% and 119%, respectively, compared to the control group. After 24 h exposure, AChE activity presented an increase of 34% and 39% in groups C and D, respectively, when compared to the control group. These results are consistent with the hypothesis that low oxygen levels increase ammonia toxicity. Moreover, the hypoxic events may increase blood flow by hypoxia increasing NTPDase activity, thus producing adenosine, a potent vasodilator.

Ammonia causes decreased brain monoamines in fathead minnows (Pimephales promelas)

Hyperammonemia, arising from variety of disorders, leads to severe neurological dysfunction. The mechanisms of ammonia toxicity in brain are not completely understood. This study investigated the effects of ammonia on monoaminergic systems in brains of fathead minnows (Pimephales promelas). Fish serve as a good model system to investigate hyperammonemic effects on brain function since no liver manipulations are necessary to increase endogenous ammonia concentrations. Using high performance liquid chromatography with electrochemical detection, monoamines and some associated metabolites were measured from whole brain homogenate. Adult males were exposed for 48 h to six different concentrations of ammonia (0.01-2.36 mg/l unionized) which bracketed the 96-h LC(50) for this species. Ammonia concentration-dependent decreases were found for the catecholamines (norepinephrine and dopamine) and the indoleamine serotonin (5-HT). After an initial increase in the 5-HT precursor 5-hydroxytryptophan it too decreased with increasing ammonia concentrations. There were also significant increases in the 5-HIAA/5-HT and DOPAC/DA ratios, often used as measures of turnover. There were no changes in epinephrine (Epi) or monoamine catabolites (DOPAC, 5-HIAA) at any ammonia concentrations tested. Results suggest that ammonia causes decreased synthesis while also causing increased release and degradation. Increased release may underlie behavioral reactions to ammonia exposure in fish. This study adds weight to a growing body of evidence demonstrating that ammonia leads to dysfunctional monoaminergic systems in brain which may underlie neurological symptoms associated with human disorders such as hepatic encephalopathy.

Ammonia poisoning causes muscular but not liver damage in cattle

Twelve steers were intraruminally administered a high dose (0.5g/kg BW) of urea to study the damage effect of ammonia poisoning on liver and/or muscles. Blood samples were collected to determine ammonia and activities of gammaGT, AST and CK. Eleven steers were successfully poisoned and treated properly, but one succumbed. Poisoned cattle showed high concentration of ammonia, and higher activities of AST and CK. The higher the ammonia, the greater were the activities of AST (r=0.59) and CK (r=0.61). The correlation between AST and CK was high and significant (r=0.80), but not between AST and gammaGT (r=0.19). The activities of AST and CK were higher after the beginning of the convulsive episodes due to ammonia poisoning. Those results showed that occurred muscle damage instead of liver damage since CK is a typical enzyme from skeletal muscle; AST is found either in skeletal muscle and hepatocytes, while gammaGT is present in hepatic cells.

Effects of amino acid-derived luminal metabolites on the colonic epithelium and physiopathological consequences

Depending on the amount of alimentary proteins, between 6 and 18 g nitrogenous material per day enter the large intestine lumen through the ileocaecal junction. This material is used as substrates by the flora resulting eventually in the presence of a complex mixture of metabolites including ammonia, hydrogen sulfide, short and branched-chain fatty acids, amines; phenolic, indolic and N-nitroso compounds. The beneficial versus deleterious effects of these compounds on the colonic epithelium depend on parameters such as their luminal concentrations, the duration of the colonic stasis, the detoxication capacity of epithelial cells in response to increase of metabolite concentrations, the cellular metabolic utilization of these metabolites as well as their effects on colonocyte intermediary and oxidative metabolism. Furthermore, the effects of metabolites on electrolyte movements through the colonic epithelium must as well be taken into consideration for such an evaluation. The situation is further complicated by the fact that other non-nitrogenous compounds are believed to interfere with these various phenomenons. Finally, the pathological consequences of the presence of excessive concentrations of these compounds are related to the short- and, most important, long-term effects of these compounds on the rapid colonic epithelium renewing and homeostasis.

Adaptative increase of ornithine production and decrease of ammonia metabolism in rat colonocytes after hyperproteic diet ingestion

Chronic high-protein consumption leads to increased concentrations of NH(4)(+)/NH(3) in the colon lumen. We asked whether this increase has consequences on colonic epithelial cell metabolism. Rats were fed isocaloric diets containing 20 (P20) or 58% (P58) casein as the protein source for 7 days. NH(4)(+)/NH(3) concentration in the colonic lumen and in the colonic vein blood as well as ammonia metabolism by isolated surface colonic epithelial cells was determined. After 2 days of consumption of the P58 diet, marked increases of luminal and colonic vein blood NH(4)(+)/NH(3) concentrations were recorded when compared with the values obtained in the P20 group. Colonocytes recovered from the P58 group were characterized at that time and thereafter by an increased capacity for l-ornithine and urea production through arginase (P < 0.05). l-Ornithine was mostly used in the presence of NH(4)Cl for the synthesis of the metabolic end product l-citrulline. After 7 days of the P58 diet consumption, however, the ammonia metabolism into l-citrulline was found lower (P < 0.01) when compared with the values measured in the colonocytes recovered from the P20 group despite any decrease in the related enzymatic activities (i.e., carbamoyl-phosphate synthetase I and ornithine carbamoyl transferase). This decrease was found to coincide with a return of blood NH(4)(+)/NH(3) concentration in colonic portal blood to values close to the one recorded in the P20 group. In response to increased NH(4)(+)/NH(3) concentration in the colon, the increased capacity of the colonocytes to synthesize l-ornithine is likely to correspond to an elevated l-ornithine requirement for the elimination of excessive blood ammonia in the liver urea cycle. Moreover, in the presence of NH(4)Cl, colonocytes diminished their synthesis capacity of l-citrulline from l-ornithine, allowing a lower cellular utilization of this latter amino acid. These results are discussed in relationship with an adaptative process that would be related to both interorgan metabolism and to the role of the colonic epithelium as a first line of defense toward luminal NH(4)(+)/NH(3) concentrations.

The preferences of laying hens for different concentrations of atmospheric ammonia

Ammonia gas is one of the most abundant aerial pollutants of modern poultry buildings. The current chronic exposure limit for ammonia of 25 ppm is set for human safety rather than animal welfare. This study assessed the behavioural preferences of laying hens (Gallus gallus domesticus) for different concentrations of ammonia found in commercial poultry houses. Six groups, each of six laying hens, were given the choice of three concentrations of ammonia ( approximately 0, 25 and 45 ppm) in a preference chamber over a period of 6 days and their location and behaviour recorded every 15 min. Hens foraged (p=0.018), preened (p=0.009) and rested (p=0.029) significantly more in fresh air than in the ammonia-polluted environments. There was a significant difference between the responses in 0 and 25 ppm (p<0.05) but not between 25 and 45 ppm (p>0.05). This suggests that ammonia may be aversive to hens with a threshold for this aversion between 0 and 25 ppm. Future studies should explore graded concentrations of ammonia between 0 and 25 ppm in order to suggest a new chronic exposure limit on the basis of animal welfare.

A review of the literature on the application of blood ammonia measurement in sports science

This article summarizes previous studies on blood ammonia levels in relation to exercise. The dynamics of blood ammonia were reviewed with consideration to its production, removal, and distribution in various tissue compartments. During intense exercise, the primary source of ammonia is adenosine monophosphate deamination. Catabolism of branched-chain amino acids becomes important during submaximal exercise. Ammonia response to various types of exercise was also compared to lactate response. A comprehensive summary on factors affecting blood ammonia levels is provided. These reveal the possibility of applying blood ammonia measurement in monitoring and prescribing exercise, indirect measurement of muscle fiber composition, and muscle glycogen levels. However, more studies need to be conducted to evaluate these possibilities before blood ammonia measurement can be widely used.

Preference for flavoured foods by lambs conditioned with intraruminal administration of nitrogen

We suggested that food preference depends on the interplay between flavour and post-ingestive effects, and we predicted that protein-restricted lambs would acquire preferences for foods paired with supplemental sources of N, including urea (Expts 1 and 2), casein (Expt 3), and gluten (Expt 4). In each experiment, twenty lambs, in two groups of ten, were conditioned as follows: on odd-numbered days, lambs in group 1 received wheat straw (Expts 1, 3, and 4) or ground barley (Expt 2) flavoured with a distinctive flavour, and lambs in group 2 received the same food but with a different flavour. On even-numbered days, flavours were switched and lambs received capsules containing different amounts of urea (ranging from 0.12 to 0.92 g N/d), casein (ranging from 0.23 to 0.69 g N/d), or gluten (ranging from 0.23 to 0.69 g N/d). After conditioning period of 8 d, lambs were given a two-choice test to determine preference for flavours paired with N. In Expts 1 and 2, lambs preferred the flavours conditioned with urea at lower doses (0.12 g N/d in Expt 1, 0.23 and 0.46 g N/d in Expt 2), but they avoided the flavour associated with urea at the highest dose (0.23 g N/d in Expt 1 and 0.92 g N/d in Expt 2). In Expts 3 and 4, lambs avoided the flavours associated with the lowest doses of casein or gluten (0.23 g N/d), but they preferred the flavours paired with casein or gluten at higher doses (0.46 and 0.69 g N/d). After conditioning, N administrations were suspended and lambs in Expts 3 and 4 were offered a choice of the two flavours at weekly intervals for 2 weeks (extinction); preferences persisted during extinction. Collectively, these results suggest that the post-ingestive effects of N in different forms and concentrations influenced the development of food preferences by lambs.

Food intake and diet selection in sheep: the effect of manipulating the rates of digestion of carbohydrates and protein of the foods offered as a choice

An experiment was designed to investigate whether the degree of synchrony between the rates of digestion of carbohydrates and N of foods offered as a choice would have an effect, through their consequences, on the short- and long-term diet selection of sheep. Four foods (RL, RH, SL and SH) with the same high metabolizable energy, and similar high metabolizable protein contents were made into pellets. Foods RL and RH were based on a rapidly fermentable carbohydrate source and foods SL and SH on a slowly fermentable carbohydrate source; within each source one food (RL or SL) had a low, and the other (RH or SH) a high, rumen-degradable protein (RDP) content. The foods within a carbohydrate source were offered either singly or as a choice (RL/RH or SL/SH) to eleven rumen-fistulated mature sheep. The design was two 3 x 3 Latin squares (replicated once) with 5-week periods; squares consisted of two single foods and their respective choice. Weeks 1, 3 and 5 were considered to be controls, and weeks 2 and 4 used for rumen infusions of either urea or fructose infused over 4 h (10.00-14.00 hours). Food intake (FI) and diet selections (DS) were recorded daily and every 2 h (08.00-16.00 hours) on days 2-5 of each week; rumen pH and NH3 concentrations were also measured during these time intervals of day 5. As expected, feeding treatment affected significantly the rumen measurements: rumen NH3 concentrations were higher on foods RH and SH, and rumen pH lowest on RL. Daily FI was lowest on treatments SL, and choice SL/SH. The mean daily proportion of the low-RDP food in the selected diet was lower when the carbohydrate source was rapidly (choice RL/RH) rather than slowly fermentable (choice SL/SH); this was consistent with the experimental hypothesis. Short-term infusions affected further rumen variables (in the expected directions), irrespective of feeding treatment. However, DS over the 4h infusion period were unaffected; these short-term DS were consistent with the ones selected over the longer term (daily). The results suggest that the long-term (daily) diet selection of sheep may be affected by the degree of synchrony of energy and protein to the rumen. The fact that diet selections were not altered further by short-term manipulations of these supplies might reflect inadequacies of the methodology (infusions) adopted here.

Effect of a low-carbohydrate diet on plasma and sweat ammonia concentrations during prolonged nonexhausting exercise

The purpose of this investigation was to examine the effect of low body glycogen stores on plasma ammonia concentration and sweat ammonia excretion during prolonged, nonexhausting exercise of moderate intensity. On two occasions seven healthy untrained men pedalled on a cycle ergometer for 60 min at 50% of their predetermined maximal O2 uptakes (VO2max) firstly, following 3 days on a normal mixed diet (N-diet) (60% carbohydrates, 25% fat and 15% protein) and secondly, following 3 days on a low-carbohydrate diet (LC-diet) (less than 5% carbohydrates, 50% fat and 45% protein) of equal energy content. Blood was collected from the antecubital vein immediately before, at 30th and at 60th min of exercise. Sweat was collected from the hypogastric region using gauze pads. It was shown that plasma ammonia concentrations after the LC-diet were higher than after the N-diet at both the 30th and 60th min of exercise. Sweat ammonia concentration and total ammonia loss through the sweat were also higher after the LC-diet. The higher ammonia concentrations in plasma and sweat after the LC-diet would seem to indicate an increased ammonia production, which may be related to reduced initial carbohydrate stores.

An in vitro study of enhanced H+ diffusion by urease action on urea. Implications for Helicobacter pylori-associated peptic ulceration

The in vitro effect of urea and hydrolysis of urea by urease on mucus H+ permeability is reported here. The effective DHCl values indicate a strong pH dependence for H+ diffusion in both water and mucus layers, with no apparent trend at concentrations between 1 and 50 mM urea. However, the estimated DHCl at near-neutral and alkaline pH are 4- to 10-fold lower through mucus than through aqueous films. Moreover, the pKa values of HCO3- and NH3 (generated by urease action on urea) had a profound effect on measured DHCl. These in vitro studies suggest that a high local concentration of NH3 and HCO3- within the mucus layer, generated by the action of Helicobacter pylori urease on endogenous intragastric urea, could greatly accelerate proton flux to the surface epithelium by operation of a buffer shuttle. This results in enhanced H+ permeability, particularly at pKa values of HCO3- and NH3, and in extreme circumstances it may result in gastric ulcer formation.

Glutamine and glucose metabolism in bovine blood lymphocytes

1. Glutamine and glucose metabolism was studied in bovine blood lymphocytes incubated at 37 degrees C in the presence of Krebs-Ringer bicarbonate buffer (pH 7.4) containing 1 mM [U-14C]glutamine and 5 mM [U-14C]glucose, respectively. 2. The major metabolic products from glutamine were ammonia, glutamate, and to a lesser extent, aspartate and CO2. Glucose was metabolized mainly to lactate and, to a lesser extent, pyruvate and CO2. These findings indicate incomplete oxidation of glutamine and glucose carbons in bovine blood lymphocytes. 3. Glucose provided three-fold greater amounts of energy to bovine blood lymphocytes than did glutamine on the basis of their measured end-products. Glycolysis accounted for 50% of glucose-derived ATP production. 4. Our findings suggest similar metabolic patterns of glutamine and glucose in lymphocytes between ruminants and non-ruminant species (e.g. rats). However, in contrast to rat peripheral lymphocytes, glucose, rather than glutamine, was a major energy substrate for bovine blood lymphocytes.

Plasma ammonia is the principal source of ammonia in sweat

Sweat contains ammonia. However, neither its source nor factors affecting its concentration in the sweat are known. The aim of this study was to examine the effect of plasma concentrations of ammonia and urea on the concentration of ammonia in the sweat. Four groups of male volunteers were examined: one control, two after ingestion of ammonium chloride, three cirrhotic, hyperammonaemic, four uraemic. Sweat was collected from each subject from the palmar side of the forearm using gauze pads, after previous iontophoresis of pilocarpine. Ammonia and urea concentrations were determined in the sweat and in the plasma. It was found that elevated plasma ammonia concentration in healthy subjects after ingestion of ammonium chloride as well in the cirrhotic patients resulted in an increase of ammonia concentration in the sweat. High plasma and sweat urea concentration in the uraemic subjects did not affect the concentration of ammonia in the sweat. It was concluded that plasma ammonia was the principal source of ammonia in the sweat.

Hypotheses on the pathogenesis and natural history of Helicobacter pylori-induced inflammation

Although Helicobacter pylori is now recognized as playing an etiologic role in chronic gastritis and peptic ulcer disease, information on the pathogenesis and natural history of infection is limited. A model is proposed in which luminal H. pylori secrete substances that mediate inflammation that is beneficial to the organism but ultimately deleterious for the host; in addition to tissue damage, inflammation also affects gastric secretory function. In this model, the host may attempt to suppress the inflammatory response, and the adequacy of this postulated down-regulation determines pathological and clinical outcome. The effects of the inflammatory process on gastrin-hydrochloric acid homeostasis may be of critical importance in the pathogenesis of peptic ulcer disease. Because the long-term consequences of H. pylori colonization reflect the continued presence of the organism in the host over years or decades, it may be useful to consider this as a "slow" bacterial infection.

Ammonia metabolism during intense dynamic exercise and recovery in humans

This study examined the dynamics for ammonia (NH3) metabolism in human skeletal muscle during and after intense one-legged exercise. Subjects (n = 8) performed dynamic leg extensor exercise to exhaustion (3.2 min). Muscle NH3 release increased rapidly to a maximum of 314 +/- 42 mumol/min and declined immediately on cessation of exercise. Recovery was complete in approximately 20 min. Arterial [NH3] increased less rapidly and reached its maximum 2-3 min into recovery. These data demonstrate that NH3 clearance is more sensitive to the cessation of exercise than is NH3 release from skeletal muscle. Muscle [NH3] increased three to fourfold during exercise and represented 74 +/- 8% of the total net NH3 formation. Thus the change in muscle [NH3] alone underestimates the NH3 production. There was no evidence that the muscle-to-venous blood NH3 ratio shifts in accordance with the H+ data. Thus other factors must contribute to the NH3 release from active muscle. The total net NH3 formed corresponded with the intramuscular inosine 5'-monophosphate accumulation, suggesting that the NH3 was derived from AMP deamination. Changes in the known modulators of AMP deaminase (ATP, ADP, H+) were moderate, so the mechanisms initiating the deamination remain obscure.

Ammonia produced by Campylobacter pylori neutralizes H+ moving through gastric mucus

We aimed to show that Campylobacter pylori infection increases the concentration of ammonia in the gastric mucus and alters the movement of H+ through the mucus. Mucus from uninfected and C. pylori-infected stomachs was collected at postmortem. Ammonia was measured enzymatically. The ammonia concentration in C. pylori-infected mucus was fourfold greater than in uninfected mucus. H+ movement experiments were carried out using an in vitro chamber, in which a layer of mucus separated a 0.1 M HCl solution from distilled H2O. The change in pH of the distilled H2O was measured over 30 min. A drop in pH was measured for uninfected mucus. A slight rise in pH was measured for C. pylori-infected mucus. We conclude that C. pylori infection is associated with reduced H+ movement through mucus and that this may be due to increased ammonia concentration within mucus.

Nitrogen digestion and metabolism in sheep consuming diets containing contrasting forms and levels of N

Nitrogen kinetics were studied in six sheep (45-55 kg live weight) consuming either a high-N grass silage or a low-N dried grass made from swards of perennial ryegrass (Lolium perenne). The diets were fed hourly at a level of 600 g dry matter/d and supplied 19.5 and 11.0 g N/d respectively. The amounts of organic matter (OM) consumed and flowing at the duodenum and ileum and excreted in the faeces were similar (P greater than 0.05) with both diets. Each diet supplied 23 g digestible OM/d per kg live weight 0.75, which was sufficient to maintain body-weight. There were no differences (P greater than 0.05) between diets in rumen fluid volume, fractional outflow rate of fluid from the rumen, total concentration of volatile fatty acids or molar proportion of acetate in the rumen. The pH and molar proportion of propionate in rumen fluid were higher (P less than 0.01), and molar proportion of butyrate lower (P less than 0.001) when the silage was given. There was a net loss of N (4.0 g/d) between mouth and duodenum when the silage was consumed but a net gain (5.5 g/d) when the dried grass was consumed. As a result, total non-ammonia-N (NAN) flow at the duodenum did not differ (P greater than 0.05) between diets. Rumen microbial NAN flow at the duodenum, based on 15N as the marker, also did not differ (P greater than 0.05) between diets but the efficiency of microbial N synthesis in the rumen (g/kg OM apparently digested) was higher (P less than 0.05) with the dried grass. When the sheep were consuming silage they had a higher concentration of ammonia in rumen fluid (P less than 0.01), a higher rate of irreversible loss of ammonia from the rumen (P less than 0.05) and a higher rate of absorption of ammonia across the rumen wall (P less than 0.01). The rate of absorption was found to be more closely related to the unionized ammonia concentration in rumen fluid (r2 0.85) than to the total ammonia concentration (r2 0.36). Endogenous N entry into the forestomachs was calculated to be 5.5 g/d when the silage was given and 9.4 g/d when the dried grass was given, of which 1.7 and 3.5 g/d respectively were in the form of urea. Thus, approximately 4-6 g N/d were derived from non-urea materials.(ABSTRACT TRUNCATED AT 400 WORDS)

Ammonia toxicity for mammalian and avian lymphocytes from blood

The effect of addition of ammonia to cultures of avian, bovine, cavian, equine, human, leporinae, murine, ovine and porcine blood lymphocytes was studied. The concentrations of ammonia in the lymphocyte cultures represented normal (0.01-0.5 mg/dl), subtoxic (0.5-1 mg/dl), and toxic (1-10 mg/dl) concentrations of ammonia in blood. Viability of the lymphocytes and their mitogenic reactivity were measured. In general, 1.0 and 10 mg/dl of ammonia (toxic concentrations) affected viability and mitogenic responsiveness of all lymphocytes from tested species. The lower concentrations of ammonia affected only avian, bovine and equine lymphocytes.

Ammonia: its effects on biological systems, metabolic hormones, and reproduction

The physical, chemical properties of ammonia, its sources and detoxification, its effects in biological systems, its influence upon insulin action and glucose metabolism, and its possible effects on reproduction are discussed. Present chemical methods do not distinguish nonionic from ionic forms. At physiological pH, nonionic ammonia concentrations remain low but are primarily responsible for toxic effects. Thus, biologically significant changes of ammonia concentrations may not be revealed by determinations of ammonia in blood plasma. For these and other reasons the subacute toxicity of ammonia often is unrecognized, and its effects on intermediary metabolism and the hormonal milieu in normal and disease states remain poorly understood. Effects of ammonia may be stimulatory at low concentrations and inhibitory as concentrations rise or exposure is extended. Extensive experiments in eight ureotelic species, including man, show that urinary excretion of orotic acid becomes significantly elevated when the quantity of ammonia presented to the liver exceeds the capacity for normal detoxification. Present evidence with arginine and other intermediates of the urea cycle suggest that these substances influence glucose metabolism and insulin action. Recent studies of dairy cattle provide speculative evidence that high protein feeding or forms of protein that lead to elevated ammonia concentrations in tissue decrease conception rates and increase the calving to conception interval of dairy cows. Limited data concerning luteinizing hormone concentrations and steroid hormone metabolism are insufficient to establish whether differences in reproductive performance are due to changes of hormonal physiology, intrauterine environment, or metabolism.

Effect of ammonia on viability and blastogenesis of bovine lymphocytes

The effect of addition of ammonia into the tissue culture on viability and functions of bovine lymphocytes was studied. The concentrations of ammonia in the tissue cultures represented toxic, subtoxic, and normal concentrations of ammonia in the bovine blood during clinical and subclinical urea toxicosis. Lymphocytes separated from peripheral bovine blood were incubated in control medium and test medium with various concentrations of ammonia and/or PHA or Con A. Viability of the lymphocytes was measured by trypan blue exclusion test and their mitogenic reactivity by incorporation of 3H thymidine into DNA of lymphocytes. Approximately 30% bovine lymphocytes were killed by ammonia in medium during 72 hours of incubation. Ammonia also affected the response of lymphocytes to stimulation with PHA or Con A as well as mixed lymphocyte culture reaction. The mitogenic response of lymphocytes was also reduced when lymphocytes were preincubated with ammonia for even 1 hour. The mitogenic response was not restored when the number of lymphocytes preincubated with ammonia was reconstituted to the initial concentration to compensate for the killed lymphocytes before stimulation with PHA. Therefore, addition of ammonia to the culture either killed lymphocytes or permanently impaired their functions.