Pulmonary hypertensive responses of broilers to bacterial lipopolysaccharide (LPS): evaluation of LPS source and dose, and impact of pre-existing pulmonary hypertension and cellulose micro-particle selection

Mogroside V ameliorates broiler pulmonary inflammation via modulating lung microbiota and rectifying Th17/Treg dysregulation in lipopolysaccharides-induced lung injury

The dysbiosis of lung microbiota and inflammatory factors play a crucial role in the occurrence of lipopolysaccharides (LPS)-induced lung injury. Recently, mogroside V (MGV) has received increasing attention due to its potential health benefits in pneumonia, but its complex mechanism needs further experimental elucidation. In this study, we established an LPS-induced chicken lung injury model to investigate the protective effect of MGV on LPS-induced acute lung injury in broiler and its related mechanisms. A total of 192 one-day-old white-finned broilers were randomly assigned into 4 groups with 6 replicates: 1) control group: basal diet (d 1-44), saline (d 43); 2) LPS group: basal diet (d 1-44), LPS (d 43); 3) MGV group: basal diet + 0.2% MGV (d 1-44), saline (d 43); 4) MGV-LPS group: basal diet + 0.2% MGV (d 1-44), LPS (d 43). The results showed that pathological examination showed that lung tissue inflammation infiltration was reduced after MGV treatment. In addition, MGV can promote the balance of Th17 and Treg cell cytokines, significantly inhibit the expression of proinflammatory cytokines (IL-1β (P < 0.01), IL-6 (P < 0.001), IL-17F (P < 0.05)), and decrease immunosuppressive target expression (PD-L1 (P < 0.01), PD-1 (P < 0.001), RORα (P < 0.001)), activating the immune system. Furthermore, 16S rRNA sequencing analysis showed that MGV treatment could increase the abundance of beneficial bacteria in the lung and reduce the abundance of bacteria associated with inflammation. Generally, MGV intervention has a preventive effect on the pathological damage induced by lipopolysaccharides. Its mechanism is related to inhibiting the inflammatory response, regulating the Th17/Treg balance, and maintaining the stability of lung microbiota.

Oleocanthal alleviated lipopolysaccharide-induced acute lung injury in chickens by inhibiting TLR4/NF-κB pathway activation

This study aimed to investigate the ameliorative effect of oleocanthal (OC) on lipopolysaccharide (LPS)-induced acute lung injury (ALI) in chickens and its possible mechanisms. In total, 20 chickens were randomly divided into 4 groups: control (CON) group, LPS group, LPS + OC group, and OC group. LPS + OC and OC groups were intragastrically administered a 5 mg/kg·d OC dose for 7 d. On d 8, the LPS group and LPS + OC group were intratracheally administered 2 mg/kg LPS for 12 h. It was found that OC ameliorated the pathological morphology and significantly suppressed apoptosis after OC treatment in LPS-induced ALI chicken (P < 0.01). Antioxidant capacity was higher in the LPS + OC group compared with the LPS group (P < 0.01). OC downregulated the related genes and proteins expression of toll-like receptor 4/nuclear factor-κB (TLR4/NF-κB) pathway in LPS group (P < 0.01). In conclusion, OC supplementation can alleviate LPS-induced ALI in chickens by suppressing apoptosis, enhancing lung antioxidant capacities and inhibiting TLR4/NF-κB pathway activation.

Dietary L-citrulline influences body temperature and inflammatory responses during nitric oxide synthase inhibition and endotoxin challenge in chickens

Recent studies have revealed the role of L-citrulline (L-CIT) in thermoregulation, but very little is known about the mechanisms involved. In this study, nitric oxide synthase inhibition and endotoxin-induced fever were used to investigate the effects of L-CIT on body temperature and inflammatory responses. In experiment 1, NW-nitro-L-arginine methyl ester (L-NAME, 150 mg/kg BW), was i. p. injected into chicks fed with basal (CON) or L-CIT diets for 14 days. In experiment 2, Lipopolysaccharide (LPS, 2 mg/kg BW) was i. p. injected following 21d feeding with CON or L-CIT diets. In experiment 3, chickens were injected with either L-NAME, LPS, or L-NAME + LPS following 26 days feeding with CON or L-CIT diets. The rectal (RT), ear (ET), and core body temperature (CBT) of chickens were examined. Results showed that L-NAME effectively decreased the RT, ET, CBT, and plasma NO concentration. In contrast, LPS increased NO levels and initiated hyperthermia by increasing RT, ET, CBT, and PGE2 levels. L-CIT diet reduced the mean CBT in experiment 1 and diminished the NO level, PGE2 level, and mean RT in experiment 3. Co-administration of L-CIT + LPS upregulated IL-6 expression, whereas, LPS injection alone induced IL-10, IL-1β, and TLR4 gene expressions. Therefore, this study reveals that L-CIT-induced hypothermia was related to NO inhibition and a decrease in PGE2 concentration. Conversely, LPS induced hyperthermia was associated with an increase in both NO and PGE2 concentrations.

Gut Health of Pigs: Challenge Models and Response Criteria with a Critical Analysis of the Effectiveness of Selected Feed Additives - A Review

The gut is the largest organ that helps with the immune function. Gut health, especially in young pigs has a significant benefit to health and performance. In an attempt to maintain and enhance intestinal health in pigs and improve productivity in the absence of in-feed antibiotics, researchers have evaluated a wide range of feed additives. Some of these additives such as zinc oxide, copper sulphate, egg yolk antibodies, mannan-oligosaccharides and spray dried porcine plasma and their effectiveness are discussed in this review. One approach to evaluate the effectiveness of these additives in vivo is to use an appropriate disease challenge model. Over the years, researchers have used a number of challenge models which include the use of specific strains of enterotoxigenic Escherichia coli, bacteria lipopolysaccharide challenge, oral challenge with Salmonella enteric serotype Typhimurium, sanitation challenge, and Lawsonia intercellularis challenge. These challenge models together with the criteria used to evaluate the responses of the animals to them are also discussed in this review.

Pulmonary arterial hypertension (ascites syndrome) in broilers: a review

Pulmonary arterial hypertension (PAH) syndrome in broilers (also known as ascites syndrome and pulmonary hypertension syndrome) can be attributed to imbalances between cardiac output and the anatomical capacity of the pulmonary vasculature to accommodate ever-increasing rates of blood flow, as well as to an inappropriately elevated tone (degree of constriction) maintained by the pulmonary arterioles. Comparisons of PAH-susceptible and PAH-resistant broilers do not consistently reveal differences in cardiac output, but PAH-susceptible broilers consistently have higher pulmonary arterial pressures and pulmonary vascular resistances compared with PAH-resistant broilers. Efforts clarify the causes of excessive pulmonary vascular resistance have focused on evaluating the roles of chemical mediators of vasoconstriction and vasodilation, as well as on pathological (structural) changes occurring within the pulmonary arterioles (e.g., vascular remodeling and pathology) during the pathogenesis of PAH. The objectives of this review are to (1) summarize the pathophysiological progression initiated by the onset of pulmonary hypertension and culminating in terminal ascites; (2) review recent information regarding the factors contributing to excessively elevated resistance to blood flow through the lungs; (3) assess the role of the immune system during the pathogenesis of PAH; and (4) present new insights into the genetic basis of PAH. The cumulative evidence attributes the elevated pulmonary vascular resistance in PAH-susceptible broilers to an anatomically inadequate pulmonary vascular capacity, to excessive vascular tone reflecting the dominance of pulmonary vasoconstrictors over vasodilators, and to vascular pathology elicited by excessive hemodynamic stress. Emerging evidence also demonstrates that the pathogenesis of PAH includes characteristics of an inflammatory/autoimmune disease involving multifactorial genetic, environmental, and immune system components. Pulmonary arterial hypertension susceptibility appears to be multigenic and may be manifested in aberrant stress sensitivity, function, and regulation of pulmonary vascular tissue components, as well as aberrant activities of innate and adaptive immune system components. Major genetic influences and high heritabilities for PAH susceptibility have been demonstrated by numerous investigators. Selection pressures rigorously focused to challenge the pulmonary vascular capacity readily expose the genetic basis for spontaneous PAH in broilers. Chromosomal mapping continues to identify regions associated with ascites susceptibility, and candidate genes have been identified. Ongoing immunological and genomic investigations are likely to continue generating important new knowledge regarding the fundamental biological bases for the PAH/ascites syndrome.

Effects of repeated intratracheally administered lipopolysaccharide on primary and secondary specific antibody responses and on body weight gain of broilers

Earlier, we reported that pathogen-associated molecular patterns such as lipopolysaccharide (LPS), when administered intratracheally (i.t.), affected primary and secondary specific antibody responses to antigens administered concurrently, either i.t. or systemically, and also affected BW gain (BWG) of layers and broilers. In the present study, we evaluated the effects of repeated i.t. challenge with LPS concurrently with or before i.t. immunizations with the specific antigens human serum albumin (HuSA) and rabbit gamma globulin (RGG) on primary (HuSA, RGG) and secondary (HuSA) systemic antibody responses and (isotype) IgM and IgG responses at 2 different ages. Broilers were challenged via the trachea at 3 and 7 wk of age with various combinations of LPS, HuSA, and RGG. All treatments affected immune responses at several time points and also affected BWG, albeit temporarily for the latter. Lipopolysaccharide enhanced primary antibody responses to HuSA and to RGG, when challenged concurrently, but birds challenged solely with LPS at 3 wk of age also showed enhanced primary antibody responses to HuSA and RGG given at 7 wk of age. This was true for IgM as well as IgG isotype responses. Lipopolysaccharide challenge negatively affected BWG at 3 wk of age, whereas the negative effects of LPS after a secondary LPS challenge at 7 wk of age were most pronounced in the birds challenged with LPS at 3 wk of age. The present results indicated that LPS, when administered i.t. at a young age, may affect specific humoral immune responsiveness to antigens administered simultaneously and to BWG of broilers, but also when challenged 4 wk later with specific antigens, suggesting an enhanced status of immune reactivity or sensitivity. The hygienic status of broiler houses at a young age may thus influence BWG, immune responsiveness, and, consequently, the vaccine efficacy and disease resistance in broilers at later ages. The consequences of our findings are discussed.

Broiler pulmonary hypertensive responses during lipopolysaccharide-induced tolerance and cyclooxygenase inhibition

Bacterial lipopolysaccharide (LPS, endotoxin) triggers pulmonary hypertension (PH) characterized by an increase in pulmonary arterial pressure (PAP) that reaches a peak value within 20 to 25 min and then gradually subsides within 60 min. As the PAP subsides PH cannot be reinitiated, signifying the onset of a period of tolerance (refractoriness) to repeated LPS exposure. The present study was conducted to determine the duration of this tolerance, and to evaluate key mediators thought to contribute to LPS-mediated PH in broilers. Tolerance was shown to persist for 4 to 5 d after the initial exposure to LPS. In tolerant broilers supramaximal i.v. injections of LPS did not reinitiate PH, nor was a significant modulatory role for nitric oxide demonstrated. The pulmonary vasculature of tolerant broilers remains responsive to the thromboxane A(2) (TxA(2)) mimetic U44069, 5-hydroxytryptamine (5-HT, serotonin), and constitutive nitric oxide. Meclofenamate successfully blocked the conversion of arachidonic acid to vasoconstrictive eicosanoids such as TxA(2); nevertheless, meclofenamate failed to inhibit PH in response to LPS. Therefore, TxA(2) does not appear to be the primary vasoconstrictor involved in the PH response to LPS and neither does 5-HT. Broilers emerging from tolerance 5 d after the initial exposure to LPS exhibited interindividual variation in their PH responsiveness to a second LPS injection, ranging from zero response (individuals that remain fully tolerant) to large increases in PAP (post-tolerant individuals). Tolerance might be an important compensatory or protective mechanism for broilers whose pulmonary vascular capacity is marginally adequate under optimal conditions, and whose respiratory systems are chronically challenged with LPS in commercial production facilities. The key vasoconstrictors responsible for the PH elicited by LPS remain to be determined.

Effect of single or combined climatic and hygienic stress on natural and specific humoral immune competence in four layer lines

Effects of long-term climatic stress (heat exposure), short-term hygienic stress [lipopolysaccharide (LPS)], or a combination of both challenges on the immune competence of 4 layer lines was investigated. The lines were earlier characterized for natural humoral immune competence and survival rate. Eighty hens per line were randomly divided over 2 identical climate chambers and exposed to a constant high temperature (32 degrees C) or a control temperature (21 degrees C) for 23 d. Half of the hens housed in each chamber were i.v. injected with LPS at d 1 after the start of the heat stress period. Within each of the treatment groups, half of the hens were s.c. immunized with human serum albumin (HuSA) at d 2 after the start of the heat stress period to measure specific antibody (Ab) titers to HuSA. The effect of heat, LPS, or a combined challenge on specific Ab titers to HuSA, natural Ab titers to keyhole limpet hemocyanin or HuSA (in hens that were not immunized with HuSA), and activity of the classical and alternative complement pathways were investigated. Heat stress enhanced specific and natural immune responses. Administration of LPS enhanced natural immune responses but decreased specific immune responses. The lack of interaction between heat stress and LPS administration, except for natural Ab titers to HuSA, suggest that these were 2 independent stressors. The lines had a similar response pattern but differed in the response level. Neither natural humoral immune competence nor survival rate, for which the lines had been characterized, was indicative of the specific and natural immune response to different stressors. Lipopolysaccharide and heat stress initiated sequential responses over time, with an earlier effect of short-term LPS exposure (within the first and second week) and a later effect of long-term heat exposure (within the second and third week). These data suggest that LPS and heat stress affect the natural and specific immune competence of laying hens.

Intratracheally Administered Pathogen-Associated Molecular Patterns Affect Antibody Responses of Poultry

Various potential immune-modulating microbially derived pathogen-associated molecular patterns (PAMP), or so called homotopes, are present in high concentrations in the environment of food animals. In previous studies, intravenously administered PAMP had variable effects on specific primary and secondary immune responses of poultry to systemically administered antigens. In the present study, we evaluated the effects of intratracheal (i.t.) challenge with the PAMP lipopolysaccharide, lipoteichoic acid (LTA), and Zymosan-A (containing 1,3 beta-glucan) on primary and secondary (total) antibody (Ab) responses and (isotype) IgM, IgG, and IgA responses to systemically administered human serum albumin (HuSA), and Ab titers to infectious bursal disease (Gumboro virus) and infectious bronchitis vaccines in layer hens at 9 and 22 wk of age. Birds were challenged via the trachea with PAMP for 5 consecutive days prior to primary and secondary immunization with HuSA. Intratracheally administered LTA and, to a minor extent, lipopolysaccharide significantly enhanced secondary total and IgG Ab responses to HuSA. 1,3 beta-Glucan did not significantly affect Ab responses to HuSA. All birds challenged with PAMP showed a decreased BW. Higher total Ab titers to infectious bursal disease and infectious bronchitis were found in birds challenged with LTA. The present results indicate that i.t. administered PAMP affect the humoral immune responsiveness of poultry, which may lead to an enhanced status of immune reactivity. Furthermore, our results suggest that the hygienic status of the environment influences BW (gain). The consequences of immune modulation by airborne PAMP or hygienic conditions in chicken husbandry for vaccine delivery and immune responsiveness of poultry are discussed.

Age- and Breed-Dependent Adapted Immune Responsiveness of Poultry to Intratracheal-Administered, Pathogen-Associated Molecular Patterns

Immune modulation of poultry by airborne pathogen-associated molecular patterns (PAMP) was studied. White and Brown layer chicks were exposed intratracheally during 5 consecutive days at 7 wk of age with Escherichia coli-derived lipopolysaccharide (LPS), Saccharomyces cerevisiae-derived 1,3 beta-glucan (BGL), a combination of both, or PBS as a control. Six weeks later, birds received similar or crossover PAMP treatments. Body weight (gain), feed conversion, (primary and secondary) specific antibody responses to model antigens, and natural antibody levels were measured. In general, BGL enhanced but LPS exposure decreased primary immune responses at 7 wk of age, whereas both PAMP-enhanced secondary immune responses but decreased primary immune responses at 13 wk of age. Body weight gain and feed conversion at both ages were negatively affected by LPS, especially in White birds, but not by BGL. Pathogen-associated molecular patterns exposure at 7 wk of age also affected Ab responses at 13 wk of age. Birds exposed to a combination of LPS + BGL at 7 wk of age had significantly lower secondary total and IgG Ab responses at 13 wk of age. Birds from both breeds showed enhanced BW gain after exposure to LPS at 13 wk of age, when initially challenged at 7 wk of age with LPS, BGL, or a combined challenge with both. Pathogen-associated molecular patterns exposure at 7 wk of age affected humoral immunity and BW gain at 13 wk of age in a positive (BGL) or negative (LPS) fashion. Repeated exposure to PAMP did not affect Ab responses, but crossover exposure to PAMP in general enhanced Ab responses. Body weight gain was positively affected by repeated exposure but not by crossover exposure, suggesting adaptation of the birds to early PAMP exposure. Our findings suggest that sensitivity of poultry for immune modulation by airborne PAMP differs between ages, is breed-dependent, and is not irreversible of nature. In addition, our data suggest different adaptation to hygienic conditions, both with respect to immune reactivity and BW gain.

Variation in the Pulmonary Hypertensive Responsiveness of Broilers to Lipopolysaccharide and Innate Variation in Nitric Oxide Production by Mononuclear Cells

Variability among broilers in their pulmonary hypertensive (PH) responsiveness to lipopolysaccharide (LPS) appears to reflect innate variation in the types or proportions of vasodilators and vasoconstrictors released by leukocytes and endothelial cells. Two experiments were designed to evaluate possible correlations between the PH responsiveness to LPS in vivo and the quantities of nitric oxide (NO; a potent pulmonary vasodilator) produced by mononuclear cells in vitro. In Experiment 1, blood samples were collected from male broilers from a base population (control group) and from survivors of a 60% lethal dose i.v. injection of cellulose microparticles (MP survivor group). In Experiment 2, blood samples were collected from male broilers from a relaxed line and from lines known to be susceptible or resistant to pulmonary hypertension syndrome. Peripheral mononuclear cells (PMNC) from each blood sample were cultured at 2 million cells per well, remained unstimulated, or were stimulated with LPS to elicit the expression of inducible NO synthase, and the 24-h production of NO was measured. In both experiments, unstimulated PMNC cultures did not produce consistently detectable levels of NO, whereas LPS-stimulated cultures produced quantities of NO that varied widely among individuals. Nitric oxide production by cultured PMNC also was evaluated by flow cytometry, demonstrating that LPS-stimulated PMNC produced substantially more NO than did unstimulated cells in all of the groups evaluated. Moreover, NO-producing PMNC were identified to be monocytes. The same broilers from which PMNC had been isolated were catheterized subsequently to record pulmonary arterial pressure, LPS was injected i.v. to assess the amplitudes of peak and postpeak PH responses, then N(omega)-nitro-L-arginine methyl ester was injected to inhibit ongoing NO production. In Experiment 1, the amplitude of the peak and postpeak PH responses to LPS were correlated with the quantity of NO produced by LPS-stimulated cultured PMNC from broilers in the control group but not for MP survivors. In Experiment 2, the postpeak PH response to LPS was correlated with the quantity of NO produced by LPS-stimulated PMNC from broilers in the relaxed line, but not in the susceptible or resistant lines. In all groups, N(omega)-nitro-L-arginine methyl ester injections triggered substantial increases in pulmonary arterial pressure (> or = 8 mm Hg), thereby revealing a significant ongoing modulation by NO of the PH response to LPS. We concluded that most of the modulatory NO generated in vivo during the acute PH response to LPS (within 60 min postinjection) likely is produced by constitutive NO synthase in the vascular endothelium. In addition, the NO produced by inducible NO synthase in PMNC appeared to have modulated the LPS-stimulated PH responses of unselected broilers having the broadest range of pulmonary vascular capacities (control broilers and relaxed line), but not in broilers whose pulmonary vascular capacities had been selected to represent the higher (MP survivors, resistant line) or lower (susceptible line) extremes of the population.

Influence of aminoguanidine, an inhibitor of inducible nitric oxide synthase, on the pulmonary hypertensive response to microparticle injections in broilers

The pulmonary hypertensive response to pulmonary vascular obstruction caused by intravenously injected microparticles is amplified by pretreatment with N(omega)nitro-L-arginine methyl ester (L-NAME). The L-NAME prevents the synthesis of the potent vasodilator nitric oxide (NO) by inhibiting both the constitutive [endothelial NO synthase (eNOS or NOS-3)] and inducible [inducible NO synthase (iNOS or NOS-2)] forms of NO synthase. In the present study we used the selective iNOS inhibitor aminoguanidine (AG) to evaluate the role of iNOS in modulating the pulmonary hypertension (PH) triggered by microparticle injections. Experiment 1 was conducted to confirm the ability of AG to inhibit NO synthesis by iNOS in broiler peripheral blood mononuclear cells exposed to bacterial lipopolysaccharide (LPS, endotoxin). Mononuclear leukocytes treated with LPS produced 10-fold more NO than untreated (control) cells. The LPS-stimulated production of NO was partially inhibited by L-NAME and was fully inhibited by AG, thereby confirming that AG inhibits LPS-mediated iNOS activation in broilers. In Experiment 2 we evaluated the responses of male progeny from a base population (MP Base) and from a derivative line selected for one generation from the survivors of an LD50 microparticle injection (MP Select). The pulmonary arterial pressure (PAP) was lower in MP Select than in MP Base broilers. Both lines exhibited similar percentage increases in PAP after microparticles were injected, and AG modestly amplified the PH triggered by microparticles in both lines. In Experiment 3 we evaluated the responses of male progeny from a second base population (PAC Base) and from a derivative line selected for 3 generations using the unilateral pulmonary artery clamp technique (PAC Select). The PAP was lower in PAC Select than in PAC Base broilers, and both lines exhibited similar percentage increases in PAP in response to the microparticles. The PH triggered by microparticles was not amplified by AG but was doubled by L-NAME. These experiments demonstrate that during the 30 min following pulmonary vascular entrapment of microparticles, iNOS modulated the PH elicited in broilers derived from the MP pedigree line, but not in broilers from the PAC pedigree line. Different NOS-mediated responses among broiler populations may affect pulmonary hemodynamic characteristics of broiler lines selected using i.v. microparticle injections.

Pulmonary hypertension triggered by lipopolysaccharide in ascites-susceptible and -resistant broilers is not amplified by aminoguanidine, a specific inhibitor of inducible nitric oxide synthase

Nitric oxide (NO) is a potent pulmonary vasodilator that modulates the pulmonary vasoconstriction and pulmonary hypertension (PH) triggered by bacterial lipopolysaccharide (LPS) in broilers. The amplitude and duration of the LPS-induced PH are markedly enhanced following pretreatment with N(omega)-nitro-L-arginine methyl ester (L-NAME), which inhibits NO synthesis by both the constitutive (endothelial) and inducible (inflammatory) forms of nitric oxide synthase (eNOS and iNOS, respectively). In the present study L-NAME and the selective iNOS inhibitor aminoguanidine (AG) were administered to differentiate between iNOS and eNOS as the primary source of NO that attenuates the pulmonary vascular response to LPS. Clinically healthy male progeny from ascites-susceptible and ascites-resistant lines were anesthetized, and their pulmonary artery was cannulated. The initial pulmonary arterial pressure (PAP) was recorded, then the broilers either remained untreated (control group) or were injected i.v. with AG. Ten minutes later all birds received an i.v. injection of LPS, followed 40 min later by an i.v. injection of L-NAME. When compared with untreated controls, AG neither increased the baseline PAP nor did it increase or prolong the PH response to LPS. The ascites-susceptible broilers maintained a higher PAP than the ascites-resistant broilers throughout the experiment, and the ascites-resistant broilers exhibited greater relative increases in PAP in response to LPS than did the ascites-susceptible broilers. Within 40 min after the LPS injection, PAP subsided to a level that did not differ from the respective preinjection value for each line. Injecting L-NAME reversed the decline in PAP, and within 5 min PAP returned to hypertensive levels approaching the maximum peak PH response to LPS. The absence of any impact of AG coupled with the profound response to L-NAME indicates that NO synthesized by eNOS rather than iNOS likely modulated the acute (within 1 h) PH elicited by LPS. Evidently eNOS is activated by the increased shear stress exerted on the endothelium during the PH response to LPS, whereas LPS-mediated up-regulation of iNOS expression may take longer than 1 h before biologically effective quantities of NO are produced.

Evaluation of Total Plasma Nitric Oxide Concentrations in Broilers Infused Intravenously with Sodium Nitrite, Lipopolysaccharide, Aminoguanidine, and Sodium Nitroprusside

Nitric oxide (NO) is a potent vasodilator that is synthesized by constitutive and inducible isoforms of the enzyme NO synthase (eNOS and iNOS, respectively). The half-life of NO averages only 3 to 4 s in biological fluids, where it is rapidly converted to the stable oxidation products nitrite (NO2-) and nitrate (NO3-). Our objectives were to use 2 commercial kits to measure total plasma NO, as NO2- + NO3-, and to assess plasma NO values during experimental protocols designed to influence NO accumulation in the plasma. One kit employed copper-coated cadmium as a catalyst for reducing NO3- to NO2-; the second kit employed the enzyme NO3- reductase for the same purpose. Both then employed Griess reagent for the colorimetric determination of NO2- as a measure of total plasma NO. Broilers in Experiment 1 were infused i.v. with solutions containing increasing concentrations of sodium NO2-. Broilers in Experiment 2 were injected with 1 mg of lipopolysaccharide (LPS), which is known to stimulate iNOS activity. Both commercial kits successfully detected increases in total plasma NO attributable to ongoing i.v. NO2- infusion or to increased iNOS expression at 5 h after the LPS injection. In Experiment 3, we compared the total plasma NO responses to LPS in the presence and absence of aminoguanidine (AG), a selective inhibitor of iNOS. The AG significantly attenuated the LPS-mediated increase in total plasma NO at 5 h post-injection. In Experiment 4, broilers were infused with sodium nitroprusside (SNP), an exogenous NO donor molecule that previously had been shown to lower the pulmonary arterial pressure in broilers. The SNP infusion did substantially reduce the pulmonary arterial pressure, but an increase in total plasma NO was not detected during the SNP infusion. Overall, NO accumulation in the plasma was successfully detected after sustained infusion of NaNO2 and administration of LPS for 5 h, but biologically effective levels of NO released from SNP were not detected. Therefore, total plasma NO concentrations (assayed as NO2- + NO3-) qualitatively reflect whole-body NO synthesis, but biologically relevant quantities of NO may be produced at levels that cannot be detected by colorimetric assays.

Nω-nitro-L-arginine methyl ester (L-NAME) amplifies the pulmonary hypertensive response to microparticle injections in broilers

We tested the hypothesis that microparticles entrapped within the pulmonary vasculature elicit the production of nitric oxide (NO) in quantities sufficient to modulate the combined impact of physical occlusion plus contemporaneously released vasoconstrictors. In experiment 1, male broilers were given an injection of the NO synthase (NOS) inhibitor Nomega-nitro-L-arginine methyl ester (L-NAME), followed by an intravenous injection of cellulose microparticles while the pulmonary arterial pressure (PAP) and cardiac output (CO) were recorded. When L-NAME was used to block NO synthesis induced by the microparticles, an early peak of pulmonary hypertension was revealed that rarely developed in the absence of L-NAME. The subsequent more prolonged increases in PAP and pulmonary vascular resistance (PVR) were greater in amplitude and duration in broilers pretreated with L-NAME than in broilers in the control group. These amplified responses occurred in spite of a simultaneous reduction in CO, thereby conclusively demonstrating that inhibiting NOS permitted the development of a much more profound increase in the PVR. In experiment 2 the mortality triggered within 48 h after injecting microparticles was evaluated in the presence and absence of L-NAME. The 48 h postinjection mortality more than doubled when L-NAME was combined with microparticle injection doses that otherwise caused relatively low mortality in the absence of L-NAME. Experiment 3 was conducted to determine whether NO contributes to the systemic hypoxemia that develops after microparticles are injected. L-NAME administration had no impact on the magnitude and duration of the microparticle induced decline in the percentage saturation of hemoglobin with oxygen (%HbO2). Evidently hypoxemia per se contributes relatively little to the amplified pulmonary vasoconstriction and 48 h postinjection mortality triggered by microparticle injections in broilers pretreated with L-NAME. These observations indicate that NO modulates the responses to vasoconstrictors released when microparticles become entrapped in the pulmonary vasculature. Inhibition of NOS by L-NAME exposed a more dramatic increase in PVR and pulmonary hypertension leading to enhanced mortality in response to microparticle injections.