Nitric oxide inhibits the replication cycle of porcine parvovirus in vitro

This study investigated the inhibitory effect and mechanism of nitric oxide (NO) on porcine parvovirus (PPV) replication in PK-15 cells. The results showed that two NO-generating compounds, S-nitroso-l-acetylpenicillamine (SNAP) and l-arginine (LA), at a noncytotoxic concentration could reduce PPV replication in a dose-dependent manner and that this anti-PPV effect could be reversed by the NO synthase (NOS) inhibitor N-nitro-l-arginine methyl ester (l-NAME). By assaying the steps of the PPV life cycle, we also show that NO inhibits viral DNA and protein synthesis. This experiment provides a frame of reference for the study of the anti-viral mechanism of NO.     

Role of nitric oxide in the vasodilator but not exudative component of mustard oil-induced inflammation in rat skin

The participation of nitric oxide (NO) in the neurogenic inflammatory reaction of the rat hindpaw skin to topical application of mustard oil was examined by the use ofN ^G-nitro-l-arginine methyl ester (l-NAME, 43 mol kg^–1 i.v.), an inhibitor of NO formation. Control rats received the same dose of the inactive enantiomerd-NAME. Vasodilatation was recorded by contactless infrared emission thermography, and plasma protein exudation was measured by the Evans Blue leakage technique and by measurement of the paw volume in anaesthetized rats.l-NAME reduced the cutaneous hyperaemia caused by topical administration of mustard oil by about 50% but did not change the exudative reaction to mustard oil. These findings indicate that NO plays a mediator role in the vasodilator component of neurogenic inflammation in the rat paw skin, whereas the increase in vascular permeability does not appear to depend on NO.     

The involvement of nitric oxide synthase in the effect of histamine on guinea-pig airway smooth musclein vitro

The influence of histamine on nitric oxide synthase (NOS) in the development of airway smooth muscle hyperresponsiveness to histamine was investigatedin vitro. In the absence of histamine,N ^G-nitro-l-arginine methyl ester (l-NAME, 100 M) had no significant effect on the basal tone. However, precontraction of the tissues with histamine (0.3 M) resulted in a significant contractile response tol-NAME in the preparations with intact epithelium. Removal of the epithelial layer decreased the responses tol-NAME.l-arginine could partially reverse the contraction produced byl-NAME.l-NAME enhanced the maximal response to histamine, but the sensitivity of the tracheal smooth muscle to histamine was not affected. These results suggest that, in the airway, histamine can activate NOS, resulting in the release of nitric oxide. The latter may be regarded as a local negative modulator to maintain the tissue in a physiological homeostasis.     

Oxymatrine Ameliorates l-Arginine-Induced Acute Pancreatitis in Rats

The aim of this study was to determine whether oxymatrine has a protective effect against acute pancreatitis (AP) in a rat model of l-arginine-induced AP. AP was induced by two intraperitoneal injections of l-arginine (250 mg/100 g) at a 1-h interval. Oxymatrine (50 mg/kg) was administered every 6 h after the induction of AP. Oxymatrine significantly reduced the plasma amylase, d-lactic acid and tumor necrosis factor alpha concentration, serum diamine oxidase and lipase activity, and pancreatic myeloperoxidase activity, which were increased in AP rats (P < 0.05). In addition, the pancreatic CD45 expression and the expression of claudin-1, but not zonula occludens-1 (ZO-1) and occludin, in the intestinal tissues were significantly reduced after the induction of AP. However, oxymatrine increased the expression of claudin-1 and CD45, but did not alter the expression of ZO-1 and occludin. In conclusion, our results demonstrated that oxymatrine is potentially capably of protecting against l-arginine-induced AP and attenuating AP-associated intestinal barrier injury by up-regulation of claudin-1.     

Oral administration ofl-arginine, a nitric oxide precursor, decreases nociceptive sensitivity in rats

Tail-flick test was used to evaluate the effect of orally administeredl-arginine on nociceptive sensitivity of albino rats, which produced a) analgesia at 30 min postadministration lasting about 1.5 h (100 mg/kg); b) short-term analgesia (50 mg/kg); and c) no analgesic effect (250 mg/kg).d-Arginine (100 mg/kg) did not affect the nociceptive sensitivity. A significant NO increase took place in cerebral cortex at 30 min postadministration ofl-arginine in the given doses. At 1 h postadministration ofl-arginine in doses of 50 and 250 mg/kg, cortical NO content was lower than that in control animals. Analgesic effect ofl-arginine is presumably related to additional synthesis of NO. This effect seems to be not directly produced by NO, but is realized via other transmitter systems. Translated fromByulleten' Eksperimental'noi Biologii i Meditsiny, Vol. 124, No. 11, pp. 498–501, November, 1997     

In vitro effects of l-arginine on motion parameters in ram epididymal sperm

This study investigated concentration/time-dependent effects of l-arginine on motion parameters of epididymal ram sperm in vitro. After incubation of epididymal sperm samples for 45 and 90 min in the presence of l-arginine (0.001, 0.01, 0.1, and 1 mM), motion parameters were evaluated by computer-aided sperm analysis. Parameters of rapid progressive motility, slow progressive motility, non-progressive motility, and immotility did not show any significant effects at the four concentrations of l-arginine after 45 and 90 min. Three motion parameters, straightness (at 45 min), curvilinear velocity, and straight-line velocity (at 90 min) were significantly (P < 0.05) decreased at an l-arginine concentration of 1 mM when compared with controls. Most other motion parameters such as average path velocity, mean angular displacement, amplitude of lateral head displacement, and linearity showed non-significant reduction at an l-arginine concentration of 1 mM at both 45 and 90 min; whereas, wobble and beat cross frequency showed a non-significant increase. In conclusion, low concentrations of l-arginine had little effect on sperm motion parameters; whereas, high concentration of l-arginine significantly decreased specific motion parameters.     

Low [NaCl]-induced neuronal nitric oxide synthase (nNOS) expression and NO generation are regulated by intracellular pH in a mouse macula densa cell line (NE-MD)

Changes in the luminal NaCl concentration ([NaCl]) at the macula densa (MD) modulate the tubuloglomerular feedback (TGF) responses via an affect on the release of nitric oxide (NO). This study was performed in a newly established mouse macula densa cell line (NE-MD) to investigate the effects of lowering [NaCl] on the neuronal NO synthase (nNOS) protein expression and l-arginine (Arg)-induced NO release. Expression of nNOS protein and release of NO were evaluated by Western blot analysis and an NO-sensitive electrode, respectively. Intracellular pH (pH_i) was monitored by the BCECF assay. Although there was weak staining of the nNOS protein expression, l-Arg-induced NO generation was negligible in normal (140 mM NaCl) solution. Both were significantly (P < 0.05) increased either in the presence of furosemide (12 μM), an inhibitor of the Na⁺–K⁺–2Cl⁻ cotransporter, or in a low (23 mM) Cl⁻ solution. Furosemide- and low Cl⁻-induced NO generation was completely inhibited by 50 μM 7-nitroindasole (7-NI), a nNOS inhibitor. Moreover, these increases were significantly (P < 0.05) inhibited by the addition of 100 μM amiloride, an inhibitor of the Na⁺/H⁺ exchanger, or by its analogue 5-(N)-ethyl-N-isopropyl amiloride (EIPA), and also at a lower pH of 7.1. Furthermore, nNOS expression and NO release were not stimulated in as low as 19 mM Na⁺ solution. In conclusion, low [Cl⁻], but not low [Na⁺] in the lumen at the MD, increased nNOS protein expression and NO generation. Changes in the luminal [NaCl] may modulate the TGF system via an effect on the NO generation from the MD.     

The effects of exogenous amino acids on the relaxant responses of pig urethral smooth muscle evoked by stimulation of the inhibitory nitrergic nerves

Inhibitory innervation of urethral smooth muscle is mediated partly through release of NO. We investigated the mechanisms involved in the supply of the substrate l-arginine to NO synthase by examining the relaxant response of the muscle to electrical field stimulation (EFS) and the effects of addition of amino acids to the bathing medium. Relaxant responses persisted during hours of repetitive stimulation but were enhanced rapidly by addition of l-arginine (the arginine paradox). Addition of l-lysine (competes with l-arginine for transport on the y⁺ carrier) and l-glutamine (competing on the y⁺L carrier) attenuated the enhancement. Enhancement persisted after washing but was reversed by application of l-lysine, suggesting that exogenous l-arginine fills an intracellular pool and that l-lysine can trans-stimulate its efflux from the pool. After prolonged depolarization in high-K⁺, Na⁺-free solution the relaxant response became purely nitrergic. Addition of l-arginine during the exposure continued to enhance the subsequent responses but l-glutamine added with l-arginine, could no longer reduce this enhancement. The results show the arginine paradox in inhibitory nerves and suggest the involvement of y⁺ and y⁺L carriers in the transport of l-arginine.     

Inhibition of superoxide anion release from circulating neutrophils by l-arginine in man

Summary In animal studies of myocardial ischemia/reperfusion l-arginine reduces necrotic injury by preservation of endothelial function and attenuation of neutrophil accumulation in ischemic cardiac tissue. Because release of oxygen radical species by circulating neutrophils is important in endothelial function and ischemia-reperfusion injury, this study investigated the effect of intravenous administration of L-arginine on the in vitro release of superoxide anion of neutrophils in healthy young adults. Neutrophils were obtained at various time points before, during, and after infusion of l-arginine (17 mg kg^–1 min^–1 for 30 min) and analyzed for superoxide dismutase inhibitable reduction of ferricytochrome c. The spontaneously occurring respiratory burst of polymorphonuclear leukocytes at basal conditions was compared with that after triggering by 1 mol/l formylpeptide or 50 ng/ml phorbolester. Infusion of l-arginine inhibited both basal (P < 0.01) and formylpeptide-triggered (P < 0.05) release of superoxide anion did, but not affect release stimulated by phorbol 12-myristate 13-acetate. Pretreatment of neutrophils with 1 mmol/l l-arginine in vitro also significantly reduced formylpeptide-triggered (1 mol/l) superoxide anion release, suggesting that the affects observed after in vivo pretreatment may be due to direct action of l-arginine on neutrophils. These findings demonstrate the ability of L-arginine to reduce release of oxygen radical species by circulating neutrophils in man.Abbreviations HBSS Hank's balanced salt solution - FMLP formyl-Met-Leu-Phe - NO nitric oxide - PMA phorbol 12-myristate 13-acetate - PMNL polymorphonuclear leukocytes - SOD superoxide dismutase     

Decreased renal haemodynamic response to inhibition of nitric oxide synthase in subtotally nephrectomized rats

To assess the renal haemodynamic response to manipulations of the nitric oxide (NO) system, we examined subtotally nephrectomized (SNX) rats and control rats (CON) 28 days after their operation. Bolus infusions of the NO synthase inhibitor N ^G-nitro-l-arginine (l-NA) were given intravenously at doses of 2 mg/kg and 10 mg/kg. Blood pressure was measured intra-arterially, glomerular filtration rate was measured by inulin clearance and fractional changes in renal blood flow (RBF) were determined by a Doppler flow probe. Both doses of l-NA caused a similar and dose dependent increase in mean blood pressure in both SNX and CON rats. In contrast, the decrease in RBF and the increase in the renovascular resistance index (RVRI) was less in SNX rats as compared to CON rats (RBF = –70.1±2.2% of baseline vs –52.7±5.2%, P<0.01; RVRI = +177±9% of baseline vs +243±24%, P<0.05). These changes were not affected by autonomic blockade (hexamethonium), or by blockade of the angiotensin II receptor (Losartan). The exogenous NO donor sodium nitroprusside (0.5 and 1.5 g · kg^–1 · min^–1) lowered mean blood pressure to a similar degree in SNX and CON rats; in contrast, RVRI decreased less in SNX rats (86.9±9.2% of baseline) than in CON rats (68.2±4.6%, P<0.05). We conclude that the reaction of the renal vasculature to manipulations of the NO system is altered in the SNX rats. The data suggest that in the remnant kidney, renovascular resistance is less dependent on endogenous NO and the vascular bed is less sensitive to exogenous NO.     

Effect of uncoupling NO/cGMP pathways on carbachol- and CCK-stimulated Ca2+ entry and amylase secretion from the rat pancreas

 Nitric oxide (NO) production reportedly regulates guanosine 3′,5′-cyclic monophosphate (cGMP) formation and Ca²⁺ influx in pancreatic acini. We have investigated the functional roles of the NO/cGMP messenger system in rat pancreatic acini. In dispersed acini, the levels of amylase secretion, cytosolic [Ca²⁺]([Ca²⁺]_i), NO synthase, and cGMP were measured. The NO synthase inhibitor N ^G-nitro-L-arginine methyl ester (L-NAME, 0.01–100 μM) had no effect on amylase secretion induced by various concentrations of carbachol, cholecystokinin octapeptide (CCK-8) or the high affinity CCK agonist, JMV-180. Similarly, L-NAME up to 100 μM did not affect the changes in Ca²⁺ spiking evoked by these secretagogues; nor was Ca²⁺ entry, refilling or oscillation altered by L-NAME. Sub- and supramaximal concentrations of these secretagogues did not change NO synthase activities compared with basal levels. While sodium nitroprusside (SNP), a NO donor, caused a 9.4-fold increase in cGMP levels compared with basal levels, carbachol, CCK-8 and JMV-180 had no effect. In addition, the guanylate cyclase inhibitor LY 83583 (10 nM to 10 μM) altered neither amylase secretion nor Ca²⁺ signaling induced by these secretagogues. These findings indicate that the stimulatory action of carbachol or CCK-8 is not mediated by NO or cGMP. To investigate whether cGMP stimulates pancreatic secretion we showed that both SNP and a cell-permeant cGMP analog at 0.1–1 mM stimulated amylase secretion and Ca²⁺ transients to a level equal to 10–15% and 13–24%, respectively, of those observed with maximal concentrations of secretagogues. The guanylate cyclase activator guanylin (1–10 μM), which increased cGMP levels 2.4-fold compared with basal levels, elicited a small amount of amylase secretion and a small Ca²⁺ transient. In conclusion, exogenous NO is capable of increasing endogenous cGMP, which results in a modest increase in the [Ca²⁺]_i transient and pancreatic amylase secretion. However, the NO/cGMP system does not appear to be involved significantly in the mediation of Ca²⁺ signaling and amylase secretion stimulated by carbachol and CCK-8. Received: 30 October 1996 / Received after revision and accepted: 13 January 1997     

Hemodynamic Regulation of Inflammation at the Endothelial–Neutrophil Interface

Arterial shear stress can regulate endothelial phenotype. The potential for anti-inflammatory effects of shear stress on TNFα-activated endothelium was tested in assays of cytokine expression and neutrophil adhesion. In cultured human aortic endothelial cells (HAEC), arterial shear stress of 10 dyne/cm² blocked by >80% the induction by 5 ng/mL TNFα of interleukin-8 (IL-8) and IL-6 secretion (50 and 90% reduction, respectively, in the presence of nitric oxide synthase antagonism with 200 μM nitro-l-arginine methylester, l-NAME). Exposure of TNFα-stimulated HAEC to arterial shear stress for 5 h also reduced by 60% (p < 0.001) the conversion of neutrophil rolling to firm arrest in a venous flow assay conducted at 1 dyne/cm². Also, neutrophil rolling lengths at 1 dyne/cm² were longer when TNFα-stimulated HAEC were presheared for 5 h at arterial stresses. In experiments with a synthetic promoter that provides luciferase induction to detect cis interactions of glucocorticoid receptor (GR) and NFκB, shear stress caused a marked 40-fold induction of luciferase in TNFα-treated cells, suggesting a role for GR pathways in the anti-inflammatory actions of fluid shear stress. Hemodynamic force exerts anti-inflammatory effects on cytokine-activated endothelium by attenuation of cytokine expression and neutrophil firm arrest.     

Nitric oxide in responses of regional kidney perfusion to renal nerve stimulation and renal ischaemia

The mechanisms underlying the relative insensitivity of medullary blood flow (MBF) to sympathetic drive remain unknown. We tested the effects of nitric oxide synthase blockade on regional kidney perfusion responses to electrical renal nerve stimulation (RNS) in pentobarbitone-anaesthetized rabbits. Under control conditions, RNS reduced renal blood flow (RBF), cortical blood flow (CBF) and MBF in a frequency-dependent manner. MBF was always reduced less than CBF or RBF. N^G-nitro-l-arginine increased mean arterial pressure (31±3 mmHg), reduced RBF (–8±1 ml/min) and MBF (–33±6 units), enhanced responses to RNS of RBF (from –48±6% to –58±6% at 2 Hz), CBF (from –38±6% to –43±4% at 2 Hz) and, particularly at low frequencies, MBF (from +1±18% to –32±11% at 2 Hz) and potentiated the RBF hyperaemic response following RNS (by 27±6% at 4 Hz). When glyceryl trinitrate was co-infused with N^G-nitro-l-arginine to restore basal nitrergic tone, responses to RNS and the subsequent hyperaemia were indistinguishable from control. Since resting renovascular tone or perfusion pressure has little impact on MBF responses to RNS, these present observations suggest that NO contributes to the blunted MBF response to RNS. Paradoxically, NO seems to blunt renal hyperaemia following acute RNS-induced ischaemia.     

Role of nitric oxide in thermoregulation during septic shock: involvement of vasopressin

We tested the hypothesis that the nitric oxide (NO) pathway in the central nervous system (CNS) plays a role in hypothermia, as well as in the febrile response during experimental septic shock, by regulating vasopressin (AVP) release. Experiments were performed on male Wistar rats treated with N ^G-nitro-l-arginine methyl ester (l-NAME), a non-selective NO synthase (NOS) inhibitor, injected intracerebroventricularly (250 µg/1 l) 30 min before lipopolysaccharide (LPS) 1.5 mg/kg i.v. injection. One hour after LPS administration we observed a significant drop in body temperature (hypothermic response), followed by a temperature increase after the second hour (febrile response), which remained until the end of the experiment. Increased plasmatic AVP levels were concomitantly observed during hypothermia, nearly returning to basal levels during the febrile phase. When l-NAME was administered with LPS, plasmatic AVP concentrations remained high throughout the experiment, hypothermia was accentuated and the febrile response was abolished. Additionally, pre-treatment with -mercapto-,-cyclopentamethylenepropionyl¹, O-Et-Tyr², Val⁴, Arg⁸-vasopressin, an AVP V1 receptor blocker (10 µg/kg) administered i.v., reduced hypothermia and exacerbated the febrile response to endotoxin. In conclusion, our data indicate that the central NO pathway plays an inhibitory role in AVP release during experimental septic shock, which seems to be critical for the thermoregulation during this pathophysiological state.     

Oral contraceptive administration aggravates nitric oxide synthesis inhibition-induced high blood pressure in female rats

The use of estrogen–progestogen oral contraceptive (OC) is associated with high blood pressure, although mechanisms responsible are still unclear. This study sought to investigate the effects of administration of OC on high blood pressure resulting from nitric oxide (NO) synthesis inhibition in female Sprague–Dawley rats. Rats were given ethinyl estradiol in combination with norgestrel and were treated with NO synthase inhibitor, N^G-nitro-l-arginine methyl ester (l-NAME) in the drinking water or drinking water alone for 6 weeks. OC treatment alone led to a significant increase in blood pressure and positive water balance. Treatment with l-NAME alone resulted in a significant elevation of blood pressure without significant positive water balance. Concomitant treatment with OC and l-NAME produced significant increases in blood pressure and water balance. These magnitudes of increases were significantly greater than those observed in rats treated with OC or l-NAME alone. Treatment with OC did not affect NO biosynthesis with or without concurrent l-NAME treatment. Treatment with OC and/or l-NAME did not significantly affect body weight, food intake, heart rate, cardiac weight/body weight ratio, plasma sodium, glomerular filtration rate and urinary sodium output. Conclusion: These data demonstrate that OC administration resulted in a modest increased blood pressure via enhanced water retention that was not associated with impaired NO synthesis. On the other hand, these results showed that increased blood pressure induced by inhibition of NO synthesis was not associated with water retention. The study also indicated that OC administration aggravated increase in blood pressure during NO synthesis inhibition, via enhanced water retention.     

Haematological and serum biochemical profile of the upside-down catfish, Synodontis membranacea Geoffroy Saint Hilaire from Jebba Lake, Nigeria

Haematological and serum biochemical studies of natural population of Synodontis membranacea from Jebba Lake, North Central Nigeria were investigated in order to establish their mean and reference values. Bi-monthly collection of 1,408 live fish samples was carried out between April 2002 and March 2004, using gill nets of various mesh sizes ranging from 5.08 to 10.16 cm. The mean baseline value established for species-specific haematological and serum biochemical parameters were red blood cell (RBC) 3.83 ± 1.49 × 10¹² l⁻¹, haemoglobin (HB) 8.38 ± 1.96 g dl⁻¹, and packed cell volume (PCV) 25.65 ± 5.89%; mean cell volume 78.25 ± 37.90 fl; mean cell haemoglobin (MCH) 33.04 ± 12.50 pg; mean cell haemoglobin concentration 26.53 ± 15.18 g dl⁻¹; white blood cell (WBC) 315.65 ± 95.37 × 10⁻⁹; agranulocytes (Agr) 82.07 ± 11.38%; monocytes (Mon) 6.37 ± 3.01%; lymphocytes (Lym) 76.49 ± 10.81%; granulocytes (Gran) 40.28 ± 17.48%; neutrophils (Neut) 24.42 ± 10.68%; eosinophils (Eos) 16.14 ± 8.25%; basophils 0.09 ± 0.04%; protein 40.19 ± 7.45 g l⁻¹; albumin 19.78 ± 5.67 g l⁻¹; creatinine 49.71 ± 16.15 μmol l⁻¹; urea 3.05 ± 0.67 nmol l⁻¹; uric acid 0.76 ± 0.33 nmol l⁻¹; glucose 4.24 ± 1.74 mmol l⁻¹; cholesterol 8.46 ± 2.27 mmol l⁻¹; calcium 2.35 ± 0.94 mmol l⁻¹; potassium 13.36 ± 4.45 mmol l⁻¹; sodium 139.39 ± 23.19 mmol l⁻¹; alanine aminotransferase (ALT) 11.79 ± 2.67 U l⁻¹; aspartate aminotransferase 16.80 ± 4.73 U l⁻¹; and alkaline phosphatase 63.01 ± 20.44 U l⁻¹. Only three of these parameters (i.e. neutrophil, glucose and potassium) differed significantly (P > 0.05) on gender basis. Pearson’s correlation coefficients indicated significant relationship of standard length and total weight with RBC, PCV, HB, WBC, Agr, Mon, Lym, Gran, Neut, Eos, sodium, and ALT only. The study has provided baseline haematological and biochemical data for use in health monitoring and productivity of S. membranacea, which would be of great value for future comparative surveys in this era of increased fish culture in Nigeria.     

Cell signalling-mediating insulin increase of mRNA expression for cationic amino acid transporters-1 and -2 and membrane hyperpolarization in human umbilical vein endothelial cells

Insulin induces vasodilatation in human subjects and increases l-arginine transport and NO synthesis in human umbilical vein endothelial cells (HUVEC). Cell signalling events associated with insulin effects on activity and mRNA expression of the human cationic amino acid transporters 1 (hCAT-1) and 2B (hCAT-2B) are unknown. l-Arginine transport and eNOS activity were determined in HUVEC exposed to insulin. mRNA levels for hCAT-1, hCAT-2B and eNOS were quantitated by real time RT-PCR and endothelial NO synthase (eNOS) protein was identified by Western blot analysis. Intracellular Ca²⁺, l-arginine and l-citrulline levels, l-[³H]citrulline formation from l-[³H]arginine, cGMP formation, nitrite level, ATP release and membrane potential were determined. Insulin increased l-arginine transport and the mRNA levels for hCAT-1 and hCAT-2B and eNOS expression and activity. Insulin also induced membrane hyperpolarization and increased intracellular Ca²⁺, l-[³H]citrulline, cGMP and nitrite formation. Insulin-mediated stimulation of the l-arginine/NO pathway is thus associated with increased hCAT-1 and hCAT-2B mRNA, and eNOS expression, via mechanisms involving membrane hyperpolarization, mitogen-activated protein kinases p42 and p44, phosphatidylinositol 3-kinase, NO and protein kinase C. We have characterized a cell signalling pathway by which hyperinsulinaemia could lead to vasodilatation in human subjects, and which could have implications in patients in whom plasma insulin levels are altered, such as in diabetes mellitus.     

The involvement of nitric oxide synthase in the effect of histamine on guinea-pig airway smooth musclein vitro

The influence of histamine on nitric oxide synthase (NOS) in the development of airway smooth muscle hyperresponsiveness to histamine was investigatedin vitro. In the absence of histamine,N ^G-nitro-l-arginine methyl ester (l-NAME, 100 μM) had no significant effect on the basal tone. However, precontraction of the tissues with histamine (0.3 μM) resulted in a significant contractile response tol-NAME in the preparations with intact epithelium. Removal of the epithelial layer decreased the responses tol-NAME.l-arginine could partially reverse the contraction produced byl-NAME.l-NAME enhanced the maximal response to histamine, but the sensitivity of the tracheal smooth muscle to histamine was not affected. These results suggest that, in the airway, histamine can activate NOS, resulting in the release of nitric oxide. The latter may be regarded as a local negative modulator to maintain the tissue in a physiological homeostasis.

     

Systemic nitric oxide clamping in normal humans guided by total peripheral resistance

Aim: We wanted to stabilize the availability of nitric oxide (NO) at levels compatible with normal systemic haemodynamics to provide a model for studies of complex regulations in the absence of changes in NO levels. Methods: Normal volunteers (23–28 years) were infused i.v. with the nitric oxide synthase (NOS) inhibitor N^G-nitro-l -arginine methyl ester (l -NAME) at 0.5 mg kg⁻¹ h⁻¹. One hour later, the NO donor sodium nitroprusside (SNP) was co-infused in doses eliminating the haemodynamic effects of l -NAME. Haemodynamic measurements included blood pressure (MABP) and cardiac output (CO) by impedance cardiography. Results: l -NAME increased MABP and total peripheral resistance (TPR, 1.02 ± 0.05 to 1.36 ± 0.07 mmHg s mL⁻¹, mean ± SEM, P < 0.001). With SNP, TPR fell to a stable value slightly below control (0.92 ± 0.05 mmHg s mL⁻¹, P < 0.05). CO decreased with l -NAME (5.8 ± 0.3 to 4.7 ± 0.3 L min⁻¹, P < 0.01) and returned to control when SNP was added (6.0 ± 0.3 L min⁻¹). A decrease in plasma noradrenaline (42%, P < 0.01) during l -NAME administration was completely reversed by SNP. Plasma renin activity decreased during l -NAME administration and returned towards normal after addition of SNP. In contrast, plasma aldosterone was increased by l -NAME and remained elevated. Conclusions: Concomitant NOS inhibition and NO donor administration can be adjusted to maintain TPR at control level for hours. This approach may be useful in protocols in which stabilization of the peripheral supply of NO is required. However, the dissociation between renin and aldosterone secretion needs further investigation.     

l-Citrulline-malate influence over branched chain amino acid utilization during exercise

Exhaustive exercise induces disturbances in metabolic homeostasis which can result in amino acid catabolism and limited l-arginine availability. Oral l-citrulline supplementation raises plasma l-arginine concentration and augments NO-dependent signalling. Our aim was to evaluate the effects of diet supplementation with l-citrulline-malate prior to intense exercise on the metabolic handle of plasma amino acids and on the products of metabolism of arginine as creatinine, urea and nitrite and the possible effects on the hormonal levels. Seventeen voluntary male pre-professional cyclists were randomly assigned to one of two groups: control or supplemented (6 g l-citrulline-malate 2 h prior exercise) and participated in a 137-km cycling stage. Blood samples were taken in basal conditions, 15 min after the race and 3 h post race (recovery). Most essential amino acids significantly decreased their plasma concentration as a result of exercise; however, most non-essential amino acids tended to significantly increase their concentration. Citrulline-malate ingestion significantly increased the plasma concentration of citrulline, arginine, ornithine, urea, creatinine and nitrite (p < 0.05) and significantly decreased the isoleucine concentration from basal measures to after exercise (p < 0.05). Insulin levels significantly increased after exercise in both groups (p < 0.05) returning to basal values at recovery. Growth hormone increased after exercise in both groups, although the increase was higher in the citrulline-malate supplemented group (p < 0.05). l-citrulline-malate supplementation can enhance the use of amino acids, especially the branched chain amino acids during exercise and also enhance the production of arginine-derived metabolites such as nitrite, creatinine, ornithine and urea.