Continuous Production Of Nitric Oxide Research Articles

Spatiotemporally responsive cascade bilayer microneedles integrating local glucose depletion and sustained nitric oxide release for accelerated diabetic wound healing

High glucose level, bacterial infection, and persistent inflammation within the microenvironment are key factors contributing to the delay of diabetic ulcers healing, while traditional therapeutic methods generally fail to address these issues simultaneously. Here, we present a spatiotemporally responsive cascade bilayer microneedle (MN) patch for accelerating diabetic wound healing via local glucose depletion and sustained nitric oxide (NO) release for long-term antibacterial and anti-inflammatory effects. The MN patch (G/AZ-MNs) possesses a degradable tip layer loading glucose oxidase (GOx), as well as a dissolvable base layer encapsulating l-arginine (Arg)-loaded nanoparticles (NPs). After wound administration, the base part rapidly dissolved, resulting in prompt separation of the MN tip within the wound tissue, which subsequently responded to the overexpressed matrix metalloproteinase-9 (MMP-9) in diabetic lesions, leading to the responsive release of GOx. The released enzyme catalyzed glucose into gluconic acid and hydrogen peroxide (H2O2), which not only reduced glucose level within the diabetic wound, but also initiated the cascade reaction between H2O2 with the Arg that was released from NPs, thereby achieving continuous production of NO for 7 days. Our findings demonstrate that a single administration of the MN patch could effectively heal non-infected or biofilm-infected diabetic wounds with the multifunctional properties.

Valproic acid up-regulates the whole NO-citrulline cycle for potent iNOS-NO signaling to promote neuronal differentiation of adipose tissue-derived stem cells

Valproic acid (VPA) remarkably promotes the differentiation of adipose tissue-derived stem cells (ASCs) to mature neuronal cells through nitric oxide (NO) signaling due to up-regulated inducible NO synthase (iNOS) as early as within 3 days. Here, we investigated mechanisms of VPA-promoted neuronal differentiation of ASCs concerning the NO-citrulline cycle, the metabolic cycle producing NO. Cultured rat ASCs were differentiated to mature neuronal cells rich in dendrites and expressing a neuronal marker by treatments with VPA at 2 mM for 3 days and subsequently with the neuronal induction medium for 2 h. Inhibitor (α-methyl-d, l-aspartic acid, MDLA) of arginosuccinate synthase (ASS), a key enzyme of the NO-citrulline cycle, abolishes intracellular NO increase and VPA-promoted neuronal differentiation in ASCs. l-Arginine, the substrate of iNOS, restores the promotion effect of VPA, being against MDLA. Immunocytochemistry showed that ASS and iNOS were increased in ASCs expressing neurofilament medium polypeptide (NeFM), a neuronal marker, by VPA and NIM synergistically. Real-time RT-PCR analysis showed that mRNAs of Ass and arginosuccinate lyase (Asl) in the NO-citrulline cycle were increased by VPA. Chromatin immunoprecipitation assay indicated that Ass and Asl were up-regulated by VPA through the acetylation of their associated histone. From these results, it was considered that VPA up-regulated the whole NO-citrulline cycle, which enabled continuous NO production by iNOS in large amounts for potent iNOS-NO signaling to promote neuronal differentiation of ASCs. This may also indicate a mechanism enabling short-lived NO to function conveniently as a potent signaling molecule that can disappear quickly after its role.

Maxillary sinus pain with radiolucent sinuses due to agenesis of the membranous ostium

IntroductionThe absence of opacities on CT scan usually eliminates paranasal sinus disease as a cause of facial pain. The authors report a case, which constitutes an exception to this general rule, corresponding to a new aetiology of sinus pain. Case reportA 16-year-old boy presented with very painful “recurrent acute sinusitis” triggered by pressure changes (altitude, diving, surfing), with no sinus opacity on CT scan. Surgical exploration demonstrated absence of a primary or accessory maxillary ostium. Middle meatus antrostomy relieved the patient's pain. DiscussionThe pathophysiology of this case of recurrent acute pseudo-sinusitis and the efficacy of antrostomy can be explained by the evo-devo theory of the origin and function of the paranasal sinuses. This case illustrates the absence of communication in the ethmoid of the membranous sac lining the maxillary sinus, formed by degeneration of the maxillary erythropoietic bone marrow. Under stable environmental conditions, the continuous production of nitric oxide by the sinus epithelium is eliminated by simple transmembrane diffusion, but is insufficiently eliminated in the case of rapid pressure changes, inducing sometimes very severe sinus pain, mimicking sinusitis. This case report paves the way for more detailed studies on the role of the paranasal sinuses in facial disease and respiratory physiology.

A paradigm shift for local blood flow regulation

a remarkable example of physiological regulation is the coordination between metabolic rate and local blood flow in microscopic volumes of an organ. In skeletal muscle an increase in oxygen consumption (Vo2) over a wide range evokes a proportional (∼5 to 6 × Vo2) increase in blood flow ([29][

Contribution of α-Adrenoceptor Stimulation by Phenylephrine to Basal Nitric Oxide Production in the Isolated Mouse Aorta

In the mouse aorta, contractions evoked by the α(1)-adrenoceptor agonist phenylephrine are strongly suppressed by the continuous production of nitric oxide (NO). We investigated whether phenylephrine itself stimulated NO production by activating endothelial α(2)-adrenoceptors. On a prostaglandin F(2α) contraction, the α(2)-adrenoceptor agonist 5-bromo-N-(4,5-dihydro-1H-imidazol-2-yl)-6-quinoxalinamine (UK14304) induced 29.3 ± 7.4% relaxation, which was inhibited by 0.1 μM 2-[(4,5-Dihydro-1H-imidazol-2-yl)methyl]-2,3-dihydro-1-methyl-1H-isoindole (BRL44408) with a pKB' corresponding to α(2)-antagonism. In the presence of NO synthase blockers, UK14304 elicited small contractions above 1 μM that were inhibited by 0.1 μM prazosin, but not influenced by 0.1 μM rauwolscine. At 3 μM or higher concentrations, phenylephrine caused only modest relaxation (up to 7.4 ± 2.3%) of segments constricted with prostaglandin F(2α) in the presence of prazosin, which was abolished with 0.1 μM BRL44408. Furthermore, BRL44408 did not increase contractions induced with 1 μM phenylephrine. These results confirm that α(1)- but not α(2)-adrenoceptors are expressed on aortic smooth muscle cells, whereas endothelial cells only express α(2)-adrenoceptors. Moreover, phenylephrine exerted a very modest relaxing effect through nonspecific stimulation of α(2)-adrenoceptors, but only at concentrations higher than 1 μM. It is concluded that the high basal output of NO in the isolated mouse aorta is not due to stimulation of α-adrenoceptors.

Cardiovascular Risk and Endothelial Dysfunction: The Preferential Route for Atherosclerosis

The vascular endothelium plays a pivotal role in the maintenance of vessel wall integrity. In this regard, endothelial cells actively regulate vascular reactivity by responding to mechanical forces and neurohormonal mediators by releasing a variety of relaxing and contracting factors. Nitric oxide (NO), an endogenous gas synthesized by NO synthases (NOSs) is the main endothelium-derived vasodilator. Continuous production of NO by constitutive NOS maintains the vasculature in a state of vasodilation, whereas its phasic generation by inducible NOS can acutely dilate an artery in response to either physiological or pathological stimuli. Under homeostatic conditions, the endothelium maintains normal vascular tone and blood flow, and there is little or no expression of proinflammatory factors. However, both traditional and novel cardiovascular risk factors initiate a chronic inflammatory process that is accompanied by a loss of vasodilator and antithrombotic factors and an increase in vasoconstrictor and prothrombotic products. Furthermore, increased oxidative stress may result in a complete derangement of the NO system, with decreased NO bioavailability and a paradoxical NOS-related oxidant generation. Because of the antiatherogenic, antithrombotic properties of NO and the proatherogenic prothrombotic actions of endogenous oxidants, a decreased NO bioavailability with increased oxidative stress will result not only in impaired endothelium-dependent vasorelaxation but also in the acceleration of atherogenesis and onset of acute atherotrombotic events. The concepts of "endothelial dysfunction" and "endothelial activation" referring to different alterations in endothelial phenotype, may contribute to the development and clinical expression of atherosclerosis.

Neurons Controlling Aplysia Feeding Inhibit Themselves by Continuous NO Production

BackgroundNeural activity can be affected by nitric oxide (NO) produced by spiking neurons. Can neural activity also be affected by NO produced in neurons in the absence of spiking?Methodology/Principal FindingsApplying an NO scavenger to quiescent Aplysia buccal ganglia initiated fictive feeding, indicating that NO production at rest inhibits feeding. The inhibition is in part via effects on neurons B31/B32, neurons initiating food consumption. Applying NO scavengers or nitric oxide synthase (NOS) blockers to B31/B32 neurons cultured in isolation caused inactive neurons to depolarize and fire, indicating that B31/B32 produce NO tonically without action potentials, and tonic NO production contributes to the B31/B32 resting potentials. Guanylyl cyclase blockers also caused depolarization and firing, indicating that the cGMP second messenger cascade, presumably activated by the tonic presence of NO, contributes to the B31/B32 resting potential. Blocking NO while voltage-clamping revealed an inward leak current, indicating that NO prevents this current from depolarizing the neuron. Blocking nitrergic transmission had no effect on a number of other cultured, isolated neurons. However, treatment with NO blockers did excite cerebral ganglion neuron C-PR, a command-like neuron initiating food-finding behavior, both in situ, and when the neuron was cultured in isolation, indicating that this neuron also inhibits itself by producing NO at rest.Conclusion/SignificanceSelf-inhibitory, tonic NO production is a novel mechanism for the modulation of neural activity. Localization of this mechanism to critical neurons in different ganglia controlling different aspects of a behavior provides a mechanism by which a humeral signal affecting background NO production, such as the NO precursor L-arginine, could control multiple aspects of the behavior.

Salicylic acid differentially affects suspension cell cultures of Lotus japonicus and one of its non-symbiotic mutants

Salicylic acid (SA) is known to play an important role in the interaction between plant and micro-organisms, both symbiotic and pathogen. In particular, high levels of SA block nodule formation and mycorrhizal colonization in plants. A mutant of Lotus japonicus, named Ljsym4-2, was characterized as unable to establish positive interactions with Rhizobium and fungi (NOD(-), MYC(-)); in particular, it does not recognize signal molecules released by symbiotic micro-organisms so that eventually, epidermal cells undergo PCD at the contact area. We performed a detailed characterization of wild-type and Ljsym4-2 cultured cells by taking into account several parameters characterizing cell responses to SA, a molecule strongly involved in defense signaling pathways. In the presence of 0.5 mM SA, Ljsym4-2 suspension-cultured cells reduce their growth and eventually die, whereas in order to induce the same effects in wt suspension cells, SA concentration must be raised to 1.5 mM. An early and short production of nitric oxide (NO) and reactive oxygen species (ROS) was detected in wt-treated cells. In contrast, a continuous production of NO and a double-peak ROS response, similar to that reported after a pathogenic attack, was observed in the mutant Ljsym4-2 cells. At the molecular level, a constitutive higher level of a SA-inducible pathogenesis related gene was observed. The analysis in planta revealed a strong induction of the LjPR1 gene in the Ljsym4-2 mutant inoculated with Mesorhizobium loti.

Expression of a Class 1 Hemoglobin Gene and Production of Nitric Oxide in Response to Symbiotic and Pathogenic Bacteria in Lotus japonicus

Symbiotic nitrogen fixation by the collaboration between leguminous plants and rhizobia is an important system in the global nitrogen cycle, and some molecular aspects during the early stage of host-symbiont recognition have been revealed. To understand the responses of a host plant against various bacteria, we examined expression of hemoglobin (Hb) genes and production of nitric oxide (NO) in Lotus japonicus after inoculation with rhizobia or plant pathogens. When the symbiotic rhizobium Mesorhizobium loti was inoculated, expression of LjHb1 and NO production were induced transiently in the roots at 4 h after inoculation. In contrast, inoculation with the nonsymbiotic rhizobia Sinorhizobium meliloti and Bradyrhizobium japonicum induced neither expression of LjHb1 nor NO production. When L. japonicus was inoculated with plant pathogens (Ralstonia solanacearum or Pseudomonas syringae), continuous NO production was observed in roots but induction of LjHb1 did not occur. These results suggest that modulation of NO levels and expression of class 1 Hb are involved in the establishment of the symbiosis.

An experimental study of altered nitric oxide metabolism as a mechanism of cyclosporin-induced renal vasoconstriction.

Nephrotoxicity caused by cyclosporin A (CSA) is the result of vasoconstriction of the renal microcirculation. The endothelium-derived relaxing factor nitric oxide (NO) regulates microvascular blood flow in various tissues, and mediates the microcirculatory response during hypertension and sepsis. This study investigated the role of NO in CSA-induced renal vasoconstriction. Hydronephrotic kidneys in rats were suspended in an environmentally controlled tissue bath, and interlobular, afferent and efferent arteriolar diameters and blood flow were measured by in vivo videomicroscopy. CSA was administered alone, with the nitric oxide synthase (NOS) inhibitor N omega-nitro-L-arginine methyl ester (L-NAME) or with exogenous NOS substrate L-arginine. CSA significantly constricted the whole of the renal microvasculature whereas L-NAME alone preferentially constricted the preglomerular vessels. L-Arginine reversed the vasoconstriction induced by CSA whereas L-NAME had no further effect. Preglomerular basal vascular tone is dependent on continuous production of NO and alterations in the L-arginine-NO pathway contribute to CSA-induced renal vasoconstriction.

Nitric oxide as a cellular antioxidant: A little goes a long way

Nitric oxide (NO ) is an effective chain-breaking antioxidant in free radical-mediated lipid oxidation (LPO). It reacts rapidly with peroxyl radicals as a sacrificial chain-terminating antioxidant. The goal of this work was to determine the minimum threshold concentration of NO required to inhibit Fe 2+-induced cellular lipid peroxidation. Using oxygen consumption as a measure of LPO, we simultaneously measured nitric oxide and oxygen concentrations with NO and O 2 electrodes. Ferrous iron and dioxygen were used to initiate LPO in docosahexaenoic acid-enriched HL-60 and U937 cells. Bolus addition of NO (1.5 μM) inhibited LPO when the NO concentration was greater than 50 nM. Similarly, using ( Z)-1-[ N-(3-ammoniopropyl)- N-( n-propyl)amino]diazen-1-ium-1,2-diolate as a NO donor we found that an average steady-state NO concentration of at least 72 ± 9 nM was required to blunt LPO. As long as the concentration of NO was above 13 ± 8 nM the inhibition was sustained. Once the concentration of NO fell below this value, the rate of lipid oxidation accelerated as measured by the rate of oxygen consumption. Our model suggests that a continuous production of NO that would yield a steady-state concentration of only 10–20 nM is capable of inhibiting Fe 2+-induced LPO.

Rho-kinase mediates spinal nitric oxide formation by prostaglandin E 2 via EP3 subtype

Prostaglandin E 2 (PGE 2), the principal pro-inflammatory prostanoid, is known to play versatile roles in pain transmission via four PGE receptor subtypes, EP1–EP4. We recently demonstrated that continuous production of nitric oxide (NO) by neuronal NO synthase (nNOS) following phosphorylation of myristoylated alanine-rich C-kinase substrate (MARCKS) and NMDA receptor NR2B subunits is essential for neuropathic pain. These phosphorylation and nNOS activity visualized by NADPH-diaphorase histochemistry were blocked by indomethacin, a PG synthesis inhibitor. To clarify the interaction between cyclooxygenase and nNOS pathways in the spinal cord, we examined the effect of EP subtype-selective agonists on NO production. NO formation was stimulated in the spinal superficial layer by EP1, EP3, and EP4 agonists. While the EP1- and the EP4-stimulated NO formation was markedly blocked by MK-801, an NMDA receptor antagonist, the EP3-stimulated one was completely inhibited by H-1152, a Rho-kinase inhibitor. Phosphorylation of MARCKS and NADPH-diaphorase activity stimulated by the EP3 agonist were also blocked by H-1152. These results suggest that PGE 2 stimulates NO formation by Rho-kinase via EP3, a mechanism(s) different from EP1 and EP4.

Nitric Oxide Derived from Human Umbilical Vein Endothelial Cells Inhibits Transendothelial Migration of Neutrophils

We evaluated the roles of nitric oxide (NO) derived from endothelial cells in neutrophil transendothelial migration (TEM). Pretreatment of human umbilical vein endothelial cells (HUVECs) with NG-nitro-L-arginine methyl ester hydrochloride (L-NAME) or NG-monomethyl L-arginine (L-NMMA), which are inhibitors of NO synthases, enhanced neutrophil TEM. Similar augmentation of TEM was observed in the presence of an NO scavenger, 2-(4-carboxyphenyl)-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide (carboxy PTIO). Neutrophil TEM across L-NAME- or L-NMMA-treated HUVECs was inhibited by continuous NO supply by NO donors. These findings support the suggestion that continuous production of NO by endothelial cells suppresses neutrophil TEM. Flow cytometric analyses revealed that NO accumulates in neutrophils co-cultured with NO-producing HUVECs. A decreased amount of NO was detected in neutrophils co-cultured with L-NAME-treated HUVECs compared with neutrophils co-cultured with untreated HUVECs. Soluble guanylyl cyclase (sGC) is known as one of the most important targets of NO in neutrophils. 3-(53-Hydroxymethyl-23furyl)-1-benzyl indazole (YC-1), an activator of sGC, inhibited L-NAME-induced neutrophil TEM. It was interesting that inhibition of neutrophil sGC with 1-H[1,2,4-]oxadiazolo[4,3-a]quinoxalin-1-1 (ODQ) was sufficient to enhance TEM. These results suggest that NO derived from HUVECs acts on neutrophils to inhibit TEM, at least in part by activating sGC. Our findings imply the role of NO constitutively generated by HUVECs in protection against excessive neutrophil extravasation and unnecessary tissue damage under physiological conditions.

P.1.000 Neurogranin: a critical molecule at the nexus of 3 major signaling pathways and mood modulation

Prostaglandin E2 (PGE2), the principal pro-inflammatory prostanoid, is known to play versatile roles in pain transmission via four PGE receptor subtypes, EP1–EP4. We recently demonstrated that continuous production of nitric oxide (NO) by neuronal NO synthase (nNOS) following phosphorylation of myristoylated alanine-rich C-kinase substrate (MARCKS) and NMDA receptor NR2B subunits is essential for neuropathic pain. These phosphorylation and nNOS activity visualized by NADPH-diaphorase histochemistry were blocked by indomethacin, a PG synthesis inhibitor. To clarify the interaction between cyclooxygenase and nNOS pathways in the spinal cord, we examined the effect of EP subtype-selective agonists on NO production. NO formation was stimulated in the spinal superficial layer by EP1, EP3, and EP4 agonists. While the EP1- and the EP4-stimulated NO formation was markedly blocked by MK-801, an NMDA receptor antagonist, the EP3-stimulated one was completely inhibited by H-1152, a Rho-kinase inhibitor. Phosphorylation of MARCKS and NADPH-diaphorase activity stimulated by the EP3 agonist were also blocked by H-1152. These results suggest that PGE2 stimulates NO formation by Rho-kinase via EP3, a mechanism(s) different from EP1 and EP4.

INTERLEUKIN 1βINCREASES ARGININE ACCUMULATION AND ACTIVATES THE CITRULLINE–NO CYCLE IN RAT PANCREATICβCELLS

Nitric oxide (NO) may contribute to pancreatic β cell damage during the development of type 1 diabetes. Its formation can be triggered by cytokines which induce the expression of the inducible form of nitric oxide synthase (iNOS) in pancreatic islets. In the iNOS-catalyzed reaction, arginine is converted into citrulline and NO. Cellular NO formation may be regulated by the availability of arginine. Arginine can be provided extracellularly, entering the cell mainly through the cationic amino acid transporter system y+CAT, and intracellularly, by protein degradation or synthesis from citrulline (the citrulline–NO cycle). This study demonstrates for the first time that the citrulline–NO cycle is induced in FACS-purified rat βcells exposed to interleukin-1β(IL-1β) and that extracellular arginine or citrulline is required for NO production byβcells. Moreover, the accumulation of arginine was higher in IL-1β-treatedβcells than in control cells.β cells expressed mRNAs for the two y+CAT transporters CAT-2A and CAT-2B with no change in transporter expression after exposure to IL-1β. It is concluded that the activation of the citrulline–NO cycle and an increase in arginine accumulation may be adaptive responses in cytokine-exposed β-cells to assure an adequate arginine supply for continuous NO production in the presence of low extracellular arginine levels which may prevail during insulitis.

Nitric oxide inhibits transcription of the Na+-K+-ATPase alpha1-subunit gene in an MTAL cell line.

Nitric oxide (NO) has been implicated as an autocrine modulator of active sodium transport. To determine whether tonic exposure to NO influences active sodium transport in epithelial cells, we established transfected medullary thick ascending limb of Henle (MTAL) cell lines that overexpressed NO synthase-2 (NOS2) and analyzed the effects of deficient or continuous NO production [with or without NG-nitro-L-arginine methyl ester (L-NAME) in the culture medium, respectively] on Na+-K+-ATPase function and expression. The NOS2-transfected cells exhibited high-level NOS2 expression and NO generation, which did not affect cell viability or cloning efficiency. NOS2-transfected cells were grown in the presence of vehicle, NG-nitro-D-arginine methyl ester (D-NAME), or L-NAME for 16 h, after which 86Rb+ uptake assays, Northern analysis, or nuclear run-on transcription assays were performed. The NOS2-transfected cells allowed to produce NO continuously (vehicle or D-NAME) exhibited lower rates of ouabain-sensitive 86Rb+ uptake ( approximately 65%), lower levels of Na+-K+-ATPase alpha1-subunit mRNA ( approximately 60%), and reduced rates of de novo Na+-K+-ATPase alpha1-subunit transcription compared with L-NAME-treated cells. These results have uncovered a novel effect of NO to inhibit transcription of the Na+-K+-ATPase alpha1-subunit gene.

Nitric Oxide and Control of Endothelial Cell-Leukocyte Interactions

In_ammation is a normal response to infection and/or cellular and tissue injury, however under certain inappropriate conditions such as reperfusion injury and unremitting sepsis, a dysregulation of the in_ammatory response leads to deleterious consequences for the host. Critical to the pathogenesis of these conditions is the persistent recruitment of leukocytes which are thought to contribute to the vascular and tissue injury. Although much work has focused on the multitude of in_ammatory mediators that contribute to leukocyte recruitment there is very little information regarding the role of endogenous anti-adhesive molecules or autocoids that are upregulated and “turn off” the in_ammatory response. In this brief overview it is our intent to summarize the data that implicate the continuous production of nitric oxide as an anti-adhesive molecule. Areas of controversy and uncertainty will be highlighted and future directions will be identi~ed.

Calcium-dependent and calcium-independent activation of the endothelial NO synthase.

Largely assumed to be a Ca2(+)-/calmodulin-dependent enzyme, the endothelial constitutive nitric oxide (NO) synthase (NOS III) can be activated by agonists as a consequence of an increase in the intracellular concentration of free Ca2+ ([Ca2+]i). This increase in [Ca2+]i is elicited by an increase in inositol 1,4,5-trisphosphate which is the consequence of tyrosine phosphorylation and activation of phospholipase C-gamma1 as well as protein tyrosine phosphatases. Following the mobilization of intracellular Ca2+, the depleted Ca2+ stores signal to cation channels in the plasma membrane by a pathway which appears to involve activation of both tyrosine and serine/threonine kinases since this portion of the Ca2+ response is attenuated by both tyrosine kinase inhibitors and serine phosphatase inhibitors. In response to fluid shear stress the continuous production of NO by native and cultured endothelial cells is associated with only a transient and minimal increase in [Ca2+]i. In the absence of extracellular Ca2+ and in the presence of the calmodulin antagonist, shear stress stimulates a continuous production of NO which is sensitive to the nonspecific kinase inhibitor staurosporine and the tyrosine kinase inhibitor erbstatin A. A pharmacologically identical activation of NOS III can be induced by protein phosphatase inhibitors suggesting that the tyrosine phosphorylation of NOS III or an associated regulatory protein is crucial for its Ca2(+)-independent activation. Thus in a departure from widely held beliefs, we propose that the endothelial cells are able to respond to mechanical and humoral stimuli activating NOS III by at least two separate pathways.

Heavy physical exercise decreases nitric oxide levels in the nasal airways in humans.

A continuous production of nitric oxide (NO) takes place in human nasal airways. NO in the nasal airways is mainly derived from the paranasal sinuses. The factors that regulate NO synthesis in the upper airways are presently not known. We have investigated the effects of physical exercise on NO levels in the nasal airways. Nasal cavity NO levels were measured by chemiluminescence technique in five healthy non-smoking male subjects before, during and after 5 min of maximal exercise (245 W) on an ergometer cycle. In addition, in one subject NO levels were measured directly in the maxillary sinus during exercise. Nasal cavity NO levels were decreased by 47% after only 1 min of exercise compared with the control situation. A maxima 76% reduction was found at the end of the exercise period and thereafter NO levels slowly increased, reaching basal levels again in about 15-20 min. NO levels in the sinus decreased in a similar manner during exercise. The decrease in nasal cavity NO levels cannot be explained merely by dilution of nasal air due to changes in nasal cavity volume or increased ventilation. We conclude that the excretion of NO in the nasal airways is decreased acutely during heavy short term physical exercise.

Effect of hypoxia on nitric oxide production in neonatal pig lung.

Nitric oxide (NO) synthase inhibitors potentiate hypoxic vasoconstriction (HV), suggesting that NO production during hypoxia normally acts to attenuate HV. To begin to examine the effect of hypoxia on lung NO production, we studied four groups of isolated neonatal pig lungs. In three groups of lungs, the accumulation of nitrite/nitrate (NOx-) was measured in the recirculating perfusate during ventilation with a control gas mixture (Cont), a hypoxic gas mixture (Hyp), or the control gas mixture with N omega-nitro-L-arginine methyl ester (L-NAME) added to the perfusate. Both hypoxia and L-NAME significantly increased perfusion pressure [pulmonary arterial pressure (Pa)-pulmonary venous pressure (Pv)] compared with control. NOx- accumulated in the perfusate at an average rate of 9.1 +/- 2.3 (SE) nmol/min in Cont, 3.7 +/- 0.8 nmol/min (P < 0.05 vs. control) in Hyp, and 3.7 +/- 0.6 nmol/min (P < 0.05 vs. control) in L-NAME. In the fourth group of lungs, exhaled NO output was measured during ventilation with the control gas mixture, the hypoxic gas mixture, and the control gas mixture with L-NAME added to the perfusate. Pa-Pv increased significantly with both hypoxia and L-NAME in these lungs. The exhaled NO output also decreased significantly with both hypoxia and L-NAME. These results suggest that in this preparation there was continuous production of NO that was decreased by hypoxia or L-NAME. It is not clear how the potentiation of HV by NO inhibitors and inhibition of NO production by hypoxia are linked.