Cardiorespiratory responses to interleukin-1beta in adult rats: role of nitric oxide, eicosanoids and glucocorticoids

Interleukin-1beta (IL-1beta) receptors are abundantly expressed in brain stem regions involved in respiratory control. We hypothesized that systemic administration of IL-1beta would increase ventilation (V(E )), and that nitric oxide, eicosanoids, and glucocorticoid receptors would modulate IL-1beta-induced cardioventilatory responses. Intravenous injections of three doses (37.5 ng kg(-1), 75 ng kg(-1 ) and 150 ng kg(-1)) of IL-1b induced monophasic increases in (V(E)), heart rate (HR), and blood pressure (BP) which had a distinctly different onset and duration of action compared to IL-1beta-induced body temperature elevations. Pre-treatment with the nitric oxide inhibitor L-NAME was associated with decreased peak V(E) responses, without affecting the latency and duration of IL-1beta. L-NAME also enhanced HR responses while pressor responses were attenuated. Eicosanoid inhibition with indomethacin resulted in markedly attenuated V responses. However, cardiovascular responses to IL-1beta were not modified by indomethacin. In contrast, pre-treatment with dexamethasone, was not associated with any changes in the IL-1beta-induced V(E), HR, or BP responses. We conclude that IL-1beta increases of V(E) are dose-dependent and are not time-locked with the pyrexic response suggesting the possibility that distinct neural pathways may underlie these responses. In addition, nitric oxide and eicosanoid-dependent mechanisms modulate IL-1beta ventilatory effects.     

Role of nitric oxide in antagonistic effects of transforming growth factor-beta and interleukin-1 beta on the beating rate of cultured cardiac myocytes.

We have recently shown that transforming growth factor-beta (TGF beta) acts in an autocrine manner to maintain the beating rate of neonatal rat cardiac myocytes cultured in serum-free medium on cardiac fibroblast matrix. Interleukin-1 beta (IL-1 beta) suppresses the myocyte-beating rate, and TGF beta antagonizes this effect. We now show that TGF beta and IL-1 beta also have antagonistic effects on the secretion of nitric oxide (NO) by these myocytes, and that NO secretion, the activity of NO synthase (NOS), and expression of the inducible form of NOS correlate inversely with the effects of these two agents on the beating rate. Western blot analysis shows that treatment of myocytes with TGF beta antagonizes the induction of NOS after treatment with IL-1 beta. Release of NO, induced by IL-1 beta, is dependent upon the availability of the substrate, L-arginine, and is suppressed by a competitive inhibitor, NG-monomethyl-L-arginine. L-Arginine (> 0.25 mM) also suppresses, and NG-monomethyl-L-arginine (> 0.5 mM) enhances the myocyte-beating rate. Treatment with IL-1 beta, but not TGF beta, increases cellular cGMP, presumably by activation of guanylate cyclase by NO. Methylene blue, an inhibitor of guanylate cyclase, reverses the suppression of beating caused by IL-1 beta. Bacterial lipopolysaccharide, present in the serum-free medium, is a coinducer of NO secretion. The suppressive effects of NO on the beating rate can be overcome by altering either the set of cytokines employed to induce NO or the matrix on which the myocytes are cultured, demonstrating that additional parameters are also involved in regulation of the beating rate.     

Neuropeptide Y modulation of interleukin-1{beta} (IL-1{beta})-induced nitric oxide production in microglia

Given the modulatory role of neuropeptide Y (NPY) in the immune system, we investigated the effect of NPY on the production of NO and IL-1β in microglia. Upon LPS stimulation, NPY treatment inhibited NO production as well as the expression of inducible nitric-oxide synthase (iNOS). Pharmacological studies with a selective Y(1) receptor agonist and selective antagonists for Y(1), Y(2), and Y(5) receptors demonstrated that inhibition of NO production and iNOS expression was mediated exclusively through Y(1) receptor activation. Microglial cells stimulated with LPS and ATP responded with a massive release of IL-1β, as measured by ELISA. NPY inhibited this effect, suggesting that it can strongly impair the release of IL-1β. Furthermore, we observed that IL-1β stimulation induced NO production and that the use of a selective IL-1 receptor antagonist prevented NO production upon LPS stimulation. Moreover, NPY acting through Y(1) receptor inhibited LPS-stimulated release of IL-1β, inhibiting NO synthesis. IL-1β activation of NF-κB was inhibited by NPY treatment, as observed by confocal microscopy and Western blotting analysis of nuclear translocation of NF-κB p65 subunit, leading to the decrease of NO synthesis. Our results showed that upon LPS challenge, microglial cells release IL-1β, promoting the production of NO through a NF-κB-dependent pathway. Also, NPY was able to strongly inhibit NO synthesis through Y(1) receptor activation, which prevents IL-1β release and thus inhibits nuclear translocation of NF-κB. The role of NPY in key inflammatory events may contribute to unravel novel gateways to modulate inflammation associated with brain pathology.     

Role of nitric oxide in the nicotine-induced pituitary-adrenocortical response.

Nitric oxide (NO) is a major signaling molecule and biological mediator of the hypothalamic-pituitary-adrenal (HPA) axis. We investigated the role of NO formed by endothelial (e), neuronal (n) and inducible (i) nitric oxide synthase (NOS) in the stimulatory effect of nicotine on the HPA axis in rats under basal conditions. Also possible interaction of NOS systems with endogenous prostaglandins (PG) in that stimulation was assessed. NOS and cyclooxygenase inhibitors were administered i.p. 15 min prior to nicotine (2, 5 mg/kg i.p.). Plasma ACTH and serum corticosterone levels were measured 1 h after nicotine injection. NOS blockers given alone did not markedly affect the resting ACTH and corticosterone levels. L-NAME (2-10 mg/kg), a broad spectrum NOS inhibitor considerably and dose dependently enhanced the nicotine-induced ACTH and corticosterone secretion. L-NNA (2 mg/kg) and 7-nitroindazole (7-NI 20 mg/kg), neuronal NOS inhibitors in vivo also significantly augmented the nicotine-induced ACTH and corticosterone levels. L-arginine greatly impaired the nicotine-induced hormone responses and reversed the L-NNA elicited enhancement of the nicotine-evoked ACTH and corticosterone response. In contrast to the constitutive eNOS and nNOS antagonists, an inducible NOS antagonist guanethidine (50-100 mg/kg i.p.) did not substantially affect the nicotine-elicited pituitary-adrenocortical responses. Indomethacin (2 mg/kg i.p.), a non-selective cyclooxygenase blocker abolished the L-NAME and L-NNA-induced enhancement of the nicotine-evoked ACTH and corticosterone response. These results indicate that NO is an inhibitory mediator in the HPA axis activity. Inhibition of its generation by eNOS and nNOS significantly enhances the nicotine-induced HPA response. Under basal conditions iNOS is not involved in the nicotine-induced ACTH and corticosterone secretion. Prostaglandins play an obligatory role in the response of HPA axis to systemic nicotine administration.     

Epidermal growth factor and interleukin-1beta synergistically stimulate the production of nitric oxide in rat intestinal epithelial cells

Epidermal growth factor (EGF) is one of the trophic factors for intestinal adaptation after small bowel transplantation (SBT). A recent report indicates that nitric oxide (NO) has cytoprotective effects on bacterial translocation (BT) after SBT. We hypothesized that EGF stimulates the expression of the inducible NO synthase (iNOS) gene in the graft after SBT, followed by increased production of NO, resulting in the decrease of BT. Intestinal epithelial cells (IEC)-6 were treated with EGF and/or IL-1beta in the presence and absence of phosphatidylinositol 3-kinase (PI3-kinase) and EGF receptor kinase inhibitors (LY-294002 and tyrphostin A25). The induction of NO production and iNOS and its signal molecules, including the inhibitory protein of NF-kappaB (IkappaB), NF-kappaB, and Akt, were analyzed. IL-1beta stimulated the degradation of IkappaB and the activation of NF-kappaB but had no effect on iNOS induction. EGF, which had no effect on the NF-kappaB activation and iNOS induction, stimulated the upregulation of type 1 IL-1 receptor (IL-1R1) through PI3-kinase/Akt. Simultaneous addition of EGF and IL-1beta stimulated synergistically the induction of iNOS, leading to the increased production of NO. Our results indicate that EGF and IL-1beta stimulate two essential signals for iNOS induction in IEC-6 cells: the upregulation of IL-1R1 through PI3-kinase/Akt and the activation of NF-kappaB through IkappaB kinase, respectively. Simultaneous addition of EGF and IL-1beta can enhance the production of NO, which may contribute to the cytoprotective effect of EGF against intestinal injury.     

Role of nitric oxide scavenging in vascular response to cell-free hemoglobin transfusion

Modified Hb solutions have been developed as O(2) carrier transfusion fluids, but of concern is the possibility that increased scavenging of nitric oxide (NO) within the plasma will alter vascular reactivity even if the Hb does not readily extravasate. The effect of decreasing hematocrit from approximately 30% to 18% by an exchange transfusion of a 6% sebacyl cross-linked tetrameric Hb solution on the diameter of pial arterioles possessing tight endothelial junctions was examined through a cranial window in anesthetized cats with and without a NO synthase (NOS) inhibitor. Superfusion of a NOS inhibitor decreased diameter, and subsequent Hb transfusion produced additional constriction that was not different from Hb transfusion alone but was different from the dilation observed by exchange transfusion of an albumin solution after NOS inhibition. In contrast, abluminal application of the cross-linked Hb produced constriction that was attenuated by the NOS inhibitor. Neither abluminal nor intraluminal cross-linked Hb interfered with pial arteriolar dilation to cromakalim, an activator of ATP-sensitive potassium channels. Pial vascular reactivity to hypocapnia and hypercapnia was unaffected by Hb transfusion. Microsphere-determined regional blood flow indicated selective decreases in perfusion after Hb transfusion in the kidney, small intestine, and neurohypophysis, which does not have tight endothelial junctions. Administration of a NOS inhibitor to reduce the basal level of NO available for scavenging before Hb transfusion prevented further decreases in blood flow to these regions compared with NOS inhibition alone. In contrast, blood flow to skeletal and left ventricular muscle increased, and cerebral blood flow was unchanged after Hb transfusion. This cross-linked Hb tetramer is known to appear in renal lymph but not in urine. We conclude that cell-free tetrameric Hb does not scavenge sufficient NO in the plasma space to significantly affect baseline tone in vascular beds with tight endothelial junctions but does produce substantial constriction in beds with porous endothelium. The data support increasing the molecular size of Hb by polymerization or conjugation to limit extravasation in all vascular beds to preserve normal vascular reactivity.     

Role of nitric oxide in the SOS response in Escherichia coli

Having one electron with unpaired spin, nitric oxide (NO) shows high reactivity and activates or inhibits free radical chain reactions. NO toxic and genotoxic effects appear to be the result of intracellular formation of peroxinitrite that can induce some cellular damages, including DNA strand breaks, DNA base oxidation, destruction of the key enzymes, etc. Taking into account the character of DNA damages being formed under NO activity, we proposed a formation of the SOS signal and induction the SOS DNA repair response in E. coli cells treated with NO physiological donors--DNIC and GSNO. The ability of NO donor compounds to induce the SOS DNA response in E. coli PQ37 with sfiA::lacZ operon fusion is reported here at the first time. So, the SOS DNA repair response induction is one of the function of nitric oxide.     

Role of endothelial nitric oxide synthase-derived nitric oxide in activation and dysfunction of cerebrovascular endothelial cells during early onsets of sepsis

Sepsis-associated encephalopathy is an early manifestation of sepsis, resulting in a diffuse dysfunction of the brain. Recently, nitric oxide (NO) has been proposed to be one of the key molecules involved in the modulation of inflammatory responses in the brain. The aim of this study was to assess the role of NO in cerebrovascular endothelial cell activation/dysfunction during the early onsets of sepsis. To this end, we employed an in vitro model of sepsis in which cultured mouse cerebrovascular endothelial cells (MCVEC) were challenged with blood plasma (20% vol/vol) obtained from sham or septic (feces-induced peritonitis, FIP; 6 h) mice. Exposing MCVEC to FIP plasma for 1 h resulted in increased production of reactive oxygen species and NO as assessed by intracellular oxidation of oxidant-sensitive fluorochrome, dihydrorhodamine 123 (DHR 123), and nitrosation of NO-specific probe, DAF-FM, respectively. The latter events were accompanied by dissociation of tight junction protein, occludin, from MCVEC cytoskeletal framework and a subsequent increase in FITC-dextran (3-kDa mol mass) flux across MCVEC grown on the permeable cell culture supports, whereas Evans blue-BSA (65-kDa mol mass) or FITC-dextran (10-kDa mol mass) flux were not affected. FIP plasma-induced oxidant stress, occludin rearrangement, and MCVEC permeability were effectively attenuated by antioxidant, 1-pyrrolidinecarbodithioic acid (PDTC; 0.5 mM), or interfering with nitric oxide synthase (NOS) activity [0.1 mM nitro-L-arginine methyl ester (L-NAME) or endothelial NOS (eNOS)-deficient MCVEC]. However, treatment of MCVEC with PDTC failed to interfere with NO production, suggesting that septic plasma-induced oxidant stress in MCVEC is primarily a NO-dependent event. Taken together, these data indicate that during early sepsis, eNOS-derived NO exhibits proinflammatory characteristics and contributes to the activation and dysfunction of cerebrovascular endothelial cells.     

Role of nitric oxide and cyclooxygenase-2 in regulating the renal hemodynamic response to norepinephrine

We have reported that the renal hemodynamic effects of norepinephrine (NE) are modulated by cyclooxygenase-2 (COX-2)-derived metabolites. Our main objective was to examine whether there is an interaction between nitric oxide (NO) and COX-2 in modulating the renal hemodynamic effects of NE. NE was infused at three doses to anesthetized dogs pretreated with vehicle (n = 8), a selective COX-2 inhibitor (nimesulide) (n = 6), an NO synthesis inhibitor [NG-nitro-l-arginine methyl ester; l-NAME] (n = 8), or with nimesulide and l-NAME (n = 5). During NE infusion, PGE2 excretion increased (125%) in the control group and did not change in the l-NAME-treated dogs. The simultaneous inhibition of NO and COX-2 potentiated to a greater extent the NE-induced renal vasoconstriction than inhibition of either NO or COX-2. The NE-induced renal vasoconstriction during NO and COX-2 inhibition was reduced (P < 0.05) by infusing an AT1 receptor antagonist (n = 6). These results suggest that there is an interaction between NO and COX-2 in protecting the renal vasculature from the NE effects and that angiotensin II partly mediates the NE-induced renal vasoconstriction when NO synthesis and COX-2 activity are reduced.     

Inhibition of brain nitric oxide synthesis enhances and prolongs the hypertensive effect of centrally administered interleukin-1beta in rats

The present study was designed to find out whether brain nitric oxide (NO) influences hemodynamic response to intracerebroventricular (ICV) infusion of interleukin-1 beta (IL-1beta). Mean arterial blood pressure (MAP) and heart rate (HR) were recorded in seven series of experiments performed on conscious Sprague-Dawley rats receiving during 60 min ICV infusion of: 0.9% NaCl (5 microl/h; series 1), IL-1beta (100 ng/h; series 2), NO synthase inhibitor (L-NAME, 1mg/h; series 3), IL-1beta together with L-NAME (series 4), IL-1beta together with inactive isomer of NO synthase inhibitor (D-NAME, 1mg/h; series 5), NO donor (SNAP, 40 microg/h; series 6) and IL-1beta together with SNAP (series 7). ICV infusion of saline did not influence MAP while administration of IL-1beta as well as IL-1beta together with D-NAME elicited a significant, though transient, increase in MAP. In series 4, combined infusion of IL-1beta and L-NAME exerted an increase in MAP, which persisted until the end of the experiment and was significantly higher than in series 2 and 5. In series 7, infusion of SNAP together with IL-1beta abolished the pressor effect of IL-1beta. HR was not significantly altered in any of the experimental series. These results demonstrate that inhibition of NO synthesis in the brain enhances and prolongs the pressor response to IL-1beta, whereas concomitant administration of NO donor abolishes the hemodynamic effect of IL-1beta. Therefore, we conclude that NO generated in the brain is involved in buffering the pressor response to IL-1beta.     

Role of nitric oxide in the airway response to exercise in healthy and asthmatic subjects.

A role of nitric oxide (NO) has been suggested in the airway response to exercise. However, it is unclear whether NO may act as a protective or a stimulatory factor. Therefore, we examined the role of NO in the airway response to exercise by using N-monomethyl-L-arginine (L-NMMA, an NO synthase inhibitor), L-arginine (the NO synthase substrate), or placebo as pretreatment to exercise challenge in 12 healthy nonsmoking, nonatopic subjects and 12 nonsmoking, atopic asthmatic patients in a double-blind, crossover study. Fifteen minutes after inhalation of L-NMMA (10 mg), L-arginine (375 mg), or placebo, standardized bicycle ergometry was performed for 6 min using dry air, while ventilation was kept constant. The forced expiratory volume in 1-s response was expressed as area under the time-response curve (AUC) over 30 min. In healthy subjects, there was no significant change in AUC between L-NMMA and placebo treatment [28.6 +/- 17.0 and 1.3 +/- 20.4 (SE) for placebo and L-NMMA, respectively, P = 0.2]. In the asthmatic group, L-NMMA and L-arginine induced significant changes in exhaled NO (P < 0.01) but had no significant effect on AUC compared with placebo (geometric mean +/- SE: -204.3 +/- 1.5, -186.9 +/- 1.4, and -318.1 +/- 1.2%. h for placebo, L-NMMA, and L-arginine, respectively, P > 0.2). However, there was a borderline significant difference in AUC between L-NMMA and L-arginine treatment (P = 0.052). We conclude that modulation of NO synthesis has no effect on the airway response to exercise in healthy subjects but that NO synthesis inhibition slightly attenuates exercise-induced bronchoconstriction compared with NO synthase substrate supplementation in asthma. These data suggest that the net effect of endogenous NO is not inhibitory during exercise-induced bronchoconstriction in asthma.     

IRE1-dependent activation of AMPK in response to nitric oxide

While there can be detrimental consequences of nitric oxide production at pathological concentrations, eukaryotic cells have evolved protective mechanisms to defend themselves against this damage. The unfolded-protein response (UPR), activated by misfolded proteins and oxidative stress, is one adaptive mechanism that is employed to protect cells from stress. Nitric oxide is a potent activator of AMP-activated protein kinase (AMPK), and AMPK participates in the cellular defense against nitric oxide-mediated damage in pancreatic β-cells. In this study, the mechanism of AMPK activation by nitric oxide was explored. The known AMPK kinases LKB1, CaMKK, and TAK1 are not required for the activation of AMPK by nitric oxide. Instead, this activation is dependent on the endoplasmic reticulum (ER) stress-activated protein IRE1. Nitric oxide-induced AMPK phosphorylation and subsequent signaling to AMPK substrates, including Raptor, acetyl coenzyme A carboxylase, and PGC-1α, is attenuated in IRE1α-deficient cells. The endoribonuclease activity of IRE1 appears to be required for AMPK activation in response to nitric oxide. In addition to nitric oxide, stimulation of IRE1 endoribonuclease activity with the flavonol quercetin leads to IRE1-dependent AMPK activation. These findings indicate that the RNase activity of IRE1 participates in AMPK activation and subsequent signaling through multiple AMPK-dependent pathways in response to nitrosative stress.     

XRCC1 and base excision repair balance in response to nitric oxide

Inflammation associated reactive oxygen and nitrogen species (RONs), including peroxynitrite (ONOO⁻) and nitric oxide (NO), create base lesions that potentially play a role in the toxicity and large genomic rearrangements associated with many malignancies. Little is known about the role of base excision repair (BER) in removing these endogenous DNA lesions. Here, we explore the role of X-ray repair cross-complementing group 1 (XRCC1) in attenuating RONs-induced genotoxicity. XRCC1 is a scaffold protein critical for BER for which polymorphisms modulate the risk of cancer. We exploited CHO and human glioblastoma cell lines engineered to express varied levels of BER proteins to study XRCC1. Cytotoxicity and the levels of DNA repair intermediates (single-strand breaks; SSB) were evaluated following exposure of the cells to the ONOO⁻ donor, SIN-1, and to gaseous NO. XRCC1 null cells were slightly more sensitive to SIN-1 than wild-type cells. We used small-scale bioreactors to expose cells to NO and found that XRCC1-deficient CHO cells were not sensitive. However, using a molecular beacon assay to test lesion removal in vitro, we found that XRCC1 facilitates AAG-initiated excision of two key NO-induced DNA lesions: 1,N⁶-ethenoadenine and hypoxanthine. Furthermore, overexpression of AAG rendered XRCC1-deficient cells sensitive to NO-induced DNA damage. These results show that AAG is a key glycosylase for BER of NO-induced DNA damage and that XRCC1's role in modulating sensitivity to RONs is dependent upon the cellular level of AAG. This demonstrates the importance of considering the expression of other components of the BER pathway when evaluating the impact of XRCC1 polymorphisms on cancer risk.     

Role of nitric oxide in the expression of hepatic vascular stress genes in response to sepsis

This study examined the role of nitric oxide (NO) on the expression of the hepatic vasoregulatory gene during polymicrobial sepsis. Aminoguanidine (AG, 100 mg/kg) or Nomega-nitro-L-arginine methyl ester (L-NAME, 100 mg/kg) was injected intraperitoneally at 0, 3, 6, 10, and 20 h after a cecal ligation and puncture (CLP). The heart rate increased 24 h after the CLP, and this increase was attenuated by L-NAME and further attenuated by AG. The mean arterial pressure in the CLP animals did not change significantly 24 h after the onset of sepsis but was increased after the L-NAME injection. Sepsis increased the serum aminotransferase levels, which were attenuated by AG but augmented by L-NAME. CLP increased the mRNA level of the ET-1 and ETB receptors in the liver. This increase was prevented by AG but augmented by L-NAME. The level of iNOS and HO-1 mRNA expression were increased by CLP, which was prevented by both AG and L-NAME. The level of TNF-alpha and COX-2 mRNA expression increased after CLP, and was attenuated by AG. These results show that iNOS and eNOS are regulated differently in sepsis. While eNOS appears to have a protective role in liver microcirculation, the strong upregulation of iNOS might contribute to a microvascular dysfunction and hepatic injury.     

Role of prostaglandins and nitric oxide in the lipopolysaccharide-induced ACTH and corticosterone response.

This study was designed to determine the role of endogenous prostaglandins (PG) and nitric oxide (NO) in the lipopolysaccharide (LPS)-induced ACTH and corticosterone secretion in conscious rats. LPS (0.5 and 1 mg/kg) given i.p. stimulated the hypothalamic-pituitary-adrenocortical (HPA) activity measured 2 h later. A non-selective cyclooxygenase inhibitor indomethacin (10 mg/kg i.p.), piroxicam (2 mg/kg i.p.), a more potent antagonist of constitutive cyclooxygenase (COX-1) and compound NS-398 (2 mg/kg i.p.), a selective inhibitor of inducible cyclooxygenase (COX-2) given 30 min before LPS (1 mg/kg i.p.) significantly diminished both the LPS-induced ACTH and corticosterone secretion. COX-2 blocker was the most potent inhibitor of ACTH secretion (72.3%). Nomega-nitro-L-arginine methyl ester (L-NAME 2 and 10 mg/kg i.p.), a non-selective nitric oxide synthase (NOS) blocker given 15 min before LPS did not substantially alter plasma ACTH and corticosterone levels 2 h later. Aminoguanidine (AG 100 mg/kg i.p.), a selective inducible nitric oxide synthase (iNOS) inhibitor, considerably enhanced ACTH and corticosterone secretion induced by a lower dose (0.5 mg/kg) of LPS and did not significantly alter this secretion after a larger dose (1 mg/kg) of LPS. L-NAME did not markedly affect the indomethacin-induced inhibition of ACTH and corticosterone response. By contrast, aminoguanidine abolished the indomethacin-induced reduction of ACTH and corticosterone secretion after LPS. These results indicate an opposite action of PG generated by cyclooxygenase and NO synthesized by iNOS in the LPS-induced HPA-response.     

Contributions of prostacyclin and nitric oxide to carbon monoxide-induced cerebrovascular dilation in piglets

Carbon monoxide (CO) is an endogenous dilator in the newborn cerebral microcirculation. Other dilators include prostanoids and nitric oxide (NO), and interactions among the systems are likely. Experiments on anesthetized piglets with cranial windows address the hypothesis that CO-induced dilation of pial arterioles involves interaction with the prostanoid and NO systems. Topical application of CO or the heme oxygenase substrate heme-L-lysinate (HLL) produced dilation. Indomethacin, N(omega)-nitro-L-arginine (L-NNA), and either iberiotoxin or tetraethylammonium chloride (TEA) were used to inhibit prostanoids, NO, and Ca(2+)-activated K(+) (K(Ca)) channels, respectively. Indomethacin, L-NNA, iberiotoxin, or TEA blocked cerebral vasodilation to CO and HLL. Vasodilations to both CO and HLL were returned to indomethacin-treated piglets by topical application of iloprost. Vasodilations to both CO and HLL were returned to L-NNA-treated piglets by sodium nitroprusside but not iloprost. In iberiotoxin- or TEA-treated piglets, dilations to CO and HLL could not be restored by either iloprost or sodium nitroprusside. The dilator actions of CO involve prostacyclin and NO as permissive enablers. The permissive actions of prostacyclin and NO may alter the K(Ca) channel response to CO because neither iloprost nor sodium nitroprusside could restore dilation to CO when these channels were blocked.     

Role of nitric oxide in the regulation of glucose kinetics in response to endotoxin in dogs.

The purpose of the present in vivo study was to determine the role of nitric oxide (NO) in the regulation of glucose metabolism in response to endotoxin by blocking NO synthesis with N(G)-monomethyl-L-arginine (L-NMMA). In five dogs, the appearance and disappearance rates of glucose (by infusion of [6,6-(2)H(2)]glucose), plasma glucose concentration, and plasma hormone concentrations were measured on five different occasions: saline infusion, endotoxin alone (E coli, 1.0 microg/kg i.v.), and endotoxin administration plus three different doses of primed, continuous infusion of L-NMMA. Endotoxin increased rate of appearance of glucose from 13.7 +/- 1.6 to 23.6 +/- 3.3 micromol x kg(-1) x min(-1) (P < 0.05), rate of disappearance of glucose from 13.9 +/- 1.1 to 24.8 +/- 3.1 micromol x kg(-1) x min(-1) (P < 0.001), plasma lactate from 0.5 +/- 0.1 to 1.7 +/- 0.1 mmol/l (P < 0.01), and counterregulatory hormone concentrations. L-NMMA did not affect the rise in rate of appearance and disappearance of glucose, plasma lactate, or the counterregulatory hormone response to endoxin. Plasma glucose levels were not affected by endotoxin with or without L-NMMA. In conclusion, in vivo inhibition of NO synthesis by high doses of L-NMMA does not affect glucose metabolism in response to endotoxin, indicating that NO is not a major mediator of glucose metabolism during endotoxemia in dogs.