Dexamethasone administered into organum vasculosum laminae terminalis of rabbits induced antipyresis via inhibiting nitric oxide pathway in situ

Preoptic nitric oxide attenuates endotoxic fever in guinea pigs by inhibiting the POA release of norepinephrine

Lipopolysaccharide (LPS) administration induces hypothalamic nitric oxide (NO); NO is antipyretic in the preoptic area (POA), but its mechanism of action is uncertain. LPS also stimulates the release of preoptic norepinephrine (NE), which mediates fever onset. Because NE upregulates NO synthases and NO induces cyclooxygenase (COX)-2-dependent PGE2, we investigated whether NO mediates the production of this central fever mediator. Conscious guinea pigs with intra-POA microdialysis probes received LPS intravenously (2 μg/kg) and, thereafter, an NO donor (SIN-1) or scavenger (carboxy-PTIO) intra-POA (20 μg/μl each, 2 μl/min, 6 h). Core temperature (Tc) was monitored constantly; dialysate NE and PGE2 were analyzed in 30-min collections. To verify the reported involvement of α2-adrenoceptors (AR) in PGE2 production, clonidine (α2-AR agonist, 2 μg/μl) was microdialyzed with and without SIN-1 or carboxy-PTIO. To assess the possible involvement of oxidative NE and/or NO products in the demonstrated initially COX-2-independent POA PGE2 increase, (+)-catechin (an antioxidant, 3 μg/μl) was microdialyzed, and POA PGE2, and Tc were determined. SIN-1 and carboxy-PTIO reduced and enhanced, respectively, the rises in NE, PGE2, and Tc produced by intravenous LPS. Similarly, they prevented and increased, respectively, the delayed elevations of PGE2 and Tc induced by intra-POA clonidine. (+)-Catechin prevented the LPS-induced elevation of PGE2, but not of Tc. We conclude that the antipyretic activity of NO derives from its inhibitory modulation of the LPS-induced release of POA NE. These data also implicate free radicals in POA PGE2 production and raise questions about its role as a central LPS fever mediator.

Lipopolysaccharide-induced fever in Pekin ducks is mediated by prostaglandins and nitric oxide and modulated by adrenocortical hormones

Information on avian fever is limited, and, in particular, very little is known about the mediators and modulators of the febrile response in birds. Therefore, in this study, the possible mediatory roles of nitric oxide (NO) and prostaglandins (PGs), together with a potential modulatory role for adrenocortical hormones in the generation of fever was investigated in conscious Pekin ducks. Their body temperatures were continuously measured by abdominally implanted temperature-sensitive data loggers. The febrile response induced by intramuscular injection of LPS at a dose of 100 μg/kg was compared with and without inhibition of NO production by N-nitro-l-arginine methyl ester (l-NAME), inhibition of PG synthesis (by diclofenac), and elevation of circulating concentrations of dexamethasone and corticosterone (by exogenous administration). LPS administration induced a marked, monophasic fever with a rise in temperature of more than 1°C after 3–4 h. In the presence of l-NAME, diclofenac, and adrenocorticoids at doses that had no effect upon normal body temperature in afebrile ducks, there was a significant inhibition of the LPS-induced fever. In addition, during the febrile response, the blood concentration of corticosterone was significantly elevated (from a basal level of 73.6 ± 9.8 ng/ml to a peak level of 132.6 ± 16.5 ng/ml). The results strongly suggest that the synthesis of both NO and PGs is a vital step in the generation of fever in birds and that the magnitude of the response is subject to modulation by adrenocorticoids.

Involvement of brain glutamate release in pyrogenic fever

Whether the glutamate release in the organum vasculosum laminae terminalis (OVLT) is attributable to genesis of a pyrogenic fever is unclear. The lack of information led us to evaluate the changes in glutamate concentrations of OVLT during the fever induced by staphylococcal enterotoxin A (SEA) in unanesthetized rabbits. Both the OVLT concentrations of glutamate and the colonic temperatures were simultaneously monitored during systemic injection of SEA, MK801 (an N-methyl-D-aspartate (NMDA) receptor channel blocker), ketamine (an NMDA receptor channel blocker), or normal saline. The extracellular dialysates in the brain were collected using a microdialysis probe previously placed in the OVLT region. The concentrations of glutamate in the microdialysates were measured by a high-pressure liquid chromatography in combination with a fluorescence detector. Systemic administration of SEA (30 ng x kg(-1) I.V.) increased both the concentrations of glutamate in the OVLT and the colonic temperatures. Glutamate appeared to rise slightly earlier than body temperature. Pretreatment or posttreatment with MK801 or ketamine significantly attenuated the SEA-induced augmenting glutamate release in the OVLT and fever in rabbits. The suppression of glutamate release appeared to start slightly earlier than temperature decline. In addition, the SEA-induced fever could be mimicked by direct injection of glutamate or SEA into the OVLT area. The fever induced by intra-OVLT injection of SEA or glutamate was significantly attenuated by pretreatment with an intra-OVLT dose of MK801 (5 microg) or ketamine (10 microg). The results suggest that glutamatergic pathways in the OVLT region are in pyrogenic fever genesis.

Interferon-gamma-primed monocytoid cell lines: optimizing their use for in vitro detection of bacterial pyrogens

In order to reduce animal testing for quality control of pharmaceutical agents intended for parenteral use, the Limulus amebocyte lysate (LAL) assay is now being accepted in many cases as an alternative to measuring pyrogenic activity of samples in rabbits. However, since the LAL test is specific for cell wall components from Gram-negative bacteria and is sometimes difficult to perform in samples containing large amounts of protein, this alternative still leaves a considerable diagnostic gap. Here, we have optimized a previously established test based on assessing the formation of neopterin or nitrite in interferon-gamma-treated human (THP-1) or murine (J774A.1, RAW264.7) monocytoid cell lines, respectively, in response to bacterial pyrogens. Optimal results were obtained either with THP-1 cells in serum-containing media and using a high concentration of interferon-gamma (IFN-gamma) or with RAW264.7 cells in serum-free media and independent of the IFN-gamma dose. Results were significantly correlated with those obtained by another cell-culture-based assay in which formation of tumor necrosis factor-alpha by THP-1 1G3 cells was assessed. Also in RAW264.7 murine monocytoid cells, formation of nitrite and of tumor necrosis factor-alpha in response to a variety of samples was correlated. Samples shown to be pyrogenic in rabbits in a previous study were unambiguously detected with the test presented here. As expected, the LAL test was negative with cell-free supernatants from Staphylococcus aureus66 kDa). Taken together, these results indicate that the use of monocytoid cell lines and the detection of metabolites which are triggered in the course of immunostimulation could fill the gap left by the LAL test and help to further reduce animal testing for pyrogens.

Involvement of tyrosine kinase in the pyrogenic fever exerted by NOS pathways in organum vasculosum laminae terminalis

Nitric oxide synthase (NOS) is an enzyme which has a distinct cytokine-inducible isoform (iNOS). Many cytokine receptors have an intracellular tyrosine kinase domain. Here we have used two tyrosine kinase inhibitors (genistein and lavendustin A) to investigate the potential role of tyrosine kinase activation in the induction on both iNOS and fever caused by lipopolysaccharide (LPS) in rabbits. Direct administration of LPS into the organum vasculosum laminae terminalis (OVLT) increased iNOS expression. These increases paralleled the increase in deep body temperature in unanesthetized rabbits. Pretreatment with genistein or lavendustin A not only reduced the fever but also attenuated the iNOS expression in the OVLT following an intra-OVLT dose of LPS. These results suggest that tyrosine phosphorylation is part of the signal transduction mechanism that mediates the induction of both iNOS and fever elicited by LPS in the OVLT of rabbit brain.

Role of hypothermia induced by tumor necrosis factor on apoptosis and function of inflammatory neutrophils in mice

Changes in body temperature and cell infiltration, mediated by cytokines including tumor necrosis factor-alpha (TNF-alpha), occur during inflammation, but a role of body temperature on inflammatory responses remains obscure. Intraperitoneal injection of 10% casein to mice resulted in transient hypothermia followed by neutrophil accumulation in peritoneal cavities. Peritoneal TNF-alpha was rapidly raised, and pretreatment of mice with an anti-TNF-alpha antibody promoted temperature restoration and partially inhibited neutrophil accumulation. To investigate direct effects of body temperature on neutrophils, peritoneal or peripheral blood neutrophils were cultured at 35 degrees C or 37 degrees C with or without recombinant murine TNF-alpha (100 ng/ml) or a protein synthesis inhibitor cycloheximide (1 microg/ml). Significant inhibition of spontaneous and TNF-alpha-induced apoptosis was obtained at 35 degrees C compared with 37 degrees C, an effect that was not altered by the addition of cycloheximide. Moreover, phagocytic ability of peritoneal neutrophils was significantly enhanced by incubating them at the lower temperature. These results indicate that mild hypothermia induced by endogenous TNF-alpha has enhancing roles on neutrophil survival and function during peritoneal inflammation.

The methanol extract of Spiraea prunifolia var. simpliciflora root inhibits the generation of nitric oxide and superoxide in RAW 264.7 cells

It is well established that nitric oxide (NO) and superoxide radicals play pivotal roles in the pathogenesis of inflammatory diseases and fever. This study is undertaken to address whether the methanol extract of Spiraea prunifolia var. simpliciflora root, a traditional medicine as an antipyretic, modulates the generation of NO and superoxide in IFN-gamma primed or polymyristic acetate (PMA) stimulated RAW 264.7 cells, respectively. The generation of NO as well as the expression of inducible nitric oxide synthase (iNOS) protein from IFN-gamma primed RAW 264.7 cells is markedly decreased by the methanol extract in a dose dependent manner. However, the methanol extract does not affect the viability of RAW 264.7 cells, as assessed by methylthiazol-2-yl-2,5-diphenyl tetrazolium bromide (MTT) assay. In addition, the methanol extract suppresses the generation of superoxide in PMA-stimulated RAW 264.7 cells in a dose and a time dependent manner. Taken together, anti-pyretic effects of Spiraea prunifolia var. simpliciflora root extract could result from direct suppression of NO and decreased superoxide generation.

Central control of blood pressure by nitrergic mechanisms in organum vasculosum laminae terminalis of rat brain

Experiments were carried out to explore the possible role played by the nitric oxide (NO) system in the organum vasculosum laminae terminalis (OVLT) of rat brain in arterial pressure regulation. Intracerebroventricular (ICV) or intra-OVLT administration of NO donors such as hydroxylamine, sodium nitro-prusside or s-nitro-acetylpenicillamine caused an up to 55 mmHg decrease in blood pressure (BP) but an increase in NO release (measured by porphyrin/nafion coated carbon fibre electrodes in combination with voltammetry) in the OVLT. In contrast, ICV or intra-OVLT administration of N(G)-nitro-L-arginine methyl ester (L-NAME; a constitutive NO synthase inhibitor) caused an up to 45 mmHg increase in BP but a fall in NO release in the OVLT. Compared with the BP responses induced by ICV injection of NO donors or NO synthase inhibitors, the OVLT route of injection required a much lower dose of NO donors or NO synthase inhibitors to produce a similar BP effect. The depressor effects induced by ICV or intra-OVLT administration of NO donors were attenuated by pretreatment with intra-OVLT injection of methylene blue (an inhibitor of guanylate cyclase), haemoglobin (a NO scavenger), L-NAME or spinal transection. On the other hand, the L-NAME-induced pressor effects were attenuated by pretreatment with intra-OVLT injection of L-arginine or spinal transection. The data suggest that activation of cyclic GMP-dependent NO synthase in the OVLT of rat brain causes cyclic GMP-dependent decreases in arterial pressure via inhibiting the sympathetic efferent activity.

Mechanisms and sites of pyrogenic action exerted by staphylococcal enterotoxin A in rabbits

The febrile responses induced by i.v. administrations of staphylococcal enterotoxin A (SEA) was mimicked by direct injection of SEA into the organum vasculosum laminae terminalis (OVLT) in unanesthetized rabbits. Compared with the febrile responses induced by i.v. injection of SEA, the OVLT route of injection required a much lower dose of SEA to produce a similar fever. Furthermore, the fever induced by intra-OVLT or i.v. injection of SEA was significantly attenuated by pretreatment with intra-OVLT injection of anisomycin (a protein synthesis inhibitor), indomethacin or diclofenac (inhibitors of cyclo-oxygenase (COX)), and aminoguanidine or dexamethasone (inhibitors of inducible nitric oxide synthase (iNOS)). These results suggest that COX or iNOS pathway in the OVLT mediate the SEA-induced fever in rabbits.