LPS fever in old rats depends on the ambient temperature

In earlier work, we found that following lipopolysaccharide (LPS) injection at an ambient temperature (Ta) of 23 degrees C, old rats developed blunted fevers compared with those of young rats. However, the old rats did become febrile if placed in a thermally graded alleyway: they spent more time in the warm end of the gradient and developed a significantly higher body temperature (Tb) than they did following saline injections. In the present experiments, we maintained old and young rats for 3 days at 20 or 31 degrees C (the Ta preferred by the old rats given LPS). After LPS (50 microg/kg ip), the young rats developed equivalent fevers at both Ta's. The old rats developed fevers that were equivalent to those of the young rats at 31 degrees C. At 20 degrees C, their fever was significantly lower. These results suggest that Ta plays a decisive role in the ability of old rats to mount febrile responses.     

The effect of prostaglandin E2 on the body temperature of restrained rats

We examined the effects of intravenous (IV) or intracerebro-ventricular (ICV) injection of prostaglandin E2 (PGE2) on the rectal temperature of restrained rats. The IV injection of PGE2 (0.5 mg/kg) caused hypothermia in rats with high initial rectal temperatures, but caused an elevation in rectal temperature in those animals whose starting temperatures were low. In contrast, the ICV injection of PGE2 induced fever, regardless of the rectal temperature at the time of injection. We also examined whether temperature changes due to the IV injection of endotoxin (lipopolysaccharide, LPS, 10 micrograms/kg) or interleukin-1 beta(IL-1 beta, 0.2 micrograms/kg) were dependent upon the rats' initial rectal temperatures. Rats with low rectal temperatures developed fevers in response to LPS, while animals with high starting temperatures showed hypothermia. In contrast, the IV injection of IL-1 beta produced fever regardless of initial rectal temperature. These data suggest that PGE2 acts centrally to cause fever and peripherally to cause hypothermia, and that following the injection of LPS, these opposing actions of PGE2 may act together to determine the thermoregulatory response.     

Age-related regional difference of interleukin-1 expression in rat brain after lipopolysaccharide treatment

Aging is associated with altered immune responses including dysregulation of cytokine production. Of cytokines, interleukin-1 (IL-1) family has been primarily involved with central nervous system. To evaluate the age-related different response of IL-1 family following peripheral administration of lipopolysaccharide (LPS), immunohistochemical study of IL-1beta and IL-1 receptor expression was performed on Sprague-Dawley rat brain. Experimental animals were divided into four groups; saline-treated young (3-5 months) and old (over 24 months), and LPS-treated young and old groups. After intraperitoneal (i.p.) injection of LPS, three to five rats within each group were killed at 1, 2, 4, 8 and 16 hr. After fixation in 4% neutral buffered formalin, the brain slices were paraffin-embedded. Immunohistochemical staining using labelled streptavidin biotin was performed. The results showed that IL-1beta immunoreactivity was seen in the endothelial cell of pons in both LPS-treated young and old rats, with slightly longer persistency in old group. IL-1RI immunoreactivity appeared initially in the neurons of cerebral cortex in LPS-treated old group, compared with predominantly the cerebellum in LPS-treated young group. In conclusion, our study shows that there is age-related, different neuronal localization of IL-1RI expression at different points of time after LPS treatment.     

Blocking NF-kappaB activation may be an effective strategy in the fever therapy

Lipopolysaccharide (LPS) stimulates peripheral mononuclear cells (PBMC) to synthesize or release pyrogenic cytokines, including interleukin-1beta (IL-1beta), IL-6, and tumor necrosis factor-alpha (TNF-alpha). Nuclear factor-kappa B (NF-kappaB) influences inflammatory responses through the regulation of genes encoding cytokines. In the present study, experiments were carried out to determine whether an inhibition of NF-kappaB mechanisms causes an inhibition of pyrogenic cytokine synthesis or release from PBMC and results in antipyresis. Intravenous administration of the supernatant fluids obtained from the human PBMC incubated with LPS caused feverlike hyperthermia in rabbits. The febrile responses were in parallel with the levels of IL-1beta, IL-6, and TNF-alpha in supernatant fluids. Both the fever and the increased levels of these cytokines in supernatant fluids were decreased by incubating LPS-PBMC with NF-kappaB inhibitors, including pyrrolidine dithiocarbamate, sodium pyrithione, N-acetyl-cysteine, and curcumin. Moreover, an intravenous administration of LPS (0.5-2 microg/kg) produced dose-dependent fever in the rabbits. The fevers were in parallel with the levels of IL-1beta, IL-6, and TNF-alpha in rabbit serum. A pretreatment of rabbits with an intravenous injection of pyrrolidine dithiocarbamate, sodium pryithione, N-acetyl-cysteine, or curcumin 1 h before the intravenous administration of LPS significantly attenuated the LPS-induced fever and/or increased levels of these cytokines in the serum of rabbits. Furthermore, pretreatment with an intravenous dose of anti-IL-1beta, anti-IL-6, or anti-TNF-alpha monoclonal antibody significantly attenuated the fever induced by the intravenous injection of LPS in rabbits. The antipyretic effects exerted by anti-L-1beta monoclonal antibody were greater than those exerted by anti-L-6 or anti-NF-alpha monoclonal antibody. The data indicate that NF-kappaB activation correlates with an LPS-induced synthesis or a release of cytokines (in particular, IL-1beta) from PBMC and triggers fever. Blocking NF-kappaB mechanisms in the PBMC with NF-kappaB inhibitors may be an effective strategy in the fever therapy.     

Fever alters characteristics of sleep in rats

This study examined the effects of a fungal infection on body temperature (Tb) and sleep states. Tb and sleep were recorded in male rats for 24 hr after a saline injection and 48 hr after a subcutaneous injection of live brewer's yeast, at ambient temperatures (Ta's) of 20 degrees and 30 degrees C. Peak fevers of 1.6-3.1 degrees C occurred within 6-10 hr at both Ta's. The rats remained febrile for the next 12-24 hr. For the first 24 hr postyeast, amounts of SWS increased by 19 +/- 3% at 20 degrees C and 12 +/- 2% at 30 degrees C. Specifically, SWS was significantly increased from hr 5-8 (lights-on) and 13-24 (lights-off) at 20 degrees, and from hr 5-8 and 17-24 at 30 degrees C. Ta did not affect the changes in Tb or the changes in SWS after either saline or yeast. Duration of REMS varied with Ta after saline. After yeast, REMS increased by 21 +/- 12% at 20 degrees and decreased by 28 +/- 6% at 30 degrees C, with the net result that REMS at the two Ta's was equal during the fever. Furthermore, while the rats were febrile the normal diurnal variation in REMS was eliminated. Sleep and Tb returned to control values during the second fever day. These results suggest that an activated immune system both increases SWS and overrides the diurnal and thermoregulatory modulations of REMS.     

Interleukin-6 and leptin mediate lipopolysaccharide-induced fever and sickness behavior

Pro-inflammatory cytokines, interleukin (IL)-1beta, IL-6 and tumor necrosis factor-alpha (TNF-alpha) synthesized by activated macrophages and monocytes in response to administration of lipopolysaccharide (LPS), are considered important mediators of fever and sickness behavior. We administered rat-specific antisera for TNF-alpha, IL-1beta, IL-6 and leptin, to determine the involvement of peripherally released cytokines in LPS-induced fever and sickness behavior, measured as suppression of voluntary wheel-running and food intake. Male Sprague-Dawley rats (approximately 200 g) selected for their predisposition to spontaneously run on running wheels were anaesthetized with a combination of ketamine hydrochloride (80 mg/kg i.m.) and xylazine (4 mg/kg i.m.) and implanted intra-abdominally with temperature-sensitive radiotelemeters. Rats were injected intraperitoneally with anti-rat sera to one of the following, TNF-alpha, IL-1beta, IL-6 or leptin or with pre-immune sheep serum, followed by a subcutaneous injection of either LPS (250 microg/kg) or sterile saline. Lipopolysaccharide administration induced a approximately 1.3 (0.2) degrees C fever lasting approximately 10 h and reduced voluntary running by 93 (8.6)% and food intake by 51 (21.3)% compared to the saline response (ANOVA, P<0.05). Injection of anti-IL-6 serum or anti-leptin serum abolished the LPS-induced fever, anti-TNF-alpha serum affected only the early phase of fever and anti-IL-1beta serum had no effect on fever (ANOVA, P<0.05). LPS-induced suppression of voluntary running and food intake were attenuated in rats receiving anti-IL-6 serum, while the decrease in food intake was totally abolished in rats receiving anti-leptin serum (ANOVA, P<0.05). Injection of anti-TNF-alpha or anti-IL-1beta serum had no effect on LPS-induced sickness behavior. Peripherally released IL-6 and leptin therefore appear to be important in regulating LPS-induced fever and sickness behavior.     

Prostaglandin E2-induced fever in young and old Long-Evans rats.

Aging is associated with a blunted or absent fever response to naturally occurring infections or to the peripheral administration of bacterial products and proinflammatory cytokines. We have recently shown that old Long-Evans rats are not defective in their capacity to develop a fever in response to brain administration of interleukin-1beta (IL-1beta). Here, we investigated the fever response of young (3-5-month) and old (24-26-month) Long-Evans rats to the intracerebroventricular (i.c.v.) microinfusion of prostaglandin E2 (PGE2), a final common mediator for the production of fever in the brain. Core body temperature was monitored by telemetry in freely moving rats. i.c.v. administered PGE2 (100 ng) induced comparable increases in body temperature in young and old Long-Evans rats. In the two groups, PGE2-induced fever was similar both in latency-to-peak fever and maximal fever response. These data, and the previous data on IL-1beta, demonstrate that the brains of old and young rats are similar with respect to fever generation in response to the i.c.v. administration of two classes of immunomodulators.     

Modulation of mouse endotoxic fever by complement

It was recently reported that the complement system may be critically involved in the febrile response of guinea pigs to systemic, particularly intraperitoneally (i.p.) injected, lipopolysaccharides (LPS). The present study was designed to identify which component(s) of the complement cascade may be specifically critical. To this end, we used mice with C3, C5, and CR2 gene deletions. To assess preliminarily the suitability of mice for such a study, we replicated our earlier studies with guinea pigs. Thus, to verify initially whether complement is similarly involved in the febrile response of wild-type (C57BL/6J) mice to i.p. LPS (Escherichia coli, 1 microg/mouse), we depleted complement with cobra venom factor (CVF; 7 U/mouse, intravenously [i.v.]). These animals did not develop fever, whereas the core temperature (T(c)) of CVF vehicle-treated controls rose approximately 1 degrees C by 80 min postinjection and then gradually abated over the following 2.5 h, confirming the involvement of complement in fever production after i.p. LPS injection and the suitability of this species for these studies. C3- and C5-sufficient (C3(+/+) and C5(+/+)) mice also developed 1 degrees C fevers within 80 min after i.p. LPS (1 or 2 microg/mouse) injection. These fevers were totally prevented by CVF (10 U/mouse, i.v.) pretreatment. C3- and C5-deficient (C3(-/-) and C5(-/-)) mice were also unable to develop T(c) rises after i.p. LPS. Both CR2(+/+) and CR2(-/-) mice responded normally to i.p. LPS (1 microg/mouse). These data indicate that C5, but not C3d acting through CR2, may play a critical role in the febrile response of mice to i.p. LPS.     

Circulating inflammatory mediators during start of fever in differential diagnosis of gram-negative and gram-positive infections in leukopenic rats

Gram-negative and gram-positive infections have been considered the most important causes of morbidity and mortality in patients with leukopenia following chemotherapy. However, discrimination between bacterial infections and harmless fever episodes is difficult. Because classical inflammatory signs of infection are often absent and fever is frequently the only sign of infection, the aim of this study was to assess the significance of serum interleukin-6 (IL-6), IL-10, macrophage inflammatory protein-2 (MIP-2), procalcitonin (PCT), and C-reactive protein (CRP) patterns in identifying bacterial infections during start of fever in normal and cyclophosphamide-treated (leukopenic) rats following an injection of lipopolysaccharide (LPS) or muramyl dipeptide (MDP) as a model for gram-negative and gram-positive bacterial infections. We found that, compared to normal rats, immunosuppressed animals exhibited significantly higher fevers and lesser production of all mediators, except IL-6, after toxin challenge. Moreover, compared to rats that received MDP, both groups of animals that received an equivalent dose of LPS showed significantly higher fevers and greater increase in serum cytokine levels. Furthermore, in contrast to those in immunocompetent rats, serum levels of IL-6 and MIP-2 were not significantly changed in leukopenic animals after MDP injection. Other serum markers such as PCT and CRP failed to discriminate between bacterial stimuli in both groups of animals. These results suggest that the use of the analyzed serum markers at an early stage of fever could give useful information for the clinician for excluding gram-negative from gram-positive infections.     

Interleukin-1 beta production in the rabbit brain during endotoxin-induced fever.

Interleukin-1 beta (IL-1 beta) production in the brain and the spleen was investigated in rabbits made febrile by intravenous (I.V.) injection of endotoxin, or human recombinant IL-1 beta (hIL-1 beta). The endotoxin used in the present study was the lipopolysaccharide (LPS) of Salmonella typhosa endotoxin. Monophasic fever was induced by I.V. injection of a low dose of LPS (0.02 micrograms kg-1) and biphasic fever by I.V. injection of a large dose of LPS (4 micrograms kg-1), a sublethal dose of LPS (40 micrograms kg-1) or hIL-1 beta (2 micrograms kg-1). In situ hybridization and immunohistochemical studies revealed that, although no IL-1 beta production was observed in the brain at 1 and 3 h after injection of a low dose of LPS (0.02 micrograms kg-1) or of hIL-1 beta (2 micrograms kg-1), IL-1 beta production was demonstrated in organum vasculosum laminae terminalis (OVLT) and some cells around the blood vessels in the parenchyma 1 h after 4 micrograms kg-1 LPS. IL-1 beta production was detected throughout the brain after 40 micrograms kg-1 LPS. Pretreatment with indomethacin, an inhibitor of prostaglandin synthesis, did not affect IL-1 beta production in the brain induced by 4 micrograms kg-1 LPS. The cell type which produces IL-1 beta in the OVLT following LPS injection was confirmed to be a macrophage by electron microscopy. The cells producing IL-1 beta in the parenchyma were determined to be microglial cells. In the spleen, each dose of LPS induced a significant increase in IL-1 beta production in polymorphonuclear cells and macrophages in the red pulp 1 h after injection. However, 2 micrograms kg-1 hIL-1 beta did not induce IL-1 beta production in the spleen. The present results show clearly that systemic administration of LPS induces IL-1 beta production in the OVLT which may be responsible for induction of the second phase of biphasic fever. The production of IL-1 beta in the OVLT was not attributable to the action of peripherally synthesized IL-1 beta or prostaglandins.     

Endogenous Interleukin-10 is Required for the Defervescence of Fever Evoked by Local Lipopolysaccharide-Induced and Staphylococcus Aureus-Induced Inflammation in Rats

We tested the hypothesis that endogenous interleukin (IL)-10 limits the fever induced by a Gram-negative bacterial toxin ( Escherichia coli lipopolysaccharide, LPS) and a Gram-positive bacterial toxin ( Staphylococcus aureus ), when these toxins are injected into a subcutaneous air pouch ( i.po .) in rats. Injection of LPS or S. aureus caused fevers that were reduced in amplitude and duration by simultaneous administration of rat recombinant IL-10. The inhibition of fever by IL-10 was accompanied by a significant reduction in the toxin-evoked increases in concentrations of immunoreactive IL-6 at the site of inflammation and of IL-6 and IL-1 receptor antagonist in the circulation. Conversely, neutralisation of endogenous IL-10 in the pouch increased the amplitude and dramatically increased the duration of toxin-evoked fever, and augmented toxin-induced increases in pouch tumour necrosis factor-α, IL-1β, and especially IL-6. Our data support a crucial regulatory role for endogenous IL-10 in limiting the fever responses during both Gram-negative and Gram-positive infections.     

Monocyte intracellular cytokine production during human endotoxaemia with or without a second in vitro LPS challenge: effect of RWJ-67657, a p38 MAP-kinase inhibitor, on LPS-hyporesponsiveness

In the present study, we investigated the effect of RWJ-67657, a p38 MAP kinase inhibitor, upon in vivo LPS-induced monocyte cytokine production and upon monocyte LPS-hyporesponsiveness. Thirty minutes before a single injection of LPS (4 ng/kg BW), healthy male volunteers received a single oral dose of RWJ-67657 at increasing dosages (0-1400 mg). Blood samples (pre-medication, 3, 6 and 24 h after LPS) were immediately incubated with LPS (reflecting LPS-hyporesponsiveness) or without LPS (reflecting in vivo monocyte stimulation) for 4 h at 37 degrees C. Following red blood cells lysis and white blood cell permeabilization, cells were labelled with alpha-CD14-FITC and alpha-IL-1beta, alpha-IL-12 or alpha-TNFalpha (PE-labelled), fixed, and analysed using flow cytometry. In vivo LPS injection resulted in an increased percentage of circulating monocytes producing IL-1beta, TNFalpha and IL-12 only at 3 h after the LPS injection. This was dose-dependently inhibited by RWJ-67657 treatment. LPS-hyporesponsiveness to in vitro LPS treatment was most prominent at 3 and 6 h after the in vivo LPS injection; compared with pre-medication monocytes, at these intervals a reduced percentage of monocytes produced IL-1beta, TNFalpha or IL-12 after the in vitro LPS stimulus. At t = 6 h, this LPS-hyporesponsiveness could dose-dependently be inhibited by RWJ-67657 treatment of the volunteers. We therefore conclude that p38 MAP kinase inhibition with RWJ-67657 inhibited monocyte production of cytokines following in vivo LPS injection. Treatment with RWJ-67657 also reversed the LPS-hyporesponsiveness. Whether this result can be extended to the clinical situation remains to be elucidated. Patients with sepsis or an otherwise high risk for multi-organ failure are potential study groups.     

Acute and chronic administration of immunomodulators induces anorexia in Zucker rats

To investigate the possible involvement of leptin signaling in lipopolysaccharide (LPS) anorexia, we compared the anorectic effect of LPS in genetically obese (fa/fa) Zucker rats and in their lean (Fa/?) counterparts. The effects of interleukin-1beta (IL-1beta) and muramyl dipeptide (MDP) were also tested. LPS [100 microg/kg body weight (BW)], IL-1beta (2 microg/kg BW) and MDP (2.2 mg/kg BW) injected intraperitoneally (i.p.) at lights out reduced food intake similarly in obese and lean rats. LPS injection at 500 or 1000 microg/kg BW (i.p.) also reduced food intake and BW similarly in obese and lean rats, but obese regained BW faster than lean rats. LPS (2.45 microg or 9.8 microg/h/rat) administered chronically with i.p. implanted osmotic pumps reduced food intake similarly on experimental day 1, regardless of the genotype. After day 3, the lean rats' anorectic response and recovery were dose-dependent, whereas the anorectic response in obese rats was minimally affected by dose (significant dose effect only on day 3). Again, obese rats regained lost BW faster than lean rats. These results do not support a role for leptin as the sole mediator of anorexia induced by bacterial products (LPS and MDP) and IL-1beta.     

Interleukin-1β-Induced Fever Does not Alter the Ability of 5- to 6-Day-Old Rat Pups to Autoresuscitate from Hypoxia-Induced Apnoea

Experiments were carried out to determine if endogenous pyrogen-induced fever impairs protective responses of newborn rats to hypoxia. Twenty-seven 5- to 6-day-old conscious rat pups received a subcutaneous injection of 0.20 microg of recombinant rat interleukin-1beta (rrIL-1beta) per kilogram of body weight to induce fever, or an equal volume of vehicle. They were then either exposed to a single period of hypoxia produced by breathing an anoxic gas mixture (97 % N(2)-3 % CO(2)) and their time to last gasp was determined, or they were exposed repeatedly to hypoxia and their ability to autoresuscitate from primary apnoea was determined. Core temperature increased significantly following administration of rrIL-1beta but did not change following administration of vehicle (i.e. vehicle, 0.0 +/- 0.1 degrees C; rrIL-1beta, 0.7 +/- 0.3 degrees C; P < 0.001) before exposure to hypoxia. IL-1beta-induced fever did not alter the time to last gasp when the pups were exposed to a single period of hypoxia or the number of successful autoresuscitations upon repeated exposure to hypoxia. Thus, our data do not support the hypothesis that endogenous pyrogen-induced fever impairs the protective responses in newborns that may prevent death during hypoxia as may occur during single or repeated episodes of prolonged sleep apnoea.     

Pregnancy influences the plasma cytokine response to intraperitoneal administration of bacterial endotoxin in rats

Rats have an attenuated febrile response to intraperitoneal (i.p.) administration of exogenous pyrogen (e.g. bacterial endotoxin) near the term of pregnancy. To investigate possible mechanisms of this unique thermoregulatory response, the present experiments were carried out on 18 non-pregnant and 16 near-term pregnant Sprague-Dawley rats to test the hypothesis that pregnancy alters the balance of pyrogenic cytokines and antipyretic and/or cryogenic (antipyretic/cryogenic) cytokines in response to exogenous pyrogen. To test our hypothesis, we measured plasma levels of interleukin (IL)-1beta, IL-6, interleukin-1 receptor antagonist (IL-1ra) and tumour necrosis factor alpha(TNFalpha) at 2 and 4 h following i.p. administration of 160 microg kg(-1) E. coli lipopolysaccharide (LPS) (i.e. EC100 dose, or the smallest dose that elicits a maximal febrile response in non-pregnant rats) in non-pregnant as well as pregnant rats at day 20 of gestation (term approximately 21 days). In non-pregnant rats, E. coli LPS elicited statistically significant increases in plasma concentrations of IL-1beta, IL-6, IL-1ra and TNFalpha as compared to that observed following administration of vehicle. However in pregnant rats, E. coli LPS elicited statistically significant increases in antipyretic/cryogenic cytokines (IL-1ra and TNFalpha) but not in pyrogenic cytokines (IL-1beta and IL-6). Thus, a differential pyrogenic and antipyretic/cryogenic plasma cytokine response may mediate in part the attenuated febrile response to exogenous pyrogen observed in rats near the term of pregnancy.     

A study of the mechanism of action of the mild analgesic dipyrone

The mechanism of action for the mild analgesics is controversial. While some have proposed that they inhibit prostaglandin synthesis in the central nervous system to interfere with nociceptive mediators in the brain, others have proposed that they act directly on nociceptive neural pathways to produce analgesia. This class of drugs also possesses antipyretic activity. We examined the antipyretic effect of one such drug, dipyrone, because this might elucidate the mechanism of its analgesic activity. In rats implanted with a femoral vein catheter and a cannula guide tube aimed towards the organum vasculosum laminae terminalis (OVLT) in the brain, an i.v. injection of 2 g/kg interleukin-1 (IL-1) produced a fever of 0.38±0.07°C while an injection of 20 ng prostaglandin E₁ (PGE) into the OVLT produced a fever of 1.18±0.18°C. Dipyrone (25 mg/kg, i.v.) decreased the IL-1 fever but had no effect on the PGE fever. After pretreatment with the immunoadjuvant, zymosan, the IL-1 fevers were enhanced to equal those induced by PGE. Only 0.1 g/kg, i.v. IL-1 raised body temperature by 1.20±0.10°C. An increased dose of dipyrone (50 mg/kg, i.v.) was required to attenuate this IL-1 fever; however, the PGE fever remained unaffected by this treatment with dipyrone. Thus, dipyrone treatment blocks IL-1 fever where synthesis of prostaglandin is a crucial step in the febrile process, but it has no effect on PGE fever where synthesis is bypassed. This suggests that dipyrone, probably through its active metabolites, inhibits prostaglandin synthesis to induce antipyresis and, by analogy, analgesia as well.     

Endotoxin-induced cytokine gene expression in vivo. II. Regulation of tumor necrosis factor and interleukin-1 alpha/beta expression and suppression.

Tumor necrosis factor alpha (TNF alpha) mRNA is present in a preformed intracellular pool in the spleen, liver, and small bowel of naive rats. Endotoxin (Salmonella typhus lipopolysaccharide) injected intravenously induces little or no increase in whole-organ TNF mRNA levels at 15', 30', 1 degree, 2 degrees, or 4 degrees, whereas serum TNF levels are markedly elevated at 1 and 2 hours. Dexamethasone pretreatment of rats suppresses LPS-induced serum TNF concentrations, but does not suppress TNF mRNA levels in the spleen or bowel. Tachyphylaxis experiments demonstrate that a second injection of endotoxin 2 hours after an initial injection fails to induce a second peak of serum TNF, although TNF mRNA levels in the spleen and bowel remain at the levels found in naive rats. Corynebacterium parvum upregulates endotoxin-induced serum TNF release and intravenous injection of IL-1 induces the release of serum TNF but neither alters whole-organ TNF mRNA levels. Interleukin-1 alpha (IL-1 alpha) mRNA was not constitutively detected in whole-organ RNA preparations of the spleen, liver, and small bowel of naive rats. Endotoxin induces IL-1 alpha mRNA most easily appreciated in the spleen beginning at 1 hour, peaking at 2 to 4 hours, and disappearing by 6 hours. Interleukin-1 beta (IL-1 beta) mRNA was not constitutively detected in the organs examined or was present in small amounts. Endotoxin induces IL-1 beta mRNA beginning at 0.5 hours, peaking at 1 hour, and disappearing by 6 hours. Dexamethasone pretreatment prevents the LPS-induced appearance of IL-1 alpha mRNA and suppresses but does not completely inhibit the appearance of IL-1 beta mRNA. C. parvum upregulates endotoxin-induced IL-1 mRNA expression. Intravenous injection of TNF or IL-1 both induce IL-1 mRNA expression. In conclusion, TNF mRNA is constitutively expressed and TNF mRNA levels as analyzed in whole-organ RNA preparations do not change in concert with serum TNF protein levels during conditions of endotoxemia, dexamethasone treatment, tachyphylaxis, priming with C. parvum, or after injection of IL-1. In contrast, IL-1 mRNA expression during endotoxemia, dexamethasone treatment, priming with C. parvum, or after injection of TNF or IL-1 shows clear increases and decreases in whole-organ RNA preparations.     

Characteristics of TNF alpha- and TNF beta-induced fever in the rabbit.

Febrile responses of rabbits to recombinant human tumor necrosis factors alpha (TNF alpha) and beta (TNF beta) were compared. Intravenous (0.1-30 micrograms/kg, I.V.) and intracerebroventricular (0.01-2.5 micrograms/kg, I.C.V.) injection of TNF alpha and TNF beta both caused monophasic and biphasic fevers depending on the dose. The magnitude of fever induced by I.V. and I.C.V. injection of TNF beta was significantly greater than that induced by TNF alpha. Moreover, the second peak of TNF beta-induced biphasic fever was attained more quickly than that of TNF alpha-induced fever. Indomethacin given subcutaneously inhibited the fevers produced by I.V. and I.C.V. injection of TNF alpha and TNF beta. Fever induced either by intravenously injected TNF beta or by intracerebroventricularly injected TNF beta was significantly inhibited by I.C.V. pre-injection of indomethacin. On the other hand, indomethacin given intracerebroventricularly did not affect the fever induced by I.V. injection of TNF alpha or that induced by I.C.V. injection of TNF alpha. These results suggest that TNF alpha and TNF beta act on the brain sites responsible for the activation of prostaglandin synthesis in somewhat different ways.     

A comparative study of the antipyretic effects of indomethacin and dipyrone in rats

OBJECTIVE: Compare the antipyretic effects of dipyrone and indomethacin. MATERIALS AND METHODS: Fever was induced in rats by i. v. LPS or i. c. v. interleukins (IL), prostaglandins (PG), arachidonic acid (AA), pre-formed pyrogenic factor (PFPF), tumour necrosis factor-alpha (TNF-alpha) or corticotrophin releasing hormone (CRH). Dipyrone and indomethacin were administered i.p., arginine vasopressin V1-receptor antagonist, d(CH2)5 Tyr(Me)AVP, into the ventral septal area. Cyclooxygenase (COX-1/-2) blocking activity was assessed in transfected COS-7 cells. CRH release from isolated hypothalami was determined by ELISA. RESULTS: Indomethacin or dipyrone reduced LPS, IL-1beta, IL-6 or TNF-alpha induced fever and CRH release from rat hypothalamus. Only dipyrone inhibited IL-8, PFPF or PGF2alpha fever. Only indomethacin inhibited fever induced by AA or IL-1beta, plus AA. Neither antipyretic affected fever caused by PGE2 or CRH. d(CH2)5Tyr(Me)AVP only blocked antipyresis induced by indomethacin. Dipyrone at a very high concentration (10 mM) inhibited only COX-1, while indomethacin (0.1 microM) blocked COX-1 and COX-2 in COS-7 cells. CONCLUSION: The antipyretic effect of dipyrone differs from that of indomethacin in that it does not depend on AVP release or inhibition of PG synthesis.     

Influence of age on the production and regulation of interleukin-1 in mice.

The decrease in T-cell proliferation with age is due, in part, to the decline in the production of IL-2. Since IL-1 is needed to trigger IL-2 production, we determined the IL-1 producing capacity of peritoneal macrophages of young (2-4 months) and old (24-26 months) BALB/c and C57BL/6 mice. Mice were stimulated with LPS, and their peritoneal macrophages were obtained 3 days later, purified, and assessed for IL-1 production by coculturing them with splenic T cells at a ratio of 1:5 in the presence of LPS. Supernatants were obtained 4 days later when the PGE2 and IL-2 activities were minimal and IL-1 activity maximal. IL-1 activity was assessed for their ability to augment the proliferative activity of indicator thymocytes in their response to PHA stimulation. The results revealed that (i) IL-1 production by cells of old BALB/c and C57BL/6 mice is reduced to about 40% and 30% that of young mice, respectively; (ii) indomethacin enhances IL-1 production by cells of both young and old mice to the same extent; and (iii) reduction in the IL-1 producing capacity by cells of old mice results from altered activities of both the IL-1 producing peritoneal macrophages and the augmenting T cells.