Pyrogen fever and prostaglandin-like activity in cerebrospinal fluid

An Updated Review on the Metabolite (AM404)-Mediated Central Mechanism of Action of Paracetamol (Acetaminophen): Experimental Evidence and Potential Clinical Impact

Paracetamol remains the recommended first-line option for mild-to-moderate acute pain in general population and particularly in vulnerable populations. Despite its wide use, debate exists regarding the analgesic mechanism of action (MoA) of paracetamol. A growing body of evidence challenged the notion that paracetamol exerts its analgesic effect through cyclooxygenase (COX)-dependent inhibitory effect. It is now more evident that paracetamol analgesia has multiple pathways and is mediated by the formation of the bioactive AM404 metabolite in the central nervous system (CNS). AM404 is a potent activator of TRPV₁, a major contributor to neuronal response to pain in the brain and dorsal horn. In the periaqueductal grey, the bioactive metabolite AM404 activated the TRPV₁ channel-mGlu5 receptor-PLC-DAGL-CB1 receptor signaling cascade. The present article provides a comprehensive literature review of the centrally located, COX-independent, analgesic MoA of paracetamol and relates how the current experimental evidence can be translated into clinical practice. The evidence discussed in this review established paracetamol as a central, COX-independent, antinociceptive medication that has a distinct MoA from non-steroidal anti-inflammatory drugs (NSAIDs) and a more tolerable safety profile. With the establishment of the central MoA of paracetamol, we believe that paracetamol remains the preferred first-line option for mild-to-moderate acute pain for healthy adults, children, and patients with health concerns. However, safety concerns remain with the high dose of paracetamol due to the NAPQI-mediated liver necrosis. Centrally acting paracetamol/p-aminophenol derivatives could potentiate the analgesic effect of paracetamol without increasing the risk of hepatoxicity. Moreover, the specific central MoA of paracetamol allows its combination with other analgesics, including NSAIDs, with a different MoA. Future experiments to better explain the central actions of paracetamol could pave the way for discovering new central analgesics with a better benefit-to-risk ratio.

Prenatal inflammation causes obesity and abnormal lipid metabolism via impaired energy expenditure in male offspring

INTRODUCTION

Obesity has becoming a global health issue. Fetus exposed to adversity in the uterine are susceptible to unhealth stimulus in adulthood. Prenatal inflammation is related to poor neonatal outcomes like neurodevelopmental impairments and respiratory complications. Recent studies suggested prenatal lipopolysaccharide (LPS) exposure could result in metabolic disorders. Thus, we hypothesized that offspring exposed to prenatal inflammation could develop into metabolic disorder.

METHODS

The pregnant C57BL/6J mice were intraperitoneally injected with 50 μg/kg LPS or saline only once at GD15. The male offspring were weighted weekly until sacrificed. Indirect calorimetry and body composition were both performed at 9 and 18 weeks old. At 20 weeks old, mice were fasted overnight before collecting blood samples and liver for metabolomics analysis and RNA sequencing, respectively. Differentially expressed genes were further verified by RT-qPCR and western blotting.

RESULTS

Prenatal inflammation resulted in obesity with increased fat percentage and decreased energy expenditure in middle-age male offspring. Abnormal lipid accumulation, changes of gene expression profile and upregulation of multi-component mechanistic target of rapamycin complex 1 (mTOR)/Peroxisome proliferator-activated receptor-γ pathway was observed in liver, accompanied with decreased bile acids level, unsaturated fatty acids androgens and prostaglandins in serum. Indirect calorimetry showed increased respiratory exchange rate and deceased spontaneous activity at 9 weeks in LPS group. Impaired energy expenditure was also observed at 18 weeks in LPS group.

CONCLUSION

Prenatal LPS exposure led to obesity and abnormal lipid metabolism through impaired energy expenditure.

Paracetamol (acetaminophen): A familiar drug with an unexplained mechanism of action

Paracetamol (acetaminophen) is undoubtedly one of the most widely used drugs worldwide. As an over-the-counter medication, paracetamol is the standard and first-line treatment for fever and acute pain and is believed to remain so for many years to come. Despite being in clinical use for over a century, the precise mechanism of action of this familiar drug remains a mystery. The oldest and most prevailing theory on the mechanism of analgesic and antipyretic actions of paracetamol relates to the inhibition of CNS cyclooxygenase (COX) enzyme activities, with conflicting views on the COX isoenzyme/variant targeted by paracetamol and on the nature of the molecular interactions with these enzymes. Paracetamol has been proposed to selectively inhibit COX-2 by working as a reducing agent, despite the fact that in vitro screens demonstrate low potency on the inhibition of COX-1 and COX-2. In vivo data from COX-1 transgenic mice suggest that paracetamol works through inhibition of a COX-1 variant enzyme to mediate its analgesic and particularly thermoregulatory actions (antipyresis and hypothermia). A separate line of research provides evidence on potentiation of the descending inhibitory serotonergic pathway to mediate the analgesic action of paracetamol, but with no evidence of binding to serotonergic molecules. AM404 as a metabolite for paracetamol has been proposed to activate the endocannabinoid and the transient receptor potential vanilloid-1 (TRPV1) systems. The current review gives an update and in some cases challenges the different theories on the pharmacology of paracetamol and raises questions on some of the inadequately explored actions of paracetamol. List of Abbreviations: AM404, N-(4-hydroxyphenyl)-arachidonamide; CB1R, Cannabinoid receptor-1; Cmax, Maximum concentration; CNS, Central nervous system; COX, Cyclooxygenase; CSF, Cerebrospinal fluid; ED50, 50% of maximal effective dose; FAAH, Fatty acid amidohydrolase; IC50, 50% of the maximal inhibitor concentration; LPS, Lipopolysaccharide; NSAIDs, Non-steroidal anti-inflammatory drugs; PGE2, Prostaglandin E2; TRPV1, Transient receptor potential vanilloid-1.

The antipyretic effect of paracetamol occurs independent of transient receptor potential ankyrin 1-mediated hypothermia and is associated with prostaglandin inhibition in the brain

The mode of action of paracetamol (acetaminophen), which is widely used for treating pain and fever, has remained obscure, but may involve several distinct mechanisms, including cyclooxygenase inhibition and transient receptor potential ankyrin 1 (TRPA1) channel activation, the latter being recently associated with paracetamol's propensity to elicit hypothermia at higher doses. Here, we examined whether the antipyretic effect of paracetamol was due to TRPA1 activation or cyclooxygenase inhibition. Treatment of wild-type and TRPA1 knockout mice rendered febrile by immune challenge with LPS with a dose of paracetamol that did not produce hypothermia (150 mg/kg) but is known to be analgetic, abolished fever in both genotypes. Paracetamol completely suppressed the LPS-induced elevation of prostaglandin E₂ in the brain and also reduced the levels of several other prostanoids. The hypothermia induced by paracetamol was abolished in mice treated with the electrophile-scavenger N-acetyl cysteine. We conclude that paracetamol's antipyretic effect in mice is dependent on inhibition of cyclooxygenase activity, including the formation of pyrogenic prostaglandin E₂, whereas paracetamol-induced hypothermia likely is mediated by the activation of TRPA1 by electrophilic metabolites of paracetamol, similar to its analgesic effect in some experimental paradigms.-Mirrasekhian, E., Nilsson, J. L. Å., Shionoya, K., Blomgren, A., Zygmunt, P. M., Engblom, D., Högestätt, E. D., Blomqvist, A. The antipyretic effect of paracetamol occurs independent of transient receptor potential ankyrin 1-mediated hypothermia and is associated with prostaglandin inhibition in the brain.

Lipid Mediators in Inflammation

Lipids are potent signaling molecules that regulate a multitude of cellular responses, including cell growth and death and inflammation/infection, via receptor-mediated pathways. Derived from polyunsaturated fatty acids (PUFAs), such as arachidonic acid (AA), eicosapentaenoic acid (EPA), and docosahexaenoic acid (DHA), each lipid displays unique properties, thus making their role in inflammation distinct from that of other lipids derived from the same PUFA. This diversity arises from their synthesis, which occurs via discrete enzymatic pathways and because they elicit responses via different receptors. This review will collate the bioactive lipid research to date and summarize the major pathways involved in their biosynthesis and role in inflammation. Specifically, lipids derived from AA (prostanoids, leukotrienes, 5-oxo-6,8,11,14-eicosatetraenoic acid, lipoxins, and epoxyeicosatrienoic acids), EPA (E-series resolvins), and DHA (D-series resolvins, protectins, and maresins) will be discussed herein.

Combined and alternating paracetamol and ibuprofen therapy for febrile children

BACKGROUND

Health professionals frequently recommend fever treatment regimens for children that either combine paracetamol and ibuprofen or alternate them. However, there is uncertainty about whether these regimens are better than the use of single agents, and about the adverse effect profile of combination regimens.

OBJECTIVES

To assess the effects and side effects of combining paracetamol and ibuprofen, or alternating them on consecutive treatments, compared with monotherapy for treating fever in children.

SEARCH METHODS

In September 2013, we searched Cochrane Infectious Diseases Group Specialized Register; Cochrane Central Register of Controlled Trials (CENTRAL); MEDLINE; EMBASE; LILACS; and International Pharmaceutical Abstracts (2009-2011).

SELECTION CRITERIA

We included randomized controlled trials comparing alternating or combined paracetamol and ibuprofen regimens with monotherapy in children with fever.

DATA COLLECTION AND ANALYSIS

One review author and two assistants independently screened the searches and applied inclusion criteria. Two authors assessed risk of bias and graded the evidence independently. We conducted separate analyses for different comparison groups (combined therapy versus monotherapy, alternating therapy versus monotherapy, combined therapy versus alternating therapy).

MAIN RESULTS

Six studies, enrolling 915 participants, are included. Compared to giving a single antipyretic alone, giving combined paracetamol and ibuprofen to febrile children can result in a lower mean temperature at one hour after treatment (MD -0.27 °Celsius, 95% CI -0.45 to -0.08, two trials, 163 participants, moderate quality evidence). If no further antipyretics are given, combined treatment probably also results in a lower mean temperature at four hours (MD -0.70 °Celsius, 95% CI -1.05 to -0.35, two trials, 196 participants, moderate quality evidence), and in fewer children remaining or becoming febrile for at least four hours after treatment (RR 0.08, 95% CI 0.02 to 0.42, two trials, 196 participants, moderate quality evidence). Only one trial assessed a measure of child discomfort (fever associated symptoms at 24 hours and 48 hours), but did not find a significant difference in this measure between the treatment regimens (one trial, 156 participants, evidence quality not graded). In practice, caregivers are often advised to initially give a single agent (paracetamol or ibuprofen), and then give a further dose of the alternative if the child's fever fails to resolve or recurs. Giving alternating treatment in this way may result in a lower mean temperature at one hour after the second dose (MD -0.60 °Celsius, 95% CI -0.94 to -0.26, two trials, 78 participants, low quality evidence), and may also result in fewer children remaining or becoming febrile for up to three hours after it is given (RR 0.25, 95% CI 0.11 to 0.55, two trials, 109 participants, low quality evidence). One trial assessed child discomfort (mean pain scores at 24, 48 and 72 hours), finding that these mean scores were lower, with alternating therapy, despite fewer doses of antipyretic being given overall (one trial, 480 participants, low quality evidence) Only one small trial compared alternating therapy with combined therapy. No statistically significant differences were seen in mean temperature, or the number of febrile children at one, four or six hours (one trial, 40 participants, very low quality evidence). There were no serious adverse events in the trials that were directly attributed to the medications used.

AUTHORS' CONCLUSIONS

There is some evidence that both alternating and combined antipyretic therapy may be more effective at reducing temperatures than monotherapy alone. However, the evidence for improvements in measures of child discomfort remains inconclusive. There is insufficient evidence to know which of combined or alternating therapy might be more beneficial.Future research needs to measure child discomfort using standardized tools, and assess the safety of combined and alternating antipyretic therapy.

Acetaminophen: old drug, new issues

INTRODUCTION

The purpose of this review was to discuss new issues related to safety, labeling, dosing, and a better understanding of the analgesic effect of acetaminophen.

METHODS

The MEDLINE, Embase, Cochrane, and PubMed databases were searched. Additionally, the bibliography of all relevant articles and textbooks were manually searched. Two reviewers independently selected the relevant articles.

RESULTS

Concerns about acetaminophen overdose and related liver failure have led the US Food and Drug Administration to mandate new labeling on acetaminophen packaging. In addition, large-scale epidemiologic studies increasingly report evidence for second-generation adverse effects of acetaminophen. Prenatal exposure to acetaminophen is associated with neurodevelopmental and behavioral disorders. Recent studies also suggest that acetaminophen is a hormone disrupter (ie, it interferes with sex and thyroid hormone function essential for normal brain development) and thus may not be considered a safe drug during pregnancy. Finally, emerging evidence suggests that although the predominant mechanism by which acetaminophen exerts its therapeutic effect is by inhibition of cyclooxygenase, multiple other mechanisms also contribute to its analgesic effect.

CONCLUSIONS

Available evidence suggests that indiscriminate usage of this drug is not warranted. and its administration to a pregnant patient should be considered with great caution.

Combined and alternating paracetamol and ibuprofen therapy for febrile children

BACKGROUND

Health professionals frequently recommend fever treatment regimens for children that either combine paracetamol and ibuprofen or alternate them. However, there is uncertainty about whether these regimens are better than the use of single agents, and about the adverse effect profile of combination regimens.

OBJECTIVES

To assess the effects and side effects of combining paracetamol and ibuprofen, or alternating them on consecutive treatments, compared with monotherapy for treating fever in children.

SEARCH METHODS

In September 2013, we searched Cochrane Infectious Diseases Group Specialized Register; Cochrane Central Register of Controlled Trials (CENTRAL); MEDLINE; EMBASE; LILACS; and International Pharmaceutical Abstracts (2009-2011).

SELECTION CRITERIA

We included randomized controlled trials comparing alternating or combined paracetamol and ibuprofen regimens with monotherapy in children with fever.

DATA COLLECTION AND ANALYSIS

One review author and two assistants independently screened the searches and applied inclusion criteria. Two authors assessed risk of bias and graded the evidence independently. We conducted separate analyses for different comparison groups (combined therapy versus monotherapy, alternating therapy versus monotherapy, combined therapy versus alternating therapy).

MAIN RESULTS

Six studies, enrolling 915 participants, are included.Compared to giving a single antipyretic alone, giving combined paracetamol and ibuprofen to febrile children can result in a lower mean temperature at one hour after treatment (MD -0.27 °Celsius, 95% CI -0.45 to -0.08, two trials, 163 participants, moderate quality evidence). If no further antipyretics are given, combined treatment probably also results in a lower mean temperature at four hours (MD -0.70 °Celsius, 95% CI -1.05 to -0.35, two trials, 196 participants, moderate quality evidence), and in fewer children remaining or becoming febrile for at least four hours after treatment (RR 0.08, 95% CI 0.02 to 0.42, two trials, 196 participants, moderate quality evidence). Only one trial assessed a measure of child discomfort (fever associated symptoms at 24 hours and 48 hours), but did not find a significant difference in this measure between the treatment regimens (one trial, 156 participants, evidence quality not graded).In practice, caregivers are often advised to initially give a single agent (paracetamol or ibuprofen), and then give a further dose of the alternative if the child's fever fails to resolve or recurs. Giving alternating treatment in this way may result in a lower mean temperature at one hour after the second dose (MD -0.60 °Celsius, 95% CI -0.94 to -0.26, two trials, 78 participants, low quality evidence), and may also result in fewer children remaining or becoming febrile for up to three hours after it is given (RR 0.25, 95% CI 0.11 to 0.55, two trials, 109 participants, low quality evidence). One trial assessed child discomfort (mean pain scores at 24, 48 and 72 hours), finding that these mean scores were lower, with alternating therapy, despite fewer doses of antipyretic being given overall (one trial, 480 participants, low quality evidence)Only one small trial compared alternating therapy with combined therapy. No statistically significant differences were seen in mean temperature, or the number of febrile children at one, four or six hours (one trial, 40 participants, very low quality evidence).There were no serious adverse events in the trials that were directly attributed to the medications used.

AUTHORS' CONCLUSIONS

There is some evidence that both alternating and combined antipyretic therapy may be more effective at reducing temperatures than monotherapy alone. However, the evidence for improvements in measures of child discomfort remains inconclusive. There is insufficient evidence to know which of combined or alternating therapy might be more beneficial.Future research needs to measure child discomfort using standardized tools, and assess the safety of combined and alternating antipyretic therapy.

Neural controls of prostaglandin 2 pyrogenic, tachycardic, and anorexic actions are anatomically distributed

Fever and anorexia are induced by immune system challenges. Because these responses are adaptive when short lasting but deleterious when prolonged, an understanding of the mediating neural circuitry is important. Prostaglandins (PGE) are a critical signaling element for these immune responses. Despite the widespread distribution of PGE receptors throughout the brain, research focuses on the hypothalamic preoptic area as the mediating site of PGE action. Paraventricular nucleus of the hypothalamus (PVH), parabrachial nucleus (PBN), and nucleus tractus solitarius (NTS) neurons also express PGE receptors and are activated during systemic pathogen infection. A role for these neurons in PGE-induced fever, tachycardia, and anorexia is unexplored and is the subject of this report. A range of PGE₂ doses was microinjected into third or fourth ventricles (v), or directly into the dorsal PVH, lateral PBN, and medial NTS, and core and brown adipose tissue temperature, heart rate, locomotor activity, and food intake were measured in awake, behaving rats. PGE₂ delivery to multiple brain sites (third or fourth v, PVH, or PBN) induced a short- latency (< 10 min) fever and tachycardia. By contrast, an anorexic effect was observed only in response to third v and PVH stimulation. NTS PGE₂ stimulation was without effect; locomotor activity was not affected for any of the sites. The data are consistent with a view of PGE₂-induced effects as mediated by anatomically distributed sites rather than a single center. The data also underscore a potential anatomical dissociation of the neural pathways mediating pyrogenic and anorexic effects of PGE₂.

Old and new generation lipid mediators in acute inflammation and resolution

Originally regarded as just membrane constituents and energy storing molecules, lipids are now recognised as potent signalling molecules that regulate a multitude of cellular responses via receptor-mediated pathways, including cell growth and death, and inflammation/infection. Derived from polyunsaturated fatty acids (PUFAs), such as arachidonic acid (AA), eicosapentaenoic acid (EPA), and docosahexaenoic acid (DHA), each lipid displays unique properties, thus making their role in inflammation distinct from that of other lipids derived from the same PUFA. The diversity of their actions arises because such metabolites are synthesised via discrete enzymatic pathways and because they elicit their response via different receptors. This review will collate the bioactive lipid research to date and summarise the findings in terms of the major pathways involved in their biosynthesis and their role in inflammation and its resolution. It will include lipids derived from AA (prostanoids, leukotrienes, 5-oxo-6,8,11,14-eicosatetraenoic acid, lipoxins and epoxyeicosatrienoic acids), EPA (E-series resolvins), and DHA (D-series resolvins, protectins and maresins).

Acetaminophen: antipyretic or hypothermic in mice? In either case, PGHS-1b (COX-3) is irrelevant

Acetaminophen (AC) reduces the core temperatures (T(c)) of febrile and non-febrile mice alike. Evidence has been adduced that the selectively AC-sensitive PGHS isoform, PGHS-1b (COX-3), mediates these effects. PGHS-1b, however, has no catalytic potency in mice. To resolve this contradiction, AC was injected intravenously (i.v.) into conscious PGHS-1 gene-sufficient (wild-type (WT)) and -deficient (PGHS-1(-/-)) mice 60 min before or after pyrogen-free saline (PFS) or E. coli LPS (10 microg/kg) i.v. T(c) was monitored continuously; brain and plasma PGE(2) levels were determined hourly. AC at <160 mg/kg did not affect T(c) when given before PFS or LPS; at 160 mg/kg, it caused a approximately 2.5 degrees C T(c) fall in 60 min. LPS given after AC (all doses) induced a approximately 1 degrees C fever, not different from that in AC-untreated mice. But this rise was insufficient to overcome the hypothermia of the 160 mg/kg-treated mice; their T(c) culminated 1 degrees C below baseline. LPS given before AC similarly elevated T(c) approximately 1 degrees C. This rise was reduced to baseline in 30 min by 80 mg AC/kg; T(c) rebounded to its febrile level over the next 30 min. At 160 mg/kg, AC reduced T(c) to 4 degrees C below baseline in 60 min, where it remained until the end of the experiment. WT and PGHS-1(-/-) mice responded similarly to all the treatments. The basal brain and plasma PGE(2) levels of PFS mice and the elevated plasma levels of LPS mice were unchanged by AC at 160 mg/kg; but the latter's brain levels were reduced at 1h, then recovered. Thus, AC could exert an anti-PGHS-2 effect when this enzyme is upregulated in the brain of febrile mice. The hypothermia it induces in non-febrile mice, therefore, is due to another mechanism. PGHS-1b is not involved in either case.

Acetaminophen inhibits prostanoid synthesis by scavenging the PGHS-activator peroxynitrite

The primary pharmacological target of acetaminophen is prostaglandin endoperoxide H2 synthase (PGHS). The enzymatic catalytic mechanism is radical-based, initiated, and maintained by the persistent presence of peroxides, particularly peroxynitrite, which is termed "peroxide tone". Whereas the prevailing concept assumes a direct reduction of the active, oxidized enzyme by acetaminophen, here we show that acetaminophen is a potent scavenger of peroxynitrite (peroxynitrite-mediated phenol nitration, IC50 approximately 72 microM; Sin-1-mediated DHR123 oxidation, IC50 approximately 11 microM) and thus inhibits PGHS by eliminating the peroxide tone. Nanomolar concentrations of peroxynitrite increased the activity of isolated PGHS and prostacyclin formation by aortic endothelial cells. This elevated activity was efficiently inhibited by pharmacologically relevant concentrations of acetaminophen (IC50 approximately 10 microM for 6-keto-PGF1alpha) and other free radical scavengers. However, when the peroxide tone was provided by H2O2 or tert-butyl-OOH, acetaminophen had only negligible inhibitory effects. Our concept could help to explain the efficacy of acetaminophen to inhibit PGHS in cell types with moderate oxidant formation. However, high levels of peroxynitrite or other peroxides such as lipid peroxides formed at inflammatory sites might overwhelm the ability of acetaminophen to decrease PGHS activation. The concept presented herein provides a molecular basis to explain the excellent analgesic and antipyretic properties of acetaminophen together with its minimal anti-inflammatory effects.

Mechanism of action of paracetamol

Paracetamol (acetaminophen) is generally considered to be a weak inhibitor of the synthesis of prostaglandins (PGs). However, the in vivo effects of paracetamol are similar to those of the selective cyclooxygenase-2 (COX-2) inhibitors. Paracetamol also decreases PG concentrations in vivo, but, unlike the selective COX-2 inhibitors, paracetamol does not suppress the inflammation of rheumatoid arthritis. It does, however, decrease swelling after oral surgery in humans and suppresses inflammation in rats and mice. Paracetamol is a weak inhibitor of PG synthesis of COX-1 and COX-2 in broken cell systems, but, by contrast, therapeutic concentrations of paracetamol inhibit PG synthesis in intact cells in vitro when the levels of the substrate arachidonic acid are low (less than about 5 mumol/L). When the levels of arachidonic acid are low, PGs are synthesized largely by COX-2 in cells that contain both COX-1 and COX-2. Thus, the apparent selectivity of paracetamol may be due to inhibition of COX-2-dependent pathways that are proceeding at low rates. This hypothesis is consistent with the similar pharmacological effects of paracetamol and the selective COX-2 inhibitors. COX-3, a splice variant of COX-1, has been suggested to be the site of action of paracetamol, but genomic and kinetic analysis indicates that this selective interaction is unlikely to be clinically relevant. There is considerable evidence that the analgesic effect of paracetamol is central and is due to activation of descending serotonergic pathways, but its primary site of action may still be inhibition of PG synthesis. The action of paracetamol at a molecular level is unclear but could be related to the production of reactive metabolites by the peroxidase function of COX-2, which could deplete glutathione, a cofactor of enzymes such as PGE synthase.

Regulation of the 24h body temperature rhythm of women in luteal phase: role of gonadal steroids and prostaglandins

An investigation into whether the rise in the 24h body temperature rhythm observed in the luteal menstrual phase is antagonized by the administration of prostaglandin synthesis inhibitors has been made. Intravaginal body temperature was monitored continuously for 24h, once in the follicular and twice in the luteal phase. In the luteal phase, women were studied both without and with the simultaneous administration of a prostaglandin synthesis inhibitor (lysine acetylsalicylate; 1.8 g every 6 h orally). The progesterone/estradiol ratio (measured at 17:00h each day) was related to mesor (r = 0.825; P < 0.001), acrophase (r = 0.682; P < 0.02), and amplitude (r = -0.731; P < 0.001) of the 24h body temperature rhythm. Luteal phase elevation of the progesterone/estradiol ratio was associated with a 0.32 +/- 0.07 degrees C increase in mesor (P < 0.01), a 0.11 +/- 0.02 degrees C decrease in amplitude (P < 0.001), and a 34.8 +/- 11.6 min delay in acrophase (P < 0.03) of the 24h body temperature rhythm. Prostaglandin synthesis inhibitors did not counteract these modifications. The present data shows that the modifications of the circadian parameters of the 24h body temperature rhythm observed during the luteal phase of the menstrual cycle are strictly related to modifications of the progesterone/estradiol ratio, and presumably independent of prostaglandin synthesis.

Brain eicosanoids and LPS fever: species and age differences

The results of the present study, summarized in Table 2, demonstrate that different species and strains of rodents (rats and mice) and birds (chickens) exhibit rather specific fever response. Systemic administration of LPS caused monophasic elevation in Tb of chickens, biphasic changes in Tb of rats (initial drop followed by an increase in Tb), whereas mice failed to develop hyperthermia and responded by a decreased Tb. The LPS-induced alterations in hypothalamic prostanoid synthesis were also rather species-specific and differ markedly even between the two strains of mice. We failed to find a common direct correlation between LPS-induced changes in Tb and hypothalamic prostanoid production in rodents (rats and mice). This observation is supported by our recent study on age-related changes in fever response in rats, where we found that hypothalami of LPS-treated old and young adult rats produced similar amounts of PGE2 and PGI2, in spite of more pronounced and prolonged hypothermia, and a delayed elevation in Tb of old rats, as compared with young (Fraifeld et al., 1995b). Moreover, the hypothalamus of febrile chickens did not display any detectable activation of PGE2 production, suggesting that PGE2 is not a common central mediator of fever in homeotherms (Fraifeld et al., 1995a). Apparently, the actual body temperature not always reflects the functional state of central thermostat, and increased PGE2 production in hypothalamus would not directly, at least in rodents, lead to body temperature elevation. Furthermore, peripheral effects, including PG-mediated ones, of pyrogens can interfere and even overcome their centrally-mediated effects (Morimoto et al., 1991; Burysek et al., 1993). Previously, we have shown that no additional elevation in hypothalamic PGE2 production occurs in response to doses of LPS over 10 micrograms in rats and 25 micrograms in mice, while the increased doses led to further changes in Tb response (Kaplanski et al., 1993). Morimoto et al. (1991) have considered that PGE2 acts centrally to cause fever and peripherally to cause hypothermia, and, hence, these opposing actions, both being induced by LPS, may act together to determine the final thermoregulatory response. Other possibilities could be related to counterbalance of endogenous antipyretics (Kluger, 1991; Kozak et al., 1995), that may occur not only at the level of thermoregulatory center but also outside the CNS (Klir et al., 1995), and to the existence of PG-independent mechanisms of LPS fever. The latter have been shown for IL-8 (Rothwell et al., 1990; Zampronio et al., 1994) and MIP-1 (Davatelis et al., 1989; Minano et al., 1990; Hayashi et al., 1995; Lopez-Valpuesta and Myers, 1995), which are, apparently, mediated via CRF (Strijbos et al., 1992; Zampronio et al., 1994), and INF-alpha, mediated via the opioid receptor mechanisms (Hori et al., 1991, 1992). However, it has been shown recently that in different species the same pyrogenic cytokines (IL-8) may induced fever via different, PG-independent (in rats; Zampronio et al., 1994) or PG-dependent (in rabbits; Zampronio et al., 1995) mechanisms. It should be noted that fever response is not always accompanied by an elevation in Tb. The final effect of pyrogens on body temperature depends upon the balance between heat production and heat loss, which in turn is highly dependent upon body size and ambient temperature, especially in small animals. Perhaps, the hypothermic response observed in our mice and rats at 22 degrees C may be in part attributed to ambient temperature, which was below a thermoneutral zone. The reduced febrile response is considered, at least in part, to contribute to an increased mortality and prolonged recovery from infections (Kluger, 1986). From this point, it is difficult to suggest whether the hypothermia observed in our mice and rats could be of somewhat adaptive significance. It has been shown that at the ambient temperature of 30 degrees C, Swiss Webster mice can re

Prostaglandin E2 may induce hyperthermia through EP1 receptor in the anterior wall of the third ventricle and neighboring preoptic regions

We have previously reported that intracerebroventricular injection of prostaglandin E2 (PGE2) induces hyperthermia possibly through EP1 receptors in the rat. In the present study, to determine the sites in the brain where PGE2 induces hyperthermia through EP1 receptors, we microinjected an EP1 receptor agonist, 17-phenyl-omega-trinor PGE2 (17-Ph-PGE2, 100 ng) into different sites in the rat brain and observed the colonic temperature (Tco) for 2 h in a 23 +/- 1 degrees C environment. Responsive sites where 17-Ph-PGE2 (100 ng) produced a rise in the Tco of more than 1.1 degrees C within 60 min after injection were found in the medial preoptic area, the subchiasmatic portion of the median preoptic nucleus, the anterior wall of the third ventricle (A3V) and the ventral portion of the diagonal band of Broca. Among these sites, the A3V was the most responsive. In contrast, microinjection of neither butaprost (an EP2 agonist, 100 ng) nor M&B28767 (an EP3 agonist, 100 ng) into these four sites had any effect on the Tco. Intracerebroventricular pretreatment with SC-19220 (an EP1 antagonist, 100 microg) inhibited the rise in the Tco which was induced by microinjection of PGE2 (50 ng) into the A3V. These results thus suggest that PGE2 induces hyperthermia by stimulating EP1 receptors in the A3V and the neighboring preoptic region.

Eicosanoid synthesis by warm- and cold-acclimated American bullfrog (Rana catesbeiana) brain

Previous studies in bullfrogs have demonstrated the presence of leukotriene (LT)C4 binding sites in the brain. However, synthesis of eicosanoids by brain tissue has not been examined. Because prostaglandin (PG) synthesis differs in warm- and cold-acclimated bullfrog lung tissue, this study compared the synthesis of prostaglandins and leukotrienes in brains from warm-(22 degrees C) and cold-acclimated (5 degrees C) animals. Initial experiments determined that leukotriene and prostaglandin production rates were greatest during the initial 30 min time period. Therefore, tissues were incubated in Munsick's solution and gassed with 95% O2, 5% CO2 for 30 min. Media were analyzed by radioimmunoassay for LTC4, LTB4, PGE2, PGF2 alpha, TXB2, and 6-keto PGF1 alpha. In warm-acclimated bullfrog brains, production was as follows: LTC4 > PGE2 > 6-keto PGF1 alpha, thromboxane (TX)B2, LTB4, and PGF2 alpha. Brain tissues from cold-acclimated animals incubated at 22 degrees C produced significantly greater quantities of PGE2 and 6-keto PGF1 alpha than did brains from warm-acclimated animals. Stimulation of TXB2 levels was observed when the animal was stunned with a blow to the head prior to decapitation. Indomethacin, a cyclooxygenase inhibitor, decreased prostaglandin but not leukotriene synthesis. Epinephrine (4 x 10(-8) M), the amphibian sympathetic postganglionic neurotransmitter, stimulated leukotriene synthesis by brains from warm-acclimated bullfrogs, and the effect was blocked with the 5-lipoxygenase inhibitor MK-886 (5 x 10(-5) M). These results clearly indicate that the bullfrog brain synthesized both leukotrienes and prostaglandins. Further studies are necessary to determine their function in the amphibian central nervous system.

Inhibition of the thermogenic and pyrogenic responses to interleukin-1 beta in the rat by dietary N-3 fatty acid supplementation

The thermogenic (increase in oxygen consumption, VO2) and pyrogenic (Tc) responses to the cytokine interleukin-1 beta (IL-1 beta) were studied in rats fed a n-3 fatty acid supplemented diet (8.75% n-3 fatty acids/kg diet). 4-6 weeks after commencing the diets, the n-3 supplemented rats exhibited reduced pyrogenic (0.5 +/- 0.1 degrees C versus 1.1 +/- 0.2 degrees C in control animals) and thermogenic (9 +/- 3% versus 22 +/- 6% in control animals) responses to intraperitoneal (i.p.) injection of IL-1 beta (1 micrograms/rat). However, responses to centrally administered IL-1 beta (5ng intracerebroventricular (i.c.v.)) were similar in both groups at this time. After 8-9 weeks of supplementation, n-3 supplemented animals exhibited attenuated responses to both ip IL-1 beta (VO2 responses reduced by 68% and Tc by 0.8 degrees C) and also i.c.v. IL-1 beta (VO2 responses reduced by 56% and Tc by 0.7 degrees C). N-3 supplementation did not, however, influence the thermogenic capacity of these animals since responses to noradrenaline were similar in control and n-3 fed animals (50% increase in VO2). These findings demonstrate that n-3 supplementation modifies the pyrogenic and thermogenic responses to IL-1 beta, probably via changes in eicosanoid metabolism. Modification of central responses to IL-1 are delayed compared to the effects of peripheral administration indicating separate mechanisms of IL-1 on fever and thermogenesis in the brain and the periphery.

Effects of pyrogenic immunomodulators on the release of corticotrophin-releasing factor-41 and prostaglandin E2 from the intact rat hypothalamus in vitro

1. The actions of the following pyrogens: lipopolysaccharide (LPS), polyinosinic:polycytidylic acid (Poly-I:C), human interleukin (IL)-1 alpha and IL-1 beta, human IL-6 and rat interferon (INF) on corticotrophin-releasing factor-41 (CRF-41) and prostaglandin E2 (PGE2) release from the intact rat hypothalamus in vitro have been studied. 2. Rat hypothalami were incubated in vitro in an artificial cerebrospinal fluid. Immunoreactive (ir)-CFR-41 and PGE2 released into the medium were measured by two-site enzyme amplified immunometric assay (EAIA) and radioimmunoassay (RIA) respectively. 3. Human IL-6 (1 to 10,000 IU ml-1) caused a dose-dependent release of irCRF-41, rising to a maximal 3-4 fold increase over basal at the highest dose tested. Human IL-1 alpha (1 to 1000 IU ml-1), human IL-1 beta (1 to 1000 IU ml-1), poly-I:C (10 pg ml-1 to 100 micrograms ml-1) and rat INF (1 to 10,000 IRu ml-1) all failed to alter irCRF-41 release. 4. LPS (1 mg ml-1) caused a 35% decrease in irCRF-41 release; however, over the dose-range of 0.1 microgram ml-1 to 100 micrograms ml-1, LPS failed to alter irCRF-41 release. The decreased irCRF-41 release in response to LPS (1 mg ml-1) was accompanied by a decrease in the subsequent 56 mM KCl stimulation of irCRF-41. 5. Human IL-1 alpha and IL-1 beta (1000 IU ml-1) were able to stimulate the release of irPGE2 from intact hypothalami, causing a 2 fold increase over basal release. Poly-I:C (100 microg ml-1), LPS (0.1 microg ml-1 to 1 mg ml-1), rat INF (10,000 IRu ml-1) and human IL-6 (1 to 10,000 iu ml-1) all failed to alter irPGE2release.6. In conclusion, these results suggest that the in vitro release of CRF-41 and PGE2, in response to pyrogens, are mediated via different cytokines. In view of this it is possible that different cytokines may mediate the temperature, prostaglandin and hypothalamo-pituitary-adrenocortical axis activation seen during pyrogenic stimulation in vivo.

Biochemical and immunohistochemical demonstration of a tightly bound form of prostaglandin E2 in the rat brain

Basal levels of prostaglandin E2 in the rat brain were determined by radioimmunoassay to be 0.68-0.79 pmol/g brain. About one-third of the prostaglandin E2 (0.23-0.28 pmol/g) was resistant to extraction with ethanol, but could be recovered with a mixture of ethanol and 1 N HCl (9:1, v/v), indicating that a tightly bound form of prostaglandin E2 exists in the brain. The amount of the bound form of prostaglandin E2 was almost unchanged by pentylenetetrazole-induced convulsion or by transcardial perfusion with a formaldehyde solution, although these treatments resulted in 40- to 80-fold increases in prostaglandin E2 content extracted with ethanol at neutral pH. A polyclonal antibody against prostaglandin E2-albumin conjugates recognized the bound form of prostaglandin E2, giving a punctate appearance in many neuronal cell bodies in the brain. Although almost all of the neuronal perikarya were immunoreactive for prostaglandin E2, intense immunoreactivity was observed in the mitral cell layer of the olfactory bulb, layer V of the cerebral neocortex, anterodorsal and reticular nuclei of the thalamus, supraoptic, paraventricular, accessory neurosecretory and lateral mammaillary nuclei of the hypothalamus, mesencephalic trigeminal nucleus, nucleus of the trapezoid body and deep cerebellar nuclei. When the cerebral neocortical regions were observed electron microscopically, immunoreaction products were seen as fine granules which were clustered into small patches in the cytoplasm of neuronal cell bodies and proximal dendrites. No immunoreaction products were seen in glial cells or endothelial cells. These results suggest that prostaglandin E2 is involved in fundamental processes of neurons.

Does an increase in prostaglandin E2 in the blood circulation contribute to a febrile response in rabbits?

We investigated the effect of intravenous injection of human recombinant interleukin-1 beta (IL-1) on rectal temperature and prostaglandin E2 concentration in venous and arterial blood and in the push-pull perfusate in the third ventricle of rabbits. Changes in plasma prostaglandin E2 concentration in blood obtained from the marginal ear vein paralleled changes in body temperature during both monophasic and biphasic fevers. The plasma concentration of prostaglandin E2 in blood obtained from the jugular vein increased during the first phase of the biphasic fever. However, no increase in the prostaglandin E2 level in the carotid arterial blood was observed during the biphasic fever. The levels of prostaglandin E2 in the push-pull perfusate in the third ventricle were markedly elevated during both monophasic and biphasic fevers. Intracarotid infusion of prostaglandin E2 did not produce a fever nor result in a change in the prostaglandin E2 concentration of the push-pull perfusate in the third ventricle. The present results suggest that prostaglandin E2 from the blood circulation does not contribute to fever production in rabbits.

Autoimmune disease and the nervous system. Biochemical, molecular, and clinical update

Autoimmunity in the central and peripheral nervous system can manifest as the result of cellular or humoral immune responses to autoantigens. There is evidence that multiple sclerosis is a cell-mediated autoimmune disease of the central nervous system in which both myelin and the cell that produces the myelin are destroyed. Diseases such as acute inflammatory demyelinating polyneuropathy (also called Guillain-Barré syndrome) and myasthenia gravis are considered antibody-mediated diseases of the peripheral nervous system and neuromuscular junctions, respectively. We review these diseases and explore mechanisms of immune-mediated destruction of these nervous system components. We specifically focus on one effective therapy aimed at countering the immune attack, that of thymectomy in patients with myasthenia gravis.

The relationship between schizophrenia and essential fatty acid and eicosanoid metabolism

Essential fatty acids (EFAs) and their eicosanoid derivatives are important constituents of the brain and regulators of neuronal function. There is direct and indirect evidence of impaired metabolism of prostaglandin (PG)E1 in schizophrenia. There is also direct evidence of abnormal EFA biochemistry with plasma phospholipids from five populations and brain phospholipids from another all showing reduced levels of linoleic acid and elevated levels of 22-carbon EFAs of both n-6 and n-3 series. Clinical trials of PGE1 and of the PGE1 precursors, gamma-linolenic acid (GLA) and dihomo-gamma-linolenic acid (DGLA) have shown modest therapeutic effects. In view of lack of therapeutic process involving drugs based on the dopamine concept of schizophrenia, it is time for new approaches based on the EFA/PG concept to be evaluated thoroughly.

Cardiovascular responses induced in free-moving rats by immune cytokines

1. We investigated the effect of intraperitoneal (I.P.) injections of the immune cytokines, interleukin-1 beta (IL-1 beta) and tumour necrosis factor (TNF) on cardiovascular responses in free-moving rats, using a biotelemetry system. 2. The I.P. injection of a small dose of IL-1 beta (1 microgram/kg) induced a monophasic increase in the heart rate, and that of a large dose (10 micrograms/kg) induced biphasic increases in the blood pressure and heart rate. However, the I.P. injection of any of several doses of TNF (1, 10 and 50 micrograms/kg) had no effect on cardiovascular responses in rats. 3. Pre-treatment with I.P. injection of indomethacin (10 mg/kg), an inhibitor of cyclo-oxygenase, significantly suppressed the cardiovascular responses and the increase in the plasma noradrenaline (NA) concentration induced by I.P. injection of IL-1 beta. 4. Microinjection of IL-1 beta (1 and 10 ng) into the preoptic and anterior hypothalamic (PO-AH) region induced dose-dependent increases in the blood pressure and heart rate in rats. These responses were also suppressed by pretreatment with I.P. indomethacin (10 mg/kg). In addition, microinjection of prostaglandin E2 (20 and 100 ng) into the PO-AH region increased blood pressure and heart rate, but that of prostaglandin D2 (100 ng) had no effect. 5. The present results suggest that IL-1 beta stimulates the release of prostaglandins, presumably E series, near regions of the hypothalamus, which act on the hypothalamus to induce activation of the sympathetic nervous system. Subsequently, the blood pressure, heart rate and the plasma level of NA increase.

Intraperitoneal injections of prostaglandin E2 attenuate hyperthermia induced by restraint or interleukin-1 in rats

1. The purpose of this study was to investigate the effect of the intraperitoneal (I.P.), intravenous (I.V.) or intrapreoptic area (POA) injection of prostaglandin E2 (PGE2) on the body temperature of restrained and unrestrained rats. The effect of I.P. PGE2 on the body temperature of rats during fever induced by I.P. injection of interleukin-1 beta (IL-1 beta) was also investigated. 2. Prior to injection, restrained rats had body temperatures of approximately 1 degree C higher than unrestrained rats. The I.P. injection of PGE2 (0.05 and 0.5 mg kg-1) caused body temperature to fall towards the pre-restraint levels in a dose-dependent manner. This fall in body temperature was preceded by a sharp increase in tail skin temperature that was also dependent on dose. The I.P. injection of PGE2 had no effect on the body temperature of unrestrained animals. 3. The I.V. injection of PGE2 caused very little change in the body temperature of restrained rats. However, when injected I.V. into unrestrained animals, PGE2 caused dose-dependent fevers. The injection of PGE2 (50 ng) into the POA resulted in fever in both restrained and unrestrained animals. 4. The I.P. injection of IL-1 beta (10 micrograms kg-1) caused a biphasic fever that lasted at least 420 min. The I.P. injection of PGE2 180 min after the injection of IL-1 beta caused a transient decrease in the rats' body temperature. This drop in body temperature was not associated with a decrease in metabolic rate. 5. These data support the hypothesis that during restraint stress hyperthermia and IL-1 beta fever, the I.P. injection of PGE2 acts peripherally to lower the body temperature of rats.

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.

Prevention of Postanesthetic Shivering with Intravenous Administration of Aspirin

There have been many reports of postanesthetic shivering (PAS); however, the causes have not been defined clearly, and the reported methods of inhibiting PAS are not always available clinically. In the present study, we assessed the effect of the intravenous administration of aspirin on the prevention of PAS in 62 patients undergoing oral or maxillofacial surgery, anesthetized with enflurane-nitrous oxide. Thirty of the patients were randomly selected, and received intravenous aspirin DL-lysine 900 mg (equivalent to aspirin 495 mg) before the end of surgery. No significant differences were noted in the rectal temperatures between the group given aspirin and the control group. Shivering was observed in 17 of the 32 patients of control group. In contrast, shivering was observed in 5 of the 30 patients who received aspirin. This was a statistically significant difference ( P < 0.01). These data indicate that intravenous administration of aspirin significantly inhibited PAS. The finding suggests that PAS is related to prostaglandin synthesis or to the formation of derivatives of arachidonic acid, since aspirin inhibits both the synthesis of prostaglandins and the formation of derivatives of arachidonic acid.

The antinociceptive activity of paracetamol in zymosan-induced peritonitis in mice: the role of prostacyclin and reactive oxygen species

1. Oral administration of high doses of paracetamol (600 mg kg-1 or more) resulted in inhibition of the writhing and reduced the levels of prostacyclin (PGI2, measured as 6-keto-PGF1 alpha) induced by intraperitoneal administration of zymosan in mice. The high oral doses of paracetamol required were accompanied by behavioural toxicity which may have contributed to the inhibition of writhing. 2. The number of writhes per mouse and the proportion of mice writhing at least once correlated significantly with the levels of 6-keto-PGF1 alpha. However, inhibition of writhing by paracetamol occurred at higher levels of 6-keto-PGF1 alpha than was previously observed with acidic non-steroidal anti-inflammatory agents. 3. When injected i.p., PGI2, carbacyclin and iloprost (agonists at the PGI2 receptor) induced writhing. Intraperitoneal injection of PGI2 reversed the inhibition of writhing induced by indomethacin (1 mg kg-1, p.o.) but not that induced by oral administration of paracetamol. 4. Paracetamol at 800 mg kg-1, p.o., inhibited carbacyclin-induced writhing but indomethacin at 1 mg kg-1 p.o. did not. Paracetamol administered i.p. at 100 mg kg-1 reduced the peritoneal levels of 6-keto-PGF1 alpha and inhibited zymosan-induced but not carbacyclin-induced writhing and did not produce behavioural toxicity. 5. The in vitro potency of paracetamol as a prostaglandin synthesis inhibitor is known to be reduced by the presence of lipid peroxides. However, no lipid peroxides, measured as thiobarbituric acid reactive material, were detected in the peritoneal lavage fluid of zymosan-injected mice. 6. Intraperitoneal administration of a mixture of superoxide dismutase and catalase reduced detectable superoxide anion by 98% without inhibiting the writhing response to zymosan or the antinociceptive potency of paracetamol. 7. The data are consistent with the suggestion that inhibition of PGI2 synthesis in the peritoneal cavity by paracetamol is responsible for only a part of its antinociceptive activity in this test. However, extremely high oral doses of paracetamol were required which produced behavioural toxicity which clearly contributed to the inhibition of writhing. The low potency of paracetamol in this model cannot be attributed to the generation of lipid peroxides via the oxidative burst.

Central action sites of interleukin-1 beta for inducing fever in rabbits

1. Intravenous (I.V.) human recombinant interleukin-1 beta (IL-1 beta) in high doses caused biphasic fever in rabbits. In lower doses it produced only the first phase of fever. 2. Intracerebroventricular (I.C.V.) or intrapreoptic-anterior hypothalamic (IPOAH) injection of IL-1 beta produced a rather rapid and marked increase in rectal temperature. 3. Subcutaneously administered indomethacin partly reduced the first phase and more substantially the second phase of the biphasic fever induced by high doses of I.V. IL-1 beta. The first phase may thus be prostaglandin independent at least in part. 4. In the fever induced by I.C.V. injection of IL-1 beta, subcutaneous indomethacin reduced the elevation of the rectal temperature considerably and delayed the onset of fever. Administration of indomethacin (I.C.V.) caused marked inhibition of the fever induced by a lower I.C.V. dose of IL-1 beta, but with a high dose the onset of the fever was delayed for about 1 h, without the total rise being affected. 5. It is concluded that the first phase of biphasic fever is caused by IL-1 beta acting via an extravascular component of the organum vasculosum laminae terminalis (OVLT) or the circumventricular organs accessible from only the blood side, to release arachidonate metabolites, presumably prostaglandin E2 (PGE2), and the second phase by IL-1 beta acting via the blood-brain interface accessible both from the blood side and the brain side, to release metabolites other than PGE2.

The effectiveness of arginine vasopressin and sodium salicylate as antipyretics in the Brattleboro rat

The infusion of either 30 micrograms/microliters (approx. 100 micrograms/kg/h) of sodium salicylate or 10 ng/microliters (10(-5) M) arginine vasopressin within the ventral septal area of the Brattleboro rat brain reduced a centrally induced prostaglandin E1 (PGE1) hyperthermia when compared with infusions of artificial cerebrospinal fluid. Conversely, the infusion of a related peptide, oxytocin (10 ng/microliters (10(-5) M), or 33 ng/kg/h) failed to alter the rise in core temperature following the PGE1 injection. These results suggest that the vasopressin receptors reported to be present in the Brattleboro rat may respond normally to exogenously administered vasopressin, thus allowing for the antipyretic action. Moreover, the antipyretic effects of sodium salicylate suggest that aspirin-like drugs may induce the release of alpha-melanocyte-stimulating hormone which, in turn, attenuates the PGE1-evoked fever. Given recent evidence, however, which suggests that the Brattleboro rat may contain vasopressin both peripherally and within the brain, the antipyretic action of sodium salicylate may be alternatively explained through the endogenous release of vasopressin.

Increased biogenic amine release in mouse hypothalamus following immunological challenge: antagonism by indomethacin

Stimulation of the acute-phase response in mice by lipopolysaccharide, pokeweed mitogen, concanavalin A or interleukin-1 was associated with increased release of biogenic amines, serotonin and norepinephrine in the hypothalamus as indexed by their primary metabolites, 5-hydroxyindoleacetic acid and 3-methoxy-4-hydroxyphenylglycol, respectively. The increases in norepinephrine and serotonin turnover observed 4 h following systemic administration of interleukin-1 were antagonized by concurrent administration of indomethacin, a potent inhibitor of cyclooxygenase. These data suggest that the increase in norepinephrine and serotonin release in mouse hypothalamus during the acute-phase response to infection is partially mediated by the actions of arachidonic acid metabolites.

Hypothalamic neuronal responses to cytokines

Fever has been extensively studied in the past few decades. The hypothesis that hypothalamic thermosensitive neurons play a major role in both normal thermoregulation and in fever production and lysis has particularly helped to advance our understanding of the neuronal mechanisms underlying the response to pyrogens. Furthermore, new data in the study of host defense responses induced by pyrogenic cytokines such as interleukin 1, interferon alpha 2, tumor necrosis factor alpha, and interleukin 6 have demonstrated that those factors have multiple, yet coordinated, regulatory activities in the central nervous system, so that our understanding of the role of the brain in the activity of these agents requires a new perspective and dimension. Thus, recent evidence from our laboratory indicates that blood-borne cytokines may be detected in the organum vasculosum laminae terminalis and transduced there into neuronal signals. Such signals may then affect distinct, but partially overlapping, sets of neuronal systems in the preoptic area of the anterior hypothalamus, mediating directly and/or indirectly the array of various host defense responses characteristic of infection that are thought to be induced by blood-borne cytokines.

Indomethacin prevents increased catecholamine turnover in rat brain following systemic endotoxin challenge

1. Key features of the acute phase response to infection are replicated by systemic administrations of lipopolysaccharide and may be mediated via the production of lymphokines and cytokines, including interleukin-1. Inhibition of prostaglandin synthesis may attenuate certain features of the acute phase response. 2. In the present study, the effects of systemic administration of the lipopolysaccharide (LPS, 250 micrograms/rat) and interleukin-1 (IL-1, 10 micrograms/rat) on catecholamine metabolism in different brain regions were compared and the effects of indomethacin, a cyclooxygenase inhibitor was determined. 3. The ratio of metabolite to parent amine was used as an index of turnover of catecholamines. 4. In hypothalamus, both epinephrine and norepinephrine concentrations were decreased and their major metabolite, 3-methoxy,4-hydroxyphenylglycol (MHPG), was elevated at 4, 8 and 24 hr following LPS. The major metabolite of dopamine (homovanillic acid, HVA) was increased at 8 hours in striatum, hypothalamus and medulla. LPS increased dopamine turnover at 8 and 24 hr and norepinephrine turnover at 4, 8 and 24 hr. 5. In all regions examined, IL-1 produced effects similar to LPS on amine and metabolite contents and norepinephrine and dopamine turnover. 6. Significantly, co-administration of a single dose of indomethacin (50 mg/kg) completely blocked LPS-induced changes in hypothalamic catecholamines and metabolites and the increase in turnover at 4 and 8 hr. Furthermore, the effects of IL-1 on hypothalamic MHPG content and norepinephrine turnover were also blocked by indomethacin, although the effects of IL-1 on regional catecholamines and HVA content and turnover were either not modified or partially antagonized by indomethacin. 7. The present results suggest that in the rat, activation of noradrenergic, dopaminergic and epinephrine-containing neurons in hypothalamus, as well as dopaminergic neurons in other regions is associated with the acute phase response to endotoxin and that synthesis of prostaglandins plays a pivotal role in catecholamine responses in all brain regions examined.

Indomethacin-induced antipyresis in the rat: role of vasopressin receptors

Infusion of 15 micrograms/microliters (approximately 120 micrograms/kg/h) of indomethacin within the ventral septal area of the rat brain significantly reduced a centrally induced prostaglandin E1 (PGE1) hyperthermia when compared with infusions of artificial cerebrospinal fluid. A bolus injection of a V1 receptor antagonist, d(CH2)5Try(Me)AVP, (200, 2000, or 20,000 pmol) within the ventral septal area had no effect of body temperature alone but did suppress the PGE1-induced fever. Similar bolus injections of the V1 receptor antagonist within the ventral septal area failed to alter the antipyretic action of indomethacin on the hyperthermia resulting from centrally administered PGE1. Central injections of a V2 receptor antagonist failed to alter either the PGE1-induced fever or the indomethacin-evoked antipyresis. The results suggest that the V1 receptor antagonist may exert non-specific neurodepressant effects which may interfere with the expression or production of PGE1 hyperthermia and may further mask any contribution of arginine vasopressin to the antipyretic effects of indomethacin.

In vitro study of mediators of inflammation in multiple sclerosis

Prostaglandin E levels have previously been demonstrated to be elevated in multiple sclerosis (MS). We have further investigated other products of activated macrophages related to inflammation. We report here on prostaglandin E and its relationship to interleukin 1, tumor necrosis factor, and leukotriene B4 produced by macrophages from blood and cerebrospinal fluid of MS patients and controls in vitro. Interleukin and tumor necrosis factor are elevated significantly after stimulation in MS, while leukotriene B4 production by blood macrophages is depressed compared to other neurological disease and normal healthy controls. In 40% of MS patients tested, peripheral blood macrophages spontaneously produced elevated levels of interleukin 1. All mediators of inflammation are produced in increased amounts by MS cerebrospinal fluid leukocytes after stimulation. Macrophages from MS blood are not as sensitive as controls to nonsteroidal inhibitors specific for lipoxygenase or cyclo-oxygenase pathways. Positive correlations of elevations in production of such mediators of inflammation as prostaglandin E, interleukin 1, and tumor necrosis factor in MS were significant. Elevated production of these mediators in combination with insensitivity to inhibitors of inflammation suggests a role for activated macrophages in the demyelination process.

Effect of prostaglandin E2 on thermoresponsive neurones in the preoptic and ventromedial hypothalamic regions of rats

1. We investigated the effect of microinjection of prostaglandin E2 (PGE2) into the preoptic (POA) or the ventromedial hypothalamic (VMH) region on rectal temperature in rats. Fever was induced by microinjection of PGE2 into the POA or the VMH regions. The febrile responses induced by PGE2 injected into the VMH region were significantly greater than those induced by injection into the POA region. 2. The effect of temperature on neuronal activity in the POA and the VMH regions was investigated by using slice preparations from rats. It was revealed that there exist many thermoresponsive neurones in the VMH region as well as in the POA region, and that the proportion of thermoresponsive neurones out of the total neurones examined in the VMH region was almost identical to that in the POA region. In addition, the warm-responsive neurones in the VMH region exhibited larger thermal coefficients than those in the POA region. 3. When PGE2 was applied in a recording chamber where the tissue slice was perfused, most of the neurones in the VMH region which responded to PGE2 showed a decrease in their firing rate, while those in the POA region showed an increase in their firing rate, regardless of their thermoresponsiveness. In the POA region, PGE2 began to affect the activities of the warm-responsive neurones in the range of 5 x 10(-7) to 7 x 10(-6) M, whereas maximum responses were obtained between the concentrations of 5 x 10(-6) and 5 x 10(-5) M. In the VMH region, PGE2 began to change the activities of the warm-responsive neurones in the range of 5 x 10(-8) to 5 x 10(-7) M, and the maximum effect of PGE2 on the VMH warm-responsive neurones occurred between the concentrations of 8 x 10(-7) and 4 x 10(-5) M. 4. The present results show that neurones exhibit different responsiveness to PGE2 and different sensitivity to PGE2 between the POA and the VMH regions. Nevertheless, microinjection of PGE2 into either the POA or the VMH region produces fever. Therefore, it is suggested that fever is produced by complex neuronal networks in the central nervous system.

Ventromedial hypothalamus is highly sensitive to prostaglandin E2 for producing fever in rabbits

1. The febrile responses induced by intraventricular or intrapreoptic (bilateral) injections of prostaglandin E2 (PGE2) were investigated in the same group of rabbits. Both injections produced dose-dependent fever over a range of 100-2000 ng. However the magnitude of febrile responses induced by ventricular injections was significantly greater than those by intrapreoptic injections. This indicates that there exist regions more sensitive to PGE2 than the preoptic region for producing fever. 2. To explore the regions sensitive to PGE2, the effects of microinjection (1 microliter) of PGE2 (50 and 100 ng) on the rectal temperature were extensively examined in the forty regions of the brain stem. The results showed that the preoptic and anterior hypothalamic region, and the ventromedial hypothalamic region are highly sensitive to PGE2 for producing fever. 3. The febrile responses to PGE2 (50-1000 ng) microinjected into the preoptic region were compared with those induced by injection in the ventromedial hypothalamic region. Fever induced by injection in the ventromedial hypothalamic region was significantly greater than that by injection into the preoptic region. 4. Fever induced by PGE2 injected into the ventromedial hypothalamic region was due to increased heat production in the cold environment (10 degrees C), while in 24 degrees C environment heat losses were reduced without significant changes in heat production. 5. The present results show that the ventromedial hypothalamic region is the most sensitive region to PGE2 for producing fever.

Multiple control of fever production in the central nervous system of rabbits

1. The effects of microinjection of prostaglandin D2, E2 and F2 alpha and of endogenous pyrogen on the rectal temperature of rabbits were extensively examined in sixty-eight brain regions and in the third cerebral ventricle. 2. Intracerebroventricular injection of both prostaglandins E2 and F2 alpha produced dose-dependent fever over a range of 100-1000 ng. The selective brain regions, the nucleus broca ventralis, preoptic area, anterior hypothalamus and the ventromedial hypothalamus, responded to microinjections of a small dose (less than 200 ng) of prostaglandins E2 and F2 alpha by producing fever. Furthermore, the lateral hypothalamus, ventral thalamus, substantia nigra and the trigeminal nucleus were also sensitive to high concentrations of prostaglandins E2 and F2 alpha, fever being produced. It is likely that prostaglandin D2 is not involved in fever induction. 3. The ventricular injection of endogenous pyrogen also produced fever. However, brain regions sensitive to microinjection of endogenous pyrogen were exclusively localized to regions near the organum vasculosum laminae terminalis (OVLT), such as the nucleus broca ventralis and the preoptic area. In contrast to the monophasic fever induced by prostaglandins E2 and F2 alpha, about 30 min after ventricular or cerebral injection of endogenous pyrogen the rectal temperature gradually started to rise and the fever was prolonged over 4 h. 4. We investigated the effect of an inhibitor of prostaglandin synthesis, sodium salicylate, on biphasic fever induced by intravenous injection of bacterial endotoxin. The microinjections of sodium salicylate into the bilateral regions near the OVLT suppressed the second peak but had no effect on the first peak. 5. The present study clarifies that there exist two separate mechanisms of induction of biphasic fever. Correlating with the first peak of biphasic fever, prostaglandins synthesized outside the blood-brain barrier act on multiple sites in the central nervous system to induce fever. Correlating with the second peak, endogenous pyrogen acts on regions near the OVLT to synthesize and release pyrogenic prostaglandins.

Neural mechanisms mediating the hyperthermia elicited by prostaglandin E2 injected into the preoptic-anterior hypothalamus

The neuromechanism mediating the hyperthermia induced by injection of PGE2 into the preoptic/anterior hypothalamus (PO/AH) was investigated in the rat. Pretreatment of rats with intraperitoneal injection of atropine sulfate blocked, whereas pretreatment with atropine methyl bromide had no significant effect on the hyperthermia. In a second series of experiments, atropine sulfate was microinjected into different regions of the hypothalamus and the thalamus in an attempt to locate the central cholinergic synapses involved in the PGE2-induced hyperthermia. The hyperthermia was blocked by atropine injection into the dorsal/dorsomedial hypothalamic area (DH), but was not significantly affected by injection into the PO/AH, ventromedial hypothalamus, or the thalamic area above the DH. Moreover, microinjection of the cholinergic agonist carbachol (0.5 microgram) into the DH could also elicit hyperthermia. Thus, our data suggest that the hyperthermia induced by PGE2 administration into the PO/AH is mediated by a cholinergic mechanism in the DH.

Blockade of prostaglandin E1 hyperthermia by sodium salicylate given into the ventral septal area of the rat brain

1. Sodium salicylate (30.0 micrograms microliter-1) or artificial cerebrospinal fluid (ACSF) was infused bilaterally into the ventral septal area (v.s.a.) of the unrestrained rat for 1 h before and 1 h after the injection of prostaglandin E1 at a concentration of 20.0 ng microliter-1 into a lateral cerebral ventricle. 2. During control (ACSF) infusions, 200.0 ng of prostaglandin E1 evoked a hyperthermic response (0.95 +/- 0.16 degrees C). During sodium salicylate infusions, the prostaglandin E1-evoked hyperthermia was significantly reduced (P less than 0.025) to 0.31 +/- 0.16 degrees C. 3. The fever index (degrees C h for 1.0 h) during the infusion of sodium salicylate was reduced 66% below that of control infusions (P less than 0.01). 4. These data indicate that sodium salicylate infused in the v.s.a. of rats can antagonize a prostaglandin E-evoked hyperthermia. This suggests that there may be an additional mechanism of action for sodium salicylate antipyresis other than inhibition of prostaglandin E synthesis.

Purification and properties of prostaglandin H-E isomerase from the cytosol of human brain: identification as anionic forms of glutathione S-transferase

Prostaglandin H-E isomerase (EC 5.3.99.3) was purified from human brain cytosol. Purification was by ammonium sulfate fractionation, diethylaminoethyl-Sepharose chromatography, gel filtration on a BioGel P-100 column, GSH-agarose chromatography, and MonoQ chromatography. The activity was eluted in two peaks from the MonoQ column, which were designated peaks 1 and 2. The molecular weights of peaks 1 and 2, determined by gel filtration, were 42,000 and 44,000, respectively. On sodium dodecyl sulfate-polyacrylamide gel electrophoresis, peak 1 showed two bands at the molecular weights of 24,500 and 25,000, and peak 2 showed a single band at the molecular weight of 25,000, results suggesting that both were dimeric proteins. The pI values of both enzymes were approximately 5.4. The enzymes catalyzed selective conversion of prostaglandin H2 to prostaglandin E2. The Km values for prostaglandin H2 of peaks 1 and 2 were 147 and 308 microM, respectively, and the Vmax values were 380 and 720 nmol/min/mg of protein, respectively. GSH was required for the catalysis of both enzymes, and no other sulfhydryl compounds could support the reaction. A part of glutathione S-transferase (EC 2.5.1.18) was copurified with peaks 1 and 2 of prostaglandin H-E isomerase. Prostaglandin H-E isomerase activity of peak 2 enzyme was competitively inhibited by 1-chloro-2,4-dinitrobenzene, a substrate of glutathione S-transferase. These results suggested that prostaglandin H-E isomerases in human brain cytosol were identical with anionic forms of glutathione S-transferase.

Evidence for separate mechanisms of induction of biphasic fever inside and outside the blood-brain barrier in rabbits

1. Intravenous bacterial endotoxin, or endogenous pyrogen, in high concentration both caused biphasic fever in rabbits. In low concentration they produced only the first phase of fever. 2. Subcutaneous indomethacin suppressed the first phase of fever produced by high concentration of intravenous endotoxin or endogenous pyrogen, but not the second phase. 3. Intraventricular cerebral injection of indomethacin reduced the second phase of fever produced by high concentration of intravenous endotoxin or endogenous pyrogen, but not the first phase. 4. Intraventricular cerebral injection of endotoxin or of endogenous pyrogen caused slow monophasic fever. This was suppressed by intraventricular, but not by subcutaneous, indomethacin. 5. It is concluded that the first phase of biphasic fever is caused by pyrogen acting via structures outside the blood-brain barrier, presumably peripheral nerves, and the second phase by pyrogen acting via structures within the blood-brain barrier, presumably hypothalamic neurones.

Prostaglandin E as the neural mediator of the febrile response

The evidence favoring a role for prostaglandin E (PGE) as the neural mediator of the febrile response is reviewed and considered under five different essential criteria which would need to be satisfied, if such a role is to be accepted. These criteria are: the ability of intracerebrally microinjected exogenous PGE to cause fever; the detection of increased levels of endogenous PGE in the brain during the normal production of fever; the ability of substances that inhibit the production and release of PGE to block normal fevers; the ability of substances that are specific PGE antagonists to inhibit normal fevers; and the identification of a specific site and cell type for the release of PGE in response to the action of pyrogens. Evidence from the literature that supports these criteria is reviewed and presented in this format, and the conclusion is drawn that the evidence available is more than sufficient to support the initial hypothesis.