Evidence that brain prostaglandin synthesis is not essential in fever

Mechanisms of fever production and lysis: lessons from experimental LPS fever

Fever is a cardinal symptom of infectious or inflammatory insults, but it can also arise from noninfectious causes. The fever-inducing agent that has been used most frequently in experimental studies designed to characterize the physiological, immunological and neuroendocrine processes and to identify the neuronal circuits that underlie the manifestation of the febrile response is lipopolysaccharide (LPS). Our knowledge of the mechanisms of fever production and lysis is largely based on this model. Fever is usually initiated in the periphery of the challenged host by the immediate activation of the innate immune system by LPS, specifically of the complement (C) cascade and Toll-like receptors. The first results in the immediate generation of the C component C5a and the subsequent rapid production of prostaglandin E2 (PGE2). The second, occurring after some delay, induces the further production of PGE2 by induction of its synthesizing enzymes and transcription and translation of proinflammatory cytokines. The Kupffer cells (Kc) of the liver seem to be essential for these initial processes. The subsequent transfer of the pyrogenic message from the periphery to the brain is achieved by neuronal and humoral mechanisms. These pathways subserve the genesis of early (neuronal signals) and late (humoral signals) phases of the characteristically biphasic febrile response to LPS. During the course of fever, counterinflammatory factors, "endogenous antipyretics," are elaborated peripherally and centrally to limit fever in strength and duration. The multiple interacting pro- and antipyretic signals and their mechanistic effects that underlie endotoxic fever are the subjects of this review.

Contrasting effects of E type prostaglandin (EP) receptor agonists on core body temperature in rats

Prostaglandin E2 (PGE2) is thought to be a principal fever mediator. There are four subtypes of PGE (EP) receptors, EP1-EP4. We investigated which EP receptors mediate PGE2-induced hyperthermia by injecting selective EP receptor agonists into the rat lateral cerebral ventricle under unrestrained condition. ONO-DI-004, an EP1 receptor agonist, increased the core temperature (T(c)) in a dose-dependent manner (1.6+/-0.1 degrees C at 20 nmol, with the peak 30 min after injection) with a time course similar to PGE2-induced hyperthermia. ONO-AE1-259-01 (20 nmol), an EP2 receptor agonist, did not change the T(c). ONO-AE-248 (20 nmol), an EP3 receptor agonist, also increased the T(c). However, the peak effect was delayed (1.2+/-0.2 degrees C, 50 min after injection) compared to PGE2. In contrast, ONO-AE1-329, an EP4 receptor agonist, decreased the T(c). These findings suggest that the EP1, EP3, and EP4 receptors all may contribute to the thermoregulatory response to PGE2, but each may have a different role.

[Pain, fever and prostanoids]

Although it has been known that prostanoids are involved in pain regulation and fever, the precise roles of their receptors and receptor subtypes are unclear. All prostanoid receptors have been cloned and mice deficient in each receptor have been developed. Recent studies using prostanoid-receptor-knockout mice are shedding some light on these issues. Nociceptive responses to an intraperitoneal injection of acetic acid and hyperalgesia induced by carrageenan were abolished by IP-receptor deficiency. In addition, the use of mice lacking prostanoid receptor is revealing an interesting role of prostanoid in neuropathic as well as inflammatory pain. With regard to pyrexia, PGE2 injected intracerebroventricularly induced the febrile response in wild-type mice, but it was without effect in mice lacking the EP3 receptor. Furthermore, febrile responses induced by IL-1 beta, an endogenous pyrogen, and LPS, an exogenous pyrogen, were specifically suppressed in mice lacking the EP3 receptor. These results indicate that PGE2 works as a common final mediator of the febrile response and that this action of PGE2 is mediated by the EP3 receptor. The determination of precise roles of prostanoids in pain and fever may provide novel targets for antipyretic analgesics with fewer side effects.

PGE2 receptor subtype EP1 antagonist may inhibit central interleukin-1beta-induced fever in rats

We have previously reported that central injection of PGE2 induces hyperthermia through its actions on EP1 receptors in rats. Because the increase in local synthesis of PGE2 is assumed to be a necessary process in a fever caused by central injection of interleukin-1beta (IL-1beta), an EP1 receptor antagonist (SC-19220) should inhibit the IL-1beta-induced fever. To test this hypothesis, we observed the effect of SC-19220 on the fever produced by injection of recombinant human IL-1beta (rhIL-1beta) into the lateral cerebroventricle (LCV) in conscious rats. Administration of SC-19220 (100 microgram) into the LCV 15 min before LCV injection of rhIL-1beta (4 ng) suppressed an initial rise in colonic temperature for 30 min, producing a fever with a longer latency to onset and a longer time to peak elevation. SC-19220, given 60 min after the central administration of rhIL-1beta, also suppressed the rhIL-1beta-induced fever 15-60 min after its injection. These findings suggest that the central IL-1beta-induced fever in rats is mediated, at least partly, by activation of EP1 receptors by PGE2.

Impaired febrile response in mice lacking the prostaglandin E receptor subtype EP3

Fever, a hallmark of disease, is elicited by exogenous pyrogens, that is, cellular components, such as lipopolysaccharide (LPS), of infectious organisms, as well as by non-infectious inflammatory insults. Both stimulate the production of cytokines, such as interleukin (IL)-1beta, that act on the brain as endogenous pyrogens. Fever can be suppressed by aspirin-like anti-inflammatory drugs. As these drugs share the ability to inhibit prostaglandin biosynthesis, it is thought that a prostaglandin is important in fever generation. Prostaglandin E2 (PGE2) may be a neural mediator of fever, but this has been much debated. PGE2 acts by interacting with four subtypes of PGE receptor, the EP1, EP2, EP3 and EP4 receptors. Here we generate mice lacking each of these receptors by homologous recombination. Only mice lacking the EP3 receptor fail to show a febrile response to PGE2 and to either IL-1beta or LPS. Our results establish that PGE2 mediates fever generation in response to both exogenous and endogenous pyrogens by acting at the EP3 receptor.

Nitric oxide synthase-cyclo-oxygenase pathways in organum vasculosum laminae terminalis: possible role in pyrogenic fever in rabbits

1. Fever was induced in rabbits by administration of Escherichia coli endotoxin (lipopolysaccharide; LPS; 0.001-10 micrograms) into the organum vasculosum laminae terminalis (OVLT). Deep body temperature was evaluated over a period of 7 h. 2. The LPS-induced febrile response was mimicked by intra-OVLT injection of the nitric oxide (NO) donors, S-nitroso-acetylpenicillamine (SNAP, 1-10 micrograms), sodium nitroprusside (SNP, 50 micrograms), or hydroxylamine (10 micrograms), the cyclic GMP analogue 8-bromo-cyclic GMP (8-Br-cyclic GMP, 10-100 micrograms), or prostaglandin E2 (PGE2, 0.2 micrograms). 3. Dexamethasone (Dex, a potent inhibitor of the transcription of inducible NO synthase, iNOS, 10 micrograms), anisomycin (a protein synthesis inhibitor, 100 micrograms), L-N5-(1-iminoethyl)ornithine (L-NIO; an irreversible NOS inhibitor, 10-200 micrograms), aminoguanidine (a specific iNOS inhibitor, 1000 micrograms), or NG-methyl-L-arginine acetate (L-NMMA, a NOS inhibitor, 100 micrograms) inhibited fever induced by LPS when injected into the OVLT 1 h before LPS injection. An intra-OVLT dose of 1000 micrograms of NG-nitro-L-arginine methyl ester (L-NAME, a potent inhibitor of constitutive NOS) did not exhibit antipyretic effects. 4. Methylene blue (an inhibitor of NOS and soluble guanylate cyclase, 1-10 micrograms), 6-(phenylamino)-5,8-quinolinedione (LY-83583; an inhibitor of soluble guanylate cyclase and NO release, 20 micrograms), or indomethacin (an inhibitor of cyclo-oxygenase, COX, 400 micrograms) inhibited fever induced by LPS when injected into the OVLT 1 h before LPS injection. Pretreatment with methylene blue or haemoglobin (a NO scavenger, 100 micrograms) attenuated the fever induced by intra-OVLT injection of SNAP. 5. The PGE2-induced fever was potentiated, rather then attenuated, by pretreatment with an intra-OVLT dose of animoguanidine (1000 micrograms), L-NMMA (100 micrograms) or L-NIO (200 micrograms). 6. These results suggest that iNOS-COX pathways in the OVLT represent an important mechanism for modulation of pyrogenic fever in rabbits.

Effect of intraventricular haemorrhage and rebleeding following subarachnoid haemorrhage on CSF eicosanoids

CSF eicosanoid levels are raised following subarachnoid haemorrhage but not sufficiently to be vasoactive per se within the cerebral circulation. Rebleeding and intraventricular haemorrhage are two factors associated with a worse outcome after aneurysmal SAH. We have examined the effects of these two factors on the CSF levels of TXB2 (TXA2 metabolite), PG6-keto F1 alpha (prostacyclin metabolite), PGF2 alpha and PGE2 in 44 patients following subarachnoid haemorrhage. In 15 patients who had received no non-steroidal anti-inflammatory agent or dexamethasone, intraventricular haemorrhage increased the median levels of all four eicosanoids in ventricular CSF by 2.1-5.1-fold. In 4 patients who rebled, the CSF median levels of all four eicosanoids were raised up to 250-fold over the normal range. These concentrations are just sufficient to have cerebrovascular and neuromodulatory effects.

Prostaglandins and hypothalamic neurotransmitter receptors involved in hyperthermia: a critical evaluation

The role of a prostaglandin of the E series (PGE) in the hypothalamic mechanisms underlying a fever continues to be controversial. This paper reviews the historical literature and current findings on the central action of the PGEs on body temperature (Tb). New experiments were undertaken to examine the local effect of muscarinic, nicotinic, serotonergic, alpha-adrenergic, or beta-adrenergic receptor antagonists at hypothalamic sites where PGE1 caused a rise in Tb of the primate. Guide tubes for microinjection were implanted stereotaxically above sites in and around the anterior hypothalamic, preoptic area (AH/POA) of male Macaque monkeys. Following postoperative recovery, 30-100 ng of PGE1 was micro-injected unilaterally in a volume of 1.0-1.5 microliter at sites in the AH/POA to evoke a rise in Tb, and once identified, pretreated with a receptor antagonist. PGE1 hyperthermia was significantly reduced by microinjections of the muscarinic and nicotinic antagonists, atropine, or mecamylamine, at PGE1 reactive sites in the AH/POA. The serotonergic antagonist, methysergide, injected at PGE1 sensitive sites in the ventromedial hypothalamus also attenuated the rise in Tb. However, the 5-HT reuptake blocker, fluoxetine, and the beta-adrenergic receptor antagonist, propranolol, injected in the AH/POA failed to alter the PGE1 hyperthermia. In contrast, the alpha-adrenergic antagonist, phentolamine, potentiated the increase in Tb at all PGE1 reactive sites in the hypothalamus. An updated model is presented to explain how the concurrent actions of aminergic neurotransmitters acting on their respective receptors in the hypothalamus can interact with a PGE to elicit hyperthermia. Finally, an evaluation of the current literature including recent findings on macrophage inflammatory protein (MIP-1) supports the conclusion that a PGE in the brain is neither an obligatory nor essential factor for the expression of a pyrogen fever.

Is the central arachidonic acid cascade system involved in the development of acute-phase response in rabbits?

1. In the present study, endogenous pyrogen (EP), prostaglandin E2 or arachidonic acid was injected into the cerebral ventricle to investigate whether central arachidonic acid metabolites are involved in the development of the acute-phase response. The central effects of a cyclo-oxygenase inhibitor, indomethacin, and of a lipoxygenase inhibitor, nordihydroguairetic acid (NDGA), on the acute-phase response induced by an intracerebroventricular injection of EP were also examined. 2. The ventricular injection of EP decreased the plasma concentrations of iron and zinc, while increasing those of copper and fibrinogen and the circulating leucocyte count. However, ventricular injection of prostaglandin E2 affected neither of them, indicating that prostaglandin E2 does not contribute to the acute-phase response production by itself. 3. Both the ventricular injections of indomethacin and NDGA had no effect on the changes in the plasma concentrations of iron, copper and fibrinogen which were induced by ventricular injection of EP. In addition, when arachidonic acid was administered into the cerebral ventricle, the changes in the plasma levels of iron, copper and fibrinogen were not induced. 4. In contrast, EP-induced hypozincaemia was observed upon pre-treatment with NDGA, but not upon pre-treatment with indomethacin. However, plasma zinc increased after the ventricular injection of arachidonic acid. Ventricular injection of EP alone and of EP with NDGA increased the number of circulating leucocytes 8 and 24 h after the ventricular injection, while ventricular injections of arachidonic acid, and of EP with administration of indomethacin induced leucocytosis 8 h after injections. 5. These results suggest that arachidonic acid metabolites do not participate in the genesis of the acute-phase response.(ABSTRACT TRUNCATED AT 250 WORDS)

Physical versus pharmacological counter-measures. Studies on febrile rabbits

128 experiments were carried out on febrile rabbits at air temperatures of 8, 18, 24 and 30 degrees C in order to analyze the thermoregulatory effects and mechanisms of physical and/or pharmacological counter-measures. Fever was achieved by injection of 0.1 micrograms Salmonella typhi endotoxin (LPS)/kg into an ear vein. As the pharmacological counter-measure, injections of acetylsalicylic acid (ASA) into an ear vein were chosen. For the physical counter-measure, cooling thermodes (5 degrees C) were constructed for the abdominal skin, for the ear and for the rectum. ASA injections had no effect on the first fever maximum, even if applied 20 to 60 min before the LPS injection, but eliminated the second fever maximum. Of course, the additional hyperthermia observed at 30 degrees C ambient temperature could not be eliminated by the injections. On the other hand, cooling procedures can obviously not affect the pyrogen-induced temperature increase, but reduce the hyperthermic effect of a higher ambient temperature. Rectal cooling was more effective than ear or abdominal skin cooling. Abdominal cooling evoked an increase in metabolic heat production. Application of combined physical and pharmacological counter-measures achieved the strongest and quickest reduction of the second maximum, whereas the first maximum was not affected, as in all other experiments. The study emphasizes the necessity of taking into account the time course of the effector mechanisms in order to discriminate between hyperthermic and febrile components of temperature increase. In the initial phase cooling measures would evoke unwanted regulatory responses of the effectors, whereas during the second febrile maximum they would achieve a quicker reduction of core temperatures.(ABSTRACT TRUNCATED AT 250 WORDS)

Examination of the subdiencephalic rat brain for sites mediating PGE1-induced pyrexia

The subdiencephalic rat brain was mapped for sites capable of mediating prostaglandin-induced pyrexia. In conscious rats, PGE1, 200 ng in a volume of 1 microliter, was injected unilaterally into 412 sites between the midmesencephalon and the caudal medulla. Injections into only 12 sites caused a reproducible, short-latency core temperature increase of at least 0.5 degrees C. None of these was located in the paramedian brainstem, which was considered a likely site of PGE1 action because of the presence there of thermosensitive and pyrogen-sensitive neurons. Rather, the reactive loci were found in the hippocampus (5 sites) and in the vicinity of the cochlear nuclei (7 sites). Injections into only 2 sites in the latter region failed to produce pyrexia. In the hippocampus, however, injections at 31 sites in the same frontal planes as the reactive loci produced no effect. The possibility that the active hippocampal sites were associated with a distribution of injectate to PGE1-sensitive neurons located within hippocampal cleavage planes rather than in a circumscribed region is discussed.

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.

Prostaglandin E2 and fever: a continuing debate

Prostaglandin (PG) E2 is a potent hyperthermic agent and has been assigned an intermediary function in the response of thermoregulatory neurons to pyrogens. Though attractive, this idea has been challenged on several grounds. The present study confirms that brain PGE2 synthesis increases during fever, the time course of the elevation according with a causative role of the compound. Our experimental data also argue against the involvement of a second cyclooxygenase product, specifically thromboxane (TX) A2, in the action of pyrogens. The sequence of events leading to PGE2 production and fever differs depending on the pyrogen, bacterial vs. leucocytic, and its route of administration. Blood-borne interleukin-1 (IL-1) acts on a discrete site in the central nervous system (CNS) which is tentatively identified with the organum vasculosum laminae terminalis (OVLT). The same site may also be the target for blood-borne endotoxin. In addition, endotoxin may promote PGE2 synthesis in the cerebral microvasculature. Both pyrogens, on the other hand, act diffusely throughout the CNS when given intrathecally. We conclude that PGE2 is well suited for an intermediary role in the genesis of fever and ascribe the reported inconsistencies to methodological factors.

Is prostaglandin E the neural mediator of the febrile response? The case against a proven obligatory role

We have reviewed the evidence in favor of a prostaglandin mediator of the thermal responses in fever and found that PGE injected into the hypothalamus does not always cause fever, that cerebrospinal fluid concentrations of PGE are not reliable reflections of hypothalamic events, and that antipyretic drugs may act in ways other than inhibiting PGE synthesis. Fever is not blocked by prostaglandin antagonists, nor by ablation of PGE-sensitive areas of the brain. There is poor correlation between the effects of pyrogens and of PGE on cerebral neurons. There is evidence that at least one prostanoid other than prostaglandin is a mediator of fever, but the prostanoid has not been identified yet. We conclude that PGE may contribute to the neural responses in fever but is not essential.

Comparison of the action of prostaglandin with endotoxin on thermoregulatory response thresholds

Prostaglandin E2 (PGE2) and lipopolysaccharide (LPS) derived from E. coli were injected into the lateral cerebral ventricle of rabbits at 30 degrees C ambient temperature. The threshold core temperatures for ear cutaneous vasoconstriction (Thv) and shivering (Thsh) were determined by whole-body cooling with an intestinal thermode. Each threshold, as determined at the plateau phase of LPS fever and PGE2 hyperthermia respectively, were compared with the control values before LPS and PGE2 injection. Thsh was not changed by the injection of LPS, while Thv was increased. After PGE2 injection both Thsh and Thv were increased in comparison to their control levels. These changes paralleled the elevation of core temperature. The present study does not exclude prostaglandins as humoral mediators involved in some of the central processes generating fever, but suggest at the same time that there are additional properties of LPS fever for which prostaglandins do not account.

Effect of prostaglandin synthetase inhibitors on non-analgesic actions of morphine

The present study investigates the results of pretreatment with five prostaglandin (PG) synthetase inhibitors on effects of morphine on body temperature, pupillary diameter, body movement and production of exophthalmos in rat. Hyperthermia, induced by a low dose of morphine, was inhibited in animals pretreated with any of the PG synthetase inhibitors. However, PG synthetase inhibitors had no clear effect on hypothermia induced by higher doses of morphine. The duration of morphine-induced catalepsy was attenuated by pretreatment with the PG synthetase inhibitors in a dose-related manner. The exophthalmos induced by all doses of morphine was either shortened in duration or inhibited by sulindac, paracetamol or ibuprofen. Morphine-induced mydriasis was either attenuated or inhibited by paracetamol, ibuprofen or meclofenamic acid. The results suggest that endogenous PGs play a role in morphine-induced hyperthermia, catalepsy, exophthalmos and mydriasis whereas a physiological role for PGs in morphine-induced hypothermia was not indicated.

Effects of ethanol on thermoregulation

Clinical reports of accidental hypothermia in alcohol intoxicated individuals exposed to low ambient temperature ( Paton , 1983) have generally been borne out by experimental studies in healthy volunteers. Small doses of ethanol, given to human subjects at normal ambient temperature (Ta), have very little effect on body temperature but a combination of large dose, low Ta and vasodilatation provoked by strenuous exercise, causes a sharp fall in rectal temperature. In experimental animals, the use of relatively larger doses of alcohol and more extreme temperatures, both above and below the thermoneutral zone, has shown that the effect of ethanol is essentially poikilothermic, i.e. an impairment of adaptation to both heat and cold. This effect has been studied in greater detail, in relation to each of the basic thermoregulatory processes. Though small doses of alcohol may increase the metabolic rate under some circumstances, the most common effect at low Ta is inhibition of shivering and therefore reduction of thermogenesis. At the same time it tends to cause increased heat loss by cutaneous vasodilatation. This makes for a greater feeling of comfort in the cold exposed subjects but increases in rate of fall of core temperature. The combination of decreased thermogenesis and increased heat loss, despite falling body temperature, is suggestive of a lowering of the set-point of the thermoregulatory control mechanisms. Consistent with this is a slight increase in ventilatory heat loss after low doses of ethanol but larger doses cause respiratory depression, so that heat loss through the lungs is minor. However, at high Ta ethanol caused hyperthermia in experimental animals and shows enhanced lethality, so that impairment of thermoregulatory effector mechanisms seems to be at least as important as change in set-point. Studies of the effects of ethanol on electrophysiological activity of single neurons in the pre-optic area and anterior hypothalamus (POAH), biochemical activities of neuronal membranes, hypothalamic blood flow, conventional neurotransmitters, amino acid putative neurotransmitters, neuropeptides, prostaglandins and inorganic ions have all failed so far to yield a clear comprehensive picture of the mechanisms by which ethanol affects thermoregulation. In each case, contradictory evidence has been obtained concerning the consequences of ethanol administration, whether by oral, intraperitoneal, intravenous, intracerebroventricular, or direct local (POAH) route.(ABSTRACT TRUNCATED AT 400 WORDS)

Role of prostaglandin D2 in the hypothermia of rats caused by bacterial lipopolysaccharide

The intraperitoneal administration of lipopolysaccharide from Salmonella typhimurium (1 mg/kg) caused a fall in the rat colonic temperature of about 2 degrees C at an ambient temperature of 22 +/- 3 degrees C. The hypothermia induced by the lipopolysaccharide was abated in a dose-dependent manner by the administration of indomethacin. Other inhibitors of prostaglandin synthetase such as aspirin, flufenamic acid, and phenylbutazone had effects similar to those of indomethacin. When various prostaglandins were injected intracerebroventricularly, only prostaglandin D2 caused a dose-dependent fall in the colonic temperature at doses between 1.2 and 6 nmol/kg. Microinjection of prostaglandin D2 into the preoptic area caused hypothermia of about 1 degree C. However, injection of prostaglandin D2 into the posterior hypothalamus had little effect on the colonic temperature. The hypothermia caused by prostaglandin D2 was not abated by the administration of indomethacin. The amount of prostaglandin D2 increased significantly in the preoptic/hypothalamic region of rat brain 1 hr after the intraperitoneal administration of the lipopolysaccharide, whereas such increase was not observed in rats pretreated with indomethacin. The in vitro incubation of the preoptic/hypothalamic slices with the lipopolysaccharide also increased the amount of prostaglandin D2. These results suggest that the intraperitoneal administration of the lipopolysaccharide induces the release of prostaglandin D2 in the preoptic/hypothalamic area of rat brain and that the latter compound is involved in the hypothermic response of rats to the lipopolysaccharide.

Inhibition, by trichothecene antibiotics, of brain protein synthesis and fever in rabbits

1. To test further the hypothesis that brain protein synthesis is necessary for fever, three structurally similar trichothecene antibiotics were injected into the cerebral ventricles of rabbits. They were 3,15-diacetoxy-12-hydroxytrichothec-9-ene (DAHT), 3,15-didesacetyl-calonectrin (DDAC) and T-2 toxin. Their actions on hypothalamic incorporation of [14C]leucine and fever were compared. 2. DDAC (60 micrograms) and T-2 toxin (10 micrograms) strongly inhibited leucine incorporation and fever. DAHT (60 micrograms) did not diminish fever and had a smaller effect upon leucine incorporation. 3. The findings strengthen considerably earlier suggestions that brain protein synthesis is an essential step in pyrogenesis.

Eicosanoids: prostaglandins, thromboxanes, leukotrienes, and other derivatives of carbon-20 unsaturated fatty acids

In recent years, knowledge of the biochemistry of oxygenated metabolites of arachidonic acid has greatly increased. Their biological functions in acceleration and prevention of platelet aggregation and in inflammatory and immune reactions are becoming much clearer. The therapeutic value, particularly of PGI2 as well as selective inhibitors of synthesis, is also rapidly advancing. Despite much effort, the functional importance of prostaglandins and thromboxanes in the cNS in normal ongoing physiological processes is still quite uncertain. However, when parenchymal or vascular elements are damaged or invaded by extraneural cells, the synthesis of one or the other member of the eicosanoids is greatly increased and contributes significantly to pathophysiological reactions. Thus, prevention of synthesis is likely to have increasing importance in clinical neurology, particularly in cerebrovascular diseases.

Role of prostaglandin E in the biphasic fever response to endotoxin

Biphasic fevers were induced in sheep with intravascular infusions or injections of 4-10 mug (80-200 ng/kg) of endotoxin, whereas monophasic fevers were obtained with doses of 1-2/mug (20-40 ng/kg). A marked increase in arterial blood pressure invariably accompanied the onset of fever; the latency of responses to the higher and lower doses of endotoxins averaged 26 min and 42 min, respectively. Prostaglandin (PG) assays of plasma from the carotid artery and jugular vein during fever episodes revealed a surge of PGE and PGF coincident with the pressor response and the first phase of fever, but PG were not detected in plasma samples taken throughout the second phase of fever. PG measurements of arterial and venous plasma collected at a distal site (hind limb) showed a similar surge of PGE and PGF in association with the early fever response, indicating that intravascular PG synthesis and release represents a generalized systemic response to circulating endotoxin. Carotid arterial infusions of PGE(2) produced immediate monophasic fevers and pressor responses, whereas PGD(2) infusions produced an immediate pressor effect but no fever. Infusions of PGF(2alpha) or prostacyclin, however, evoked neither fever nor pressor effects. Intracarotid infusions of leukocyte pyrogen (LP) caused monophasic fevers with latent periods of 15-20 min but pressor responses were not seen and neither PGE nor PGF were detected in plasma samples from the carotid artery or jugular vein before or during fever. Indomethacin, a potent inhibitor of arachidonic acid metabolism, blocked fever responses to endotoxin and to LP. These findings implicate PGE as the mediator of the early phase of endotoxin fever and imply a role for another pyrogenic metabolite ofarachidonic acid in the mediation of the second phase of fever, i.e., the phase associated with circulating LP. It is possible that both pyrogenic metabolites are generated within the vascular compartment, reaching thermoregulatory centers of the brain by transfer across the blood-brain interface.

Changes in body temperature after administration of antipyretics, LSD, delta 9-THC, CNS depressants and stimulants, hormones, inorganic ions, gases, 2,4-DNP and miscellaneous agents

This survey concludes a series of complications of data from the literature, primarily published since 1965, on thermoregulatory effects of antipyretics in afebrile as well as in febrile subjects, LSD and other hallucinogens, cannabinoids, general CNS depressants, CNS stimulants including xanthines, hormones, inorganic ions, gases and fumes, 2,4-dinitrophenol and miscellaneous agents including capsaicin, cardiac glycosides, chemotherapeutic agents, cinchona alkaloids, cyclic nucleotides, cycloheximide, 2-deoxy-D-glucose, dimethylsulfoxide, insecticides, local anesthetics, poly I:poly C, spermidine and spermine, sugars, toxins and transport inhibitors. The information listed includes the species used, route of administration and dose of drug, the environmental temperature at which the experiments were performed, the number of tests, the direction and magnitude of body temperature change and remarks on the presence of special conditions such as age or lesions, or on the influence of other drugs, such as antagonists, on the response to the primary agents.

Changes in body temperature after administration of acetylcholine, histamine, morphine, prostaglandins and related agents

This survey, the second in a series, presents extensive tabulations of literature, primarily since 1965, on thermoregulatory effects of cholinergic agonists and antagonists, histamine and H1- and H2-receptor antagonists, narcotic analgesics and antagonists in both non-tolerant and tolerant subjects and of prostaglandins and related agents. The information listed includes the species used, route of administration and dose of drug, the environmental temperature at which the experiments were performed, the number of tests, the direction and magnitude of body temperature change and remarks on the presence of special conditions, such as age or lesions, or on the influence of other drugs, such as antagonists, on the response to the primary drug.

Prostaglandin E levels in third ventricular cerebrospinal fluid of rabbits during fever and changes in body temperature

1. A method was devised to sample cerebrospinal fluid (c.s.f.) from the third ventricle of conscious rabbits.2. Levels of PGE were measured in c.s.f. withdrawn from the third ventricle of rabbits exposed to a variety of manipulations of both brain and body core temperatures which mimicked various facets of fever in these animals. These results were compared to the levels of PGE in the c.s.f. of the same rabbits made febrile by I.V. injections of endogenous pyrogen.3. Levels of PGE in ventricular c.s.f. remained unaltered at 2-3 ng/ml. during exposure to cold, hyperthermia due to heat exposure, hypothalamic cooling or hypothalamic heating, whereas during fever produced by endogenous pyrogen, they rose to an average of 11-12 ng/ml. Furthermore, a significant positive correlation was established between the level of PGE measured in the c.s.f. and the subsequent height of the fever produced by the pyrogen.4. Since production of PGE within the brain is not caused by changes in the brain or body temperatures which are comparable to those observed during fever, and yet greater than fivefold increases in the PGE levels in c.s.f. are produced by I.V. injections of endogenous pyrogen, it is concluded that PGE production in the brain is involved in the pathogenesis of fever.

Effects of intracerebroventricular floctafenine and indomethacin on body temperature in febrile rabbits

1. We injected the potent prostaglandin synthesis inhibitors, floctafenine and indomethacin, intravenously and intracerebroventricularly in rabbits made febrile by intravenous injection of leucocyte pyrogen. 2. Floctafenine (75 mumol) injected intravenously failed to affect the fever, whereas indomethacin (15 mumol) markedly reduced the fever. 3. When injected into the cerebral ventricles, floctafenine was feebly antipyretic, and then only at a dose ten times the antipyretic dose of indomethacin. 4. Our results support the suggestion that floctafenine has no antipyretic action when administered peripherally. However, its lack of antipyretic effect cannot be explained solely on the grounds that it fails to cross the blood-brain barrier.

The antipyretic effect of UP 517-03 in the rabbit

The antipyretic effect of UP 517-03 was studied in rabbits, provided with a cannula in the lateral cerebral ventricle. Given orally as a curative treatment, UP 517-03 can abolish hyperthermic reactions induced by intracerebroventricular injection of sodium arachidonate or bacterial endotoxin. A comparison with acetylsalicylic acid and indomethacin is given. UP 517-03 does not modify the temperature of normothermic rabbits. These results suggests that the antipyretic action of UP 517-03 can be explained by an effect of this substance on the metabolism of arachidonic acid in brain.

Intraventricular microinjections of a stable analogue of prostaglandin endoperoxide cause fever in rabbits

1. Derivatives of arachidonic acid other than prostaglandin are pyrogenic, the likely candidates being the prostaglandin endoperoxides and/or the thromboxanes. 2. Intraventricular microinjections in rabbits of a stable analogue of prostaglandin endoperoxide resulted in dose-dependent increases of rectal temperature. The pyrexia was delayed in onset; no significant change in body temperature occurred for at least an hour. 3. The pyrexia was unaltered by simultaneous injection of the potent prostaglandin synthetase inhibitor indomethacin. 4. We suggest that both prostaglandins and prostaglandin endoperoxides may be implicated in fever.

Effects of central administation of probenecid on fevers produced by leukocytic pyrogen and PGE2 in the rabbit

1. Single intracerebroventricular (I.C.V.) injections of probenecid (PBCD, 0.125--0.5 mg) enhanced and prolonged fever caused by I.V. administration of leukocytic pyrogen (LP) in rabbits resting in neutral (23 degrees C), cold (10 degrees C) and hot (30 degrees C) environments. Similar effects were produced by single I.C.V. injections of PBCD given before PGE2 (0.5 microgram) was injected I.C.V. in the three ambient temperatures. 2. Fever produced by IV. LP was also prolonged by infusion and by multiple injections of PBCD. 3. PBCD given I.P. (100 mg/kg) enhanced and prolonged fever caused by I.V. injection of Salmonella typhosa endotoxin. 4. Hyperthermia produced by I.C.V. PGE2 was not augmented by subsequent PBCD infusion. However, pre-treatment with PBCD followed by PGE2 injection and PBCD infusion caused hyperthermia that was very high and prolonged, and, in some cases, lethal. 5. Acetaminophen (2 mg, I.C.V.) and indomethacin (10 mg/kg, I.V.) lowered body temperature when given during fever induced by LP and prolonged by PBCD infusion. 6. The concentration of PGE in cerebrospinal fluid (c.s.f.) samples taken from the third or lateral ventricles rose or stabilized during PBCD infusions made during LP fever. However, similar changes in PGE concentration also occurred during control infusions when body temperature was low. 7. We conclude that termination of the actions of both central endogenous pyrogen and centrally administered PGE2, and the subsequent reduction of fevers produced by them, require a PBCD-sensitive facilitated transport system. The reduction of PBCD-prolonged PL fevers by antipyretics which block PGE synthesis suggests that prolongation by PBCD of LP fever is not due to blockade of PGE transport in a subsequent step in fever mediation per se, but is due to inhibition of transport of LP itself, or of other mediators associated with it.

Prostaglandin E1 fever in the crayfish Cambarus bartoni

Groups of 10 crayfish were injected with prostaglandin E1, at 1 of 3 pharmacological doses (0.5, 0.1 or 0.05 mg), into the haemocoel, and individually allowed to thermoregulate in electronic shuttleboxes for 24 hr. The mean preferred temperature of each group was then compared with their mean preferred temperature for 24 hr prior to injection, and with the mean preferred temperature of 10 crayfish injected with pyrogen-free saline. Dosage-dependent increases in preferred temperature were observed in the crayfish injected with PGE1, ranging from 1 degrees C at the lowest dosage to 3,4 degrees C at the highest dosage, above the normal thermal preferendum for this species of 22.1 degrees C.

Stereotaxic implant microinjection and temperature recording system for rabbits

Modification of standard rabbit stereotaxic apparatus to allow adjustment of the tooth bar in the vertical plane may be accomplished by simple machining of a standard laboratory clamp and aluminum rod. The modification greatly increases speed of head positioning for implant surgery. Machining the chrome and brass luer hub of standard stainless steel hypodermic needles to the described configurations produces improved guide tubes for brain temperature recording and cannulae for brain microinjections. Data from hypothalamic injection of prostaglandin E1 and records of resulting changes in brain temperature support the effectiveness of the methods described.

Endotoxin fever in the new-born guinea-pig and the modulating effects of indomethacin and p-chlorophenylalanine

1. At 30 degrees C ambient temperature E. coli endotoxin injected into the cerebral ventricles evokes a febrile response in 0-3 day-old guinea-pigs. If the dose is sufficiently high, the fever is biphasic: two rising phases separated by a transient fall.2. At 20 degrees C ambient temperature the change in body temperature after the endotoxin is still biphasic, but the transient fall is more pronounced and, finally, hypothermia develops. The relatively large surface area of the new-born cannot explain, by itself, the hypothermia.3. The phasic changes in body temperature following endotoxin administration are unlikely to be mediated by a single central factor, and a sequence of several factors could be postulated.4. Indomethacin prevents the first-phase febrile rise in body temperature, and also the consequent fall, but not the second-phase rise.5. p-Chlorophenylalanine pre-treatment prevents the transient fall only, it slightly increases the first-phase rise and does not influence the second-phase rise.6. Prostaglandins and/or other derivatives of endogenous arachidonic acid in the brain might be responsible for the first rising phase of the endotoxin fever, and might also initiate a central serotonergic mechanism which, in turn, could lead to the transient falling phase between the two rising phases of fever. The mechanism of the second-phase febrile rise in body temperature awaits some other explanation.

Hyperthermic effects of arachidonic acid, prostaglandin E2 and F2alpha in rats

The aim of the present study was to investigate the possibility that endotoxin fever in rats is mediated by arachidonic acid (AA) which in turn is converted to the active metabolites such as prostaglandin (PG) E2, PGF2alpha, thromboxane A2 (TxA2), or prostacyclin (PGI2). Evidence is presented indicating that PGE2 induces fever (not hyperthermia) by acting on the anterior hypothalamic preoptic area. Conversely, both PGF2alpha and AA produce mutually similar hyperthermia and there is no correlation between their microinjection sites in the diencephalon and the observed hyperthermic response. In addition, evidence is presented suggesting that involvement of other metabolites of AA, namely TxA2 and PGI2 in the mediation of endotoxin fever in rats seems unlikely. Only PGE2-induced fever is significantly similar, consistent with the parameters of this study, to endotoxin-induced fever in rats. AA-induced hyperthermia is probably brought about by increased levels of PGF2alpha or both PGF2alpha and PGE2 in the hypothalamus following AA injection. It seems highly unlikely that endotoxin produces fever in rats through the increased availability of free AA or through the activation of the PG endoperoxide synthetase in the hypothalamus. The mechanism by which endotoxin may increase PGF2 levels in the rat hypothalamus remains unknown.

The antipyretic effect of tilorone hydrochloride in the cat

1 The antipyretic activity of tilorone hydrochloride was studied in conscious, unrestrained cats provided with implanted jugular venous catheters, third cerebral ventricular (i.c.v.) cannulae and retroperitoneal thermocouples. 2 In afebrile animals, 10 mg/kg i.v. or 1 mg i.c.v. tilorone hydrochloride did not alter body temperature, but 20 mg/kg i.v. or 2 to 5 mg i.c.v. caused hypothermia and various behavioural responses. 3 Non-hypothermogenic doses of tilorone (i.v. or i.c.v.) antagonized hyperthermic responses to leucocytic pyrogen (i.v. or i.c.v.), bacterial pyrogen (i.c.v.) and sodium arachidonate (i.c.v.) but did not antagonize prostaglandin E1 (i.c.v.). 4 These results indicate that tilorone has an antipyretic action within the central nervous system that is distinct from its hypothermogenic action. Although there is no published evidence to indicate that tilorone can inhibit prostaglandin synthesis peripherally, its ability to reduce hyperthermic responses to arachidonate suggests that it can inhibit prostaglandin synthesis within the brain.

Effects of prostaglandin antagonism on sodium arachidonate fever in rabbits

1. Sodium arachidonate, the prostaglandin precursor substance, when injected intraventricularly into rabbits, results in dose-dependent hyperthermia, which is rapid in onset and of several hours duration. 2. Arachidonate fever was inhibited by intraventricular injection of indomethacin, but not by the simultaneous intraventricular injection of either of the two prostaglandin antagonists SC 19220 or HR 546. 3. Both antagonists effectively inhibited the fever induced by the intraventricular injection of an equipotent dose of PGE1. 4. Our results show that a derivative of arachidonic acid other than prostaglandin is pyrogenic.

Mediation of hyperthermia by prostaglandin E2: a new hypothesis

In rat hypothalamus prostaglandin (PG) E2, unlike PGF2 or arachidonic acid shared the site of hyperthermic action with E. coli endotoxin. The in vitro catabolism of PGE2 in the hypothalami of endotoxin-treated rats was significantly suppressed. It is proposed that endotoxin fever in rats is due to the inhibition of PGE2 breakdown in the hypothalamus.