Fever responses in newborn lambs

Neonatal lambs failed to respond with an increase in body temperature to i.v. injection of both endotoxin (0.4 g/kg), a Gram-negative bacterial pyrogen, and the cell walls of Staphylococcus aureus (1×10⁹), a Gram-positive bacterial pyrogen. However, the fall in serum iron concentration that normally accompanies injection of both the pyrogens in adults was not attenuated in the neonates. We believe that the central nervous system origin of the fever pathway is suppressed in neonatal lambs.     

Fever response of sheep in the peripartum period to Gram-negative and Gram-positive pyrogens

We have measured body temperatures and serum iron concentrations of sheep in the peripartum period following administration of endotoxin and Staphylococcus aureus cell walls. Both the rise in rectal temperature and the fall in serum iron concentration following intravenous injection of S. aureus were the same immediately pre- and postpartum as they were 5 weeks after parturition. The rise in rectal temperature following intravenous endotoxin injection immediately pre- and postpartum was significantly less than that of the same ewes 5 weeks later. However, the fall in serum iron concentration following endotoxin injection was significantly suppressed only prepartum. We conclude that fever is not suppressed in sheep in the peripartum period, but the response to endotoxin is suppressed, through complex processes incidental to the mechanisms responsible for the maintenance of gestation and induction of labour.     

Restoration of normal febrile response to endotoxin in pyrogen-tolerant rabbits by injection with human beta interferon.

Early-phase pyrogen tolerance was induced in rabbits by two consecutive daily injections of 125 ng of endotoxin per kg of body weight. The second injection of the same dose of endotoxin evoked only a monophasic fever with a peak response 1.5 h after the injection; no second peak was observed. The rabbits were released from the tolerance to develop a typical biphasic fever by an injection of 125 ng of endotoxin along with human beta interferon (HuIFN-beta), although the tolerance-inducing amount of endotoxin alone could not. The profile of the febrile response of tolerant rabbits injected with both endotoxin and HuIFN-beta could not be distinguished from that of normal rabbits. There was no essential difference between natural and recombinant HuIFN-beta in breaking tolerance. Heat-stable (70 degrees C, 30 min) endogenous pyrogen or tumor necrosis factor was increased significantly in concentration in the serum of tolerance-broken rabbits. These results suggest that HuIFN-beta stimulates the production of tumor necrosis factor in tolerant rabbits to elicit the second peak of febrile response.     

The role of tumour necrosis factor-alpha (TNF-α) in fever and the acute phase reaction in rabbits

We investigated the role of tumour necrosis factor-alpha (TNF-α) in fever and the acute phase reaction using a specific type-IV phosphodiesterase inhibitor, rolipram, that inhibits the production of TNF-α. The body temperatures and serum iron concentrations of rabbits were measured following injections of lipopolysaccharide (LPS) or Staphylococcus aureus (S. aureus) with either rolipram, diclofenac sodium or the appropriate control solutions. Rolipram significantly (P<0.05) inhibited the first phase of both LPS and Staphylococcal fever, but had no effect on the second phase. The fall in serum iron concentration was not significantly affected by the injection of rolipram together with LPS or S. aureus. These results suggest that TNF-α is a pyrogen that plays a role during the first phase of fever, at least. However, TNF-α appears not to mediate the fall in serum iron concentration during the acute phase reaction. Received: 19 November 1998 / Received after revision: 11 March 1999 / Accepted: 16 March 1999     

Fever in rats after intravenousE. coli endotoxin administration

Summary In conscious unrestrained rats, at an ambient temperature of 22°C, oesophageal temperature was measured and temperature effect of single and repeated intravenous injection ofE. coli endotoxin was examined. The first injection of endotoxin in a dose of 10.0 g/rat did not change the rat body temperature. The second injection of this dose in the same animals repeated after 48 h produced fever. With following injections the fevers observed were less pronounced. The absence of fever after a single injection of endotoxin was accompanied by the rapid loss of pyretic activity of the rat plasma samples (bioassayed in rabbits). When fever was observed (48 h interval between endotoxin injections) the pyretic activity of the rat plasma remained unchanged for 90 min following endotoxin injection. It was concluded that after a single injection endotoxin is rapidly detoxified in the rat circulation while this process does not take place after the second endotoxin injection (48 h interval). The process of endotoxin detoxification can be depressed by the pretreatment with nitrogen mustard. Analysis of changes of skin temperature following endotoxin injections and the influence of aspirin on endotoxin-induced fever suggest that the fever observed was of central origin.     

Effect of ibuprofen on fever and metabolic changes induced by continuous infusion of leukocytic pyrogen (interleukin 1) or endotoxin

Many of the metabolic sequelae to infection and inflammation, such as fever, trace mineral redistribution, skeletal muscle catabolism, and the acute-phase protein response, are mediated by leukocytic pyrogen (interleukin 1). In the anterior hypothalamus and in skeletal muscles leukocytic pyrogen appears to induce the synthesis of prostaglandin E2 which mediates fever and skeletal protein catabolism. It is unclear whether any additional metabolic responses to leukocytic pyrogen result from prostaglandin production. This study was undertaken to investigate the ability of ibuprofen, a specific cyclooxygenase inhibitor, to alter protein and trace metal responses to leukocytic pyrogen or endotoxin when given in quantities sufficient to block the febrile response. In guinea pigs given continuous infusions of leukocytic pyrogen or endotoxin, a 0.6 to 0.8 degrees C fever was observed within 4 h, and zinc and iron concentrations in serum fell by 63 to 78% (P less than 0.01). Rates of whole body amino acid appearance, oxidation, and incorporation into protein were all significantly increased by leukocytic pyrogen and endotoxin treatment, (P less than 0.05) as were the fractional hepatic and seromucoid protein synthesis rates in leukocytic pyrogen-treated animals (P less than 0.01). Muscle protein synthesis was unchanged. Although pretreatment with infusions of ibuprofen completely ablated the febrile response to leukocytic pyrogen and endotoxin, decreases in zinc and iron concentrations in serum and leukocytosis were unaffected. Overall increases in whole body amino acid kinetics induced by leukocytic pyrogen or endotoxin were only minimally affected by ibuprofen. We concluded that treatment with prostaglandin synthesis inhibitor ibuprofen did not affect whole body trace metal, hematological, or hepatic acute-phase-induced responses to leukocytic pyrogen or endotoxin, either because these responses are prostanoid independent or because they are only partially mediated by eicosanoid products.     

Fever and circulating cytokines induced by double-stranded RNA in guinea pigs: dependence on the route of administration and effects of repeated injections

Aims: The aim of this study was to characterize the properties of synthetic double‐stranded RNA to induce fever and circulating cytokines in guinea pigs with special emphasis on the route of administration and on a putative development of tolerance to this pyrogen. Methods: Changes in abdominal temperature were recorded in unrestrained animals by use of intra‐abdominally implanted radiotransmitters. Circulating concentrations of tumour necrosis factor‐α (TNF‐α) and interleukin‐6 (IL‐6) were measured by use of specific bioassays. Results: The pyrogenic effect of double‐stranded RNA at a dose of 500 μg kg^?1 depended on the route of its administration. Intra‐arterial (i.a.) or intraperitoneal injections of double‐stranded RNA induced pronounced fevers and strong elevations of circulating TNF‐α and IL‐6. Intramuscular injections of the synthetic pyrogen caused rather moderate febrile and cytokine responses. Administration of synthetic RNA into artificial subcutaneously implanted Teflon chambers had no pyrogenic and cytokine‐inducing effects. I.a. injections of double‐stranded RNA, repeated five times at intervals of 3 days, resulted in fevers of similar shape and duration and similar cytokine response patterns. However, the strength of fever and cytokine formation was significantly reduced, although not abolished, in response to the repeated injections compared with the first injection, indicating a partial development of tolerance. Conclusions: The modulation of the strength of RNA‐induced fever, dependent on the route of administration, or the state of partial tolerance to this pyrogen, may thus be related to the formation of pyrogenic cytokines.     

Fever response induced by intravenous and intracerebroventricular injection of pyrogen in thyroidectomised and protein-calorie malnourished rabbits

The development of a fever in response to intravenous (IV, 1.5 g/kg body mass) and intracerebroventricular (ICV, 1.5 g/animal) injections of Escherichia coli lipopolysaccharide (LPS) was studied in control, thyroidectomised and protein-calorie malnourished rabbits (New Zealand Whites, n=55). ICV injection of LPS in control rabbits produced a fever response, the characteristics of which differed from those obtained after IV pyrogen injection. Thyroid deficiency caused an attenuated fever response, irrespective of whether LPS had been administered by IV or ICV injection. Protein-calorie malnourished rabbits showed a smaller fever response after IV or ICV pyrogen injections. Malnourished rabbits, refed over a period of 15 days, showed a typical biphasic fever response, but with lower magnitude than controls. The results of these experiments suggest that ICV injection of LPS is not an appropriate model for the study of fever mechanisms in disease states, and that the attenuated fever response observed in proteincalorie malnourished rabbits may be related, at least in part, to a decreased ability to produce the endogenous pyrogen interleukin-1.     

Changes in body temperature and vasopressin content of brain neurons,in pregnant and non-pregnant guinea pigs,during fevers produced by Poly I : Poly C

The synthetic polyribonucleotide pyrogen Poly I : Poly C (800 g · kg^–1) was injected intramuscularly on alternate days into pregnant and non-pregnant female guinea pigs. Pregnant animals, close to term, had smaller fevers in response to the pyrogen than did non-pregnant animals. Repeated injections of the pyrogen caused sequentially smaller fevers for the first 3–4 injections, particularly in non-pregnant animals, and this appeared to be like the tolerance usually developed to repeated injections of endotoxin. Continued pyrogen injections then caused, in non-pregnant animals, fevers of increasing magnitude until the original fever levels were reached, whereas in pregnant guinea pigs the fever responses remained reduced until parturition. The development of tolerance was associated with an increase in immunoreactivity for arginine vasopressin (AVP) in some neurons in the medial part of the paraventricular nucleus, and in terminals in the lateral septum and amygdala similar to changes found in these areas at term of pregnancy. These observations raise the possibility that AVP in these regions may have a role in the development of tolerance to pyrogens, and further quantitative studies of the AVP content of, and release from, nerve terminals projecting to the limbic system seem warranted.     

Effect of age on fever and acute-phase response of rats to endotoxin and Salmonella typhimurium.

Age-related effects on endogenous pyrogen-mediated febrile and acute-phase responses to endotoxin and Salmonella typhimurium challenge were investigated in young adult and aged Fisher 344 rats. After injection of endotoxin, the febrile response over 6 h and the fall in plasma iron and zinc after 6 h were determined in 14 young adult and 14 aged rats in their thermoneutral zone (26 degrees C) and in 14 young adult and 14 aged rats maintained in a cold environment (15 degrees C). Although at 26 degrees C aged rats showed only a slightly diminished febrile response compared with that of young adult rats, at 15 degrees C they had a markedly diminished febrile response compared with that of young adult rats. At both 26 and 15 degrees C, the injection of endotoxin led to a fall in iron and zinc concentrations in the plasma of both young adult and aged rats. The intact trace metal response diminished but febrile response suggest that aged rats are able to produce endogenous pyrogen but have a reduced capacity to respond to this substance. In 22 aged and 22 young adult rats maintained at 26 degrees C and challenged with S. typhimurium, the febrile response was significantly less in the aged rats but the survival rate was virtually identical. When 10 young adult and 10 aged rats were placed at a temperature of 15 degrees C after injection with S. typhimurium, the febrile response in the aged rats was significantly lower than that in the young adult rats at only one time point, and the survival rate did not differ between the two age groups. Survival after challenge with S. typhimurium was not influenced adversely by the diminished febrile response.     

Naloxone does not influence a pyrogen fever in rabbits

Rabbits were made febrile by an intravenous injection of homologous endogenous pyrogen (Interleukin 1). When naloxone (0.1 mg/kg i.v.) followed by 0.06 mg (kg·hr)^–1 infusion) was given at the same time as the pyrogen, the resulting fever was indistinguishable from that following pyrogen alone. It appears unlikely that opioid receptors which are blocked by naloxone play any important part in the fever process.     

Fever produced by endotoxin injected into the hypothalamus of the monkey and its antagonism by salicylate

1. A suspension of the killed cell bodies of either E. coli, S. dysenteriae or S. typhosa was micro-injected through cannulae implanted chronically at specific sites within the diencephalon and mid-brain of the unanaesthetized monkey. A biphasic, monophasic or an undifferentiated fever could be induced by each type of micro-organism, but the type of response depended solely upon the locus of injection.2. Although little difference in the potency of the three pyrogens was found, the rise in body temperature was in each instance dependent upon the concentration of the endotoxin. A more intense fever was accompanied by shivering, vasoconstriction of the ear vessels, piloerection and huddling behaviour. Tolerance to the pyrexic effect of repeated injections of endotoxin did not develop.3. The febrile response having the shortest latency, greatest maximum rise in temperature and largest 10-hr fever index was evoked by micro-injections into the anterior hypothalamic, preoptic area. The incidence of biphasic fevers was also greater after endotoxin was injected into this same region. Endotoxin given similarly in the posterior hypothalamus or in the mesencephalon had either no effect or produced a smaller elevation in temperature after a longer latency. The distance of an injection site from the coronal plane formed by the optic chiasm and anterior commissure correlated significantly with the latency and magnitude of the temperature change as well as the fever index.4. When given intravenously, endotoxin in a quantity at least 100 times greater was required to evoke a fever similar to that produced when the pyrogen was micro-injected into the anterior hypothalamic, preoptic region. However, a biphasic fever was evoked with a latency of from 3 to 15 min when a larger amount of endotoxin was injected intravenously. Tolerance developed rapidly to the febrile effect of endotoxin administered by this route although toxic reactions were not observed.5. After the fever evoked by the hypothalamic injection of endotoxin had reached a plateau, 300-1200 mg sodium salicylate administered intragastrically produced a dose-dependent fall in temperature, but had no effect on the body temperature of an afebrile monkey.6. It is concluded that in the rhesus monkey, a bacterial pyrogen can evoke a fever which is mediated entirely by an action on the central nervous system, the principal site being the anterior hypothalamic, preoptic area. The first phase of a biphasic fever caused by bacteria acting either by the central or peripheral route seems to be due either to a direct action of the pyrogen on the cells of the anterior hypothalamus, or to the secondary release within this region of an intermediary thermogenic substance such as 5-hydroxytryptamine or prostaglandin. The finding that sodium salicylate counteracts a centrally evoked fever is not compatible with the hypothesis that an antipyretic exerts its action by preventing a pyrogen that is circulating in the blood stream from entering the central nervous system.     

Reduced Febrile Responses to Peripheral and Central Administration of Pyrogen in Aged Squirrel Monkeys

There is long-standing controversy as to whether fever capacity is reduced in aged man. Although loss of this cardinal sign of disease would be an impediment to diagnosis and treatment, there has been no previous research on altered febrile responses using aged primate models. In the present experiments the febrile reaction to IV Salmonella typhosa endotoxin was reduced in monkeys over 14 years old and in one-third of those 10–14 years of age compared with that of younger animals. In response to injections of endotoxin into the lateral cerebral ventricle (ICV), animals over 10 years old showed small or no fevers. Injections of probenecid (ICV), an inhibitor of central inactivation of leukocytic pyrogen and prostaglandin, augmented fever caused by IV and ICV endotoxin and hyperthermia caused by ICV PGE₂ in animals under 10 years of age. However, in older animals probenecid increased fever caused by ICV endotoxin only, although the increased response was still less than one quarter that of younger animals. The results indicate that old squirrel monkeys have decreased febrile responses that may be traced to alterations in central sensitivity to pyrogens.     

Role of nitric oxide in thermoregulation during septic shock: involvement of vasopressin

We tested the hypothesis that the nitric oxide (NO) pathway in the central nervous system (CNS) plays a role in hypothermia, as well as in the febrile response during experimental septic shock, by regulating vasopressin (AVP) release. Experiments were performed on male Wistar rats treated with N ^G-nitro-l-arginine methyl ester (l-NAME), a non-selective NO synthase (NOS) inhibitor, injected intracerebroventricularly (250 µg/1 l) 30 min before lipopolysaccharide (LPS) 1.5 mg/kg i.v. injection. One hour after LPS administration we observed a significant drop in body temperature (hypothermic response), followed by a temperature increase after the second hour (febrile response), which remained until the end of the experiment. Increased plasmatic AVP levels were concomitantly observed during hypothermia, nearly returning to basal levels during the febrile phase. When l-NAME was administered with LPS, plasmatic AVP concentrations remained high throughout the experiment, hypothermia was accentuated and the febrile response was abolished. Additionally, pre-treatment with -mercapto-,-cyclopentamethylenepropionyl¹, O-Et-Tyr², Val⁴, Arg⁸-vasopressin, an AVP V1 receptor blocker (10 µg/kg) administered i.v., reduced hypothermia and exacerbated the febrile response to endotoxin. In conclusion, our data indicate that the central NO pathway plays an inhibitory role in AVP release during experimental septic shock, which seems to be critical for the thermoregulation during this pathophysiological state.     

Renal excretion of prostaglandin metabolites, arginine vasopressin, and sodium during endotoxin and endogenous pyrogen induced fever in the goat

Responses to intravenous injections of an endotoxin (E. coli-lipopolysaccharide, 1 microgram/kg b.wt.) and endogenous pyrogen were studied in euhydrated and hyperhydrated goats. The biphasic febrile response to the endotoxin was associated with a pronounced increase in the renal excretion of measured prostaglandin (PG) metabolites (11-ketotetranor PGF metabolites). This increase was time-correlated with the elevation of the rectal temperature, and (in hyperhydrated animals) with an inhibition of the water diuresis and an increase in renal excretion of arginine vasopressin (AVP). Other effects of the endotoxin were an immediate depression of renal Na and K excretion followed by the development of pronounced natriuresis, and a reduction of plasma Fe and Zn concentrations. The appearance of the febrile reactions (peripheral vasoconstriction and shivering) was accompanied by miosis. The maximum elevation of the rectal temperature was significantly greater during euhydration than during hyperhydration. Also endogenous pyrogen elicited miosis concomitant with febrile reactions, and an elevation of the renal excretion of PG metabolites which was closely correlated in time with the monophasic febrile response, and (during hyperhydration) with temporary inhibition of the water diuresis and an increase in the renal AVP excretion. However, the responses were much weaker than the corresponding endotoxin effects. No appreciable changes in renal excretion of Na and K were observed in response to the endogenous pyrogen. It is concluded that the observed effects on renal cation excretion were manifestations of direct endotoxin influences on kidney function.(ABSTRACT TRUNCATED AT 250 WORDS)     

Thermosensitivity is reduced during fever induced by Staphylococcus aureus cells walls in rabbits

Thermosensitivity (TS) and threshold core temperature for metabolic cold defence were determined in six conscious rabbits before, and at seven different times after i.v. injection of killed Staphylococcus aureus (8⋅10⁷ or 2⋅10⁷ cell walls⋅kg⁻¹) by exposure to short periods (5–10 min) of body cooling. Heat was extracted with a chronically implanted intravascular heat exchanger. TS was calculated by regression of metabolic heat production (M) and core temperature, as indicated by hypothalamic temperature. Threshold for cold defence (shivering threshold) was calculated as the core temperature at which the thermosensitivity line crossed preinjection resting M. The shivering thresholds followed the shape of the fever response. TS was significantly reduced (up to 49%) during the time course of fever induced by the highest dose of pyrogen only. At both high and low doses of pyrogen TS correlated negatively with shivering threshold (r = 0.66 and 0.79 respectively) with similar slopes. The reduction in TS during fever was thus associated with the increase in shivering threshold resulting from the pyrogen injection and not by the dose of pyrogen. Model considerations indicate, however, that changes in sensitivity of the thermosensory input to the hypothalamic controller may affect threshold changes but cause negligible TS changes. It is more likely that the reduction in TS is effected in the specific hypothalamic effector pathways. Received: 25 August 1995/Received after revision: 27 November 1995/Accepted: 30 November 1995     

二甲亚砜对家兔内毒素性发热的影响

目的:观察二甲亚砜(DMSO)对家兔内毒素性发热的影响。方法:以健康封闭群新西兰兔为实验对象,随机分组。经耳缘静脉注射内毒素(ET)和DMSO,用WRY-B型微机热原测温仪测定家兔的结肠温度。结果:静脉注射ET引起家兔结肠温度双相性升高,其发热反应指数明显高于对照组。静脉注射ET10min前注射不同剂量DMSO组,家兔发热反应指数明显低于静脉注射内毒素组,并呈剂量依赖关系。静脉注射ET(0.4μg/mL,1mL/kg)10min后注射DMSO(60%,1mL/kg)组,发热反应指数同样明显低于静脉注射内毒素组。结论:DMSO明显抑制家兔内毒素性发热。     

Evaluation of the In Vitro Pyrogen Test System Based on Proinflammatory Cytokine Release from Human Monocytes: Comparison with a Human Whole Blood Culture Test System and with the Rabbit Pyrogen Test

The reliability of an in vitro pyrogen test system based on proinflammatory cytokine release from human monocytic cells was assessed by comparison with a test system based on a human whole blood culture as well as with the conventional rabbit pyrogen test. The human cells used as the pyrogen indicator cells were newly selected by subcloning of a human monocytic cell line, Mono-Mac-6. The selected cells, named MM6-CA8, responded to various pyrogens, including endotoxin, peptidoglycan (PG), Staphylococcus aureus Cowan 1 (SAC), and poly(I·C), with a high sensitivity and produced proinflammatory cytokines, such as interleukin 1 (IL-1), IL-6, and tumor necrosis factor alpha. Among these cytokines, IL-6 was produced most sensitively in response to traces of the pyrogens and detected in the largest quantities in the culture medium. The cytokine-producing responses of MM6-CA8 cells correlated significantly with the responses of cultured human whole blood, which represents an ex vivo culture test system reproducing pyrogen-induced cytokine production in the human body. In terms of cytokine inducibility, the pyrogens were ranked in the order endotoxin > PG > poly (I·C) > SAC in both culture systems, a ranking which almost agreed with the ranking of their pyrogenicity as assessed by the rabbit pyrogen test. These results suggest that the in vitro responsiveness of MM6-CA8 cells to various pyrogens is highly relevant for human pyrogenic reactions. Therefore, the in vitro test system is useful and reliable for detecting the presence of materials that are pyrogenic for humans.     

Effects of actinomycin on in vivo and in vitro formation of endogenous rabbit pyrogen induced with myxoviruses or stimulated with endotoxin

Summary The synthesis of virus-induced endogenous pyrogen and of interferons is inhibited by actinomycin both in rabbits and in exudate granulocytes from the peritoneal cavities of rabbits; the degree of inhibition is a function of the administered dose. The process involves an intracellular inhibition of pyrogen synthesis rather than a blocking of its release from the cell. Only in extracts from controls not treated with actinomycin it proved possible to trace endogenous pyrogen.However, when bacterial endotoxin is used as a stimulus, neither the formation of endogenous pyrogenin vivo norin vitro is influenced by actinomycin. It is known that the same also applies to endotoxin-induced Interferon synthesis.One may assume that in order to generate virus-induced endogenous pyrogen and Interferon,de novo protein synthesis is required. The endogenous pyrogen found in consequence to endotoxin stimulation, however, appears to be present in the cells in a pre-formed state. In a similar way to that of interferons it is apparently released upon administration of the stimulus.Actinomycin had a moderate blocking effect on the formation of thermic pyrogen in exudate granulocytes.Supported by the Deutsche Forschungsgemeinschaft.     

A new sensitive method for detecting human endogenous (leukocyte) pyrogen

Endogenous, or leukocyte pyrogen (EP), the mediator of fever, is currently detected by injection of pyrogen-containing supernatants into rabbits. This assay has been of little value in the study of human fever because it required injection of relatively large amounts of pyrogen. We now report that injection of medium containing human EP produces fever in mice. Supernatant from 1 × 10⁵ granulocytes, stimulated by phagocytosis of staphylococci and incubated overnight, or 1 × 10⁴ monocytes similarly treated, produce clear pyrogenic responses. This method for detecting EP is about 100-fold more sensitive than the rabbit assay, and it appears to be specific for EP. Preliminary studies of EP released by small samples of needle liver biopsies from febrile and afebrile patients suggests that this sensitive assay may be useful for investigations into the mechanisms of clinical fever.Supported by U.S. Public Health Service Grant No. AI 01564-20 and CA 14655-04