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PubMed1998

[First Results in the prevaluation of the human whole blood assay for pyrogens in biological pharmaceuticals]

When establishing the whole blood assay for pyrogens in our laboratory we did several investigations on the standard pyrogen to be used. Because of the hydrophobicity of the lipopolysaccharid (LPS) it is difficult to get a homogeneous solution. Therefore we used ultrasonic and biphenyl hydroxyl amine chloride for a better dispergation. Surprisingly the reactivity of the LPS in the whole blood assay for pyrogens dropped the more the LPS was dispergated. That's right inverse to the situation in the LAL. There are first experiences in the whole blood assay for pyrogens with biological pharmaceuticals. This includes immunoglobulins, vaccines and coagulation factors. Except of the vaccines and albumin the rabbit assay is the only way to test these pharmaceuticals for pyrogens. The albumins show a little amplification of the reactivity of LPS in the whole blood assay for pyrogens. The testing of albumin in the whole blood assay for pyrogens showed highly reproproducible results and a detection limit under 50 pg/ml LPS. The immunoglobulins show an amplifying effect as well. Immunoglobulins spiked with LPS were detected as pyrogenic in all cases. Some vaccines show a slight pyrogenity in the whole blood assay which gets visible when diluting the sample. Undiluted vaccines may cover a LPS contamination in the whole blood assay for pyrogens.

Journal Article↗
PubMed1962

Studies on the pathogensis of fever. IX. The production of endogenous pyrogen by polymorphonuclear leucocytes.

Determination of the dose-response curve for rabbit leucocytic pyrogen reveals a hyperthermic "ceiling" at which there is a marked insensitivity to dosage. This finding has important implications in relation to the quantitative assay of leucocytic pyrogen. Polymorphonuclear leucocytes separated from normal rabbit blood possess the capacity to produce less than 5 per cent of the pyrogen generated by the same number of rabbit granulocytes collected from acute peritoneal exudates. Blood granulocytes, separated in the cold from the buffy coat, contain no detectable preformed pyrogen. The amount of preformed pyrogen within exudate granulocytes represents but a small fraction of the pyrogen which the cells are capable of generating when incubated in normal saline at 37 degrees C. It is suggested that the active pyrogen is formed from an inactive precursor within the cells. Under the conditions tested, cell fragments of rabbit granulocytes fail to produce endogenous pyrogen. The fact that the production of pyrogen is blocked at 4 degrees C is in keeping with the hypothesis that it involves metabolic reactions within the cell.

Animals↗
PubMed1966

Mechanisms of endotoxin tolerance. IV. Specificity of the pyrogenic refractory state during continuous intravenous infusions of endotoxin.

The mechanisms underlying the pyrogenic refractory state which develops rapidly during a continuous intravenous infusion of bacterial endotoxin have been further explored. The findings demonstrate that: (a) rabbits rendered refractory to a continuous intravenous infusion of E. coli endotoxin at a standard rate (18 x 10(-4) microg/min) become highly refractory to a single intravenous test bolus of endotoxin, but remain fully responsive to preformed endogenous pyrogen and to substances known to release endogenous pyrogen, i.e. influenza virus, old tuberculin in specifically sensitized rabbits, and staphylococcal enterotoxin; (b) administration of fresh whole blood from normal donors containing an average of 1.6 - 10(8) granulocytes fails to restore febrile responsiveness to the continuing E. coli endotoxin infusion; (c) refractory phase plasma and liver homogenates exhibit no enhanced capacity to inactivate E. coli endotoxin pyrogenicity; (d) splenectomized animals readily develop the pyrogenic refractory state during E. coli endotoxin infusions and exhibit diminished, rather than the increased inflammatory responses to intradermal endotoxin seen in sham-operated controls; (e) continuous intravenous infusions of gelatin-stabilized, heat-killed pneumococci produce sustained fevers; and (f) continuous intravenous infusions of old tuberculin into specifically sensitized animals rapidly elicit a pyrogenic refractory state. The present observations, considered together with those of other investigators, support the hypothesis that pyrogenic unresponsiveness to endotoxin involves two distinct immunologic mechanisms. In terms of this hypothesis, the rapid reduction in febrile responsiveness to endotoxin is mediated by desensitization at the cellular level. With small doses of endotoxin, such as those employed in the present studies, this desensitization is primarily specific; with larger doses, nonspecific mechanisms are superimposed. So long as the subsequent doses of endotoxin are closely spaced or continuously infused, optimal conditions are provided for cellular desensitization and pyrogenic unresponsiveness to a given quantity of endotoxin can be induced rapidly and maintained without the requirement for antibody. However, as the interval between endotoxin challenge is lengthened, cellular desensitization wanes and tolerance becomes increasingly dependent upon those antibodies directed against the common toxophore groupings responsible for endotoxin pyrogenicity which assist the reticuloendothelial system in the clearance and destruction of this molecule.

Animals↗
PubMed1973

Synthesis of endogenous pyrogen by rabbit leukocytes.

Rabbit ieukocytes from peritoneal exudates and from blood were stimulated to form leukocyte pyrogen in the presence of radiolabeled amino acids. The stimuli used were endotoxin, phagocytosis, and tuberculin. The crude leukocyte pyrogen samples were purified; pyrogen from exudate cells was rendered homogeneous; pyrogen from blood cells was still contaminated with other proteins. All the purified pyrogens were radioactive; and for all it was shown that radioactivity and pyrogenic activity coincided on electrophoresis at pH 3.5 and pH 9 in acrylamide and on isoelectric focusing in acrylamide. Furthermore, pyrogens obtained from exudate cells stimulated in different ways, or from blood cells and exudate cells stimulated with endotoxin, appeared to be identical. These results suggest that leukocyte pyrogen was synthesized de novo from amino acid precursors and that leukocytes made the same pyrogen whatever the stimulus used to activate them.

Amino Acids↗
PubMed1974

Demonstration and characterization of two distinct human leukocytic pyrogens.

Human monocytes and neutrophils were separated from buffy coats of blood obtained from normal donors. Following incubation with heat-killed staphylococci, monocyte preparations contained 20 times more pyrogenic activity in the supernatant media than did supernates from an equal number of neutrophils. During purification of these pyrogens it was discovered that these cell preparations each produced a distinct and different pyrogen. The pyrogen obtained from neutrophils had a mol wt of 15,000 following Sephadex G-75 gel filtration, an isoelectric point of 6.9, and could be precipitated and recovered from 50% ethanol at -10 degrees C. In contrast, the pyrogen derived from monocyte preparations had a mol wt of 38,000, an isoelectric point of 5.1, and was destroyed in cold ethanol. Both molecules were unaffected by viral neuraminidase but biologically destroyed at 80 degrees C for 20 min and with trypsin at pH 8.0. The febrile peak produced by partially purified neutrophil pyrogen occurred at 40 min while that from monocytes was at 60 min. In addition, monocyte pyrogen produced more sustained fevers for the same peak elevation as neutrophil pyrogen. These studies demonstrate for the first time two chemically and biologically distinctive pyrogens derived from circulating human white blood cells and have important implications for our understanding of the pathogenesis of fever in man.

Animals↗
PubMed1974

Studies on the mechanism of endogenous pyrogen production. III. Human blood monocytes.

The characteristics of pyrogen production and release by human blood monocytes were investigated. A dose-response assay of monocyte pyrogen in rabbits indicated a linear relationship of temperature elevation to dose of pyrogen at lower doses. Monocytes did not contain pyrogen when first obtained, nor did they release it spontaneously even after 5 days of incubation in vitro. Pyrogen production was apparent 4 h after stimulation by endotoxin or phagocytosis, and continued for 24 h or more. Puromycin, an inhibitor of protein synthesis, prevented both initiation and continuation of pyrogen production and release. Pyrogen-containing supernates retained most pyrogenic activity during overnight incubation even in the presence of activated cells. Lymphocytes appeared to play no role in either initiation or continuation of pyrogen production in these studies.

Animals↗
PubMed1979

Hypothalamic sensitivity to leukocytic pyrogen of adult and new-born guinea-pigs.

1. Experiments were conducted to localize the hypothalamic site of action of microinjected leucocytic pyrogen and to compare the pyrogenic sensitivity of this locus in adult and new-born guinea-pigs.2. To identify the site reactive to leucocytic pyrogen, bilateral (0.8-1.0 mm from the mid line) injections of 1 microliter were made into conscious adult guinea-pigs via cannulas stereotaxically palced at 0.5 mm intervals and varying depths from the olfactory tegmentum to the mammillary bodies. Injections into the preoptic area produced sharp monophasic fevers with short latencies, whereas injections into circumjacent sites evoked smaller fevers with longer latencies. 3. To assess the ontogeny of the pyrogenic sensitivity of this locus, the febrile response to 1.00, 0.50, and 0.25 microliter leucocytic pyrogen injected bilaterally was compared to 0 to 5-, 6 to 12-, and 13 to 16-day old and in adult guinea-pigs. The minimum pyrogenic dose in both new-born and adult guinea-pigs was 0.25 microliter, but the 0 to 5-day old animals which responded with a fever to this dose were few in number and large in weight; 'small-for age' neonates became hypothermic. 4. The number of febrile animals increased with age; it also could be increased by increasing the dose of leucocytic pyrogen at any age. 5. These results suggest that febrile responsiveness may depend on the stage of development of, presumably, the pyrogen-receptive mechanism. They further imply that the preoptic sites where leucocytic pyrogen acts and thermoafferents are integrated may not be the same, since thermoregulatory capability is fully competent from birth.

Aging↗
PubMed1968

Pyrogenic principle of the ribonucleic acid from the yeast Candida utilis.

Experiments were performed to characterize the pyrogenic principle of ribonucleic acid (RNA) from the yeast Candida utilis. It was shown that ribonuclease hydrolysis of the RNA does not lead to inactivation of the pyrogenicity. Pyrogenicity was, however, destroyed by treatment with sodium deoxycholate. On column chromatography with Biogel under sterile and pyrogen-free conditions, the pyrogenic principle of yeast RNA was eluted together with the RNA. After treatment of the RNA with ribonuclease, it was possible to separate the pyrogenic activity from the RNA (hydrolysis products) to a great extent. Column chromatography of Escherichia coli endotoxin showed that the endotoxin was eluted in the same fractions as the pyrogenic activity of yeast RNA. On the basis of the behavior of the pyrogen, it may very well be that the fever reaction is produced not by the nucleic acid but by pyrogenic contaminants of the RNA preparation.

Animals↗
PubMed1978

Spontaneous pyrogen production by mouse histiocytic and myelomonocytic tumor cell lines in vitro.

Tumor-associated fever occurs commonly in acute leukemias and lymphomas. We investigated the capacity for in vitro production of pyrogen by three mouse histiocytic lymphoma cell lines (J-774, PU5-1.8, p 388 D1), one myelomonoyctic line (WEHI-3), and tow lymphoma-derived lines, RAW-8 and R-8. Pyrogen was released spontaneously into the culture medium during growth by all cell lines with macrophage or myeloid characteristics including lysozyme production; R-8 cells, of presumed B-lymphocyte origin, did not produce pyrogen. When injected into mice, the pyrogens gave fever curves typical of endogenous pyrogen, were inactived by heating to 56 degrees C and by pronase digestion, and appeared to be secreted continuously by viable cells. Two pyrogenic molecular species produced by H-774 cells were identified by Sephadex filtration, one of mol wt approximately equal to 30,000, and the other greater than or equal to 60,000. By contrast, three carcinoma cell lines of human origin and SV-40 3T3 mouse fibroblasts did not produce pyrogen in vitro. These results suggest that some malignant cells derived from phagocytic cells of bone marrow origin retain their capacity for pyrogen production, and may spontaneously secrete pyrogen during growth.

Adenocarcinoma↗
PubMed1977

Tests alternative to the rabbit bioassay for pyrogens.

The rabbit bioassay is currently the only legally acceptable method to test for pyrogenic contamination of parenteral preparations and medical devices designed to enter the parenterum. However, research efforts have recently made available alternative procedures to test for pyrogens which may have significant value in quality control. Part of the reluctance to accept tests other than the rabbit test may be due to the low visibility of emerging understanding of a significant theory of testing in which it is contended that the parameters of sensitivity and specificity are inversely related and that accuracy is an ideal. The rabbit pyrogen assay will detect 1 to 10 ng of enterobacteriaceal endotoxin (ET). The limulus test will detect 0.01 to 0.1 ng/ml of ET; some of the other tests approach the rabbit assay in sensitivity. Since it is current dogma that pyrogen is equivalent to ET, the basis for the use of ET to standardize pyrogen tests is rationalized. The source of ET in practice is bacterial contamination; therefore, numbers of bacteria that contaminate parenteral preparations can be directly related to potential pyrogenicity. Further, viable counts of bacteria in parenteral preparations, prior to sterilization, is a reliable test for pyrogens. Other tests such as nitroblue tetrazolium reduction and actinomycin-D enhancement of lethality of pyrogen for mice deserve consideration in quality control procedures. The limulus test, the most practical of currently available alternative tests for detection of ET and therefore, of pyrogen has application where the rabbit test cannot be used. Therefore, control personnel must learn of the availability, performance and interpretation of the limulus test. Practical considerations must govern the choice of an alternative test when the use of a test other than the rabbit bioassay is indicated.

Animals↗
PubMed1998

[Development and evaluation of a pyrogen test based on human whole blood]

When cells of the immune system, especially blood monocytes and macrophages, come into contact with pyrogenic (fever-inducing) contaminations, they secrete messenger molecules which initiate an hyperthermic reaction in the organism. Of this group of endogenous pyrogens, most is known about interleukin-1 (IL-1). A new pyrogen test makes use of this reaction as a system for detection: The substances which are to be screened are incubated with a small volume of blood from a healthy donor. Any pyrogens present induce the production of IL-1 which can be detected by ELISA. This test has a higher sensitivity and is more economical than the conventional pyrogen test in rabbits and furthermore reflects the reaction of the relevant species. In contrast to the customary alternative method, the Limulus amoebocyte lysate test (LAL), this test is not restricted to endotoxins from Gram-negative bacteria and is also not hindered by substances which bind endotoxins, such as blood proteins, to the same extent. Consequently, more than 50 non-endotoxin pyrogens have already been traced by this test. The whole blood test is even superior to the LAL in regard to the detection of endotoxins: in a comparison of about 60 endotoxins, there was a correlation of the potency of the individual endotoxins between the whole blood test and the pyrogen test in rabbits, but neither test correlated with the LAL test. In some cases, endotoxins with equal effects in the LAL test differed in potency in the human blood model by a factor of 10 000. A method has been developed by which cryopreserved blood can be put to use in the test. In this way, blood donations from a donor can be pre-tested so that uniform material may be employed in the test. This test opens up entirely new perspectives on pyrogen testing for Gram-positive or fungal pyrogens as well as in medicinal products. In addition, it could fill the dangerous security gap which might result from the limitations of testing medications and blood products with LAL only. The project was supported by ZEBET, D-Berlin, BMBF, D-Bonn, and set, D-Mainz.

Journal Article↗
PubMed1964

STUDIES ON THE PATHOGENESIS OF FEVER. 13. THE EFFECT OF PHAGOCYTOSIS ON THE RELEASE OF ENDOGENOUS PYROGEN BY POLYMORPHONUCLEAR LEUKOCYTES.

1. Phagocytosis promotes the release of endogenous pyrogen from polymorphonuclear leucocytes. 2. The release of pyrogen, though initiated by the phagocytic event, is not synchronous with it. 3. The postphagocytic release mechanism is not inhibited by sodium fluoride and, therefore, appears not to require continued production of energy by the cell. 4. The release process, on the other hand, is inhibited by arsenite, suggesting the participation of one or more sulfhydryl-dependent enzymes in the over-all reaction. 5. Particle for particle, the ingestion of heat-killed rough pneumococci causes the release of approximately 100 times as much pyrogen as the ingestion of polystyrene beads of the same size. 6. The pyrogen release mechanism of polymorphonuclear leucocytes separated directly from blood, unlike that of granulocytes in acute inflammatory exudates, is not readily activated by incubation of the cells in K-free saline. Despite this difference, both blood and exudate leucocytes following phagocytosis release large amounts of pyrogen, even in the presence of K(+). The fact that the postphagocytic reaction is uninhibited by the concentrations of K(+) which are present in plasma and extracellular fluids, suggests that this mechanism of pyrogen release may well operate in vivo. 7. As might be expected from the foregoing observations, the intravenous injection of a sufficiently large number of heat-killed pneumococci causes fever in the intact host. Intravenously injected polystyrene beads, on the other hand, are significantly less pyrogenic. Evidence is presented to support the conclusion that the fever in both instances is caused by pyrogen released from the circulating leucocytes which have phagocyted the injected particles. 8. The possible relationships of these findings to the pathogenesis of fevers caused by acute bacterial infections are discussed.

Animals↗
PubMed2006

In vitro pyrogen test for toxic or immunomodulatory drugs.

Pyrogenic contaminations of some classes of injectable drugs, e.g. toxic or immunomodulatory as well as false-positive drugs, represent a major risk which cannot yet be excluded due to the limitations of current tests. Here we describe a modification of the In vitro Pyrogen Test termed AWIPT (Adsorb, Wash, In vitro Pyrogen Test), which addresses this problem by introducing a pre-incubation step in which pyrogenic contaminations in the test sample are adsorbed to albumin-coated beads. After rinsing, the beads are incubated with human whole blood and the release of the endogenous pyrogen interleukin-1beta is measured as a marker of pyrogenic activity. Intentional contaminations with lipopolysaccharide were retrieved from the chemotherapeutic agents paclitaxel, cisplatin and liposomal daunorubicin, the antibiotic gentamicin, the antifungal agent liposomal amphotericin B, and the corticosteroid prednisolone at lower dilutions than in the standard in vitro pyrogen test. This represents a promising new approach for the detection of pyrogenic contamination in drugs or in drugs containing interfering additives and should lead to improved safety levels.

Adsorption↗
PubMed1983

Stimulation of muscle protein degradation and prostaglandin E2 release by leukocytic pyrogen (interleukin-1). A mechanism for the increased degradation of muscle proteins during fever.

To clarify the mechanisms underlying the loss of body protein during fever and sepsis, we incubated rat muscles with highly purified human leukocytic pyrogen. This polypeptide, which appears identical to interleukin-1, is released by leukocytes and signals the onset of fever in the hypothalamus. In muscles incubated at 37 degrees C, leukocytic pyrogen stimulated net protein degradation by 62 to 118 per cent (P less than 0.001). Proteolysis increased, but rates of muscle-protein synthesis did not change. The pyrogen also dramatically stimulated muscle synthesis of prostaglandin E2, which promotes protein breakdown in this tissue. Addition of indomethacin with leukocytic pyrogen prevented prostaglandin E2 synthesis and abolished the increase in proteolysis. The acceleration of protein breakdown induced by pyrogen was also blocked by Ep-475, an inhibitor of lysosomal thiol proteases. When muscles were incubated at 39 degrees C to mimic fever, protein breakdown increased, but addition of leukocytic pyrogen caused a further marked increase in proteolysis and prostaglandin E2 production. Thus, human leukocytic pyrogen can act on skeletal muscle to stimulate intralysosomal proteolysis by increasing the production of prostaglandin E2. These findings suggest that cyclooxygenase inhibitors may be useful in the treatment of negative nitrogen balance in fever. In addition, the release of prostaglandin E2 induced by leukocytic pyrogen may account for the myalgia that accompanies fever.

Animals↗
PubMedDate not supplied

Differentiation between endotoxin and non-endotoxin pyrogens in human albumin solutions using an ex vivo whole blood culture assay.

Purified E.coli endotoxin, Gram negative bacteria and Gram positive bacteria induce IL-6 secretion by whole blood cultures (WBC's). Polymyxin B at concentrations greater than 2 U/ml completely inhibits IL-6 secretion caused by 10 EU/ml of endotoxin. Polymyxin B has no effect on IL-6 secretion by WBC's in the absence of endotoxin. The inhibition of endotoxin induced IL-6 secretion is Polymyxin B concentration dependent at concentrations less than 1 U/ml. IL-6 induction caused by E.coli is only partially inactivated by 8 U/ml Polymyxin B. Polymyxin B has no effect on IL-6 secretion caused by B.subtilis. Two pyrogenic batches of human serum albumin (HSA), as tested by the rabbit assay for pyrogens, were also investigated. Polymyxin B at 4 U/ml inhibits less than 40 % of IL-6 secretion caused by these pyrogenic HSA batches. All the endotoxin activity in HSA samples spiked with purified endotoxin is inhibited by Polymyxin B indicating that HSA does not protect endotoxin against Polymyxin B inhibition. These results indicate that the pyrogenicity of these HSA batches are caused by Polymyxin B inhibitable and non-inhibitable fractions. This study shows that pyrogenic substances other than endotoxin can contaminate batches of pharmaceutical products and that results obtained using the Limulus Amoebocyte Lysate (LAL) assay does not necessarily indicate the pyrogenic status of pharmaceutical products. The WBC assay for pyrogens, having a broader sensitivity range than the LAL assay, is a better indicator of the pyrogenic status of pharmaceutical products.

Animals↗
PubMed1955

Studies on the antipyretic action of cortisone in pyrogen-induced fever.

The mode of action of cortisone as an antipyretic has been studied in rabbits challenged with intravenous injections of bacterial pyrogens. The fever induced by pyromen or dextran was found to be markedly suppressed when cortisone was administered in liberal amounts (25 mg. twice daily) for 3 days prior to the challenge. Although the cortisone effectively blocked the febrile response to both pyrogens, it failed to influence the transient but marked leucopenia which characteristically precedes the onset of fever. The antipyretic action of the drug also was shown to bear no relation to the activity of the serum factor recently demonstrated by Farr, Grant, and others to be involved in the production of pyrogen-induced fever. In preliminary experiments with typhoid vaccine as the inciting pyrogen, the presence of serum factor activity in normal blood and its absence in the blood of pyrogen-tolerant rabbits was confirmed. Subsequently the blood of rabbits treated with antipyretically effective doses of cortisone was shown to contain just as much serum factor activity as that of normal rabbits. In addition, previous incubation of the pyrogen with serum factor failed to influence the antipyretic effect of the drug. It is concluded from these findings that in suppressing pyrogen fever, cortisone acts neither upon the leucopenic reaction nor upon the fever-accelerating factor of the serum. By exclusion it would appear that the drug must influence some later stage of the fever-producing process. The mechanisms involved in the later stages of the response to exogenous pyrogen remain undefined, and the need for determining whether they are related to the prefebrile leucopenia is emphasized.

Animals↗
PubMed1958

Studies on the pathogenesis of fever with influenzal viruses. II. The effects of endogenous pyrogen in normal and virus-tolerant recipients.

Observations have been made on the fever-inducing properties of an endogenous pyrogen found in the circulation of rabbits after the intravenous inoculation of Newcastle disease virus (NDV). When endogenous pyrogen was given to a normal recipient, a biphasic fever was produced which simulated that seen with bacterial endotoxins. With the use of a technique of serial passive transfer, it has been shown that the "double-humped" response results from two separate actions of the injected pyrogen. The first of these appears to be a direct stimulation of the thermoregulatory centers. The second involves the release of further endogenous pyrogen in the normal recipient to cause, in turn, the second fever peak. Since the injection of endogenous pyrogen did not produce a significant change in the number of circulating leukocytes, it is inferred that this substance is different from either bacterial or tissue polysaccharides. In rabbits rendered tolerant by a previous injection of virus the second fever peak failed to appear and the response to endogenous pyrogen was monophasic. Evidence indicates that the absence of a second fever peak in the tolerant recipient was not due to rise in temperature on the preceding day of virus injection or to the development of either serum inhibitors or tolerance to virus itself. It is postulated that prior mobilization of endogenous pyrogen by virus may have modified the ability of the tolerant recipient to liberate further amounts of this substance in response to an injection of endogenous pyrogen.

Animals↗
PubMed1973

Effect of pyrogen and antipyretics on prostaglandin acitvity in cisternal c.s.f. of unanaesthetized cats.

1. Samples of cisternal cerebrospinal fluid (c.s.f.) were collected from unanaesthetized cats while rectal temperature was continuously recorded. From the same cat, samples were collected during normal body temperature, during pyrogen fever and when the fever was brought down by an I.P. injection of an antipyretic. Fever was produced by injection of the bacterial pyrogen of Shigella dysenteriae either into the third ventricle, cisterna magna or I.V. The samples of c.s.f. were assayed for PGE(1)-like activity on the rat stomach fundus strip preparation rendered insensitive to 5-HT.2. In samples of c.s.f. collected during normal body temperature, usually either no PGE(1)-like activity was detected, or its activity was low. Higher values were obtained in only a few cats.3. In each experiment the PGE(1)-like activity increased, often many-fold, in samples collected during the pyrogen fever, irrespective, of the route of administration of the pyrogen. However, on I.V. injection, about 1000 times larger doses of the pyrogen were required than on injection into the liquor space to produce fever and the increase in PGE(1)-like activity of cisternal c.s.f.4. The antipyretic drugs indomethacin, paracetamol and aspirin, injected I.P. during the pyrogen fever, brought down temperature, and the PGE(1)-like activity of the cisternal c.s.f. again became low.5. When samples of cisternal c.s.f. were subjected to thin layer chromatography the prostaglandin-like activity was solely or mainly found in the zone corresponding to the prostaglandins of the E series.6. These findings support the theory that pyrogens produce fever by increasing synthesis and release of prostaglandin in the preoptic anterior hypothalamic area, and that antipyretics of the aspirin type bring down this fever because they inhibit this synthesis.7. It is concluded that pyrogen increases prostaglandin synthesis not only in the preoptic anterior hypothalamic area. When injected into the liquor space increased synthesis of prostaglandin probably occurs in many regions near the surface of the brain stem, and when injected I.V. may occur in other parts of the C.N.S. as well. But to produce fever the prostaglandin has to act on the preoptic anterior hypothalamic area.

Acetaminophen↗