CCK-8 and PGE1: central effects on circadian body temperature and activity rhythms in rats.

Cholecystokinin-octapeptide (CCK-8) has been shown to possess an acute thermogenic and hyperthermic action when given intracerebroventricularly in slightly restrained rats. To substantiate the febrile nature of that hyperthermia freely moving animals should be used and together with body core temperature, at least one behavioral parameter, such as general activity, should also be recorded. In the present studies, Wistar rats (N=34) exposed to thermoneutral (26-28 degrees C) or cold (4 degrees C) ambient temperature and to a 12:12-h light/darkness schedule were infused intracerebroventricularly with CCK-8 or prostaglandin E1 (PGE1) for several days using ALZET minipump and changes in body core temperature and general activity were recorded by biotelemetry (Minimitter). In rats exposed to a thermoneutral ambient temperature, low doses of CCK-8 induced slight but significant rises of day minima of circadian body temperature rhythm (CBTR) and with a high dose (1 microg/h) of the peptide--infused either at thermoneutrality or during cold exposure--an increase of acrometron could also be recorded. All of these changes were observed only during the first 2-4 days of 7-day-long infusions. Intracerebroventricular infusion of PGE1 administered at thermoneutrality in a dose of 1 microg/h for 7 days induced a marked rise in body core temperature with a disappearance of CBTR in some rats for 2-3 days or with rises of day minima/acrometron in others. General activity--running parallel with CBTR in periods without infusions--tended to be decreased when core temperature rose during the first couple of days of intracerebroventricular infusion of higher doses of CCK-8 or of PGE1. The decreased general activity--one component of sickness behavior--together with an increased body core temperature found in the present study, supports the view that they are components of a genuine fever induced by the central effect of the two mediators used.

Signaling the brain in systemic inflammation: role of sensory circumventricular organs.

The sensory circumventricular organs (CVOs) are specialized brain regions that lack a tight blood-brain barrier. A role for these brain structures in signaling the brain during systemic inflammation is based on the following sets of observations. In spite of some conflicting data from literature, lesions of CVOs have been shown to block several components of brain controlled illness responses (i.e. fever or neuroendocrine modifications). Receptors for inflammatory cytokines and for bacterial fragments are constitutively expressed in cells within the sensory CVOs. The expression of most of these receptors is upregulated under conditions of systemic inflammation. Cellular responses in theses brain areas can be recorded and documented after stimulation of these respective receptors. Such responses include changes in electrical activity of neurons, induction of transcription factors leading to modifications in gene expression during inflammation and to a localized release of secondary signal molecules. These molecules may influence or even gain access to neural structures inside the blood-brain barrier, which can normally not directly be reached by circulating cytokines or bacterial fragments.

Role of the nitric oxide/cyclic GMP/Ca2+ signaling pathway in the pyrogenic effect of interleukin-1beta.

Interleukin-1beta (IL-1beta) has a wide spectrum of inflammatory, metabolic, haemopoietic, and immunological properties. Because it produces fever when injected into animals and humans, it is considered an endogenous pyrogen. There is evidence to suggest that Ca2+ plays a critical role in the central mechanisms of thermoregulation, and in the intracellular signaling pathways controlling fever induced by IL-1beta and other pyrogens. Data from different labs indicate that Ca2+ and Na+ determine the temperature set point in the posterior hypothalamus (PH) of various mammals and that changes in Ca2+ and PGE2 concentrations in the cerebrospinal fluid (CSF) of these animals are associated with IL-1beta-induced fever. Antipyretic drugs such as acetylsalicylic acid, dexamethasone, and lipocortin 5-(204-212) peptide counteract IL-1beta-induced fever and abolish changes in Ca2+ and PGE2 concentrations in CSF. In vitro studies have established that activation of the nitric oxide (NO)/cyclic GMP (cGMP) pathway is part of the signaling cascade transducing Ca2+ mobilization in response to IL-1beta and that the ryanodine (RY)- and inositol-(1,4,5)-trisphosphate (IP3)-sensitive pools are the main source of the mobilized Ca2+. It is concluded that the NO/cGMP/Ca2+ pathway is part of the signaling cascade subserving some of the multiple functions of IL-1beta.

Evidence that platelet-derived growth factor may be a novel endogenous pyrogen in the central nervous system.

Platelet-derived growth factor (PDGF) exerts neurotrophic and neuromodulatory actions in the mammalian central nervous system (CNS). Like the cytokines, PDGF primarily signals through tyrosine phosphorylation-dependent pathways that activate multiple intracellular molecules including Janus family kinases. We previously showed that microinjection of PDGF-BB into the lateral ventricle induced a febrile response in rats that was reduced by pretreatment with Win 41662, a potent inhibitor of PDGF receptors (Pelá IR, Ferreira MES, Melo MCC, Silva CAA, and Valenzuela CF. Ann NY Acad Sci 856: 289-293, 1998). In this study, we further characterized the role of PDGF-BB in the febrile response in rats. Microinjection of PDGF-BB into the third ventricle produced a dose-dependent increase in colonic temperature that peaked 3-4 h postinjection. Win 41662 attenuated fever induced by intraperitoneal injection of bacterial lipopolysaccharide, suggesting that endogenous PDGF participates in the febrile response to this exogenous pyrogen. Importantly, febrile responses induced by tumor necrosis factor-alpha, interleukin-1beta, and interleukin-6 were unchanged by Win 41662. Both indomethacin and dexamethasone blocked the PDGF-BB-induced increase in colonic temperature, and, therefore, we postulate that PDGF-BB may act via prostaglandin- and/or inducible enzyme-dependent pathways. Thus our findings suggest that PDGF-BB is an endogenous CNS mediator of the febrile response in rats.

Vagotomy attenuates the behavioural but not the pyrogenic effects of interleukin-1 in rats.

Vagal afferent signals, have been implicated in cytokine mediated interactions between the periphery and the central nervous system. Studies in experimental animals have shown that cytokine induced activation of brain mediated responses to infection such as fever, sickness behaviour and pituitary-adrenal activation, are inhibited by subdiaphragmatic vagotomy. We have previously proposed that the peripheral signal to the brain in fever is of a humoral nature while others have suggested that either neural afferents or a mixture of both humoral and neural signals may be involved. The objective of the present study was to examine further the role of vagal transmission, in mediating the febrile response to a systemic injection of IL-1beta in rats and to compare this with changes in social exploration behaviour. Intraperitoneal injection of IL-1beta (1.0-30.0 microg/kg) inhibited social exploration in rats and this was attenuated in vagotomized animals. Injection of increasing concentrations of IL-1beta (0.1-1.0 microg/rat) induced significant (P<0.001) increases in core body temperature. However, in contrast to effects on social exploration, the increase in temperature was not inhibited by vagotomy at any of the doses used. These observations demonstrate a dissociation between the two brain mediated events, one of which is dependent on the integrity of the vagus nerve (social exploration) while the other (fever) is apparently generated by different mechanisms which may include circulating pyrogens.

Antagonism of central glucagon-like peptide-1 receptors enhances lipopolysaccharide-induced fever.

Lipopolysaccharide (LPS; a model of systemic bacterial infection) causes fever and activates glucagon-like peptide-1 (GLP-1) neurons in the caudal brainstem. The present study examined whether central GLP-1 receptor signaling plays a functional role in LPS-induced fever. Adult male Sprague-Dawley rats were injected i.p. with LPS (0 or 100 microg/kg), then were infused intracerebroventricularly with GLP-1 receptor antagonist (0 or 10 microg) delivered 2.5 h after injection of LPS or vehicle. Core body temperature was measured at 30-min intervals for 6.5 h after LPS treatment. Consistent with previous reports, body temperature was significantly elevated within 90 min and remained elevated for the remainder of the monitoring period. The pyrogenic effect of LPS was amplified in rats that received central infusion of GLP-1 receptor antagonist, although the antagonist by itself did not alter body temperature. These findings suggest that endogenous GLP-1 acts at central receptors to limit the fever response in rats after i.p. administration of LPS.

Cytokines as endogenous pyrogens.

Cytokines are pleiotropic molecules mediating several pathologic processes. Long before the discovery of cytokines as immune system growth factors or as bone marrow stimulants, investigators learned a great deal about cytokines when they studied them as the endogenous mediators of fever. The terms "granulocytic" or "endogenous pyrogen" were used to describe substances with the biologic property of fever induction. Today, we recognize that pyrogenicity is a fundamental biologic property of several cytokines and hence the clinically recognizeable property of fever links host perturbations during disease with fundamental perturbations in cell biology. In this review, the discoveries made on endogenous pyrogens are revisited, with insights into the importance of the earlier work to the present-day understanding of cytokines in health and in disease.

Streptococcal pyrogenic exotoxin B induces apoptosis and reduces phagocytic activity in U937 cells.

Treatment of U937 human monocyte-like cells with Streptococcus pyogenes led to an induction of apoptosis in these cells. A comparison between the wild-type strain and its isogenic protease-negative mutant indicated that the production of streptococcal pyrogenic exotoxin B (SPE B), a cysteine protease, caused a greater extent of apoptosis in U937 cells. Further study using purified SPE B showed that this protease alone could induce U937 cells to undergo apoptosis, which was characterized by morphologic changes, DNA fragmentation laddering on the gel, and an increase in the percentages of hypodiploid cells. The protease activity of SPE B was required for apoptosis to proceed, since treatment with cysteine protease inhibitor E64 or heat inactivation abrogated this death-inducing effect. The SPE B-induced apoptosis pathway was interleukin-1beta converting enzyme (ICE) family protease dependent. Further experiments showed that the phagocytic activity of U937 cells was reduced by SPE B. Treatment with E64 and heat inactivation both abrogated this phagocytosis-inhibitory effect. Taken together, the present data show that SPE B not only possesses the ability to induce apoptosis in monocytic cells but also helps bacteria to resist phagocytosis by host cells.

Plasmodium falciparum produces prostaglandins that are pyrogenic, somnogenic, and immunosuppressive substances in humans.

Plasmodium falciparum causes the most severe form of human malaria, which kills approximately 1.5-2.7 million people every year, but the molecular mechanisms underlying the clinical symptoms and the host-parasite interaction remain unclear. We show here that P. falciparum produces prostaglandins (PGs) D2, E2, and F2alpha. After incubation with 1 mM arachidonic acid (AA), cell homogenates of P. falciparum produced PGs as determined by enzyme immunoassay and gas chromatography-selected ion monitoring. PG production in the parasite homogenate was not affected by the nonsteroidal antiinflammatory drugs aspirin and indomethacin, and was partially heat resistant, whereas PG biosynthesis by mammalian cyclooxygenase was completely inhibited by these chemicals and by heat treatment. Addition of AA to the parasite cell culture markedly increased an ability of the parasite cell homogenate to produce PGs and of parasitized red blood cells to accumulate PGs in the culture medium. PGD2 and PGE2 accumulated in the culture medium at the stages of trophozoites and schizonts more actively than at the ring stage. These findings are the first evidence of the direct involvement of a malaria parasite in the generation of substances that are pyrogenic and injurious to the host defenses. We will discuss a possible contribution of the parasite-produced PGs to pathogenesis and host-parasite interaction of P. falciparum.

Fever, temperature, and the immune response.

Fever's ability to manipulate the character and extent of physiological temperature gradients correlates with the unusual influence different physiological temperatures have upon model immune responses in vitro. This relationship may help to explain the remarkable evolutionary conservation of the febrile response to infection. A very restricted range of the upper physiological temperatures supports the activation of resting lymphocytes for proliferation and effector formation in the two major limbs of the immune system, cell-mediated immunity and humoral immunity. In contrast, once effectors are formed they can function in a fashion which is nearly independent of physiological temperature. This suggests that physiological temperature change acts to regulate the emergence of new immune responses but does not restrict the activity of existing effector mechanisms once they have been formed. The differential sensitivity of these processes to different physiological temperatures suggests that fever's biological purpose with respect to the immune system is the elimination of lower peripheral tissue temperatures rather than the elevation of core temperatures. However, further studies may reveal that some functions are amplified by the core temperature transitions while other functions are selectively regulated by peripheral tissue temperature transitions. The critical cell for the temperature dependence of immune responses seems to be the Th since its ability to produce cytokines is highly temperature dependent. In contrast, macrophages produce cytokines equally well at all temperatures except those of the febrile core, a feature which may serve to downregulate the production of endogenous pyrogens.

The toxins of group A streptococcus, the flesh eating bacteria.

Streptococcus pyogenes causes a wide variety of infections in individuals of all ages in most countries of the world. Because of the frequency with which these infections occur, physicians are quite familiar with the diversity of clinical presentations associated with the Group A streptococcus. Yet in the late 1980's, a severe form of streptococcal infection, the Streptococcal Toxic Shock Syndrome, emerged and has persisted for the last 10 years. This syndrome is associated with invasive soft tissue infections and the early onset of shock and organ failure. The purpose of this paper is to briefly describe the epidemiologic and clinical features of the Streptococcal Toxic Shock Syndromes and to emphasize the role that toxins produced by S. pyogenes play in the pathogenesis of this disease.

Perioperative fever.

Unlike normal thermoregulatory control, which is largely neuronally mediated, fever is activated by circulating pyrogens. Pyrogens are triggered by either infectious or non-infectious etiologies, all of which may be present in patients undergoing ambulatory surgery. Fever is a regulated elevation in the setpoint temperature for all thermoregulatory responses (warm and cold defenses). To increase core temperature according to the newly elevated setpoint, cold defenses such as vasoconstriction and shivering are activated. In contrast, anesthesia widens the interthreshold range, thus resulting in hypothermia. As a result, general anesthesia impairs the febrile response to pyrogenic stimulation. However, the precise nature of the interaction between fever and anesthesia has yet to be determined. Postoperative fever continues to be a major problem. Wound infections are responsible for many such fevers, although numerous other etiologies contribute. Initial diagnosis should thus focus on determining the etiology of fever. Once that is established, treatment can focus on the specific cause.

Thermoregulation and the pathogenesis of fever.

Infections, trauma, inflammatory processes, and some malignant diseases induce a constellation of host responses that are collectively referred to as the "acute-phase response." Elevation of core temperature is certainly part of the acute-phase response, and cytokines that raise core temperature in pathologic states are some of the same cytokines that account for other manifestations of the acute-phase response. This article examines fever as a part of the acute-phase reaction and the role of cytokines in thermoregulation.

Thermoregulation and hyperthermia.

Despite minor daily and monthly cyclical variations, body temperature remains relatively constant. Core temperature is maintained by thermoregulatory responses such as sweating, vasoconstriction and shivering, which are largely controlled by the hypothalamus. Within the hierarchy of neural structures regulating autonomic thermoregulatory responses, the preoptic area of the anterior hypothalamus plays a dominant role. In contrast, the posterior hypothalamus mediates behavioral defenses. Neurons in both regions sense core temperature and integrate central and peripheral thermal information. The setpoint temperature is then determined by relative synaptic inputs to warm-sensitive, cold-sensitive, and temperature-insensitive neurons. Fever is a regulated elevation in the preoptic setpoint temperature. Endogenous pyrogens and other fever mediators inhibit preoptic warm-sensitive neurons that normally facilitate heat loss and suppress heat production. This elevates the setpoint temperature for all thermoregulatory responses and activates cold-defenses such as vasoconstriction (which decreases heat loss) and shivering (which increases metabolic heat production). When pyrogen concentrations decrease, the setpoint temperature returns towards normal, triggering active vasodilation and sweating, which increases heat loss from the skin surface. The increasing phase of fever is often associated with shivering, which can markedly increase heart rate and cardiac output. Defervescence (and passive hyperthermia) is also often accompanied by tachycardia resulting from active precapillary vasodilation. Thus, cardiovascular complications are common throughout the febrile course and constitute the major clinical consequence of fever.

Pyrogenic activity of human native and human recombinant interleukins-1 beta: stabilization with albumin enhances the pyrogenic action of recombinant IL-1 beta delivered into the rabbit brain.

The pyrogenic potential of natural and recombinant human IL-1 beta in rabbits was found to be very similar when the substances were given intravenously. Under these conditions, stabilization of rIL-1 beta with human serum albumin (HSA) failed to affect the pyrogenic activity of recombinant IL-1 beta. When the two preparations were administered directly into the PO/AH area of the brain, recombinant IL-1 beta was less pyrogenic than its natural counterpart. This lower pyrogenicity of recombinant IL-1 beta was corrected if the injected material contained HSA, which is known to stabilize in vitro the biological activities of IL-1 beta against slow degradation. The possibility is now considered that the central and peripheral systems for IL-1 inactivation are different. The existence of an intrabrain IL-1 pool is suggested and its significance for neuroimmunomodulation is stressed.

Fever: friend or foe?

Fever is one of the most common manifestations of disease. The patients' relatives and physicians' concern about it is due to the fact that fever reflects that something in the body is not working well. However, the question on fever as convenient or harmful is not yet completely answered. The porpose of this paper is to examine the arguments on both sides and to guide on the convenience of antipyretic treatment

Microbial cell-wall contaminants in peptides: a potential source of physiological artifacts.

Microbial cell-wall products (MCWP) such as endotoxins are easily introduced into peptides produced under standard laboratory conditions. Because these products stimulate the induction of cytokines and other mediators, which, in turn, trigger a broad range of physiological responses. MCWP in peptide preparations are potential sources of artifacts. This brief tutorial outlines the physical/chemical nature of MCWP, some of their sources, their physiological effects, and a simple method to control for them in some peptide preparations.

[The action of pyrogenal and endogenous pyrogen on visceral afferent systems]. / Deistvie pirogenala i éndogennogo pirogena na vistseral'nye afferentnye sistemy.

Pyrogenal in the dose 5 mcg increased the adrenaline release in dogs. Interleukin-1 increased the noradrenaline release. Neither capsaicin, nor M- and N-cholinoreceptor blockade, nor pre-decentralization of the inferior mesenteric ganglion, abolished the effects. Mechanical and chemical stimuli during continuous perfusion of the colon with subliminal doses of pyrogenal increased the adrenaline release, too. A possible direct effect of endotoxins on peripheral adrenergic neurons, is discussed.