Fever and trace metal changes in endotoxin-challenged neonates

Tumor necrosis factor and interferon activity in the circulation of calves after repeated injection of low doses of lipopolysaccharide

The effect of two intravenous (i.v.) injections of low doses of lipopolysaccharide (LPS)(0.1 microgram/kg of body weight) administered at 7-day intervals on the systemic release of tumor necrosis factor (TNF) and interferon (IFN), on the rectal temperature, breathing and heart rate, and on packed cell volume (PCV), plasma glucose concentration, white blood cell (WBC) counts in 3-week-old calves, was estimated. The first injection of LPS caused a significant increase in breathing and heart rate, rectal temperature, prolonged hypoglycemia and leukopenia, but no significant changes in PCV were observed. TNF and IFN activity peaked at 2 h after LPS injection and disappeared from circulation by 4 h and 5 h, respectively. After the second injection of LPS, the reaction of calves was similar to that observed after the first injection, however, the breathing rate and TNF systemic production were significantly reduced. The results obtained indicate that a low dose of LPS leads to the development of 'late' tolerance manifested by hyporeactivity to TNF production but with maintained responsivity to IFN production, pyrogenic, hypoglycemic and leukemic response to the second injection of LPS. In conclusion, these results demonstrate that the tolerance response is not universal to all hematologic and immunologic parameters, and that the response needs to be evaluated with respect to the specific variable.

Infection-induced anorexia: active host defence strategy

In association with fever production, decreased food consumption is the most common sign of infection. This effect is often regarded as an undesirable manifestation of sickness. However, evidence suggests that just as many behaviours have now been shown to modify immunocompetence, infection-induced anorexia is a behaviour systematically organised for pathogen elimination. That is, anorexia is an active defence mechanism that is beneficial for host defence. This review details the mechanism of infection-induced anorexia, placing it within the framework of the intricately organised acute phase response--the host response to infection. Furthermore, the evolutionary, behavioural, metabolic and immunological consequences of infection-induced anorexia are outlined, each providing evidence for the beneficial nature of this response. The evidence suggests that food restriction is one of the important behavioural strategies that organisms have evolved for the fight against pathogenic invasion. Nevertheless, such benefits require fine homeostatic control, as chronic undernutrition has deleterious consequences for host defence.

Paradoxical conditioning of the plasma copper and corticosterone responses to bacterial endotoxin

The cascade of physiologic mechanisms in response to infection, the acute phase response, is recognized as having a major role in host defense. Two such responses are an increase in plasma copper and activation of the hypothalamic-pituitary-adrenal axis, which are consistently reported to occur during bacterial infection. We aimed to determine whether the alterations in plasma copper and corticosterone were conditionable using the conditioned taste aversion paradigm. The regime involved the pairing of a novel-tasting saccharine solution (the conditioned stimulus) with lipopolysaccharide (the unconditioned stimulus). Seven days after the initial pairing of these stimuli (the test day), the saccharine solution was represented. Animals exposed to this condition displayed a significant decrease in plasma copper levels. In addition, these rats experienced a reduction in plasma corticosterone that was time dependent. Paradoxically, the conditioned response of both these variables were in a direction contrary to that reported during bacterial infection. These results suggest that some acute phase responses may condition as a rebound response, or in an opposing trend to that occurring as the initial reaction.

Behavioral conditioning of endotoxin-induced plasma iron alterations

The cascade of physiologic mechanisms in response to infection, the acute-phase response, is recognized as playing a major role in host defence. One such response is the hypoferremia that is consistently reported to occur during bacterial infection. This study aimed to determine whether the alterations in plasma iron were conditionable using the conditioned taste aversion (CTA) paradigm. The regime involved the pairing of a novel-tasting saccharin solution with bacterial endotoxin. Seven days after the initial pairing of these stimuli (the test day), the saccharin solution was represented. Animals exposed to this condition displayed a significant reduction in the level of plasma iron. Animals treated with an intraperitoneal dose of 400 micrograms/Kg lipopolysaccharide (LPS) displayed lower conditioned iron levels than rats infused with 100 micrograms/Kg LPS; however, this difference was not significant. These results showed that in addition to other acute-phase responses (fever and anorexia), plasma iron alterations are able to be manipulated through behavioral manipulations.

Body temperatures of lambs and their mothers measured by radio-telemetry during parturition

Using temperature-sensitive radio-telemeters chronically implanted in the abdomens of 8 fetal lambs and their mothers, we measured body temperature changes induced by parturition. Maternal body temperature rose at 0.70 +/- 0.06 degrees C/hour (mean +/- SEM) in the final stages of labour. Fetal body temperature also rose, but at a significantly lower rate, 0.45 +/- 0.06 degrees C/hour (p < 0.05). The fetus appears to be protected from excessive hyperthermia during the birth process.

Fever: causes and consequences

The present review distinguishes pathogenic, neurogenic, and psychogenic fever, but focuses largely on pathogenic fever, the hallmark of infectious disease. The data presented show that a complex cascade of events underlies pathogenic fever, which in broad outline - and with frank disregard of contradictory data - can be described as follows. An invading microorganism releases endotoxin that stimulates macrophages to synthesize a variety of pyrogenic compounds called cytokines. Carried in blood, these cytokines reach the perivascular spaces of the organum vasculosum laminae terminalis (OVLT) and other regions near the brain where they promote the synthesis and release of prostaglandin (PGE2). This prostaglandin then penetrates the blood-brain barrier to evoke the autonomic and behavioral responses characteristic of fever. But then once expressed, fever does not continue unchecked; endogenous antipyretics likely act on the septum to limit the rise in body temperature. The present review also examines fever-resistance in neonates, the blunting of fever in the aged, and the behaviorally induced rise in body temperature following infection in ectotherms. And finally it takes up the question of whether fever enhances immune responsiveness, and through such enhancement contributes to host survival.

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 microgram/kg), a Gram-negative bacterial pyrogen, and the cell walls of Staphylococcus aureus (1 x 10(9), 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.

Effect of ambient temperature and E. coli endotoxin upon the plasma iron level in wild house mice in winter season

The effects of ambient temperatures of 10 degrees C and 30 degrees C and of E. coli endotoxin on brain temperature and plasma iron level were investigated in unrestrained wild house mice, Mus musculus. In control animals (i.p. saline-injected) exposed to cold environment the brain temperature decreased and plasma iron levels were lower than those observed under thermoneutral conditions (30 degrees C). Animals injected i.p. with endotoxin (0.5 micrograms.kg-1) and placed at 30 degrees C showed a drop in plasma iron level during the fever episode. The results provide strong evidence for a relationship between brain temperature and plasma iron level in control mice under thermoneutral conditions, and show that during cold exposure or after injection of endotoxin, there is no linear correlation between brain temperature and plasma iron. Moreover, it was found that cold stress influences plasma iron level and that this influence is not mediated by changes in brain temperature.

Hypozincemia during fever may trigger febrile convulsion

Febrile convulsions are generally thought to be induced by metabolic changes during the rise-phase of body temperature. The mechanism by which convulsions are induced, however, is not fully elucidated. In this article, we propose a new hypothesis about the induction mechanism of febrile convulsions that takes into account the hypozincemia during fever. This hypozincemia activates the NMDA receptor, one of the glutamate family of receptors, which may play an important role in the induction of epileptic discharge.

Clinical, haematological and blood biochemical changes in goats after experimental infection with tick-borne fever

Tick-borne fever in goats caused by Ehrlichia (Cytoecetes) phagocytophila was characterised by high fever, dullness, anorexia, tachycardia and a slight to moderate inhibition of rumen motility. The animals developed a gradual decline in the total number of circulating white blood cells. There was a decrease in lymphocytes over a short period, followed by an increase. The number of neutrophils was higher on the 3rd day, causing considerable change in the lymphocyte:neutrophil ratios. The number of eosinophils increased slightly. Serum alkaline phosphatase (ALP) decreased during the febrile episodes, and a marked decline was observed in both plasma zinc and iron concentrations. Furthermore, there was a small but progressive decrease of haemoglobin and haematocrit values. Circulating endogenous pyrogen/leucocyte endogenous mediator could not be detected in plasma from febrile goats. Tick-borne fever was passively transmitted to kids with plasma obtained from these febrile animals.

Fever and changes in plasma zinc and iron concentrations in the goat: the role of leukocytic pyrogen

In goats with trypanosomiasis (T. vivax or T. congolense) no marked fall in plasma zinc concentration was seen despite high temperature peaks, whereas plasma concentrations of iron tended to undergo some decline. In goats infected with Ehrlichia phagocytophila, there was a marked decline in plasma zinc and iron to low values on the 3rd and 4th day, respectively. Circulating endogenous pyrogen (EP) or leukocytic endogenous mediator (LEM) could not be detected in plasma from febrile goats with tick-borne fever. The intravenous injection of leukocytic pyrogen (LP) in kids caused characteristic monophasic febrile reactions, whereas no significant changes in plasma trace metals were found. So, previous evidence purporting to show that LP is similar to or may be identical with LEM is demonstrably inconclusive. Intravenous injection of E. coli lipopolysaccharide (LPS) or staphylococcal enterotoxin B (SEB) induced fever and lowering of plasma zinc and iron concentrations. The decrease in those trace metal values was more persistent in goats given SEB than in those given E. coli LPS. After intramammary infusion of SEB or E. coli LPS, fever and significant decreases in plasma zinc and iron concentrations were observed but no clear relationship was found between the temperature responses and the alterations in plasma trace metal concentrations. Furthermore, the decrease in plasma iron concentration developed more rapidly in goats given SEB than in those given E. coli LPS, whereas the decrease in plasma zinc concentrations in the former was more delayed. These data support the theory that the concentrations of zinc and iron in plasma are regulated by different mechanisms, whereas febrile reactions are mediated by another type of endogenous protein.

Differential acute-phase responses in febrile and cold- and heat-exposed rabbits

Endotoxin (LPS) characteristically provokes both fever and the acute-phase reaction (APR). The present studies were undertaken to determine whether these two responses are mutually dependent or controlled separately. Rabbits were injected with LPS (2 micrograms/kg, IV) or exposed to heat (37 +/- 1 degree C) such that the patterns and magnitudes of the body temperature (Tco) rises (1.6 +/- 0.5 degrees C) were similar. While the plasma levels of Fe and Zn decreased, and those of Cu and N-acetylneuraminic acid (NANA) increased significantly after LPS-induced fever, no such changes occurred after heat-induced hyperthermia. In subsequent study, different rabbits were exposed to cold (3 +/- 1 degree C), first furred, then sheared. While furred, they thermoregulated by cutaneous vasoconstriction, whereas, while shaved, they additionally increased their metabolic rates. However, in neither case were the plasma levels of Fe, Zn, Cu, or NANA different in comparison to their pre-cooling values (Ta = 22 +/- 1 degree C). It would seem, therefore, that the acute-phase blood responses to LPS (and ultimately, to endogenous pyrogen [EP]) probably are not mediated merely by the rise in the Tco or by the concomitantly induced vascular and/or thermogenic effectors of fever; but rather, the APR appears to be a regulated, separate response to LPS/EP.

Activation of acute-phase responses by intrapreoptic injections of endogenous pyrogen in guinea pigs

The acute-phase reaction (APR) is the concatenation of events that develops in response to infectious or other acute inflammatory stimuli. It includes fever and changes in plasma trace metal and glycoprotein levels. Endogenous pyrogen (EP) is believed to be the mediator of the APR. It acts within the preoptic-anterior hypothalamus (PO) to initiate fever; prostaglandins E (PGE) may modulate this action. To determine whether the nonfebrile responses to EP also are mediated by the PO and through PGE, guinea pigs were injected bilaterally intra-PO (iPO) with homologous EP (1 microliter) or PGE2 (0.1 microgram), and their colonic temperatures (Tco) and plasma iron (Fe), zinc (Zn), copper (Cu), and N-acetylneuraminic acid (NANA) levels were measured. For comparison, EP (2 ml) also was injected intraperitoneally (IP). Heat-denatured EP (delta EP) or pyrogen-free saline (PFS) was the corresponding control. Fevers were induced by IP EP (1.0 +/- 0.1 degrees C [mean +/- SD]), iPO EP (1.1 +/- 0.2 degrees C), and iPO PGE2 (1.4 +/- 0.2 degrees C); neither delta EP nor PFS was pyrogenic. Plasma Fe and Zn levels were decreased significantly after IP EP, but unchanged after iPO EP and PGE2. Plasma Cu and NANA levels were elevated significantly following both IP and iPO EP, but not after iPO PGE2. delta EP or PFS did not cause any changes, by either route. It appears, therefore, that EP-induced fever and rises in plasma Cu and NANA are mediated by the PO, while the decreases of plasma Fe and Zn are direct, peripheral effects. On the other hand, PGE2 appears to be involved only in the central febrile response. Indeed, guinea pigs, pretreated with indomethacin (5 mg/kg, IP), and injected iPO with EP or IP with S. enteritidis endotoxin (2 micrograms/kg), did not develop fever, but exhibited the rise in plasma Cu and NANA.

Suppression of fever after lesions of the anteroventral third ventricle in guinea pigs

Endogenous pyrogen (EP), injected systemically or intracerebrally, evokes fever and certain changes in plasma trace metal and glycoprotein levels which are characteristic of the acute-phase reaction. It is generally assumed that EP enters the brain from the blood, although it has not yet been demonstrated that EP crosses the blood-brain barrier (BBB). The possibility that EP might penetrate the brain through the organum vasculosum laminae terminalis (OVLT), which is outside of the BBB and located in close proximity to the medial preoptic region (MPO, the primary site sensitive to locally applied EP), was investigated by making electrolytic lesions (3 mA, 20 sec, anodal) in the anteroventral wall of the third ventricle of guinea pigs (AV3V-X). After 10 days, their febrile and selected acute-phase responses (plasma iron, zinc, copper, and sialic acid levels) to endotoxin (LPS, S. enteritidis, 2 micrograms/kg, IP), which induces EP production by the host, were measured; controls were sham-operated guinea pigs. LPS did not induce in the AV3V-X animals either fever or rises in plasma copper and sialic acid levels; however, as in the controls, it caused hypoferremia and hypozincemia. To exclude damage to the MPO as a cause of these responses, sham and AV3V-X guinea pigs were administered homologous EP intrapreoptically (1 microliter bilaterally). Comparable fevers developed in both groups of animals. Hence, the integrity of the AV3V region including the OVLT seems to be critical for the EP-induced elevations of both body temperature and plasma levels of acute-phase proteins, but not for the fall of plasma iron and zinc levels. It may be that EP passes into the brain through the OVLT.

Characterization of a leukocyte-derived endogenous mediator responsible for increased plasma fibrinogen

Fibrinogen has been the plasma protein most frequently studied after tissue injury. This report presents evidence that leukocytic endogenous mediator (LEM) from macrophages promotes fibrinogen synthesis. LEM has a molecular weight of 13,000-16,000, an isoelectric point (pI) at pH 7.3, is heat labile, and is inactivated by trypsin or sulfhydryl reactive agents. LEM not only promotes increased synthesis of acute phase proteins, but also causes increased neutrophilia and alterations in metal metabolism. There is considerable evidence that LEM may be the same protein as endogenous pyrogen and Interleukin 1 (IL-1). There was no increase in plasma fibrinogen when endotoxin was injected in C3H/HeJ mice; however, this strain of mice responded the same as normal mice to injections of LEM. This provides further evidence that LEM is the endogenous mediator for acute phase protein synthesis during tissue injury. The half-life of LEM is still circulation following its iv injection into rats was less than 10 minutes. There is still considerable doubt about the mechanism LEM uses in promoting increased hepatocyte synthesis of fibrinogen. Some evidence indicates a direct action of LEM upon the hepatocyte, whereas other data suggest an indirect role through other mediators or the central nervous system. In addition to LEM with pI of 7.3, there are proteins with a pI near 5 that will increase plasma fibrinogen. These proteins also have a molecular weight between 13,000 to 16,000 but do not have essential sulfhydryl groups. These proteins also have pyrogenic and IL-1 activities. LEM shows a limited amount of species specificity. For example, the pI 7 LEM prepared from human monocytes or rabbit peritoneal leukocytes will increase plasma fibrinogen in rats, mice, and rabbits; but the pI 5 LEM from rabbits is inactive in rats.