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

Systemic administration of lipopolysaccharide upregulates angiotensin II expression in rat renal tubules: immunohistochemical and ELISA studies

We investigated whether angiotensin II (AII) peptide is induced in the rat kidney under endotoxemic conditions. Immunohistochemistry revealed strong AII-like immunoreactivity in the renal tubules of rats given high-dose lipopolysaccharide (LPS; 1000 microg/kg) intraperitoneally (i.p.). AII-like immunoreactivity in renal tubules was slight at 1h after the LPS injection, but marked at 3 h. There were few signals in the kidney in saline-injected control rats. When injected at 0.1, 10, or 1000 microg/kg i.p., LPS-induced a dose-related increase in AII-like immunoreactivity in renal tubules that was unaffected by treatment with the prostaglandin-synthesis blocker indomethacin. ELISA measurement of the AII concentration in the whole kidney supported the above findings. These results suggest that systemically administered LPS induces AII peptide expression in renal tubules by a prostaglandin-independent mechanism.

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.

Modification of body temperature and sleep state using behavioral conditioning

Previous research has demonstrated the conditionability of events within the acute-phase response. This study examined whether two such responses, fever and sleep alterations, were conditionable in the rat during the dark photoperiod. The experimental animals were administered a novel saccharin solution as the conditioned stimulus (CS) in conjunction with lipopolysaccharide as the unconditioned stimulus (UCS). This group displayed significantly higher body temperatures than controls upon saccharin representation, 7 days after the original CS-UCS pairing. The experimental animals additionally displayed a conditioned increase in slow wave sleep (SWS); however, the LPS-induced reduction in rapid eye movement (REM) sleep was unable to be reenlisted. Similar to the acute-response, the conditioned alteration in SWS appeared to be due to an increase in episode frequency, rather than duration. These results suggest that the multiple acute-phase events may be simultaneously conditionable, producing an optimum environment for pathogen elimination.

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.

Effects of endotoxin, interleukin-1 beta and prostaglandin injections on fever response in broilers

1. The effect of endotoxin, interleukin-1 beta and prostaglandin on fever response was studied in 80 broilers (Hubbard strain). Endotoxin (E. coli, LPS) was injected i.v. (1.5 micrograms/kg) and icv (1.5 micrograms/bird); interleukin-1 (human recombinant IL-1 beta, 80 pg/bird) and prostaglandin E2 (5 micrograms/bird) were injected icv. Indomethacin (10 mg/kg, i.v.) pretreatment was also used before i.v. endotoxin injection. 2. The results showed that indomethacin was able to block the fever response induced by i.v. endotoxin injection, and IL-1 beta and PGE2 were both effective in producing fever when injected icv. These data suggest a prostaglandin-mediated fever response by broilers, and also a strong evidence of the involvement of endogenous pyrogen (interleukin-1) in fever response in birds.

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.

Leukotrienes in brain: natural occurrence and induced changes

Peptidoleukotrienes (SP-LTs) (both total product and individual LTC4 and LTE4 and LTB4 were measured by radioimmunoassay in cerebrospinal fluid (CSF) collected from the third ventricle of conscious cats. Total SP-LT was expressed as LTE4 after treating samples with crude gamma-glutamyltranspeptidase. Prostaglandin (PG) E2 and thromboxane (TX) B2, the stable metabolite of TXA2, were also assayed in part of the experiments. Under basal conditions, SP-LT and LTC4 were consistently measurable (respectively, 327 +/- 14 and 244 +/- 41 pg/ml), while native LTE4 was below the threshold of the assay (60-280 pg/ml) in most cases. LTB4 was barely detectable (30 +/- 2 pg/ml) or not detectable at all. PGE2 was normally less abundant than TXB2 (31 +/- 4 vs 281 +/- 47 pg/ml). Intracerebroventricular (i.c.v.) administration of arachidonic acid (40 microgram) caused a 4-fold increase in SP-LT levels which was relatively small and transient compared to PGE2 (76-fold) and TXB2 (23-fold), while there was no change in either native LTE4 or LTB4. A similar response was obtained with platelet-activating factor (PAF, 1 microgram i.c.v.), though SP-LT elevation (4-fold) was more persistent. A further rise in SP-LT (9-fold) was noted when PAF administration was preceded by indomethacin (500 microgram i.c.v.), whereas PAF effect was reversed by pretreatment with either the PAF antagonist, BN52021 (1 microgram i.c.v.), or the 5-lipoxygenase inhibitors, U-60,257 (75 micrograms i.c.v.) and L-651,392 (10 mg/kg p.o.). PAF was also effective in causing a 3-fold rise in LTC4. Unlike PAF, pyrogens (endotoxin i.c.v. or i.v.; interleukin-1 i.v.) at doses above threshold for fever had no effect on LT levels in CSF, both in the absence and presence of indomethacin pretreatment. We conclude that SP-LTs are a normal constituent of CSF, LTC4, being the major species. The response to PAF accords with a pathogenetic role of the compounds in inflammatory processes and the reactive changes to injury. No evidence was obtained for the involvement of SP-LTs in the central mechanism of fever.

Leucocytosis induced in rabbits by intravenous or central injection of granulocyte colony stimulating factor

1. We investigated the effect of intravenous, intracerebroventricular and intrapreoptic injections of human recombinant granulocyte colony stimulating factor (GCSF) on body temperature and acute phase responses in the rabbit, including changes in the plasma concentration of iron, zinc, copper and fibrinogen and in circulating leucocyte count. 2. Neither intravenous nor intracerebroventricular injection of GCSF had any effect on the body temperature. 3. Both the intravenous and the intracerebroventricular injections of GCSF induced a dose-dependent increase in the circulating leucocyte count but neither affected the plasma concentration of iron, zinc, copper and fibrinogen. Furthermore, intrapreoptic injection of GCSF produced leucocytosis but had no effect on the red blood cell count. 4. The present results suggest that GCSF induces leucocytosis through its action on both the peripheral target organs and the central nervous system.

Neuromodulative actions of cytokines

Interleukin 1, interferon alpha 2, and tumor necrosis factor alpha are cytokines that centrally mediate various reactions typical of the host defense responses to infection. The preoptic-anterior hypothalamus is an important, but not exclusive, integrative and controlling region for several of these effects. Although these cytokines display some common functional activities (e.g., pyrogenicity, somnogenicity), the characteristics of the responses they induce are different. Their effects, moreover, can be evoked or suppressed selectively, indicating that the neuronal substrates and/or neuromodulators used are distinct, each possessing discrete but partially overlapping sensory combinations. Nevertheless, it is not yet obvious how these systems are organized and integrated in host defense. It is also unclear whether these cytokines are elaborated peripherally and gain access to the brain or whether they are induced centrally. The available data suggest that circulating cytokines probably do not penetrate the brain but may activate elements in the organum vasculosum laminae terminalis. This site appears to be critically important for the production of the centrally mediated effects of blood-borne cytokines; it is speculated that the cytokines evoke there local signals that transduce their message; serotonin may be linked to these signals.

Brain regions involved in the development of acute phase responses accompanying fever in rabbits

1. The effects of microinjection of rabbit endogenous pyrogen and human recombinant interleukin-1 alpha on rectal temperature and acute phase responses were extensively examined in forty different brain regions of rabbits. The acute phase responses that were investigated were the changes in plasma levels of iron, zinc and copper concentration and the changes in circulating leucocyte count. 2. The rostral hypothalamic regions, such as nucleus broca ventralis, preoptic area and anterior hypothalamic region, responded to the microinjection of endogenous pyrogen or interleukin-1 by producing both fever and acute phase responses. 3. The microinjection of endogenous pyrogen or interleukin-1 into the rostral hypothalamic regions significantly decreased the plasma levels of iron and zinc concentration 8 and 24 h after injection. The circulating leucocyte count increased 8 h after injection. However, neither the injections of endogenous pyrogen nor interleukin-1 affected the number of red blood cells. 4. The present results show that the rostral hypothalamic regions respond directly to endogenous pyrogen or interleukin-1 with the consequent development of fever and acute phase responses.

Possible involvement of prostaglandin E in development of ACTH response in rats induced by human recombinant interleukin-1

1. Intravenous (I.V.) injection of human recombinant interleukin-1 alpha (IL-1 alpha) produced dose-dependent monophasic fevers in rats. Moreover, the I.V. injection of IL-1 alpha produced dose-dependent rises in the plasma concentrations of adrenocorticotrophic hormone (ACTH) 30 min after injections with dosages of 5 micrograms/kg and 15 micrograms/kg of IL-1 alpha. 2. The febrile responses induced by the I.V. injection of IL-1 alpha (15 micrograms/kg) were completely abolished, and conversely hypothermia occurred, when the animals were pre-treated with a cyclo-oxygenase inhibitor, indomethacin (INDO). Pre-treatment with INDO also inhibited the increase in the plasma concentrations of ACTH induced by I.V. injection of IL-1 alpha (15 micrograms/kg), indicating that enhancement of plasma concentrations of ACTH induced by I.V. injection of IL-1 alpha is processed through the action of prostaglandins. 3. Intrapreoptic injection of prostaglandin E2 produced a dose-dependent fever with a rapid onset at doses of 25 and 100 ng. Moreover, the intrapreoptic injection of prostaglandin E2 increased the plasma concentrations of ACTH in a dose-dependent manner 30 min after injections. 4. The intrapreoptic injection of IL-1 alpha (20 ng) caused slow monophasic fever. However, no significant elevation of plasma concentrations of ACTH was observed 30, 90 and 180 min after the intrapreoptic injection of IL-1 alpha, as compared with the ACTH levels at each time in the control group which received an intrapreoptic injection of saline. 5. These results suggest that intrapreoptic prostaglandin E plays an important role in the ACTH response by inducing the release of corticotrophin-releasing factor (CRF).

Leukocytosis induced by microinjection of endogenous pyrogen or interleukin-1 into the preoptic and anterior hypothalamus

We investigated the effect of microinjection of endogenous pyrogen or interleukin-1 (EP/IL-1) into 40 selected brain regions on the circulating leukocyte count in rabbits. The results show that injections into the rostral region of the hypothalamus, especially the preoptic and anterior hypothalamus, induce leukocytosis.