Neuropeptide alpha-MSH antagonizes IL-6- and TNF-induced fever.

The pro-opiomelanocortin-derived peptide melanocyte stimulating hormone (alpha-MSH) antagonizes the fever induced by several stimuli including endotoxin, endogenous pyrogen, and certain cytokines. To determine if alpha-MSH can antagonize the pyrogenic action of recombinant IL-6 and TNF directly within the central nervous system, the cytokines were injected with and without alpha-MSH (200 ng) into a lateral cerebral ventricle of rabbits and rectal temperature was monitored continuously. Central administration of both cytokines caused fever. However, when alpha-MSH was injected after cytokine administration, the fevers were markedly reduced. The results are consistent with previous observations on the antipyretic effect of alpha-MSH and they show that the peptide can act within the brain to antagonize pyrogenic actions of specific cytokines believed to be important in CNS mediation of fever.     

Antipyretic properties of centrally administered α-MSH fragments in the rabbit

alpha-Melanocyte stimulating hormone (alpha-MSH 1-13) has marked antipyretic effects when administered centrally or peripherally in small doses. A C-terminal fragment, alpha-MSH (11-13), contains an antipyretic message sequence of alpha-MSH; however, the lesser potency of this fragment relative to that of the entire molecule suggests that other amino acids of the alpha-MSH sequence are essential for the full antipyretic effect. Graded doses of alpha-MSH (11-13) (Ac LysProVal NH2), alpha-MSH (10-13) (Ac GlyLysProVal NH2), and alpha-MSH (8-13) (Ac ArgTrpGlyLysProVal NH2), were injected into the cerebral ventricles of rabbits made febrile by IV administration of crude interleukin-1. All three fragments reduced fever in a dose-related manner. The (8-13) sequence was much more effective than the other two fragments, and the (10-13) portion was less effective than the (11-13) tripeptide. None of the fragments was as potent as alpha-MSH (1-13). The results confirm that an antipyretic message resides within alpha-MSH (11-13) and sequential addition of amino acids to alpha-MSH (11-13) can both enhance and reduce the potency of the fragment.     

Intravenous alpha-MSH reduces fever in the squirrel monkey

alpha-MSH reduces fever in rabbits when administered IV, ICV, or by gavage; however, the applicability of this finding to higher species, specifically to primates, has not been determined. In this study, we chose the squirrel monkey as an appropriate primate model since it responds reliably to peripheral administration of bacterial endotoxins that cause fever in man. From pilot studies, doses of S. typhosa endotoxin necessary to produce maximum fever and doses of alpha-MSH which did not cause hypothermia were determined for each animal. In the main experiments endotoxin was given via an indwelling catheter in the saphenous vein, followed by alpha-MSH injections when the rectal temperature increased 0.3 degrees C. alpha-MSH (100-400 micrograms) reduced the area under the fever curve an average of 50.0%, but had no effect on afebrile temperature. Molar equivalent amounts of the antipyretic drug acetaminophen had little effect on fever. These findings support the idea, based on research on rabbits, that alpha-MSH has a role in central modulation of fever.     

Antipyretic activity of a potent alpha-MSH analog

[Nle4,D-Phe7]-alpha-MSH has exceptional potency in certain biological assays of alpha-MSH activity such as skin darkening in frogs. However, this analog was equipotent to alpha-MSH in induction of grooming in the rat and had opposite effects on the performance of a visual discrimination task. These results led to the suggestion that distinct differences may exist between the melanocyte and CNS receptors for alpha-MSH. We determined the antipyretic and hypothermic potencies of centrally and peripherally administered [Nle4,D-Phe7]-alpha-MSH, relative to those of alpha-MSH, in the rabbit. Central injections of 40 and 80 ng of [Nle4,D-Phe7]-alpha-MSH caused hypothermia in afebrile rabbits, whereas 20 and 10 ng, which had no effect on afebrile body temperature, caused greater than 40% reduction in leukocytic pyrogen-induced fever. These results indicate that this analog is approximately 10 times more potent in reducing fever than alpha-MSH, making it the most potent antipyretic substance yet described. In contrast, IV administration of 16 micrograms of the analog, an extremely large dose relative to established antipyretic doses of alpha-MSH, elicited weak, variable responses. Since this analog is said to be resistant to degradation by serum enzymes, the contrast between the effects of central and peripheral administration may reflect a limited ability of the analog to cross the blood brain barrier when given IV. Our results do not suggest any distinct differences between the melanocyte receptors for alpha-MSH and those involved with CNS control of temperature. The marked central potency of [Nle4,D-Phe7]-alpha-MSH could result from an increased duration of action and/or a greater affinity for central receptor sites relative to alpha-MSH.     

A discrete mode of the antipyretic action of AVP, alpha-MSH and ACTH.

The antipyretic effect of AVP, alpha-MSH and ACTH consists in lowering the thermoregulatory threshold and in shortening the time span of the fever. Thus, neuropeptides influence activity of hypothalamic neurones regulating body temperature. This was confirmed by recent experiments of Moravec (this volume) which indicate that spontaneous activity and thermosensitivity of neurones in hypothalamic slices can be influenced, by AVP. Why neuropeptides of different chemical structure such as AVT, on one hand, and alpha-MSH and ACTH, on the other hand, induce the same effect on thermoregulation remains to be elucidated.     

Effect of heat stress on LPS-induced febrile response in D-galactosamine-sensitized rats

We have previously reported that heat conditioning augments lipopolysaccharide (LPS)-induced fever in rats, which is accompanied by an accumulation of heat shock protein (HSP) in the liver and the reduction of the plasma level of tumor necrosis factor (TNF-alpha) (Kluger MJ, Rudolph K, Soszynski D, Conn CA, Leon LR, Kozak W, Wallen ES, and Moseley PL. Am J Physiol Regulatory Integrative Comp Physiol 273: R858-R863, 1997). In the present study we have tested whether inhibition of protein synthesis in the liver can reduce the effect of this heat conditioning on the LPS-induced febrile response in the rat. D-galactosamine (D-gal) was used to selectively inhibit liver protein synthesis. D-gal (500 mg/kg) or PBS as control was administered intraperitoneally 1 h before heat stress. LPS (50 microg/kg ip) was injected 24 h post-heat exposure. Treatment with D-gal blunted the febrile response to LPS. Moreover, heat-conditioned rats treated first with D-gal and subsequently with LPS demonstrated a profound fall in core temperature 10--18 h post-LPS. A significant increase of serum TNF-alpha accompanied this effect of D-gal on fever. Heat-conditioned animals receiving D-gal showed an inhibition in inducible HSP-70 in the liver. These data support the role of hepatic function in modulating the febrile response to LPS.     

α-黑色素细胞刺激素对白细胞介素-1β发热的解热机理研究

本研究观察了α－黑色素细胞刺激素（α－ＭＳＨ）对家兔白细胞介素－１β（ＩＬ－１β）发热效应及下丘脑组织腺苷环－磷酸（ｃＡＭＰ）含量的影响;同时观察了下丘本外培养过程中,α－ＭＳＨ对ＩＬ－１β刺激下丘脑释放ｃＡＭＰ的影响。结果显示：α－ＭＳＨ能显著降低ＩＬ－１β引起的体温升高（Ｐ〈０．０５）;同时抑制下丘脑组织ｃＡＭＰ含量的增高（Ｐ〈０．０１）。ＩＬ－１β与下丘脑组织培养,其上清液的ｃＡＭＰ含量明显     

The effect of α-MSH on fever caused by Staphylococcus aureus cell walls in rabbits

The role of endogenous pyrogens induced by gram-positive bacterial pyrogens is not known. Intravenous alpha-MSH (2.5 micrograms) significantly reduced only the first phase of the biphasic thermal response to IV S. aureus cell walls (5 x 10(7)). Intracerebroventricular alpha-MSH (200 ng) had no effect on the fever response. The fall in serum iron concentration was significantly attenuated by the IV alpha-MSH but was not affected by the ICV alpha-MSH. Intravenous alpha-MSH had no effect on fever or the serum iron response caused by muramyl dipeptide (MDP). We conclude that the first phase of the thermal response to S. aureus cell walls is mediated by an endogenous pyrogen (EP) and the second phase of the response by a mechanism not involving EP, but possibly a muramyl peptide.     

Antipyretic effect of centrally administered CRF

CRF injected into the third cerebral ventricle (0.5-2.5 micrograms) caused dose-related reductions in fever induced in rabbits by IV administration of leukocytic pyrogen. Control injections of CRF when the same animals were afebrile did not alter normal body temperature. Intravenous injections of 5 and 20 micrograms CRF, doses known to release ACTH and corticosteroids into the bloodstream in other species, did not reduce fever. CRF injected into the cerebral ventricles may be antipyretic per se, or it may reduce fever by virtue of central release of the antipyretic peptides ACTH and alpha-MSH.     

The effects of pentoxifylline on lipopolysaccharide (LPS) fever, plasma interleukin 6 (IL 6), and tumor necrosis factor (TNF) in the rat

The purpose of these studies was to test whether pentoxifylline, a drug that can inhibit the production and action of cytokines hypothesized to be endogenous pyrogens (for example, interleukin 1 and tumor necrosis factor [TNF]), is antipyretic. We also tested the effects of pentoxifylline on plasma activities of interleukin 6 (IL 6) and TNF in response to an injection of a fever-inducing dose of lipopolysaccharide (LPS). Our results showed that a high dose of pentoxifylline (200 mg/kg) caused hypothermia in control rats and blocked LPS fever, while a low dose (50 mg/kg) did not have these effects. Injection of the high dose of pentoxifylline in control rats caused a rise in plasma IL 6 but not in plasma TNF. However, the peak levels of plasma IL 6 and TNF activities following an injection of LPS were significantly reduced by pretreatment with pentoxifylline. Overall, the data are consistent with the hypothesis that pentoxifylline is an antipyretic drug, which may act at least in part by inhibiting the secretion of pyrogenic cytokines.     

Genetic Models in Applied Physiology. Differential role of nitric oxide synthase isoforms in fever of different etiologies: studies using Nos gene-deficient mice.

Male C57BL/6J mice deficient in nitric oxide synthase (NOS) genes (knockout) and control (wild-type) mice were implanted intra-abdominally with battery-operated miniature biotelemeters (model VMFH MiniMitter, Sunriver, OR) to monitor changes in body temperature. Intravenous injection of lipopolysaccharide (LPS; 50 microg/kg) was used to trigger fever in response to systemic inflammation in mice. To induce a febrile response to localized inflammation, the mice were injected subcutaneously with pure turpentine oil (30 microl/animal) into the left hindlimb. Oral administration (gavage) of N(G)-monomethyl-l-arginine (l-NMMA) for 3 days (80 mg. kg(-1). day(-1) in corn oil) before injection of pyrogens was used to inhibit all three NOSs (N(G)-monomethyl-d-arginine acetate salt and corn oil were used as control). In normal male C57BL/6J mice, l-NMMA inhibited the LPS-induced fever by approximately 60%, whereas it augmented fever by approximately 65% in mice injected with turpentine. Challenging the respective NOS knockout mice with LPS and with l-NMMA revealed that inducible NOS and neuronal NOS isoforms are responsible for the induction of fever to LPS, whereas endothelial NOS (eNOS) is not involved. In contrast, none of the NOS isoforms appeared to trigger fever to turpentine. Inhibition of eNOS, however, exacerbates fever in mice treated with l-NMMA and turpentine, indicating that eNOS participates in the antipyretic mechanism. These data support the hypothesis that nitric oxide is a regulator of fever. Its action differs, however, depending on the pyrogen used and the NOS isoform.     

Role of cytochrome P-450 in endogenous antipyresis

In previous reports, we (15, 18) and others (29) demonstrated data showing that various inhibitors of cytochrome P-450/epoxygenase augment fever in rats and mice, indicating that the enzyme may be involved in endogenous antipyresis. The aim of this study was to further test the hypothesis that the P-450-dependent epoxygenase pathway of arachidonic acid is part of the homeostatic system to control the height of fever. Sprague-Dawley rats were implanted with biotelemeters to monitor body temperature. Fever was induced by intraperitoneal injection of lipopolysaccharide (LPS; 80 microg/kg). We demonstrate that intraperitoneal administration of P-450 inducers (bezafibrate and dehydroepiandrosterone, 10 and 100 mg/kg) before LPS reduced fever in rats in a dose-dependent manner. In complementary experiments, rats were implanted with brain cannulas in addition to the biotelemeters. Various isomers of epoxyeicosanoids were administered into the lateral ventricle at doses of 0.01 to 10 microg/rat to test their influence on LPS-induced fever in rats. Four of five isomers were antipyretic in a dose-dependent manner. The most potent antipyretic isomers were 11, 12-epoxyeicosatrienoic acid (EET) followed by 14,15-EET, 8,9-EET, and 12(R) hydroxyeicosatetraenoic acid. These data support the hypothesis that the cytochrome P-450/epoxygenase pathway of arachidonate metabolism is part of the endogenous antipyretic system.     

Alpha-MSH peptides inhibit acute inflammation induced in mice by rIL-1 beta, rIL-6, rTNF-alpha and endogenous pyrogen but not that caused by LTB4, PAF and rIL-8.

The neuropeptide alpha-melanocyte stimulating hormone [alpha-MSH(1-13)] occurs in the pituitary, brain, skin and other tissues and receptors for this molecule are likewise widespread. In previous research, this tridecapeptide, which shares its amino acid sequence with ACTH(1-13), was shown to have both potent antipyretic activity and a role in the endogenous control of the febrile response. alpha-MSH(1-13) and its COOH-terminal tripeptide were subsequently found to inhibit inflammation induced by general stimuli such as topical application of an irritant. The aim in the present experiments was to determine if these peptides can inhibit acute inflammatory responses induced in mice by injection of individual cytokines, endogenous pyrogen (EP), a natural cytokine mixture, and other mediators of inflammation. Inflammation induced in the mouse ear by rIL-1 beta, rIL-6 or rTNF-alpha was inhibited by alpha-MSH and a D-valine-substituted analog of alpha-MSH(11-13) whereas substantial doses of alpha-MSH(1-13) did not alter inflammation induced by LTB4, PAF and IL-8. Both peptides inhibited edema caused in the mouse paw by local injection of EP. The results indicate that alpha-MSH molecules antagonize the actions of certain cytokine mediators of inflammation, consistent with previous observations of anti-cytokine activity of these peptides. Failure to inhibit edema caused by LTB4, PAF and IL-8 suggests that, in inflammation induced by general stimuli, such as EP, the peptides act prior to the release of these mediators of the inflammatory response. Because of the anticytokine/anti-inflammatory actions of the alpha-MSH molecules they may be useful in understanding the cytokine network and for treatment of inflammatory diseases.     

Antipyretic effect of arginine vasotocin in toads

Arginine vasotocin (AVT) is a nonmammalian analog of the mammalian hormone arginine vasopressin (AVP). These peptides are known for their antidiuretic and pressor effects. More recently, AVP has been recognized as an important antipyretic molecule in mammals. However, no information exists about the role of AVT in febrile ectotherms. We tested the hypothesis that AVT is an antipyretic molecule in the toad Bufo paracnemis. Toads equipped with a temperature probe were placed in a thermal gradient, and preferred body temperature was recorded continuously. A behavioral fever was observed after lipopolysaccharide (LPS) was injected systemically (200 microg/kg). Systemically injected AVT (300 pmol/kg) alone caused no significant change in body temperature, but abolished LPS-induced fever. Moreover, a smaller dose of AVT (10 pmol/kg), which did not affect LPS-induced fever when injected peripherally, abolished fever when injected intracerebroventricularly. We therefore conclude that AVT plays an antipyretic role in the central nervous system, by means of behavior, in an ectotherm, a fact consistent with the notion that AVT/AVP elicits antipyresis by reducing the thermoregulatory set point.     

Exogenous ghrelin attenuates endotoxin fever in rats

Ghrelin is a gut-derived peptide that plays a role in energy homeostasis. Recent studies have implicated ghrelin in systemic inflammation, showing increased plasma ghrelin levels after endotoxin (lipopolysaccharide, LPS) administration. The aims of this study were (1) to test the hypothesis that ghrelin administration affects LPS-induced fever; and (2) to assess the putative effects of ghrelin on plasma corticosterone secretion and preoptic region prostaglandin (PG) E₂ levels in euthermic and febrile rats. Rats were implanted with a temperature datalogger capsule in the peritoneal cavity to record body core temperature. One week later, they were challenged with LPS (50 μg/kg, intraperitoneal, i.p.) alone or combined with ghrelin (0.1 mg/kg, i.p.). In another group of rats, plasma corticosterone and preoptic region PGE₂ levels were measured 2 h after injections. In euthermic animals, systemic administration of ghrelin failed to elicit any thermoregulatory effect, and caused no significant changes in basal plasma corticosterone and preoptic region PGE₂ levels. LPS caused a typical febrile response, accompanied by increased plasma corticosterone and preoptic PGE₂ levels. When LPS administration was combined with ghrelin fever was attenuated, corticosterone secretion further increased, and the elevated preoptic PGE₂ levels were relatively reduced, but a correlation between these two variables (corticosterone and PGE₂) failed to exist. The present data add ghrelin to the neurochemical milieu controlling the immune/thermoregulatory system acting as an antipyretic molecule. Moreover, our findings also support the notion that ghrelin attenuates fever by means of a direct effect of the peptide reducing PGE₂ production in the preoptic region.     

Intracerebroventricular and septal injections of arginine vasopressin are not antipyretic in the rabbit

Arginine vasopressin (AVP) has been reported to have an antipyretic effect in the ewe and guinea pig near term. Perfusions with AVP of sites in the septal region also reduced fever in non-pregnant sheep. In the present experiments adult rabbits with third cerebral ventricular or septal cannulas were restrained in a 23°C environment, and rectal temperature was recorded every 10 min. Fever induced by IV administration of leukocytic pyrogen was not reduced by AVP (25–100 ng) given intraventricularly 20 min later. Doses of 1–5 μg AVP injected into the septum likewise were not antipyretic but actually caused an increase in fever. This augmentation of the febrile response is consistent with results of previous studies in this laboratory in which AVP increased hyperthermia in a hot environment and enhanced hyperthermic responses to PGE₂. The data from these experiments provide no evidence that central AVP is an endogenous antipyretic in rabbits; rather, it may be that central AVP augments fever in this species.     

Fever induction by localized subcutaneous inflammation in guinea pigs: the role of cytokines and prostaglandins.

In guinea pigs, dose-dependent febrile responses can be induced by injection of a high (100 micro g/kg) or low (10 micro g/kg) dose of bacterial lipopolysaccharide (LPS) into artificial subcutaneously implanted Teflon chambers. In this fever model, LPS does not enter the systemic circulation from the site of localized tissue inflammation in considerable amounts but causes a local induction of the proinflammatory cytokines tumor necrosis factor (TNF) and interleukin-6 (IL-6), which can be measured in lavage fluid collected from the chamber area. Only in response to the high LPS dose, small traces of TNF are measurable in blood plasma. A moderate increase of circulating IL-6 occurs in response to administration of both LPS doses. To investigate the putative roles of TNF and prostaglandins in this fever model, a neutralizing TNF binding protein (TNF-bp) or a nonselective inhibitor of cyclooxygenases (diclofenac) was injected along with the high or low dose of LPS into the subcutaneous chamber. In control groups, both doses of LPS were administered into the chamber along with the respective vehicles for the applied drugs. The fever response to the high LPS dose remained unimpaired by treatment with TNF-bp despite an effective neutralization of bioactive TNF in the inflamed tissue area. In response to the low LPS dose, there was an accelerated defervescence under the influence of TNF-bp. Blockade of prostaglandin formation with diclofenac completely abolished fever in response to both LPS doses. In conclusion, prostaglandins seem to be essential components for the manifestation of fever in this model.     

Central and peripheral actions of alpha-MSH in the thermoregulation of rats.

The effect of alpha-MSH on thermoregulation in rats at room temperature was examined. alpha-MSH (1 microgram ICV or 30 micrograms IP) alone did not alter temperature. However, this peptide was a potent antipyretic when administered centrally or peripherally in rats treated with pyrogen derived from Salmonella typhi.     

Anxiety-like behavior induced by IL-1beta is modulated by alpha-MSH through central melanocortin-4 receptors

The proinflammatory cytokine interleukin-1beta (IL-1beta) influences neuroendocrine activity and produces other effects, including fever and behavioral changes such as anxiety. The melanocortin neuropeptides, such as alpha-melanocyte-stimulating hormone (alpha-MSH), antagonize many actions of IL-1, including fever, anorexia and hypothalamic-pituitary-adrenal (HPA) axis activation through specific melanocortin receptors (MC-R) in the central nervous system. The objective of the present study was to establish the effect of MSH peptides on IL-1beta-induced anxiety-like behavior and the melanocortin receptors involved. We evaluated the effects of intracerebroventricular (i.c.v.) administration of IL-1beta (30 ng) and melanocortin receptor agonists: alpha-MSH, an MC3/MC4-R agonist (0.2 microg) or gamma-MSH, an MC3-R agonist (2 microg) or HS014, an MC4-R antagonist (2 microg), on an elevated plus-maze (EPM) test. Injection of IL-1beta induced an anxiogenic-like response, as indicated by reduced open arms entries and time spent on open arms. The administration of alpha-MSH reversed IL-1beta-induced anxiety with co-administration of HS014 inhibiting the effect of alpha-MSH. However, the associated treatment with gamma-MSH did not affect the anxiety response to IL-1beta. These data suggest that alpha-MSH, through central MC4-R can modulate the anxiety-like behavior induced by IL-1beta.     

ANTIPYRETIC ACTION OF DEXAMETHASONE ON EGTAZIC ACIDINDUCED FEVER IN RABBITS

本文用脑室灌注和Ｆｕｒａ２测定细胞内游离钙技术观察了地塞米松（ｄｅｘａｍｅｔｈａｓｏｎｅ,ＤＥＸ）对家兔乙二醇双（２氨基乙醚）四乙酸性发热效应和下丘脑细胞内游离钙浓度（［Ｃａ２＋］ｉ）的影响,借此深入探讨地塞米松解热作用的中枢机制。结果发现：脑室灌注乙二醇双（２氨基乙醚）四乙酸（０６ｎｍｏｌ）引起家兔结肠温度明显升高,静脉注射地塞米松（５ｍｇ／ｋｇ）显著抑制家兔乙二醇双（２氨基乙醚）四乙酸性发热,地塞米松（６０～１２０μｍｏｌ／Ｌ）并不影响下丘脑细胞内［Ｃａ２＋］ｉ,而事先脑室灌注抑制基因转录的放线菌素Ｄ（３ｎｍｏｌ）则完全取消了地塞米松对乙二醇双（２氨基乙醚）四乙酸性发热的解热作用。这些结果提示：地塞米松显著抑制家兔乙二醇双（２氨基乙醚）四乙酸性发热,其机制与地塞米松激活脑内某些基因的表达有关,而与下丘脑神经细胞跨膜钙离子流无关。