alpha-MSH injected into the septal region reduces fever in rabbits

The Importance of Melanocortin Receptors and Their Agonists in Pulmonary Disease

Melanocortin agonists are ancient neuropeptides that have steroidogenesis and anti-inflammatory properties. They activate melanocortin receptors (MCR), a family of five seven-transmembrane G-protein coupled receptors. MC1R and MC3R are mainly involved in immunomodulatory effects. Adrenocorticotropin hormone (ACTH) and alpha-Melanocortin stimulating hormone (α-MSH) reduce pro-inflammatory cytokines in several pulmonary inflammatory disorders including asthma, sarcoidosis, and the acute respiratory distress syndrome. They have also been shown to reduce fibrogenesis in animal models with pulmonary fibrosis. By understanding the functions of MCR in macrophages, T-helper cell type 1, and T-helper cell type 17, we may uncover the mechanism of action of melanocortin agonists in sarcoidosis. Further translational and clinical research is needed to define the role of ACTH and α-MSH in pulmonary diseases.

Melanocortin Regulation of Inflammation

Adrenocorticotropic hormone (ACTH), and α-, β-, and γ-melanocyte-stimulating hormones (α-, β-, γ-MSH), collectively known as melanocortins, together with their receptors (melanocortin receptors), are components of an ancient modulatory system. The clinical use of ACTH in the treatment of rheumatoid arthritis started in 1949, originally thought that the anti-inflammatory action was through hypothalamus-pituitary-adrenal axis and glucocorticoid-dependent. Subsequent decades have witnessed extensive attempts in unraveling the physiology and pharmacology of the melanocortin system. It is now known that ACTH, together with α-, β-, and γ-MSHs, also possess glucocorticoid-independent anti-inflammatory and immunomodulatory effects by activating the melanocortin receptors expressed in the brain or peripheral immune cells. This review will briefly introduce the melanocortin system and highlight the action of melanocortins in the regulation of immune functions from in vitro, in vivo, preclinical, and clinical studies. The potential therapeutic use of melanocortins are also summarized.

Mechanisms of fever production and lysis: lessons from experimental LPS fever

Fever is a cardinal symptom of infectious or inflammatory insults, but it can also arise from noninfectious causes. The fever-inducing agent that has been used most frequently in experimental studies designed to characterize the physiological, immunological and neuroendocrine processes and to identify the neuronal circuits that underlie the manifestation of the febrile response is lipopolysaccharide (LPS). Our knowledge of the mechanisms of fever production and lysis is largely based on this model. Fever is usually initiated in the periphery of the challenged host by the immediate activation of the innate immune system by LPS, specifically of the complement (C) cascade and Toll-like receptors. The first results in the immediate generation of the C component C5a and the subsequent rapid production of prostaglandin E2 (PGE2). The second, occurring after some delay, induces the further production of PGE2 by induction of its synthesizing enzymes and transcription and translation of proinflammatory cytokines. The Kupffer cells (Kc) of the liver seem to be essential for these initial processes. The subsequent transfer of the pyrogenic message from the periphery to the brain is achieved by neuronal and humoral mechanisms. These pathways subserve the genesis of early (neuronal signals) and late (humoral signals) phases of the characteristically biphasic febrile response to LPS. During the course of fever, counterinflammatory factors, "endogenous antipyretics," are elaborated peripherally and centrally to limit fever in strength and duration. The multiple interacting pro- and antipyretic signals and their mechanistic effects that underlie endotoxic fever are the subjects of this review.

Biphasic effect of melanocortin agonists on metabolic rate and body temperature

The melanocortin system regulates metabolic homeostasis and inflammation. Melanocortin agonists have contradictorily been reported to both increase and decrease metabolic rate and body temperature. We find two distinct physiologic responses occurring at similar doses. Intraperitoneal administration of the nonselective melanocortin agonist MTII causes a melanocortin-4 receptor (Mc4r)-mediated hypermetabolism/hyperthermia. This is preceded by a profound, transient hypometabolism/hypothermia that is preserved in mice lacking any one of Mc1r, Mc3r, Mc4r, or Mc5r. Three other melanocortin agonists also caused hypothermia, which is actively achieved via seeking a cool environment, vasodilation, and inhibition of brown adipose tissue thermogenesis. These results suggest that the hypometabolic/hypothermic effect of MTII is not due to a failure of thermoregulation. The hypometabolism/hypothermia was prevented by dopamine antagonists, and MTII selectively activated arcuate nucleus dopaminergic neurons, suggesting that these neurons may contribute to the hypometabolism/hypothermia. We propose that the hypometabolism/hypothermia is a regulated response, potentially beneficial during extreme physiologic stress.

Alpha-melanocyte-stimulating hormone and related tripeptides: biochemistry, antiinflammatory and protective effects in vitro and in vivo, and future perspectives for the treatment of immune-mediated inflammatory diseases

Alpha-MSH is a tridecapeptide derived from proopiomelanocortin. Many studies over the last few years have provided evidence that alpha-MSH has potent protective and antiinflammatory effects. These effects can be elicited via centrally expressed melanocortin receptors that orchestrate descending neurogenic antiinflammatory pathways. alpha-MSH can also exert antiinflammatory and protective effects on cells of the immune system and on peripheral nonimmune cell types expressing melanocortin receptors. At the molecular level, alpha-MSH affects various pathways implicated in regulation of inflammation and protection, i.e., nuclear factor-kappaB activation, expression of adhesion molecules and chemokine receptors, production of proinflammatory cytokines and mediators, IL-10 synthesis, T cell proliferation and activity, inflammatory cell migration, expression of antioxidative enzymes, and apoptosis. The antiinflammatory effects of alpha-MSH have been validated in animal models of experimentally induced fever; irritant and allergic contact dermatitis, vasculitis, and fibrosis; ocular, gastrointestinal, brain, and allergic airway inflammation; and arthritis, but also in models of organ injury. One obstacle limiting the use of alpha-MSH in inflammatory disorders is its pigmentary effect. Due to its preserved antiinflammatory effect but lack of pigmentary action, the C-terminal tripeptide of alpha-MSH, KPV, has been delineated as an alternative for antiinflammatory therapy. KdPT, a derivative of KPV corresponding to amino acids 193-195 of IL-1beta, is also emerging as a tripeptide with antiinflammatory effects. The physiochemical properties and expected low costs of production render both agents suitable for the future treatment of immune-mediated inflammatory skin and bowel disease, fibrosis, allergic and inflammatory lung disease, ocular inflammation, and arthritis.

Effects of electrical stimulation of ventral septal area on firing rates of pyrogen-treated thermosensitive neurons in preoptic anterior hypothalamus from rabbits

Although there is considerable evidence supporting that fever evolved as a host defense response, it is important that the rise in body temperature would not be too high. Many endogenous cryogens or antipyretics that limit the rise in body temperature have been identified. Endogenous antipyretics attenuate fever by influencing the thermoregulatory neurons in the preoptic anterior hypothalamus (POAH) and in adjacent septal areas including ventral septal area (VSA). Our previous study showed that intracerebroventricular (I.C.V.) injection of interleukin-1beta (IL-1beta) affected electrophysiological activities of thermosensitive neurons in VSA regions, and electrical stimulation of POAH reversed the effect of IL-1beta. To further investigate the functional electrophysiological connection between POAH and VSA and its mechanisms in thermoregulation, the firing rates of thermosensitive neurons in POAH of forty-seven unit discharge were recorded by using extracellular microelectrode technique in New Zealand white rabbits. Our results show that the firing rates of the warm-sensitive neurons decreased significantly and those of the cold-sensitive neurons increased in POAH when the pyrogen (IL-1beta) was injected I.C.V. The effects of IL-1beta on firing rates in thermosensitive neurons of POAH were reversed by electrical stimulation of VSA. An arginine vasopressin (AVP) V1 antagonist abolished the regulatory effects of VSA on the firing rates in thermosensitive neurons of POAH evoked by IL-1beta. However, an AVP V2 antagonist had no effects. These data indicated that VSA regulates the activities of the thermosensitive neurons of POAH through AVP V1 but not AVP V2 receptor.

Targeting Melanocortin Receptors as a Novel Strategy to Control Inflammation

Adrenocorticotropic hormone and alpha-, beta-, and gamma-melanocyte-stimulating hormones, collectively called melanocortin peptides, exert multiple effects upon the host. These effects range from modulation of fever and inflammation to control of food intake, autonomic functions, and exocrine secretions. Recognition and cloning of five melanocortin receptors (MCRs) has greatly improved understanding of peptide-target cell interactions. Preclinical investigations indicate that activation of certain MCR subtypes, primarily MC1R and MC3R, could be a novel strategy to control inflammatory disorders. As a consequence of reduced translocation of the nuclear factor kappaB to the nucleus, MCR activation causes a collective reduction of the major molecules involved in the inflammatory process. Therefore, anti-inflammatory influences are broad and are not restricted to a specific mediator. Short half-life and lack of selectivity could be an obstacle to the use of the natural melanocortins. However, design and synthesis of new MCR ligands with selective chemical properties are already in progress. This review examines how marshaling MCR could control inflammation.

The central melanocortin system and fever

Fever is a phylogenetically ancient response that is mounted upon exposure of the host to pathogens or inflammatory agents. Melanocortin agonists act centrally to inhibit fever by acting at receptors, including the melanocortin-4 receptor, which is prominently expressed in key hypothalamic thermoregulatory centers. Furthermore, endogenous melanocortins act centrally as physiological modulators of fever, recruited during the febrile response to restrain its intensity. Functionally, these actions lie at the interface between the anti-inflammatory effects of melanocortins, which involve suppression of the synthesis and actions of proinflammatory cytokines, and the central control of thermoregulation. Considering the extensive neuroanatomic and functional overlaps between central pathways and peripheral effectors involved in thermoregulation and energy balance, it is not surprising that melanocortins have been found to influence the metabolic economy profoundly in pathological as well as normal states. For example, despite suppressing endotoxin-induced fever, endogenous melanocortins appear to mediate the associated anorexia, a classic component of the "illness syndrome" accompanying acute infections, and promote a negative energy balance. The thermoregulatory actions of melanocortins are in several respects functionally opposed, and are remarkably dependent on physiological state, indicating that responsiveness to melanocortins is a physiologically modulated variable. Elucidating the anti-inflammatory and thermoregulatory roles of central melanocortin receptors during inflammatory states may lead to novel pharmacotherapeutic targets based on selective targeting of melanocortin receptor subtypes, for clinical benefit in human disease states involving neuroinflammatory components and metabolic wasting.

Endogenous antipyretics

Fever is the hallmark of the stereotyped host response to microbial infection, although it is just one of a number of high-risk strategies employed by the infected host to clear itself of invading pathogens. The febrile response is accompanied by activation of multiple endogenous antipyretic systems that serve to suppress its magnitude or duration. These include neuroactive substances of neural and humoral origin, some of which (e.g., glucocorticoids, melanocortins, and IL-10) have broad-ranging anti-inflammatory actions. Glucocorticoids, vasopressin, and melanocortins appear to exert their antipyretic effects by acting on receptors within the brain, but beyond this the mechanisms involved are unknown. It is hypothesized, but not proven, that endogenous antipyretic systems protect the host against the destructive consequences of unchecked fever. Importantly, pharmacological blockade of the actions of endogenous antipyretic systems increases fevers of even low to moderate intensity. Therefore, in addition to protecting against catastrophic consequences of high fever, endogenous antipyretic systems seem to play a fundamental physiological role in determining the normal course of fever. Elucidating the neural and biochemical mechanisms involved in suppression of fever by physiological antipyretic systems will yield a rich benefit, both by advancing the basic understanding of host defense strategies, and by permitting the design of novel antipyretic and anti-inflammatory strategies for therapeutic intervention in human disease.

Pituitary adenylate cyclase-activating polypeptide induces hyperthermia in the rat

The effects of centrally administered pituitary adenylate cyclase-activating polypeptide (PACAP-38) on body temperature were investigated in rats. Intracerebroventricular (i.c.v.) administration of PACAP-38 in doses of 500 and 1000 ng induced a dose-related elevation in colon temperature 2, 3, 4, 5 and 6 h after injection. The i.c.v. pretreatment of the animals with different dilutions of PACAP-38 antiserum prevented the development of hyperthermia in PACAP-38-treated animals, whereas PACAP-38 antiserum alone did not modify the colon temperature. An intramuscular injection of noraminophenazone (a cyclooxygenase inhibitor) abolished the PACAP-38-induced hyperthermia. Our data indicate that PACAP may induce hyperthermia via the central nervous system, and this hyperthermic effect may be mediated via a cyclooxygenase-involved pathway.

Isatin (Indole-2, 3-dione) inhibits natriuretic peptide-induced hyperthermia in rats

The effects of an endogenous indole, isatin (indole-2, 3-dione), on the hyperthermia induced by atrial natriuretic peptide (ANP-28), brain natriuretic peptide (BNP-32), and C-type natriuretic peptide (CNP-22) were investigated in rats. Intracerebroventricular administration of each peptide in a dose of 1 microg caused elevations in colon temperature 30 and 60 min after injection. An intraperitoneal (i.p.) injection of isatin (50 mg/kg) abolished the natriuretic peptide-induced hyperthermia. These data reinforce the possible involvement of natriuretic peptides in thermoregulatory processes in the central nervous system, and suggest that isatin might counteract their hyperthermic effect in vivo.

Hyperthermic effect of centrally administered natriuretic peptides in the rat

The effects of atrial natriuretic peptide (ANP-28), brain natriuretic peptide (BNP-32) and C-type natriuretic peptide (CNP-22) on body temperature were investigated in rats. Intracerebroventricular administration of each peptide in doses of 400 or 1000 ng caused a dose-related elevation in colon temperature 30 and 60 min after injection. A 40 ng dose of ANP-28 was also hyperthermic at 60 min. An intramuscular (i.m.) injection of noraminophenazone (a cyclooxygenase inhibitor) abolished the natriuretic peptide-induced hyperthermia. The results show that natriuretic peptides may participate in thermoregulatory processes in the central nervous system, and that their hyperthermic effect may be mediated via a cyclooxygenase-involved pathway.

The long term acute phase-like responses that follow acute stressor exposure are blocked by alpha-melanocyte stimulating hormone

Both intracerebroventricular (i.c.v.) IL-1beta and exposure to inescapable tail shock (IS) activate acute phase responses (APRs) that include increases in core body temperature (CBT), increases in hypothalamic-pituitary-adrenal activity, decreases in carrier proteins such as corticosterone binding globulin (CBG), aphagia and adipsia. A variety of data suggested that stressors produce APRs by inducing brain IL-1beta. The current series of studies further explored this possibility by determining whether the functional IL-1beta antagonist, alpha-melanocyte-stimulating hormone (alpha-MSH(1-13)), would block IS-induced APRs. Immediately following i.c.v. alpha-MSH(1-13) administration, rats were exposed to a single session of 100, 5 s, 1.6 mA ISs, or control treatment (home cage control). alpha-MSH(1-13) blocked IS-induced increased CBT, increased plasma corticosterone (CORT), decreased CBG, aphagia and adipsia 24 h after IS. The inhibitory effects of alpha-MSH(1-13) were shown not to be a consequence of alpha-MSH(1-13) producing its actions 24 h after its administration because alpha-MSH(1-13) given 24 h before IS did not block IS-induced increased CBT and CORT during IS. Additionally, alpha-MSH(1-13), given 24 h before IS, had no effect on increased CBT, increased CORT, decreased CBG, adipsia, or aphagia 24 h after IS. These data provide support for a specific mode of action for i.c.v. alpha-MSH(1-13), namely blockade of APRs with no impact on acute hyperthermia or increased levels of CORT produced during IS.

Localization of corticotropin-releasing factor in primary and secondary lymphoid organs of the rat

Cells of the immune system produce a variety of neuropeptides or peptide hormones, either constitutively or upon induction, and possess specific neuropeptide receptors that display ligand-receptor interactions similar to those described in the central nervous system (CNS). These findings suggest that specific subsets of lymphoid cells can produce and respond to peptides previously thought to be principally neural mediators. Recently, corticotropin releasing factor (CRF) mRNA was detected in the rat thymus and spleen, although the cells that synthesize CRF were not identified. We examined the localization of CRF and its mRNA in the rat spleen, thymus, and mesenteric lymph nodes using immunocytochemistry (ICC) and in situ hybridization (ISH), respectively. Immunoreactive CRF was present in cells in the marginal zone and red pulp of the spleen, in connective tissue septa and the subcapsular region of the thymus, and in the medullary cords and sinuses of the mesenteric lymph nodes. Dual ICC/ISH for CRF and its mRNA, respectively, demonstrated CRF mRNA over CRF-immunoreactive cells, suggesting CRF synthesis. Double-label ICC for CRF and markers for specific immunocyte subsets suggest that CRF+ cells in the spleen and thymus are macrophages. CRF+ cells in primary and secondary lymphoid organs reside in compartments that are innervated by sympathetic nerves, and some cells appears to be contacted by noradrenergic sympathetic nerve fibers, suggesting that CRF release may be influenced by the sympathetic nervous system, as it is in the hypothalamo-pituitary-adrenal axis. The presence of CRF in organs of the immune system suggests that this neuropeptide may modulate immune functions after paracrine release.

Antipyretic role of endogenous melanocortins mediated by central melanocortin receptors during endotoxin-induced fever

Bacterial infection causes fever, an adaptive but potentially self-destructive response, in the host. Also activated are counterregulatory systems such as the pituitary-adrenal axis. Antipyretic roles have also been postulated for certain endogenous central neuropeptides, including the melanocortins (alpha-MSH-related peptides). To test the hypothesis that endogenous central melanocortins have antipyretic effects mediated by central melanocortin receptors (MCRs), we determined the effect of intracerebroventricular injection of a synthetic MCR antagonist, Ac-Nle4,c-[Asp5,DNal(2')7,Lys10]alpha-MSH(4-10)-NH2 (SHU-9119) in endotoxin-challenged rats. The efficacy and specificity of SHU-9119 as an MCR antagonist in the rat was first validated in vitro and in vivo. In vitro, in heterologous cells expressing either rat MC3-R or MC4-R, the major MCR subtypes expressed in brain, SHU-9119 showed no intrinsic agonism, but it inhibited alpha-MSH-induced cAMP accumulation (IC50 = 0.48 +/- 0.19 and 0.41 +/- 0.28 nM, respectively) and [125I]-[Nle4,DPhe7]-alpha-MSH binding (IC50 = 1.0 +/- 0.1 and 0.9 +/- 0.3 nM, respectively). In vivo, exogenous alpha-MSH (180 pmol) inhibited fever in rats when administered intracerebroventricularly 30 min after Escherichia coli lipopolysaccharide (LPS) (25 microg/kg, i.p.). When co-injected with alpha-MSH, SHU-9119 (168 pmol, i.c.v.) prevented the antipyretic action of exogenous alpha-MSH. In contrast, neither alpha-MSH nor SHU-9119, alone or in combination, affected body temperatures in afebrile rats. In LPS-treated rats, intracerebroventricular injection of SHU-9119 significantly increased fever, whereas intravenous injection of the same dose of SHU-9119 had no effect. Neither intracerebroventricular nor intravenous SHU-9119 significantly affected LPS-stimulated plasma ACTH or corticosterone levels. The results indicate that endogenous central melanocortins exert an antipyretic influence during fever by acting on MCRs located within the brain, independent of any modulation of the activity of the pituitary-adrenal axis.

The immune effects of neuropeptides

Current evidence indicates that the neuroendocrine system is the highest regulator of immune/inflammatory reactions. Prolactin and growth hormone stimulate the production of leukocytes, including lymphocytes, and maintain immunocompetence. The hypothalamus-pituitary-adrenal axis constitutes the most powerful circuit regulating the immune system. The neuropeptides constituting this axis, namely corticotrophin releasing factor, adrenocorticotrophic hormone, alpha-melanocyte stimulating hormone, and beta-endorphin are powerful immunoregulators, which have a direct regulatory effect on lymphoid cells, regulating immune reactions by the stimulation of immunoregulatory hormones (glucocorticoids) and also by acting on the central nervous system which in turn generates immunoregulatory nerve impulses. Peptidergic nerves are major regulators of the inflammatory response. Substance P and calcitonin gene-related peptide are pro-inflammatory mediators and somatostatin is anti-inflammatory. The neuroendocrine regulation of the inflammatory response is of major significance from the point of view of immune homeostasis. Malfunction of this circuit leads to disease and often is life-threatening. The immune system emits signals towards the neuroendocrine system by cytokine mediators which reach significant blood levels (cytokine-hormones) during systemic immune/inflammatory reactions. Interleukin-1, -6, and TNF-alpha are the major cytokine hormones mediating the acute phase response. These cytokines induce profound neuroendocrine and metabolic changes by interacting with the central nervous system and with many other organs and tissues in the body. Corticotrophin releasing factor functions under these conditions as a major co-ordinator of the response and is responsible for activating the ACTH-adrenal axis for regulating fever and for other CNS effects leading to a sympathetic outflow. Increased ACTH secretion leads to glucocorticoid production. alpha-melanocyte stimulating hormone functions under these conditions as a cytokine antagonist and an anti-pyretic hormone. The sympathetic outflow, in conjunction with increased adrenal activity. leads to the elevation of catecholamines in the bloodstream and in tissues. Current evidence suggests that neuroimmune mechanisms are essential in normal physiology, such as tissue turnover, involution, atrophy, intestinal function, and reproduction. Host defence against infection, trauma and shock relies heavily on the neuroimmunoregulatory network. Moreover, abnormalities of neuroimmunoregulation contribute to the aetiology of autoimmune disease, chronic inflammatory disease, immunodeficiency, allergy, and asthma. Finally, neuroimmune mechanisms play an important role in regeneration and healing.

Alpha-melanocyte-stimulating hormone (MSH) inhibits insulin secretion in HIT-T 15 cells

alpha-Melanocyte-stimulating hormone (MSH) antagonizes the binding of interleukin-1 beta (IL-1) to its type I receptors on T cells. IL-1 modulates insulin secretion in the insulin-secreting tumor cell line, HIT-T 15 cells. In the present studies, we examined a hypothesis that alpha-MSH may modulate insulin secretion in HIT-T 15 cells. The addition of alpha-MSH over the concentrations of 10(-10) M inhibited insulin secretion for 4 h. In addition, the carboxyl-terminal tripeptide of alpha-MSH [alpha-MSH(11-13)], which is supposed to be an important sequence of alpha-MSH on its antipyretic effects, significantly inhibited insulin secretion at the concentration of 10(-9) M. In contrast, acetyl-[Nle4,D-Phe7] alpha-MSH(4-10)-amide (10(-11) to 10(-9) M) failed to inhibit insulin secretion. The maximal effect of alpha-MSH on insulin secretion was obtained at the concentration of 10(-9) M. The addition of alpha-MSH from 10(-11) to 10(-9) M significantly inhibited 7.5 mM glucose-stimulated insulin secretion at each period of 0-5, 5-15, and 15-30 min. Radioreceptor assay suggested that HIT-T 15 cells possess the specific binding sites for 125I-labeled alpha-MSH. The present studies indicated that alpha-MSH inhibits insulin secretion through the specific binding site in HIT-T 15 cells.

Glycyl-L-glutamine antagonizes alpha-MSH-elicited thermogenesis

The objective of this study was to determine whether glycyl-L-glutamine [beta-endorphin(30-31)] modulates the thermoregulatory actions of alpha-MSH. Microinjection of alpha-MSH (0.06 nmol) into PGE2-responsive thermogenic sites in the medial preoptic area of rats generated a hyperthermic response, inducing a 0.85 +/- 0.19 degrees C rise in colonic temperature (Tc) within 45 min. Coadministration of glycyl-L-glutamine (3.0 nmol) completely blocked the response, maintaining Tc at baseline levels. This was not attributable to glycyl-L-glutamine hydrolysis because coadministration of glycine and glutamine had no effect on alpha-MSH-induced thermogenesis. Glycyl-L-glutamine, injected alone, was similarly without effect. These data indicate that glycyl-L-glutamine inhibits alpha-MSH-induced thermogenesis but is devoid of thermoregulatory activity itself.

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.

The dipeptide Lys-Pro attenuates interleukin-1 beta-induced anorexia

The carboxyl-terminal tripeptide of alpha-MSH(1-13), Lys-Pro-Val, antagonizes anorexia induced by interleukin-1 beta (IL-1). The present studies were undertaken to determine if the Lys-Pro dipeptide portion of this tripeptide likewise antagonizes anorexia induced by ICV administration of 0.5 pmol IL-1 in rats previously deprived of food. This dose of Lys-Pro did significantly attenuate the IL-1-induced anorexia, but only for 1 h after infusion. Simultaneous administration of a larger dose (5.0 pmol) of Lys-Pro reversed the IL-1-induced anorexia during both the 0-1-h and 2-4-h periods. In addition, both 0.5 and 5.0 pmol of the D-substitute tripeptide, Lys-D-Pro-Thr (LDPT), similarly attenuated the IL-1-induced anorexia. The ICV administration of 5.0 pmol Lys-Pro also did not have any significant effects on food consumption. These results indicate that the dipeptide Lys-Pro may have a short-term antagonistic action against the anorexia induced by IL-1, and it is possible that this action may be partially mediated by the blockade of IL-1 on its own receptor.

Carboxyl-terminal tripeptide of alpha-melanocyte-stimulating hormone antagonizes interleukin-1-induced anorexia

Interleukin-1 beta (IL-1), a cytokine released from inflammatory cells, is thought to be involved in the anorexia associated with severe infection. To assess a possible role of the amino acid sequence found in the supposed IL-1 receptor binding sites, we determined the antagonistic effects of alpha-melanocyte-stimulating hormone (MSH) and the carboxyl-terminal tripeptide of alpha-MSH-(11-13) (alpha-MSH-(11-13)) on the anorexia induced by intracerebroventricular (i.c.v.) administration of 0.5 pmol IL-1. The parent alpha-MSH molecule completely prevented the induction of anorexia by IL-1 at both doses tested, 0.5 and 5.0 pmol. In contrast, alpha-MSH-(11-13) prevented the IL-1-induced anorexia only at 5.0 pmol, but not at 0.5 pmol. Intracerebroventricular injection of 5 pmol of the parent alpha-MSH molecule alone temporarily decreased food consumption at 1-2 h; 5.0 pmol of alpha-MSH-(11-13) alone did not affect food consumption. These data indicate that alpha-MSH can antagonize the anorexic effects of IL-1. The carboxyl-terminal tripeptide portion of alpha-MSH may be important for the antagonistic action of alpha-MSH on the anorexia induced by IL-1.

Alpha-melanocyte-stimulating hormone suppresses fever and increases in plasma levels of prostaglandin E2 in the rabbit

1. The effect of alpha-melanocyte-stimulating hormone (alpha-MSH) on changes in body temperature and plasma levels of prostaglandin E2 (PGE2) were measured in the rabbit following intravenous injection of bacterial lipopolysaccharide (LPS), rabbit endogenous pyrogen (EP), human recombinant tumour necrosis factor-alpha (TNF-alpha), human recombinant interleukin-1 beta (IL-1 beta) and intracerebroventricular injection of PGE2. 2. LPS (25 ng kg-1), EP (25 microliters kg-1), TNF-alpha (11 micrograms kg-1) and IL-1 beta (5 ng kg-1) produced increases in body temperature simultaneously with increases in plasma PGE2 levels. alpha-MSH (5 or 10 micrograms kg-1) attenuated both the increase in body temperature and increases in plasma levels of PGE2. 3. Intracerebroventricular injection of PGE2 (500 ng) produced a monophasic increase in body temperature. alpha-MSH (5 micrograms kg-1) administered 20 min after PGE2 had no effect on the hyperthermic response. 4. alpha-MSH (10 micrograms kg-1) had no effect on either body temperature or plasma levels of PGE2 in response to I.V. injection of sterile saline. 5. These data demonstrate that alpha-MSH inhibits both the pyrogenic actions of LPS, EP, TNF-alpha and IL-1 beta and their ability to increase PGE2 release without affecting the direct actions of PGE2, suggesting the possibility that alpha-MSH may prevent the synthesis of PGE2 either by preventing the actions or release of mediators such as TNF-alpha and IL-1 in response to LPS.

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.

Anti-inflammatory activity of alpha-MSH(11-13) analogs: influences of alteration in stereochemistry

D-Amino acid substitutions in the anti-inflammatory/antipyretic Ac-alpha-MSH(11-13)-NH2 tripeptide of Ac-alpha-MSH(1-13)-NH2 were made and the altered peptides were injected in mice treated with picryl chloride. Ear swelling, measured 3 and 6 h after application of the irritant, was reduced by IP injections of Ac-alpha-MSH(11-13)-NH2, in confirmation of previous observations. Ac-[D-Lys11]alpha-MSH(11-13)-NH2 effected similar anti-inflammatory activity but Ac-[D-Pro12]alpha-MSH(11-13)-NH2 was inactive. Ac-[D-Val13]alpha-MSH(11-13)-NH2 and Ac-[D-Lys11,D-Val13]alpha-MSH(11-13)-NH2 generally had greater anti-inflammatory activity than the parent tripeptide molecule; the dose-response relations exhibited the bell-shaped characteristics seen previously with MSH peptides. The results indicate that the L-Pro12 is essential for the anti-inflammatory activity of Ac-alpha-MSH(11-13)-NH2 whereas the L-Lys11 is not. D-Val13 substitution increased anti-inflammatory activity approximately four-fold over Ac-alpha-MSH(11-13)-NH2. These results provide new structure-activity relationships of the anti-inflammatory Ac-alpha-MSH(11-13)-NH2 molecule. The data support the developing idea that alpha-MSH and its COOH-terminal fragments modulate host responses, perhaps by antagonizing the actions of cytokines.

Alpha-melanocyte-stimulating hormone reduces interleukin-1 beta effects on rat stomach preparations possibly through interference with a type I receptor

Contractions elicited by CaCl2 on isolated rat stomach strip preparations have been reported to be potentiated by interleukin-1 beta (IL-1 beta). We have investigated whether this effect can be reduced by the putative IL-1 beta antagonist, alpha-melanocyte-stimulating hormone (alpha MSH). Additionally, the effects of alpha MSH on the specific binding of IL-1 beta to B- and T-cells have been investigated to further clarify its inhibitory activities. Both alpha MSH and its carboxyl terminal tripeptide concentration dependently reduced the potentiation of CaCl2-induced contractions caused by IL-1 beta but not those caused by leukotriene D4, the parent molecule being approximately 250 times more active. Additionally, both peptides potently and selectively reduced 125I-IL-1 beta binding to the T-cell sub-clone EL4-6.1 but not to the B-cell sub-clone 1H7. The results indicate that IL-1 beta effects on rat stomach may be mediated through a type-I (80 kDa) IL-1 beta receptor.

Neurohormonal immunoregulation

The immune system may be divided into primary lymphoid organs (bone marrow, bursa of Fabricius, and thymus), which produce mature leukocytes and secondary organs (spleen, lymph nodes, tonsils, Peyer's patches, etc.), which are concerned with specific immune responses. In the primary organs, stem cells proliferate and differentiate into various subsets of polymorphonuclear and mononuclear cells. Evidence is increasing that cell proliferation in the primary lymphoid organs is dependent on pituitary growth hormone (GH) and prolactin (PRL), which control the expression of growth regulatory genes (protooncogenes) such as c-myc and also induce essential growth factors (insulinlike growth factor, thymic and bursal hormones, etc.) and, possibly, their receptors. The adrenocorticotropic hormone-adrenal axis serves as an inhibitory pathway, antagonizing the action of PRL and GH on primary lymphoid tissue. The effect of glucocorticoids is especially forceful on thymocytes through the activation of the genetically programmed suicide pathway. Sex hormones also regulate the primary lymphoid organs, but their mechanism of action remains to be clarified. Thymus-derived feedback signals toward the pituitary gland have already been described. The pituitary gland exerts a similar regulatory influence on mature lymphocytes during their antigen-driven differentiation. PRL or GH is required for primary immune reactions; however, the secondary immune response may be less dependent on these hormones. Once the immune system is primed, antigen itself becomes a primary regulator. Exposure of memory cells to antigen leads to the production of growth factors (interleukins) and to the expression of their receptors. Therefore, antigen appears to fulfill, at this stage, a role that is originally played by GH or PRL in the primary lymphoid organs and, to some extent, also during antigen-driven differentiation. During immune reactions, interleukin-1 and tumor necrosis factor activate the adrenocorticotropic hormoneadrenal axis, which plays an important role in setting upper limits to and terminating responses. Lymphocytes have receptors for and react to numerous hormones, neurotransmitters, and mediators derived from a number of organs and tissues. Therefore, ultimately the reaction of a lymphocyte will be the vector of all positive and negative signals received. A hierarchy and sequential system of signals exists. Primary regulatory signals (competence signals) represent the most powerful regulators (e.g., PRL, GH or antigen) of lymphoid cells. The delivery of a competence signal is the prerequisite for subsequent lymphoproliferation, which is regulated by growth factors that are specific for a certain developmental stage of the lymphoid cell and act sequentially. Hormonal factors that promote growth and differentiation deliver the second regulatory signals. Competence factors and growth and differentiation hormones regulate gene expression in lymphocytes. The third class of signals modulate the function of mature effector cells (e.g., locomotion, secretion, phagocytosis, cytotoxicity). Neuro-transmitters appear to function as secondary signal modulators and tertiary functional regulators.

Depletion of brain alpha-MSH alters prostaglandin and interleukin fever in rats

Alpha-melanocyte stimulating hormone (alpha-MSH), a putative endogenous antipyretic agent, is synthesized largely within neurons in the arcuate nucleus. To test the hypothesis that destruction of this area would increase the febrile response, male Wistar rats, treated as neonates with intraperitoneal injections of monosodium glutamate (MSG) or saline, were given intracerebroventricular (i.c.v.) injections of prostaglandin E1 (20 ng; 200 ng) or purified interleukin-1 (20 U) and body temperature was monitored. The fevers displayed by the MSG-treated animals were significantly greater (P less than 0.05) than those of the controls for the lower dose of PGE1 at 10-30 min and for IL-1 at 3-6 h after the injections. MSG-treated rats showed significant reduction (P less than 0.01) in alpha-MSH content of the medial basal hypothalamus and lateral septum when compared to saline controls. Body temperature response of non-febrile animals to high ambient temperature was not affected by the MSG treatment. These data support the hypothesis that alpha-MSH is an endogenous antipyretic in the rat.

Alpha-MSH peptides inhibit acute inflammation and contact sensitivity

Alpha-melanocyte stimulating hormone [alpha-MSH(1-13)] occurs within the CNS, skin, circulation and in other body sites. This tridecapeptide and its COOH-terminal tripeptide, alpha-MSH (11-13), have antipyretic and anti-inflammatory actions. Studies of the anti-inflammatory effects of these molecules have been confined mainly to tests of inhibition of histamine and endogenous pyrogen-induced increases in capillary permeability in rabbits and acute inflammation of ear tissue in mice. The aim in the present experiments was to learn if alpha-MSH peptides also antagonize inflammation in two additional models: acute edema induced in the mouse paw and contact sensitivity. Significant anti-inflammatory effects were observed with MSH peptides in both models. These findings converge with previous results to indicate that alpha-MSH peptides modulate inflammation. Because circulating alpha-MSH increases after treatment of animals with endogenous pyrogen or endotoxin, administration of the peptides may simply mimic a naturally occurring modulation of host defense reactions.

The effectiveness of arginine vasopressin and sodium salicylate as antipyretics in the Brattleboro rat

The infusion of either 30 micrograms/microliters (approx. 100 micrograms/kg/h) of sodium salicylate or 10 ng/microliters (10(-5) M) arginine vasopressin within the ventral septal area of the Brattleboro rat brain reduced a centrally induced prostaglandin E1 (PGE1) hyperthermia when compared with infusions of artificial cerebrospinal fluid. Conversely, the infusion of a related peptide, oxytocin (10 ng/microliters (10(-5) M), or 33 ng/kg/h) failed to alter the rise in core temperature following the PGE1 injection. These results suggest that the vasopressin receptors reported to be present in the Brattleboro rat may respond normally to exogenously administered vasopressin, thus allowing for the antipyretic action. Moreover, the antipyretic effects of sodium salicylate suggest that aspirin-like drugs may induce the release of alpha-melanocyte-stimulating hormone which, in turn, attenuates the PGE1-evoked fever. Given recent evidence, however, which suggests that the Brattleboro rat may contain vasopressin both peripherally and within the brain, the antipyretic action of sodium salicylate may be alternatively explained through the endogenous release of vasopressin.

Antipyretic effect of central alpha-MSH summates with that of acetaminophen or ibuprofen

The neuropeptide alpha-melanocyte stimulating hormone has potent antipyretic properties when given centrally or systemically. Little is known about the mechanism of the antipyretic action and virtually nothing is known about interactions among the antipyretic effects of alpha-MSH and commonly used antipyretic agents. Randomized studies in which alpha-MSH, acetaminophen or ibuprofen, or a combination of alpha-MSH and antipyretic drug, were given IV to rabbits made febrile by endogenous pyrogen, indicate that the antipyretic effect of the peptide is summative with those of the drugs. alpha-MSH has been shown to have a wide safety margin in earlier research and the results suggest that combinations of peptide and antipyretic drugs might be safer and have fewer side effects than larger quantities of the drugs alone.

Repeated central administration of alpha-MSH does not alter the antipyretic effect of alpha-MSH in young and aged rabbits

alpha-Melanocyte-stimulating hormone is a potent antipyretic when administered centrally or peripherally; however, there are no previous data on development of tolerance to the antipyretic action of this neuropeptide. In previous research, aged rabbits were more sensitive to low doses of alpha-MSH than young rabbits. We tested the antipyretic action of alpha-MSH in young and old rabbits after twice daily injections of the peptide for 10 days. Neither aged nor younger rabbits showed altered responses to alpha-MSH. This lack of tolerance underscores the importance of alpha-MSH to physiological control and survival of the host.

Antipyretic properties of centrally administered alpha-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.

Eugenol: antipyretic activity in rabbits

The analgesic agent eugenol reduced fever when given intravenously in small doses to rabbits made febrile by interleukin 1. To test this observation further, the drug was given intragastrically and its antipyretic effect was compared with that of a molar equivalent dose of acetaminophen. Eugenol was more effective in reducing fever than acetaminophen. Tests with intracerebroventricular injections indicated that eugenol could act centrally to reduce fever in doses much smaller than those which were effective peripherally. Other tests with the presumed fever mediators sodium archidonate and prostaglandin E2 (PGE2), suggest that the central action of eugenol is similar to that of acetaminophen. Eugenol, a derivative of clove oil, has marked antipyretic activity when given intravenously, intragastrically and centrally and may reduce fever primarily through a central action that is similar to that of common antipyretic drugs such as acetaminophen.

Is the endogenous antipyretic neuropeptide alpha-MSH responsible for reduced fever in aged rabbits?

The reduced febrile response in aged man has been noted since the beginning of clinical thermometry. Our previous research on aged rabbits and squirrel monkeys disclosed a similar reduced fever, presumably due to a decrease in central receptors for endogenous pyrogen. However, because central alpha-melanocyte stimulating hormone (MSH) appears to have a potent role in physiological control of fever, it may be that increased release of the peptide is responsible for the reduced febrile response in aged animals. To test this idea, antiserum specific to MSH was administered intracerebroventricularly to rabbits of known age. The antiserum given according to three schedules of treatment augmented fever caused by IV injections of interleukin-1 (IL-1) in young (less than 2 years) male and female rabbits. Aged female rabbits (3-5+ years) and females aged 2-3 years showed significant augmentation of fever only after pretreatment plus acute injection of antiserum. A single ICV injection of MSH (200 ng) reduced fever in all groups with the greatest antipyretic effect in the aged females. The results indicate that while aged rabbits have an increased antipyretic response to central MSH, binding of the endogenous peptide does not result in marked increases in fever in these animals. Thus, whereas a change in central MSH sensitivity may contribute to reduced fever in aged homeotherms, a reduction in central pyrogen receptors appears to be the most parsimonious explanation.

Effects of preoptic microinjections of alpha-MSH on fever and normal temperature control in rabbits

alpha-MSH within the septal region of the brain has been implicated in fever control; this peptide and ACTH (1-24), which contains the alpha-MSH amino acid sequence, reduce fever when given intracerebroventricularly (ICV) or peripherally. These peptides also cause hypothermia when given in doses larger than those required to reduce fever. Both peptides occur naturally within the preoptic PO region of the brain, the CNS locus of primary temperature control. alpha-MSH (350 ng) injected bilaterally into the PO region via chronic cannulas reduced fever caused in six rabbits by IV injection of IL-1 (interleukin 1, endogenous or leukocyte pyrogen) but had no effect in afebrile animals. A larger dose (1.5 micrograms) not only reduced fever but caused hypothermia in 12 rabbits. In separate experiments PO injections of ACTH (1-24) (1 microgram) reduced normal temperature. In the same six rabbits alpha-MSH (1 microgram) caused slightly smaller hypothermia. alpha-MSH (1.5 micrograms) also had no effect in 8 afebrile rabbits when injected into the septum. The primary conclusion is that alpha-MSH receptors within the PO region can contribute to both the antipyretic and hypothermic actions that are observed after ICV and peripheral administration of the peptide.

Changes in body temperature after administration of antipyretics, LSD, delta 9-THC and related agents: II

Antipyretics, in particular acetaminophen, aspirin and ibuprofen, constitute the single most important class of drugs used therapeutically for an effect on body temperature. Hallucinogens exert prominent actions on the central nervous system, and it is not surprising that, like so many other centrally-acting agents, they too often affect temperature. This compilation primarily covers the considerable amount of data published from 1981 through 1985 on the interactions of these drugs and thermoregulation, but data from many earlier papers not included in a previous compilation are also tabulated. The effects of agents not classically considered as antipyretics on temperatures of febrile subjects are also covered. The information listed includes the species used, the route of administration and dose of drug, the environmental temperature at which experiments were performed, the number of tests, the direction and magnitude of change in body temperature and remarks on special conditions, such as age or brain lesions. Also indicated is the influence of other drugs, such as antagonists, on the response to the primary agent.

Neuropeptide regulation of interleukin-1 activities. Capacity of alpha-melanocyte stimulating hormone to inhibit interleukin-1-inducible responses in vivo and in vitro exhibits target cell selectivity

alpha-Melanocyte stimulating hormone (alpha-MSH), a 13 amino acid neuropeptide produced by the pituitary gland, was found to markedly inhibit the capacity of exogenously administered interleukin-1 (IL-1) to stimulate the enhanced synthesis of acute-phase proteins and induce neutrophilia in vivo. The administration of ACTH or glucocorticosteroids lacked most of these direct IL-1 inhibitory properties. Therefore, in addition to the previously reported antipyretic action of alpha-MSH, this hormone can also inhibit two other known IL-1 sensitive cellular targets in vivo. Further, alpha-MSH was incapable of modifying the comitogenic influence of IL-1 on murine thymocytes or on an IL-1 responsive T-cell line. These findings suggest a target cell specificity to the IL-1 inhibitory activities of alpha-MSH and fail to support the hypothesis that alpha-MSH functions through competitive inhibition of specific cellular receptors for IL-1.

Central nervous system effects of peptides, 1980-1985: a cross-listing of peptides and their central actions from the first six years of the journal Peptides

A tabular synopsis is presented for articles concerned with the effects of peptides on the central nervous system that appeared in the journal Peptides from 1980-1985. A table arranged alphabetically by peptide and one arranged by effects, both listing routes of injection, species, direction of change, and qualifying notes, provides easy cross-referencing of peptides and their effects. Over 80 peptides and over 135 effects are listed. The list of peptides includes, but is not limited to: ACTH, angiotensin, bombesin, bradykinin, calcitonin, casomorphin, CCK, ceruletide, CGRP, CRF, dermorphin, DSIP, dynorphin, endorphins, enkephalins, GRF, gastrin, LHRH, litorin, metkephamid, MIF-l, motilin, MSH, NPY, NT, oxytocin, ranatensin, sauvagine, substances P and K, somatostatin, TRH, VIP, vasopressin, and vasotocin. The list of effects includes, but is not limited to: aggression, alcohol, analgesia, attention, avoidance, behavior, cardiovascular regulation, catalepsy, conditioned behavior, convulsions, dopamine binding and metabolism, discrimination, drinking, EEG, exploration, feeding, fever, gastric secretion, GI motility, grooming, learning, locomotor behavior, mating, memory, neuronal activity, open field, operant behavior, rearing, respiration, satiety, scratching, seizure, sleep, stereotypy, temperature, thermoregulation and tolerance.

alpha-Melanocyte-stimulating hormone infused ICV fails to affect body temperature or endotoxin fever in the cat

Permanent cannulae for intracerebroventricular (ICV) infusion were implanted bilaterally in cats following stereotaxic procedures. After colonic temperature was recorded for a one-hour baseline, a 300 microliter ICV infusion was given of CSF control vehicle, 1:100 dilution of W3110 E. coli endotoxin (10(8) organisms/ml) or alpha-melanocyte-stimulating hormone (alpha-MSH) in one of seven doses ranging from 50.0 ng to 50.0 micrograms. Whereas ICV E. coli always induced an intense and prolonged fever of rapid onset, alpha-MSH infused similarly was essentially without effect on the deep body temperature of the normothermic cat. When each of the doses of alpha-MSH was infused ICV, either during the rising phase of an E. coli fever or after the febrile response had reached its asymptote, the core temperature of the cat was unaffected. Similarly, a mixture of E. coli combined with alpha-MSH given ICV failed to alter the characteristics of the rapidly developing fever produced in the cat by this endotoxin. On the other hand, either excess Ca++ ions (50 mM) given ICV or the antipyretic drug. Dipyrone, administered systematically during the course of an endotoxin fever effectively attenuated the animal's elevated body temperature. These results demonstrate that alpha-MSH is apparently neither involved in the central mechanisms underlying normal thermoregulation, nor does it act as an endogenous antipyretic in the cat as has been postulated in another species.