Interleukin-1 induces changes in norepinephrine metabolism in the rat brain

Central action of interleukin 1 beta on intestinal motility in rats: mediation by two mechanisms

BACKGROUND

Interleukin 1 (IL-1) can influence gut functions by inhibiting gastric acid secretion. This study was performed to investigate the effects of IL-1 on intestinal motility and the mechanisms involved.

METHODS

The effects of IL-1 beta were determined by electromyography in conscious rats with implanted electrodes and a permanent catheter in a lateral brain ventricle.

RESULTS

Intracerebroventricular IL-1 beta (15 ng) administered to fed rats immediately stimulated cecocolonic spike bursts and caused a migrating myoelectric complex pattern after a delay in the small intestine. Tenfold higher doses of peripherally administered IL-1 beta did not promote similar reactions. The IL-1 antagonist reduced the small intestinal effect of IL-1 beta and blocked the cecocolonic stimulation. Indomethacin and SC 19220 reduced the small intestinal effects but did not antagonize the increase in cecocolonic contractions. In contrast, alpha-helical CRF9-41 blocked the increase of cecocolonic contractions but did not antagonize the IL-1 beta-induced effects on the small intestine.

CONCLUSION

IL-1 beta's effects on intestinal motility can be mainly ascribed to a central action. The cecocolonic stimulation may be mediated by brain corticotropin-releasing factor, whereas the small intestinal effects involve a prostaglandin mediation.

Differential induction of c-Fos immunoreactivity in hypothalamus and brain stem nuclei following central and peripheral administration of endotoxin

Lipopolysaccharide (LPS), an endotoxin associated with gram-negative bacteria, is a potent activator of the immune system. We have tested the effects of ICV infusions of LPS (10 ng) or Ringer's solution on the induction of the proto-oncogene protein c-Fos in the brain as well as plasma levels of corticosterone and splenic concentrations of norepinephrine (NE) and VIP. At 3 h post-ICV infusion of LPS, numerous labeled neurons were observed in the paraventricular nucleus (PVN) of the hypothalamus and the nucleus tractus solitarius (A2) region of the brain stem. Also, corticosterone and splenic NE and VIP levels were all elevated post-ICV LPS. Analysis of the time course for the induction of c-Fos protein in the brain following IP injections of LPS indicated that, relative to control injections, increased numbers of c-Fos-positive cells were detected in the PVN 0.5 h following IP injections (100 micrograms), peaked at 2-3 h postinjection, and then returned to control levels at later intervals. Additional dose-response data for IP LPS indicated a small increase in the number of labeled cells at a dose of 4.0 micrograms, and the number and staining intensity increased up to a dose of 100 micrograms. Corticosterone levels followed a similar pattern and were elevated at the 4.0 micrograms IP dose of LPS and increased to peak levels at 40 micrograms and higher. In contrast to ICV injections, splenic NE levels were unaltered by IP injections of LPS.(ABSTRACT TRUNCATED AT 250 WORDS)

Continuous in vivo treatment with catecholamines suppresses in vitro reactivity of rat peripheral blood T-lymphocytes via α-mediated mechanisms

A 20 h continuous treatment of rats with catecholamines, using subcutaneously implantable retard tablets, had either no (adrenaline, isoproterenol, midodrine) or a slight (noradrenaline) suppressive effect on the in vitro responsiveness of peripheral blood T-lymphocytes. A marked suppression of the mitogen response ensued when adrenaline, noradrenaline or midodrine, but not isoproterenol, was applied together with the beta-receptor blocker propranolol, whereas the combination with the alpha-receptor blocker phentolamine had no effect. The mitogen response of splenic lymphocytes was not affected by any of these treatments. This alpha-mediated adrenergic suppression of peripheral blood T-cells was not correlated with general metabolic alterations, shifts in white blood cell counts or CD4+/CD8+ subsets, or with elevated glucocorticoid levels. The data suggest that to consistently influence the reactivity of rat peripheral blood lymphocytes by chronic adrenergic stimuli in vivo requires both high catecholamine levels and a bias towards alpha-adrenergic receptivity.

Tumor necrosis factor modulates the inactivation of catecholamine secretion in cultured sympathetic neurons

Cytokines exert multiple effects on cellular functions. We studied the effects of cytokines on the calcium-dependent release of catecholamines in cultured neurons from neonatal rat superior cervical ganglia. Incubation of sympathetic neurons with recombinant human interleukin-1 beta (0.14-0.7 nM) or recombinant human tumor necrosis factor-alpha (1 nM) for 24-48 h had no effect on the baseline spontaneous release and the initial K(+)-evoked [3H]norepinephrine release, compared with untreated cells. A repeat K(+)-induced depolarization after 6 min resulted in a decrease of [3H]norepinephrine secretion to 69 +/- 5.8% (n = 11) of the initial secretion in recombinant human tumor necrosis factor-treated cells, but not in control cells. The secretory response was restored when the interval between the two K+ challenges was increased to 10 min. We conclude that the diminished secretory response to a repeat stimulus in recombinant human tumor necrosis factor-treated superior cervical ganglia neurons is due to a prolonged recovery from inactivation of secretion in these cells.

Interleukin-1 inhibits serotonin release from the hypothalamus in vitro

During a 60-min incubation period, the in vitro release of serotonin (5-HT) from the hypothalami of control male rats decreased by 12.3 +/- 3.1%. In contrast, the presence of 25 ng of interleukin-1 beta (IL-1 beta) in the incubation medium more than doubled this decrease to 29.3 +/- 3.3% (P < 0.001), and the presence of 50 ng of IL-1 beta more than quadrupled this decrease to 53.7 +/- 7.4% (P < 0.001). The decrease produced by the higher dose of IL-1 beta was significantly greater than that produced by the lower dose (P < 0.01), indicating a dose response. During the next two 60-min periods when the hypothalami of the control as well as treatment groups were incubated without IL-beta, 5-HT release continued to decrease and then became stabilized in the control group. In contrast, 5-HT release in the treatment groups rebounded before becoming stabilized at levels that were not significantly different from those in the control group. It is concluded that IL-1 beta inhibits the release of serotonin from the hypothalamus in vitro.

Hypothalamic noradrenergic pathways exert an influence on neuroendocrine and clinical status in experimental autoimmune encephalomyelitis

The immunomodulatory action of corticosteroids and the ability of central noradrenergic systems to activate the hypothalamic-pituitary-adrenal (HPA) axis led us to investigate the relationship between neuroendocrine status and the clinical course of encephalomyelitis (EAE) following adrenalectomy and depletion of noradrenaline (NA) centrally or peripherally. A significant inverse correlation was found between hypothalamic NA and serum corticosterone (CS) at peak clinical signs of EAE in all the sham groups or when NA was depleted only in the peripheral nervous system. A positive correlation was found between serum CS and disease severity, and in all experimental groups with intact peripheral and/or central noradrenergic pathways a uniformly increased splenic NA content was also observed at peak disease. Administration of 6-OHDA i.p. to neonatal or adult Lewis rats produced a significant depletion of splenic NA alone which resulted in increased disease severity, despite the fact that circulating CS was elevated. Thus the rise in the NA content of lymphoid tissue at peak clinical signs contributes to recovery. A single i.c.v. injection of 6-OHDA into the hypothalamic region resulted in an 80% reduction in NA content, which subsequently modified the clinical severity of EAE. Serum CS levels rose preclinically in the treated group and remained high despite milder clinical disease than that seen in the sham group. The overriding immunoregulatory influence of glucocorticoids is demonstrated by the rapid onset of clinical EAE and morbidity in adrenalectomized animals. However, the strong inverse correlation found between hypothalamic NA and circulating CS indicates that regulation of the HPA axis may ultimately be controlled by central sympathetic pathways.

Stress- and endotoxin-induced increases in brain tryptophan and serotonin metabolism depend on sympathetic nervous system activity

Stressful treatments and immune challenges have been shown previously to elevate brain concentrations of tryptophan. The role of the autonomic nervous system in this neurochemical change was investigated using pharmacological treatments that inhibit autonomic effects. Pretreatment with the ganglionic blocker chlorisondamine did not alter the normal increases in catecholamine metabolites, but prevented the increase in brain tryptophan normally observed after footshock or restraint, except when the duration of the footshock period was extended to 60 min. The footshock- and restraint-related increases in 5-hydroxyindoleacetic acid (5-HIAA) were also prevented by chlorisondamine. The increases in brain tryptophan caused by intraperitoneal injection of endotoxin or interleukin-1 (IL-1) were also prevented by chlorisondamine pretreatment. The footshock-induced increases in brain tryptophan and 5-HIAA were attenuated by the beta-adrenergic antagonist propranolol but not by the alpha-adrenergic antagonist phenoxybenzamine or the muscarinic cholinergic antagonist atropine. Thus the autonomic nervous system appears to be involved in the stress-related changes in brain tryptophan, and this effect is due to the sympathetic rather than the parasympathetic limb of the system. Moreover, the main effect of the sympathetic nervous system is exerted on beta- as opposed to alpha-adrenergic receptors. We conclude that activation of the sympathetic nervous system is responsible for the stress-related increases in brain tryptophan, probably by enabling increased brain tryptophan uptake. Endotoxin and IL-1 also elevate brain tryptophan, presumably by a similar mechanism. The increase in brain tryptophan appears to be necessary to sustain the increased serotonin catabolism to 5-HIAA that occurs in stressed animals, and which may reflect increased serotonin release.

Time-dependent variations of central norepinephrine and dopamine following antigen administration

Administration of sheep red blood cells (10(6) cells, i.p.) resulted in central norepinephrine (NE) and dopamine (DA) changes which corresponded with the time of the peak immune response. These amine variations, however, appeared to be specific to certain brain regions. The increased accumulation of the NE metabolite, 3-methoxy-4-hydroxyphenylethylene glycol, was evident in hypothalamus, locus coeruleus and hippocampus and a moderate reduction of NE was evident in the hypothalamus. Alterations of DA levels or utilization appeared in mesocorticolimbic structures (i.e. nucleus accumbens and prefrontal cortex) but not in striatum. This profile of transmitter changes was reminiscent of that previously shown to be induced by uncontrollable stressors and the possibility was offered that antigenic challenge is interpreted as a stressor by the central nervous system.

Cytokine-induced activation of the neuroendocrine stress axis persists in endotoxin-tolerant mice

Chronic administration of lipopolysaccharide (LPS) to mice markedly reduced activation of the neuroendocrine stress axis elicited by an acute challenge dose of LPS. LPS-induced elevation in norepinephrine turnover in the hypothalamus showed complete tolerance whereas elevation of plasma corticosterone showed only partial tolerance. Challenge-induced increased turnover of dopamine in hypothalamus persisted in LPS-tolerant animals. Neuroendocrine activation persisted following acute challenge with interleukin-1 and tumor necrosis factor following chronic LPS exposure.

Interleukin-1, interleukin-6: messengers in the neuroendocrine immune system?

Recent findings indicate that interleukin-1 (IL-1) and interleukin-6 (IL-6), cytokines secreted by immunologically activated monocytes and macrophages modulate neuroendocrine function. The site of production (centrally, peripherally), the site of action and the physiological significance of IL-1 and IL-6 as "classical hormones" are questioned.

Immunoregulators in the nervous system

The nervous system, through the production of neuroregulators (neurotransmitters, neuromodulators and neuropeptides) can regulate specific immune system functions, while the immune system, through the production of immunoregulators (immunomodulators and immunopeptides) can regulate specific nervous system functions. This indicates a reciprocal communication between the nervous and immune systems. The presence of immunoregulators in the brain and cerebrospinal fluid is the result of local synthesis--by intrinsic and blood-derived macrophages, activated T-lymphocytes that cross the blood-brain barrier, endothelial cells of the cerebrovasculature, microglia, astrocytes, and neuronal components--and/or uptake from the peripheral blood through the blood-brain barrier (in specific cases) and circumventricular organs. Acute and chronic pathological processes (infection, inflammation, immunological reactions, malignancy, necrosis) stimulate the synthesis and release of immunoregulators in various cell systems. These immunoregulators have pivotal roles in the coordination of the host defense mechanisms and repair, and induce a series of immunological, endocrinological, metabolical and neurological responses. This review summarizes studies concerning immunoregulators--such as interleukins, tumor necrosis factor, interferons, transforming growth factors, thymic peptides, tuftsin, platelet activating factor, neuro-immunoregulators--in the nervous system. It also describes the monitoring of immunoregulators by the central nervous system (CNS) as part of the regulatory factors that induce neurological manifestations (e.g., fever, somnolence, appetite suppression, neuroendocrine alterations) frequently accompanying acute and chronic pathological processes.

Lymphocyte-mediated regulation of neurotransmitter gene expression in rat sympathetic ganglia

It has been previously shown that sympathetic noradrenergic nerve fibers, in addition to supplying the smooth muscle of the splenic capsule, trabeculae and blood vessels, also form very tight appositions with lymphocytes of the periarteriolar lymphatic sheath. To determine whether there is a direct communication between the sympathetic neurons and the immune cells we have grown dissociated superior cervical ganglion (SCG) neurons together with splenic lymphocytes. Sympathetic neurons were grown both as mixed preparations (neurons and non-neuronal ganglion cells) and neuron-enriched preparations. These systems were used to investigate whether coculture with splenocytes alters neurotransmitter gene expression in SCG cultures. Northern blot analysis was used to measure changes in neurotransmitter mRNA expression. The results showed that expression of mRNA for tyrosine hydroxylase (TH), the rate-limiting enzyme in catecholamine biosynthesis, was significantly decreased when SCG cultures were grown in the presence of spleen cells compared to control SCGs grown either alone or in the presence of erythrocytes. When the mitogen concanavalin A (ConA) was used to stimulate the spleen cells in the cocultures the decrease in TH was more pronounced. In contrast, preprotachykinin-A (PPT-A) mRNA expression in cultured SCGs increased in the cocultures. Another neuropeptide, neuropeptide Y (NPY), showed different responses in the presence of stimulated vs. unstimulated splenocytes. NPY mRNA was slightly increased in the presence of resting spleen cells, but showed a 70% decrease when ConA was added to the cocultures. Thus, our results suggest that lymphocytes can differentially regulate neurotransmitter gene expression in sympathetic ganglia.

Reduction of exploratory behavior by intraperitoneal injection of interleukin-1 involves brain corticotropin-releasing factor

The behavior of mice was scored in a multicompartment chamber one hour following intraperitoneal injection of recombinant human interleukin-1 (IL-1). Both IL-1 alpha and IL-1 beta dose-dependently reduced the mean duration for which mice were in contact with novel stimuli without altering measures of locomotor activity, such as movements between the compartments or rears. These behavioral changes resemble those previously observed with prior restraint or intracerebroventricular (ICV) injection of corticotropin-releasing factor (CRF). Effective doses were in the range 0.1-10 ng for IL-1 alpha, and 1-10 ng for IL-1 beta. The reduction in stimulus-contact times induced by 1 ng of IL-1 beta was reversed by prior ICV injection of the CRF antagonist, alpha-helical CRF9-41, suggesting that IL-1 causes secretion of brain CRF which in turn elicits the behavioral changes. These results indicate that peripheral administration of IL-1 alpha or IL-1 beta in low doses can alter behavior. They provide additional evidence that IL-1 administration stimulates brain CRF secretion, and that brain CRF can modulate exploratory behavior, and thus reinforces the concept that IL-1 administration can induce stress.

Intracerebroventricular administration of interleukin-1 to mice alters investigation of stimuli in a novel environment

The behavior of mice administered recombinant interleukin-1 (IL-1) was observed in a novel multicompartment chamber. Doses of human IL-1 alpha (4 pg to 40 ng) injected intracerebroventricularly (ICV) 20 min before testing significantly reduced the mean time mice spent in contact with novel stimuli. No other behavior scored (locomotor activity, grooming, scratching) was significantly affected. Similar results were obtained with murine IL-1 alpha (770 pg or 77 ng) and hIL-1 beta (1 pg to 10 ng). This behavioral change resembled that induced following restraint or ICV injection of corticotropin-releasing factor (CRF). The behavioral effect of ICV IL-1 was lost after it was heated for 10 min at 100 degrees C. Neither the CRF antagonist, alpha-helical CRF9-41 (10 or 20 micrograms ICV) nor the prostaglandin synthesis inhibitor indomethacin (50 mg/kg IP) significantly altered the hIL-1 alpha-induced behavioral changes, but naloxone (0.7 mg/kg SC) or sulpiride (5 mg/kg IP) completely prevented them. Our results suggest that intracerebral administration of IL-1 reduces the exploratory behavior of mice. This effect does not apparently involve CRF or prostaglandins, but may involve opioid and dopaminergic systems. This behavioral response to IL-1 administration is consistent with the behavioral effects of IL-1 reported previously, and strengthens the hypothesis that IL-1 secretion may be responsible for behavioral changes associated with immune activation.

The central inhibitory effect of interleukin-1 on gastric acid secretion

The effect of interleukin-1 (IL-1) on gastric secretory functions was examined in pylorus-ligated conscious rats. Intracisternal (i.c.) injection of IL-1 beta (1-100 ng) induced dose-related, long-lasting inhibition of gastric acid output, which was due to the reductions of both the amount and the acid concentration of the gastric juice. A much higher dose of IL-1 alpha was required to achieve identical effects on gastric acid secretion when it was given by intravenous routes. The i.c. injection of IL-1 alpha also had an inhibition of gastric secretion. This inhibitory effect of i.c. applied IL-1 beta on gastric acid secretion was completely abolished in indomethacin-pretreated animals but not in reserpine-pretreated ones. These results suggest that IL-1 may have an inhibitory action on the regulation of gastric secretory functions by its central action which is dependent on the eicosanoid metabolism.

Increased ratio of quinolinic acid to kynurenic acid in cerebrospinal fluid of D retrovirus-infected rhesus macaques: relationship to clinical and viral status

Increased concentrations of excitotoxin quinolinic acid in cerebrospinal fluid (CSF) are associated with infection with the human immunodeficiency virus (HIV-1) and have been implicated in the pathogenesis of the acquired immune deficiency syndrome (AIDS) dementia complex. In the present study, inoculation of macaques with D/1/California, an immunosuppressive serotype 1 type D retrovirus, was associated with acute and chronic increases in CSF and serum quinolinic acid concentrations in macaques that had developed SAIDS, a simian disease analogous to AIDS in humans--particularly macaques with demonstrable opportunistic infections. Kynurenic acid, an antagonist of excitatory amino acid receptors as well as the excitotoxic effects of quinolinic acid, was also increased in the CSF of SAIDS macaques, but to a significantly lesser degree than was quinolinic acid (kynurenic acid, 1.8-fold; quinolinic acid, 15.6-fold). CSF quinolinic acid, but not kynurenic acid, was also increased in viremic macaques with SAIDS-related complex (2.4-fold) and asymptomatic virus positive carriers (3.4-fold). Macaques that had recovered from D/1/California infection and were antibody positive and virus negative had normal CSF quinolinic acid and kynurenic acid concentrations. Increased activity of indoleamine-2,3-dioxygenase, the first enzyme of the kynurenine pathway, was indicated in the macaques with SAIDS by reduced serum L-tryptophan and elevated serum L-kynurenine concentrations. Macaques infected with D/1/California may provide a primate model for investigation of the mechanisms involved in increases in CSF quinolinic acid in retrovirus and other infectious diseases, including HIV-1. It remains to be determined whether the increased CSF quinolinic acid concentrations and the increased ratio of quinolinic acid to kynurenic acid have neurological significance or are a useful "marker" of infection.

Cytokine modulation of pituitary hormone secretion

A rapidly expanding body of evidence indicates that cytokines do indeed regulate pituitary hormone secretion. Recent studies with cytokines in vivo and in vitro support the idea that cytokines are the principal mediators of the neuroendocrine responses previously observed in infectious and inflammatory states. The dominant route of this modulation appears to be via the brain and hypothalamus, although a role for direct effects on the pituitary has not been excluded. These effects may be mediated by circulating cytokines, endogenously produced cytokines, or both. A number of receptor systems and second messengers may be involved, and a role for arachidonate metabolite pathways appears particularly likely. A final question: Of what use to the organism is the ability of immune activation to control pituitary hormone secretion? For some pituitary secretions there is a reasonable basis for speculation. Glucocorticoids serve to limit the severity of immune responses and recent studies argue that defects in this pathway permit the expression of autoimmune disease. Inhibition of thyroid function may limit the catabolic side effects of infectious illness. Stimulation of growth hormone could have the same effect, and growth hormone and prolactin may serve to enhance some immune responses.

Increased biogenic amine release in mouse hypothalamus following immunological challenge: antagonism by indomethacin

Stimulation of the acute-phase response in mice by lipopolysaccharide, pokeweed mitogen, concanavalin A or interleukin-1 was associated with increased release of biogenic amines, serotonin and norepinephrine in the hypothalamus as indexed by their primary metabolites, 5-hydroxyindoleacetic acid and 3-methoxy-4-hydroxyphenylglycol, respectively. The increases in norepinephrine and serotonin turnover observed 4 h following systemic administration of interleukin-1 were antagonized by concurrent administration of indomethacin, a potent inhibitor of cyclooxygenase. These data suggest that the increase in norepinephrine and serotonin release in mouse hypothalamus during the acute-phase response to infection is partially mediated by the actions of arachidonic acid metabolites.

Splenic noradrenergic and adrenocortical responses during the preclinical and clinical stages of adoptively transferred experimental autoimmune encephalomyelitis (EAE)

When experimental autoimmune encephalomyelitis (EAE) is induced by adoptive transfer of myelin basic protein (MBP)-specific lymphocytes the splenic noradrenergic and adrenocortical responses mirror in most respects those that occur following sensitization with spinal cord and Freund's adjuvant (CFA), despite the absence of the primary immune challenge. An early drop in splenic noradrenaline (NA), observed only when purified protein derivative-primed cells are transferred may reflect a vigorous proliferative response in vitro, not observed with MBP-specific cells. However, serum corticosterone (CS) levels and the density of splenocyte beta-adrenergic receptors were increased in both experimental groups within 3 days of cell inoculation. The stress of clinical signs of EAE resulted in highly significant increases in both splenic NA and plasma CS. Thus adoptively transferred EAE provides a well-delineated model of autoimmune disease for investigating the immunomodulatory role of the neural and endocrine systems.

Indomethacin prevents increased catecholamine turnover in rat brain following systemic endotoxin challenge

1. Key features of the acute phase response to infection are replicated by systemic administrations of lipopolysaccharide and may be mediated via the production of lymphokines and cytokines, including interleukin-1. Inhibition of prostaglandin synthesis may attenuate certain features of the acute phase response. 2. In the present study, the effects of systemic administration of the lipopolysaccharide (LPS, 250 micrograms/rat) and interleukin-1 (IL-1, 10 micrograms/rat) on catecholamine metabolism in different brain regions were compared and the effects of indomethacin, a cyclooxygenase inhibitor was determined. 3. The ratio of metabolite to parent amine was used as an index of turnover of catecholamines. 4. In hypothalamus, both epinephrine and norepinephrine concentrations were decreased and their major metabolite, 3-methoxy,4-hydroxyphenylglycol (MHPG), was elevated at 4, 8 and 24 hr following LPS. The major metabolite of dopamine (homovanillic acid, HVA) was increased at 8 hours in striatum, hypothalamus and medulla. LPS increased dopamine turnover at 8 and 24 hr and norepinephrine turnover at 4, 8 and 24 hr. 5. In all regions examined, IL-1 produced effects similar to LPS on amine and metabolite contents and norepinephrine and dopamine turnover. 6. Significantly, co-administration of a single dose of indomethacin (50 mg/kg) completely blocked LPS-induced changes in hypothalamic catecholamines and metabolites and the increase in turnover at 4 and 8 hr. Furthermore, the effects of IL-1 on hypothalamic MHPG content and norepinephrine turnover were also blocked by indomethacin, although the effects of IL-1 on regional catecholamines and HVA content and turnover were either not modified or partially antagonized by indomethacin. 7. The present results suggest that in the rat, activation of noradrenergic, dopaminergic and epinephrine-containing neurons in hypothalamus, as well as dopaminergic neurons in other regions is associated with the acute phase response to endotoxin and that synthesis of prostaglandins plays a pivotal role in catecholamine responses in all brain regions examined.

Interleukins, signal transduction, and the immune system-mediated stress response

Overwhelming evidence indicates that the administration of cytokines such as IL-1 alpha and beta, IL-6, and TNF-1 alpha stimulates one or more components of the HPA axis. The hypothesis driving this research is that host infection and tissue injury trigger the synthesis and release of several cytokines that act locally at sites of trauma and distally upon entering the circulation. Available evidence suggests that the primary source of HPA axis-acting or circulating cytokines is activated monocytes or macrophages; therefore, a direct relationship should exist between the appearance of monokines in plasma and the subsequent appearance of pituitary-adrenocortical hormones in plasma as well. Clarification of the physiological role of monokines as mediators of the host stress response will come from in vivo studies in which the type, sequence of appearance, duration of elevation, and quantification of each monokine is monitored along with ACTH and glucocorticoids, following an appropriate immune challenge. In several recent reports, investigators have administered bacterial-derived endotoxin or LPS to stimulate the physiological events associated with infection or injury and chronicled plasma levels of IL-1, IL-6, and TNF-alpha (37,56,57). In human subjects, endotoxin challenge enhanced plasma TNF-alpha levels by 1 hour, which returned to basal levels by 4 hours (37), whereas, IL-6 plasma activity increased at 2 hours post-challenge and returned to baseline by 6 hours (56). Thus, both of these monokines are implicated as possible acute activators of the HPA axis. In perhaps the most revealing study to date, LPS challenge of mice indicated both a differential appearance and disappearance rate in serum for TNF-alpha and IL-1 and a differential regulation of these monokines by glucocorticoid feedback (57). Serum TNF was detected 45 minutes post-LPS, peaked by 1 hour, and returned to control levels by 3 hours. Serum corticosterone concentrations rose rapidly over a time course similar to that of TNF. Even after serum TNF concentration had returned to basal conditions, corticosterone levels remained maximally elevated, and serum corticosterone was still significantly above basal levels 24-hour post-LPS. The rapid return of circulating TNF to pre-LPS challenge levels appeared to be regulated by negative glucocorticoid feedback, because TNF remained maximally elevated for at least 6 hours in adrenalectomized or hypophysectomized mice. LPS-induced levels of IL-1 were delayed as compared to serum TNF, peaked at 4 hours, and remained elevated even at 24 hours.(ABSTRACT TRUNCATED AT 400 WORDS)

Mechanism of virus-induced stimulation of the hypothalamus-pituitary-adrenal axis

Increased blood levels of glucocorticoids are observed during certain viral infections. In this paper, we report data obtained from a model in rodents showing that the pituitary-adrenal axis is stimulated following inoculation of Newcastle Disease Virus (NDV). No evidence for an ectopic, lymphoid source of ACTH-like immunoreactive material capable of inducing this effect was obtained. Administration of virus-free supernatants from cocultures of human peripheral blood leukocytes with NDV also stimulated ACTH and glucocorticoid output in normal mice. This observation showed the immunological cell origin of the mediator of the hormonal effect. Pretreatment of the supernatant with anti-IL-1 sera neutralized its capacity to induce an increase in glucocorticoid and ACTH levels in blood. Furthermore, injection of IL-1 in nanogram amounts also increased ACTH and glucocorticoid blood levels. Thus, we conclude that IL-1 is the most likely mediator of the stimulation of the pituitary-adrenal axis during viral infection. The reported data are also discussed in the general context of the postulated glucocorticoid-associated immunoregulatory circuit.