Lipopolysaccharide transport from the peritoneal cavity to the blood: is it controlled by the vagus nerve?

Vagotomy suppresses fever and hyperalgesia caused by intraperitoneal lipopolysaccharide (LPS) but has little effect on the febrile response to intravenous or intramuscular LPS. This suggests that some vagus-mediated mechanisms are recruited only when LPS is administered via the intraperitoneal route. We hypothesized that such mechanisms are associated with LPS transport from the peritoneal cavity to the circulation. Adult Wistar rats underwent total subdiaphragmatic, bilateral selective celiac, or sham vagotomy. On day 28-32 after surgery, they were injected IP with Escherichia coli LPS (5, 20, or 100 microg/kg) or saline and decapitated 90 min thereafter. Their plasma levels of LPS and their plasma interleukin-6, adrenocorticotropin, and corticosterone responses to LPS were measured. Success of intraperitoneal administration of LPS was verified by increased interleukin-1beta and interleukin-6 concentrations in the peritoneal lavage fluid. Effectiveness of vagotomies was confirmed by increased stomach mass (food retention) and pancreas mass (hypertrophy). In the shams, LPS caused a dose-dependent endotoxemia and increased plasma levels of interleukin-6, adrenocorticotropin, and corticosterone. Neither celiac nor total vagotomy affected any of these responses. LPS escapes from the peritoneal cavity by two primary routes, viz., the hematogenous (via the portal vein) and lymphogenous (via the lymphatic system). The design of the present study did not allow for evaluating the rapid, hematogenous transport. The results obtained suggest that the abdominal vagus does not control the slow. lymphogenous escape of LPS from the peritoneal cavity.

Central administration of rat IL-6 induces HPA activation and fever but not sickness behavior in rats.

Interleukin (IL)-6 has been proposed to mediate several sickness responses, including brain-mediated neuroendocrine, temperature, and behavioral changes. However, the exact mechanisms and sites of action of IL-6 are still poorly understood. In the present study, we describe the effects of central administration of species-homologous recombinant rat IL-6 (rrIL-6) on the induction of hypothalamic-pituitary-adrenal (HPA) activity, fever, social investigatory behavior, and immobility. After intracerebroventricular administration of rrIL-6 (50 or 100 ng/rat), rats demonstrated HPA and febrile responses. In contrast, rrIL-6 alone did not induce changes in social investigatory and locomotor behavior at doses of up to 400 ng/rat. Coadministration of rrIL-6 (100 ng/rat) and rrIL-1beta (40 ng/rat), which alone did not affect the behavioral responses, reduced social investigatory behavior and increased the duration of immobility. Compared with rhIL-6, intracerebroventricular administration of rrIL-6 (100 ng/rat) induced higher HPA responses and early-phase febrile responses. This is consistent with a higher potency of rrIL-6, compared with rhIL-6, in the murine B9 bioassay. We conclude that species-homologous rrIL-6 alone can act in the brain to induce HPA and febrile responses, whereas it only reduces social investigatory behavior and locomotor activity in the presence of IL-1beta.

Biological activity and brain actions of recombinant rat interleukin-1alpha and interleukin-1beta.

IL-1alpha and IL-1beta have potent effects on the central nervous system resulting in fever, activation of the hypothalamic-pituitary-adrenal axis and behavioural depression. These effects have mainly been studied in rats, using recombinant human and mouse IL-1. Because IL-1alpha and IL-1beta show some species specificity in the potency of their biological activities, the objective of the present work was to directly compare the effects of recombinant rat IL-1alpha and IL-1beta in the rat system as a first step to dissect out the mechanisms that are involved in these effects. In vitro, recombinant rat IL-1alpha and IL-1beta bound with the same affinity as human IL-1 to the rat insulinoma Rin m5F cell line that mainly expresses type I IL-1 receptors. This binding activated IL-1 receptors, as shown by induction of the synthesis of TNF-alpha mRNA. In vivo, recombinant rat IL-1alpha and IL-1beta enhanced body temperature, increased plasma levels of corticosterone and ACTH, and depressed social behaviour. All these effects were obtained at doses 100-1,000 fold lower when IL-1 was injected centrally than when it was administered peripherally, indicating that they are centrally mediated. The relative potencies of recombinant rat IL-1alpha and IL-1beta were not the same depending on the endpoint and the route of injection, indicating that different mechanisms are likely to be involved in the various effects of IL-1 on the brain.

Interleukin 1 (IL-1) type I receptors mediate activation of rat hypothalamus-pituitary-adrenal axis and interleukin 6 production as shown by receptor type selective deletion mutants of IL-1beta.

The cytokine interleukin 1 (IL-1) plays an important role in the activation of the hypothalamus-pituary-adrenal (HPA)-axis and interleukin 6 (IL-6) production during infection or inflammation. Which of the interleukin-1 receptor types mediates these effects is not known. To investigate this issue a pharmacological approach was chosen by using recently developed IL-1 receptor type selective ligands. Rats were given one of various doses of recombinant human IL-1beta (rhIL-1beta; 1 and 10 microg/kg) and of several IL-1beta mutants (DeltaSND, DeltaQGE and DeltaI; 1, 10 and 100 microg/kg), that differ in their affinities for the IL-1 type I receptor but have similar affinities for the IL-1 type II receptor. One hour after intravenous administration of rhIL-1beta or IL-1beta mutants, plasma levels of ACTH, corticosterone (cort) and IL-6 were measured. Doses of 1 and 10 microg/kg rhIL-1beta markedly elevated plasma levels of ACTH, cort and IL-6. However, 10-100-fold higher doses of IL-1beta mutants DeltaSND and DeltaQGE and at least 100-fold higher doses of DeltaI have to be administered to increase plasma levels of ACTH, cort and IL-6. The potency differences correlate with their respective affinity for the type I receptor but not with that of the IL-1 type II receptor. It is concluded that IL-1beta induced ACTH, cort and IL-6 production is mediated by interleukin 1 type I receptors.

Individual variation in hypothalamus-pituitary-adrenal responsiveness of rats to endotoxin and interleukin-1 beta.

Intraperitoneal (i.p.) administration of lipopolysaccharide (LPS) or interleukin (IL)-1 beta induces activation of the hypothalamus-pituitary-adrenal (HPA) axis. In some experiments, a marked individual variation has been observed in HPA responses to these stimuli. We reasoned that only parameters that correlate with this variability may reflect signals involved in HPA activation. Although IL-1 beta is found in the peritoneal cavity and has been implicated in the HPA response to i.p. LPS, IL-1 beta levels in peritoneal lavage fluid did not correlate with the variation in HPA responsiveness and neither did IL-1 beta concentrations in plasma. In contrast, IL-6 concentrations in plasma, but not in peritoneal lavage fluid, correlated with this variation to i.p. LPS or IL-1 beta. We conclude that IL-6 in the plasma represents a major determinant of the individual variation in HPA responses to i.p. LPS or IL-1 beta. Because of its positive correlation with Fos expression in various brain-stem nuclei, we suggest that circulating IL-6 may facilitate the generation of signals in vagal afferents or potentiate vagal information transfer to lower brain-stem nuclei.

Role of circulating endotoxin and interleukin-6 in the ACTH and corticosterone response to intraperitoneal LPS.

Peripheral administration of lipopolysaccharide (LPS) may activate the hypothalamus-pituitary-adrenal (HPA) axis by way of both neural and humoral mechanisms. We have investigated whether biologically active endotoxin appears in the general circulation after intraperitoneal administration of LPS (5 or 100 micrograms/kg) to rats and whether this is a prerequisite for activation of this HPA axis. Within 15 min, endotoxin appeared in the general circulation, whereas elevations of plasma adrenocorticotropic hormone (ACTH), corticosterone, and interleukin (IL)-6 concentrations were not detected until 90 min after LPS injection. At this time, a marked interindividual variation was observed in plasma concentrations of endotoxin, ACTH, corticosterone, and IL-6. Elevated levels of plasma endotoxin were associated with elevated levels of ACTH, corticosterone, and IL-6. Intravenous administration of the LPS antagonist cationic antimicrobial protein 18 (5 mg/kg), which did not affect cytokine production in the peritoneal cavity, markedly reduced plasma ACTH, corticosterone, and IL-6 levels after 5 micrograms/kg LPS. Our results suggest that circulating endotoxin is required for the activation of the HPA axis. They also favor a role for circulating IL-6 in this response.

Effects of flavonoids on aromatase activity, an in vitro study.

In the study, the inhibitory effect of flavonoids, including isoflavonic phytoestrogens, on the ovarian aromatase enzyme complex from the rainbow trout, Oncorhynchus mykiss, was assessed in vitro. Some of the compounds tested on fish were also tested on human placental aromatase activity as a comparison between the two sources of enzyme. It was found that flavone, dl-aminoglutethimide, apigenin, quercetin, 7,4'- dihydroxyflavone, alpha-naphthoflavone and equol were potent inhibitors of the ovarian aromatase activity in rainbow trout. Relative potencies (RP) of these compounds compared to flavone (assigned an effect of 1) were, respectively, 19.0, 8.7, 5.3, 3.7, 3.2 and 0.9. Two other phytoestrogens, namely biochanin A and genistein, slightly inhibited aromatase activity. Finally, 7-hydroxyflavone, formononetin, daidzein, coumestrol, chrysin, flavanone and estradiol-17beta did not inhibit ovarian aromatase activity at doses up to 1000 microM. Experiments on human placental aromatase showed inhibitory effects of dl-aminoglutethimide, flavone, flavanone and equol with RP values of 2.8. 1, 1.5 and 0.4, respectively. These results are in accordance with previous studies. The influence of the experimental procedure on IC50 values and RP is discussed.

Steroid hormone secretion by testicular tissue from African catfish, Clarias gariepinus, in primary culture: identification and quantification by gas chromatography - mass spectrometry.

With the final aim of identifying the testicular steroids involved in the feedback mechanism of the hypothalamus-pituitary-gonad axis, steroid secretion by the testis of African catfish, Clarias gariepinus, was studied in vitro, by means of gas chromatography followed by mass spectrometry. Testicular fragments of sexually mature catfish raised in captivity were incubated in L-15 medium with and without catfish pituitary extract (cfPE). Without adding cfPE, 22 steroids could be identified, amongst which 11ß-hydroxyandrostenedione, 11ß-hydroxytestosterone, 11-ketotestosterone and 11-ketoandrostenedione were dominating. After incubation in the presence of cfPE, the concentrations of the four 11-oxygenated steroids were increased about 4-fold. The amounts of pregnane derivatives in the incubation medium showed the largest increases in the presence of cfPE. 5ß-Pregnane-triol levels, for example, were 60-fold higher than in the medium from control incubations. The secretion of 5α- and 5ß-androstanes was also stimulated by cfPE.The stimulation was not equal for all steroids, indicating that cfPE not only stimulates total steroidogenesis by increasing the availability of cholesterol, but also by influencing specific steroid converting enzyme activities.