Central CRF, urocortins and stress increase colonic transit via CRF1 receptors while activation of CRF2 receptors delays gastric transit in mice

Recently characterized selective agonists and developed antagonists for the corticotropin releasing factor (CRF) receptors are new tools to investigate stress-related functional changes. The influence of mammalian CRF and related peptides injected intracerebroventricularly ( i.c.v. ) on gastric and colonic motility, and the CRF receptor subtypes involved and their role in colonic response to stress were studied in conscious mice. The CRF₁/CRF₂ agonists rat urocortin 1 (rUcn 1) and rat/human CRF (r/h CRF), the preferential CRF₁ agonist ovine CRF (oCRF), and the CRF₂ agonist mouse (m) Ucn 2, injected i.c.v. inhibited gastric emptying and stimulated distal colonic motor function (bead transit and defecation) while oCRF_9–33OH (devoid of CRF receptor affinity) showed neither effects. mUcn 2 injected peripherally had no colonic effect. The selective CRF₂ antagonist astressin₂-B ( i.c.v. ), at a 20 : 1 antagonist: agonist ratio, blocked i.c.v. r/hCRF and rUcn 1 induced inhibition of gastric transit and reduced that of mUcn 2, while the CRF₁ antagonist NBI-35965 had no effect. By contrast, the colonic motor stimulation induced by i.c.v. r/hCRF and rUcn 1 and 1h restraint stress were antagonized only by NBI-35965 while stimulation induced by mUcn 2 was equally blocked by both antagonists. None of the CRF antagonists injected i.c.v. alone influenced gut transit. These data establish in mice that brain CRF₁ receptors mediate the stimulation of colonic transit induced by central CRF, urocortins (1 and 2) and restraint stress, while CRF₂ receptors mediate the inhibitory actions of these peptides on gastric transit.     

Role of cysteinyl leukotriene receptor antagonists in the management of allergic rhinitis

The cysteinyl leukotrienes (CysLTs) are lipid mediators that have been implicated in the pathogenesis of allergic diseases. Pharmacological studies using CysLTs indicate that there exist two classes of receptors named CysLT₁ and CysLT₂. The former is sensitive to CysLT₁ receptor antagonists currently used for the treatment of asthma and allergic rhinitis. Our previous immunohistochemical and autoradiographic studies showed that anti-CysLT₁ receptor antibody adhered to eosinophils, mast cells, macrophages, neutrophils, and vascular endothelial cells in human nasal mucosa, and that a novel radioactive CysLT₁ receptor antagonist, [³H]-pranlukast, bound specifically to CysLT₁ receptors in human inferior turbinate and its binding sites were localized to vascular endothelium and interstitial cells. These data suggest that in allergic rhinitis, the major targets of CysLT₁ receptor antagonists are the vascular bed and infiltrating leucocytes such as mast cells, eosinophils, and macrophages. Clinical trials have demonstrated that CysLT₁ receptor antagonists are as effective as antihistamines, but are less effective than intranasal steroids for the treatment of allergic rhinitis. The use of CysLT₁ receptor antagonists in combination with antihistamines has generally resulted in greater efficacy than when these agents were used alone.     

Cyclic AMP-dependent Cl− secretion induced by thromboxane A2 in isolated human colon

Increased release of thromboxane A₂ (TXA₂) has been shown to be involved in inflammatory bowel diseases. In the present study, we have investigated the effect of a stable TXA₂ analogue (STA₂) on the electrical parameters in isolated human colonic mucosa. In the human mucosa set between Ussing chambers, STA₂ stimulated Cl⁻ secretion in a concentration-dependent manner with an EC₅₀ of 0.06 μ m . The STA₂-induced Cl⁻ secretion was significantly inhibited by ONO-3708 (10 μ m ), a specific TXA₂ receptor antagonist. The effect of STA₂ (0.3 μ m ) was independent of the colonic segment from which the tissue was obtained, from caecum to rectum. Chromanol 293B, an inhibitor of the cAMP-dependent KvLQT1 channel, attenuated the STA₂-induced Cl⁻ secretion in the human colonic mucosa (IC₅₀ value 1.18 μ m ). We found that KvLQT1 mRNA and protein were expressed in all the tested segments of the human colon. The STA₂-induced Cl⁻ secretion was significantly inhibited by 8-bromo-2'-monobutyryladenosine-3',5'-cyclic monophosphorothioate (50 μ m ), a membrane-permeant cAMP antagonist. STA₂ (0.3 μ m ) significantly increased the intracellular cAMP levels and the short-circuit current via TXA₂ receptor in a human colonic cell line. These results suggest that the TXA₂-induced Cl⁻ secretion in the colon is mediated via the cAMP pathway in addition to the Ca²⁺–calmodulin pathway which was previously reported.     

Role of vasopressin in rat distal colon function

The specific role of vasopressin in colonic crypt function and its possible synergistic action with aldosterone were studied. Sprague-Dawley rats fed a high-Na⁺ (HS; 150 m m NaCl) or a low-Na⁺ (LS; 150 μ m NaCl) diet were deprived of water or infused with vasopressin, and some animals were treated with specific vasopressin receptor subtype V₁ and V₂ antagonists. The expression of the epithelial Na⁺ channel (ENaC), α-smooth muscle actin (α-SMA) and aquaporin-2 (AQP-2) were determined by immunolocalization in distal colonic mucosa. The pericryptal Na⁺ concentration was determined by confocal microscopy, using a low-affinity Na⁺-sensitive fluorescent dye (sodium red) and crypt permeability was measured by the rate of escape of fluorescein isothiocyanate-labelled dextran (10 kDa) from the crypt lumen into the pericryptal space in isolated rat distal colonic mucosa. A high plasma concentration of vasopressin raised α-SMA expression in the pericryptal sheath ( P < 0.05), increased the pericryptal Na⁺ accumulation in this space ( P < 0.01) and caused a reduction of crypt wall permeability ( P < 0.01). All these effects were reversed by selective blockade of V₁ and V₂ receptors. No synergistic effects with aldosterone were observed. Dehydration and vasopressin infusion increased AQP-2 expression in distal colonic mucosa ( P < 0.05). This action of vasopressin was prevented by tolvaptan, a specific V₂ receptor antagonist ( P < 0.05). It is concluded that vasopressin has trophic effects in the rat distal colon, increasing pericryptal myofibroblast growth which affects crypt absorption, and these effects are independent of the presence of aldosterone.     

In vitro and in vivo analysis of the Effects of corticotropin releasing factor on rat dorsal vagal complex

In vivo and in vitro electrophysiological experiments were performed on the rat dorsal vagal complex (DVC, i.e. nucleus of the tractus solitarius, NTS, and dorsal motor nucleus of the vagus, DMV) to examine the effects of corticotropin releasing hormone (CRF) on the central components of the vago-vagal reflex control of gastric function. When applied to gastrointestinal projecting DMV neurones, CRF (10-300 n m ) induced a concentration-dependent membrane depolarization, an increase in action potential firing rate and decrease in amplitude of the action potential afterhyperpolarization ( P < 0.05). Pretreatment with the non-selective CRF antagonist, astressin (0.5-1 μM) or the selective CRF₂ receptor antagonist, astressin 2B (500 n m ) attenuated the CRF-induced increase in firing rate but did not alter basal discharge rate. CRF (30-300 n m ) increased the amplitude of excitatory postsynaptic currents (EPSCs) evoked by stimulation of the NTS ( P < 0.05). An alteration in the paired pulse ratio indicated the EPSC's increase occurred due to actions at presynaptic sites. In the in vivo anaesthetized rat preparation, bilateral microinjections (20 fmol in 20 nl for each site) of CRF in the DVC decreased gastric motility in rats pretreated with the muscarinic agonist, bethanecol ( P < 0.05). The effects of CRF were abolished by systemic administration of the NOS inhibitor, L -NAME, or by bilateral vagotomy. We concluded that CRF had both a direct and an indirect excitatory effect on DMV neurones via activation of CRF₂ receptors and the decrease in gastric motility observed following microinjection of CRF in the DVC is due to the activation of an inhibitory non-adrenergic non-cholinergic input to the gastrointestinal tract.     

Acute Stress Modulates the Histamine Content of Mast Cells in the Gastrointestinal Tract Through Interleukin-1 and Corticotropin-Releasing Factor Release in Rats

Stress results in activation of the hypothalamic pituitary adrenal axis and affects illnesses such as neuroinflammatory syndrome. In vivo acute stress (restraint stress) induces gastrointestinal function disturbances through colonic mast cell activation. This study investigated the effect of acute stress in histamine content of colonic mast cells, and the central role of interleukin-1 (IL-1) and corticotropin-releasing factor (CRF) in this effect. After a restraint stress session colonic segments were isolated and submitted to three protocols: (i) determination of histamine levels by radioimmunoassay (RIA) after incubation with 48/80 compound, (ii) evaluation by histology of mucosal mast cell (MMC) number and (iii) determination of histamine immunoreactivity of MMC. These procedures were conducted (1) in sham or stressed rats, (2) in stressed rats previously treated with intracerebroventricular ( i.c.v. ) IL-1ra or α-helical CRF9-41, (3) in naive rats pretreated with i.c.v. rhIL-1β or CRF and (4) in rats treated with central IL-1β and CRF plus α-helical CRF and IL-1ra, respectively (cross-antagonism reaction). Acute stress increases histamine content in colonic mast cells, without degranulation. i.c.v. pretreatment with IL-1ra or α-helical CRF9-41 blocked stress-induced mast cell histamine content increase. Both i.c.v. rhIL-1β and CRF injections reproduced the stress-linked changes. i.c.v. treatment with CRF antagonist blocked i.c.v. rhIL-1β-induced mast cell histamine content increase, whereas central IL-1ra did not affect stress events induced by i.c.v. CRF administration. These results suggest that in rats acute stress increases colonic mast cell histamine content. This effect is mediated by the release in cascade in the brain first of IL-1 and secondly of CRF.     

Src family kinases and lipid mediators in control of allergic inflammation

Summary:  The Src family kinases Fyn and Lyn are important modulators of the molecular events initiated by engagement of the high-affinity IgE receptor (FcɛRI). These kinases control many of the early signaling events and initiate the production of several lipid metabolites that have an important role in regulating mast cell responses. The intracellular level of phosphatidylinositol (3,4,5)-trisphosphate (PIP₃), which is produced by phosphatidylinositol 3-OH kinase, plays an important role in determining the extent of a mast cells response to a stimulus. Enhanced levels lead to a hyperdegranulating phenotype (as seen in SHIP-1^−/− and Lyn^−/− mast cells), whereas decreased levels cause hypodegranulation (as seen in Fyn^−/− mast cells). Downregulation of mast cell phosphatase and tensin homologue deleted on chromosone 10 expression, a phosphatase that reduces cellular levels of PIP₃, caused constitutive cytokine production, demonstrating that this response is particularly sensitive to PIP₃ levels. Lyn and Fyn are also intimately linked to other lipid kinases, like sphingosine kinases (SphK). By producing sphingosine-1-phosphate (S1P), SphKs contribute to mast cell chemotaxis and degranulation. In vivo studies now reveal that circulating S1P as well as that found within the mast cell is important in determining mast cell responsiveness. These studies demonstrate the connection between Src protein tyrosine kinases and lipid second messengers that control mast cell function and allergic responses.     

Role of human FcεRI+ cells in HIV-1 infection

Summary: Enhanced serum IgE levels in adults and children with HIV-1 infection could be a marker of poor prognosis. HIV-1 infection is believed to involve a switch toward a "T_H2-like" cytokine pattern. HIV-1 gp120 from different clades is a potent stimulus for histamine release from human basophils and mast cells. Gp120 also induces IL-4 and IL-13 synthesis from basophils. It functions as a viral superantigen by interacting with the V_H3 region of IgE to induce mediator release from human FcεRI⁺ cells. The chemokine receptor CCR3, which binds the chemokines eotaxin and RANTES, is expressed by basophils and lung mast cells. By interacting with the CCR3 receptor on FcεRI⁺ cells, HIV-1 Tat protein is a potent chemoattractant for basophils and lung mast cells. Tat protein also induces IL-4 and IL-13 release from basophils. Incubation of basophils with Tat protein upregulates the surface expression of the CCR3 receptor, a co-receptor of HIV-1 infection. Extracellular Tat affects the directional migration of human FcεRI⁺ cells, CCR3 expression and T_H2 cytokines release. We have shown that HIV-1 proteins gp120 and Tat trigger the release of cytokines critical for T_H2 polarization from FcεRI⁺ cells through two distinct mechanisms. In addition, Tat upregulates the β-chemokine receptor CCR3, making FcεRI⁺ cells more susceptible to infection with CCR3 tropic HIV-1 isolates.
This paper is dedicated to Rita Levi-Montalcini who first suggested an involvement of FcεRI⁺ cells in HIV-1 infection. This work was supported by a grant from the Istituto Superiore Sanità (AIDS project 40B.64 and 40A.67), CNR (Target project Biotechnology No. 99.00216.PF31 and No. 99.00401. PF49) and MURST (Rome, Italy).     

Increased responsiveness of rat colonic splanchnic afferents to 5-HT after inflammation and recovery

5-Hydroxytryptamine (5-HT) activates colonic splanchnic afferents, a mechanism by which it has been implicated in generating symptoms in postinfectious and postinflammatory states in humans. Here we compared mechanisms of colonic afferent activation by 5-HT and mechanical stimuli in normal and inflamed rat colon, and after recovery from inflammation. Colonic inflammation was induced in rats by dextran sulphate sodium. Single-fibre recordings of colonic lumbar splanchnic afferents revealed that 58% of endings responded to 5-HT (10⁻⁴ m ) in controls, 88% in acute inflammation ( P < 0.05) and 75% after 21 days recovery ( P < 0.05 versus control). Maximal responses to 5-HT were also larger, and the estimated EC₅₀ was reduced from 3.2 × 10⁻⁶ to 8 × 10⁻⁷ m in acute inflammation and recovered to 2 × 10⁻⁶ m after recovery. Responsiveness to mechanical stimulation was unaffected. 5-HT₃ receptor antagonism with alosetron reduced responses to 5-HT in controls but not during inflammation. Responses to the mast cell degranulator 48/80 mimicked those to 5-HT in inflamed tissue but not in controls, and more 5-HT-containing mast cells were seen close to calcitonin gene-related peptide-containing fibres in inflamed serosa. We conclude that colonic serosal and mesenteric endings exhibit increased sensitivity to 5-HT in inflammation, with both an increase in proportion of responders and an increase in sensitivity, which is maintained after healing of inflammation. This is associated with alterations in the roles of 5-HT₃ receptors and mast cells.     

Increased glomerular angiotensin II binding in rats exposed to a maternal low protein diet in utero

In the rat, protein restriction during pregnancy increases offspring blood pressure by 20–30 mmHg. We have shown in an earlier study that this is associated with a reduction in nephron number and increased glomerular sensitivity to angiotensin II (Ang II) in vivo . Hence, we hypothesized that exposure to a maternal low-protein diet increases glomerular Ang II AT₁ receptor expression and decreases AT₂ receptor expression. To test this hypothesis, pregnant Wistar rats were fed isocalorific diets containing either 18% (control) or 9% (LP) protein from conception until birth. At 4 weeks of age, the kidneys of male offspring were harvested to measure cortical AT₁ and AT₂ receptor expression, ¹²⁵I-Ang II glomerular binding, tissue renin activity, tissue Ang II and plasma aldosterone concentrations. AT₁ receptor expression was increased (62%) and AT₂ expression was decreased (35%) in LP rats. Maximum ¹²⁵I-Ang II (¹²⁵I-Ang II) binding ( B _max) was increased in LP rats (control n = 9, 291.6 ± 27.4 versus LP n = 7, 445.7 ± 27.4 fmol (mg glomerular protein)⁻¹, P < 0.01), but affinity ( K _D) was not statistically different from controls (control 2.87 ± 0.85 versus LP 0.84 ± 0.20 pmol ¹²⁵I-Ang II, P = 0.059). Renal renin activity, tissue Ang II and plasma aldosterone concentrations did not differ between control and LP rats. Increased AT₁ receptor expression in LP rat kidneys is consistent with greater haemodynamic sensitivity to Ang II in vivo . This may result in an inappropriate reduction in glomerular filtration rate, salt and water retention, and an increase in blood pressure.     

Regulation of pacemaker frequency in the murine gastric antrum

PGE₂ has been linked to the production of gastric arrhythmias such as tachygastria. The interstitial cells of Cajal (ICC) generate electrical rhythmicity in gastrointestinal muscles, and may therefore be a target for PGE₂ in gastric muscles. We cultured ICC from the murine gastric antrum, verified that cells were Kit immunoreactive, and measured spontaneous slow waves. These events were caused by spontaneous inward (pacemaker) currents that were not blocked by nifedipine. Forskolin and 8-bromoadenosine 3':5'-cyclic monophosphate (8-Br-cAMP) reduced the frequency of pacemaker currents in ICC and of slow waves in intact antral muscles. The effects of forskolin and 8-Br-cAMP were not blocked by inhibitors of protein kinase A, suggesting that cAMP has direct effects on pacemaker activity. PGE₂ mimicked the effects of forskolin and 8-Br-cAMP on ICC, but increased slow-wave frequency in intact muscles. Therefore, the chronotropic effects of specific prostaglandin EP receptor agonists were examined. Butaprost and ONO-AE1-329, EP₂ and EP₄ receptor agonists, mimicked the effects of forskolin and 8-Br-cAMP on ICC and intact muscles. Sulprostone (EP₃>EP₁ agonist), GR63799, and ONO-AE-248 (EP₃ agonists) enhanced the frequencies of pacemaker currents in ICC and slow waves in intact muscles. The effects of sulprostone were not blocked by SC-19220, an EP₁ receptor antagonist. These observations suggest that the positive chronotropic effects of PGE₂ in intact muscles are mediated by EP₃ receptor stimulation. The effects of PGE₂ in intact muscles may be dependent upon the relative expression of EP receptors and/or proximity of receptors to sources of PGE₂.     

Differential Expression of T-Cell Adhesion Molecules and LFA-1-Dependent Intercellular Adhesion in HgCl2-Induced Autoimmunity and Immune Suppression

Exposure of Brown Norway (BN) rats to HgCl₂ induces Th2-mediated systemic autoimmunity. In contrast, in Lewis rats, HgCl₂ induces immune suppression, mediated by CD8⁺ T cells. HgCl₂ was previously found to enhance expression of LFA-1, ICAM-1 and CD134 (OX40) on T cells in BN rats. In the present study, T cells from Lewis rats were studied at day 4 after injection of HgCl₂. CD8⁺ T lymphoblasts were significantly increased, which were predominantly CD45RC^hi, and which showed enhanced LFA-1 expression. Furthermore, CD4⁺CD45RC^hi T cells showed increased numbers of ICAM-1⁺ cells, whereas expression of CD134 and CD26 was relatively decreased in CD4⁺ T lymphoblasts. Ex vivo experiments demonstrated that HgCl₂- exposure of BN rats, but not of Lewis rats, significantly enhances PMA [phorbol 12-myristate 13-acetate]-induced lymphocyte aggregation, mediated by LFA-1 and ICAM-1. In conclusion, HgCl₂-injected Lewis rats show early signs of T-lymphocyte activation, predominantly on CD8⁺ cells. Strain-dependent effects of HgCl₂ on cell adhesion molecules and expression of CD134 may play an important role in development of either autoimmunity or immune suppression.     

Enhanced T Lymphocyte Expression of LFA-1, ICAM-1, and the TNF Receptor Family Member OX40 in HgCl2-Induced Systemic Autoimmunity

Injection of mercuric chloride into Brown Norway (BN) rats induces a T lymphocyte-dependent autoimmune syndrome. In order to investigate whether modification of adhesion and costimulatory molecules on T lymphocytes may be involved in early T lymphocyte activation by HgCl₂, the authors analysed expression of these molecules in peripheral lymph node cells from BN rats at day 4 after injection of HgCl₂. Tri-colour flow cytometry was performed for expression analysis within CD45RC-defined subsets of CD4⁺ and CD8⁺ cells. Compared to control rats, HgCl₂-exposed rats showed increased numbers of lymphocytes, especially of T lymphocyte blast cells. The levels of LFA-1 expression as well as the fractions of ICAM-1⁺ cells were significantly increased in all CD45RC-defined subsets of CD4⁺ and CD8⁺ cells. Within the CD4⁺CD45RC^lo T lymphocyte population, HgCl₂-injected rats showed a highly significant increase in the number of cells expressing OX40, which is a member of the TNF receptor family. Moreover, only CD4⁺CD45RC^lo blast cells of HgCl₂-exposed rats showed decreased expression of CD43, increased expression of CD49d and decreased numbers of CD26⁺ cells. The results indicate that induction of autoimmunity by HgCl₂ in BN rats is associated with altered expression of T lymphocyte costimulatory molecules, predominantly on CD4⁺CD45RC^lo cells, which may be caused by a direct effect of HgCl₂ on these cells, and may precipitate further activation of T and B lymphocytes by HgCl₂     

Expression of α5 (CD49e) and α6 (CD49f) Integrin Subunits on T Cells in the Circulation and the Lamina Propria of Normal and Inflammatory Bowel Disease Colonic Mucosa

Intestinal lamina propria T cells are believed to be derived, via the systemic circulation, from gut-associated lymphoid tissue. After migration into the lamina propria, T cells are capable of luminally directed migration following the loss of surface epithelial cells. For adhesion and migration within the extracellular matrix, T cells are likely to utilize the integrin family of adhesion molecules. The aim of this study was to quantitatively and qualitatively investigate the expression of α₅ and α₆ integrin subunits on the surface of human T cells that: (a) migrated out of the lamina propria, (b) remained resident within the matrix and (c) were present in the circulation. In both subpopulations of CD4 and CD8-positive T cells, from both normal and inflamed (inflammatory bowel disease) colonic mucosa, there were significantly fewer α₅ and α₆-positive cells than in the peripheral blood. In addition, there were significantly fewer α₆ integrin molecules on the surface of CD4 and CD8-positive lamina propria T-cell subpopulations, compared with those in the circulation. Our studies suggest that, following migration into the lamina propria, there is down-regulation of α₅ and α₆ integrin-subunit expression on the surface of T cells. Molecules other than members of very late activation antigen-5 (VLA-5) (α₅β₁) and VLA-6 (α₆β₁) families of adhesion molecules are likely to be important in interactions with extracellular components in the lamina propria of normal and inflamed human colonic mucosa.     

Differential corticosterone responses to stress in the lung in two strains of Flinders rats

Background Acute stress affects a variety of organs and cellular systems. These include the hypothalamic–pituitary–adrenal (HPA) axis, corticotropin‐releasing factor (CRF), mast cells and nerves. Flinders‐sensitive (FSL) rat strains have hypercholinergic responses and are more sensitive than Flinders‐resistant rats (FRL) to anaphylaxis. Objective To investigate the effects of acute water avoidance stress (1 h) on FSL and FRL tracheal epithelial tissue. Methods We measured short circuit current (I_sc) as a measure of tracheal response, and the effect of substance P (SP) on tracheal epithelium in Ussing chambers. Electron microscopy was performed to assess mast cell activation. Results Both strains showed increased I_sc responses to stress, inhibited by prior injection of the CRF receptor 1 and 2 antagonist, α‐helical CRF‐(9–41). No increases in conductance were seen. Stress responses were accompanied by electron microscopic morphologic evidence for mast cell degranulation, which was not completely inhibited by α‐helical CRF‐(9–41) pre‐treatment. Stress primed the epithelium for an enhanced response to SP in FSL, but this again was not inhibited by α‐helical CRF‐(9–41). FRL had 2.5 times the corticosterone response of FSL. Conclusion Acute stress affects the tracheal epithelium, not accompanied by changes in ion permeability, but associated with mast cell degranulation. Because blunted HPA axis responses are associated with vulnerability to inflammation, this may partially explain the findings. These stress effects on the lung have a genetic basis associated with relative corticosterone responses, are complex and only in part mediated by CRF.     

Prostaglandin mediates endotoxaemia-induced hypophagia by activation of pro-opiomelanocortin and corticotrophin-releasing factor neurons in rats

Corticotrophin-releasing factor (CRF) and α-melanocyte-stimulating hormone (α-MSH), both of which are synthesized by hypothalamic neurons, play an essential role in the control of energy homeostasis. Neuroendocrine and behavioural responses induced by lipopolyssacharide (LPS) have been shown to involve prostaglandin-mediated pathways. This study investigated the effects of prostaglandin on CRF and α-MSH neuronal activities in LPS-induced anorexia. Male Wistar rats were pretreated with indomethacin (10 mg kg⁻¹; i.p .) or vehicle; 15 min later they received LPS (500 μg kg⁻¹; i.p .) or saline injection. Food intake, hormone responses and Fos–CRF and Fos–α-MSH immunoreactivity in the paraventricular and arcuate nuclei, respectively, were evaluated. In comparison with saline treatment, LPS administration induced lower food intake and increased plasma ACTH and corticosterone levels, as well as an increase in Fos–CRF and Fos–α-MSH double-labelled neurons in vehicle-pretreated rats. In contrast, indomethacin treatment partly reversed the hypophagic effect, blunted the hormonal increase and blocked the Fos–CRF and Fos–α-MSH hypothalamic double labelling increase in response to the LPS stimulus. These data demonstrate that the activation of pro-opiomelanocortin and CRF hypothalamic neurons following LPS administration is at least partly mediated by the prostaglandin pathway and is likely to be involved in the modulation of feeding behaviour during endotoxaemia.     

Interaction of viral infections with muscarinic receptors

Both in humans and in experimental animals, much of the airway hyperresponsiveness that accompanies viral infections is the result of increased reflex bronchoconstriction. The M₃ muscarinic receptors on the airway smooth muscle function normally during viral infections so that the direct effects of acetylcholine on the smooth muscle are not altered. In contrast, the M₂ muscarinic receptors on the vagal nerve endings, which normally inhibit acetycholine release, are markedly dysfunctional during viral infections. This leads to substantial increases in acetylcholine release and potentiated reflex bronchoconstriction. Multiple mechanisms account for virus-induced M₂ receptor dysfunction. Viral neuraminidase may deglycosylate the M₂ receptor, decreasing acetylcholine affinity. Furthermore, both viruses and interferon-γ decrease M₂ receptor gene expression. Finally, in atopic hosts, viral infection causes M₂ receptor dysfunction by activating eosinophils, causing them to release major basic protein which binds to the M₂ receptor, functioning as an endogenous antagonist.     

Renal (pro)renin receptor upregulation in diabetic rats through enhanced angiotensin AT1 receptor and NADPH oxidase activity

Recent studies have demonstrated the presence of the (pro)renin receptor (PRR) in the glomerular mesangium and the subendothelial layer of the renal arteries. We hypothesized that diabetes upregulates PRR expression through enhanced angiotensin subtype 1 (AT₁) receptor–NADPH oxidase cascade activity. Using real-time polymerase chain reaction, Western blot analysis and immunostaining, we studied renal localization of the PRR in the streptozotocin-induced diabetic rat model and in response to 1 week of treatment with the AT₁ receptor blocker valsartan (10 mg kg⁻¹ day⁻¹), the angiotensin AT₂ receptor blocker PD123319 (0.5 mg kg⁻¹ day⁻¹) or the NADPH oxidase inhibitor diphenylene iodonium (DPI; 0.5 mg kg⁻¹ day⁻¹) 6 weeks post-induction of diabetes. Both PRR mRNA and protein were expressed constitutively in the kidneys of normal rat renal cortex and medulla, mainly in glomerular mesangium, proximal, distal and collecting tubules. Compared with normal rats (100%), diabetic rats demonstrated an increase in renal PRR mRNA (184%), protein (228%) and immunostaining. Valsartan and DPI prevented the increase in the PRR mRNA (106 and 126%, respectively), protein (97 and 140%, respectively) and immunostaining that was seen in the kidneys of diabetic rats. The AT₂ blocker PD123319 did not have significant effects on PRR mRNA (157%) or protein expression (200%) in the kidneys of diabetic rats. These results demonstrate that the PRR is constitutively expressed in renal glomeruli and tubules. Expression of the PRR is upregulated in diabetes via enhancement of AT₁ receptor–NADPH oxidase activity.