Corticotropin-releasing hormone inhibits lowering of interstitial pressure in rat trachea after neurogenic inflammation

A Modern View of the Interstitial Space in Health and Disease

Increases in the volume of the interstitial space are readily recognized clinically as interstitial edema formation in the loose connective tissue of skin, mucosa, and lung. However, the contents and the hydrostatic pressure of this interstitial fluid can be very difficult to determine even in experimental settings. These difficulties have long obscured what we are beginning to appreciate is a dynamic milieu that is subject to both intrinsic and extrinsic regulation. This review examines current concepts regarding regulation of interstitial volume, pressure, and flow and utilizes that background to address three major topics of interest that impact IV fluid administration. The first of these started with the discovery that excess dietary salt can be stored non-osmotically in the interstitial space with minimal impact on vascular volume and pressures. This led to the hypothesis that, along with the kidney, the interstitial space plays an active role in the long-term regulation of blood pressure. Second, it now appears that hypovolemic shock leads to systemic inflammatory response syndrome principally through the entry of digestive enzymes into the intestinal interstitial space and the subsequent progression of enzymes and inflammatory agents through the mesenteric lymphatic system to the general circulation. Lastly, current evidence strongly supports the non-intuitive view that the primary factor leading to inflammatory edema formation is a decrease in interstitial hydrostatic pressure that dramatically increases microvascular filtration.

Corticotropin-releasing factor reduces tumor volume, halts further growth, and enhances the effect of chemotherapy in 4T1 mammary carcinoma in mice

The present study examines the effect of the endogenous neuroendocrine factor, corticotropin-releasing factor (CRF), alone or in combination with 5-fluorouracil (5-FU), on 4T1 mammary tumor cells in vitro and in vivo. CRF has been detected in breast cancer tissues; however, the biological effects reported in the literature are sparse and variable. We found that exogenously administered CRF significantly reduced tumor growth without influencing angiogenesis or cell death. Furthermore, CRF reduced tumor interstitial fluid pressure (Pif) and potentiated the effect of 5-FU. These results show that CRF has antitumor effect on mammary carcinoma in mice.

Transcapillary exchange: role and importance of the interstitial fluid pressure and the extracellular matrix

This review will summarize current knowledge on the role of the extracellular matrix (ECM) in general and on the interstitial fluid pressure (P(if)) in particular with regard to their importance in transcapillary exchange. The fluid volume in the interstitial space is normally regulated within narrow limits by automatic re-adjustment of the interstitial hydrostatic and colloid osmotic pressures in response to perturbations in capillary filtration and by the lymphatics. Contrary to this commonly accepted view, P(if) can become an active force and create a fluid flux across the capillaries in several inflammatory reactions and trauma situations rather than limit the changes occurring. The molecular mechanisms involved in the lowering of P(if) include the release of cellular tension exerted on the collagen and microfibril networks in the connective tissue via the collagen-binding beta(1)-integrins, thereby allowing the glycosaminoglycan ground substance, which is normally underhydrated, to expand and take up fluid. Several growth factors and cytokines, including the platelet-derived growth factor BB, are able to reverse a lowering of P(if) and restore the normal compaction of the ECM. The magnitude of the lowering of P(if) varies with the inflammatory response. In several inflammatory reactions, a lowering of P(if) to -5 to -10 mmHg is seen, which will increase capillary filtration by 10-20 times since the normal capillary filtration pressure is usually 0.5-1 mmHg (skin and skeletal muscle). Unless this lowering of P(if) is taken into account, the enhanced solute flux resulting from an inflammatory response will be ascribed to an increased capillary permeability.

Lowering of interstitial fluid pressure after neurogenic inflammation in mouse skin is partly dependent on mast cells

Neurogenic inflammation is known to induce lowering of interstitial fluid pressure (Pif) in mouse skin. This study examined the possible role of mast cell activation secondary to neuropeptide release in lowering of Pifby using KitW/ KitW-vmice, which are devoid of mast cells, including connective tissue mast cells (CTMCs). Pifwas measured in paw skin of anesthetized (fentanyl-fluanison and midazolam, 1:1) mice with glass capillaries connected to a servo-controlled counterpressure system. In contrast to wild-type mice, intravenous administration of mast cell-activating compound 48/80 induced no lowering of Pifin KitW/ KitW-vmice. Intravenous challenge with substance P (SP), calcitonin gene-related peptide (CGRP), or capsaicin induced a significant ( P < 0.05) lowering of Pifin wild-type mice to −2.16 ± 0.28, −1.96 ± 0.11, and −2.22 ± 0.19 mmHg, respectively, compared with vehicle (−0.49 ± 0.11 mmHg). In KitW/ KitW-vmice the Pifresponse to SP was completely abolished (−0.53 ± 0.32 mmHg) while the response to CGRP and capsaicin was attenuated (−1.33 ± 0.13 and −1.42 ± 0.13 mmHg, respectively) although significantly ( P < 0.05) lowered compared with vehicle. Immunohistochemical analysis revealed no difference in distribution or density of SP- and CGRP-immunoreactive fibers in paws of KitW/ KitW-vcompared with wild-type mice. We conclude that lowering of Pifnormally depends on mast cells. However, the sensory nerves can also elicit a lowering of Pifthat is independent of mast cells.

Immunoreactivity of corticotropin-releasing hormone, adrenocorticotropic hormone and alpha-melanocyte-stimulating hormone in alopecia areata

Psychological factors are believed to play a role in the pathogenesis of alopecia areata (AA), a frequently encountered hair disorder. In our study, statistically significant elevation of psychological stress was felt by AA patients prior hair loss compared with control, which was strongly believed contributory to hair loss (t-test, P < 0.01). The corticotropin-releasing hormone (CRH) and proopiomelanocortin (POMC) mRNA have been identified in the basal layer of the epidermis and pilosebaceous units of the normal scalp. And with the recent discovery of melanocytes and dermal fibroblasts capable of corticosterone production, the presence of a local stress response system resembling the hypothalamic-pituitary-adrenal (HPA) axis has been suggested. The local stress response system is involved in regulation of the normal hair cycle, but its precise role in AA is unknown. The influence of a local HPA axis or rather, CRH-POMC axis in AA was investigated by analysing immunohistochemically the expression levels of CRH and POMC peptides, including the adrenocorticotropic hormone (ACTH) and alpha-melanocyte-stimulating hormone (alpha-MSH), in a number of AA lesions and normal scalp (as control). The epidermis and pilosebaceous units of normal scalp stained weakly with CRH, ACTH and alpha-MSH, whereas those from the affected sites of the AA group showed intense expression of the peptides (chi-square test, P < 0.01). The meaning of this enhanced expression and their role in the pathogenesis of AA should be further evaluated in future.

Corticotropin releasing hormone and the skin

Cotricotropin-releasing hormone (CRH) and related peptides are produced in skin that is dependent on species and anatomical location. Local peptide production is regulated by ultraviolet radiation (UVR), glucocorticoids and phase of the hair cycle. The skin also expresses the corresponding receptors (CRH-R1 and CRH-R2), with CRH-R1 being the major receptor in humans. CRH-R1 is expressed in epidermal and dermal compartments, and CRH-R2 predominantly in dermal structures. The gene coding for CRH-R1 generates multiple isoforms through a process modulated by UVR, cyclic adenosine monophosphate (cAMP) and phorbol 12-myristate 13-acetate. The phenotypic effects of CRH in human skin cells are largely mediated by CRH-R1alpha through increases in concentrations of cAMP, inositol triphosphate (IP3), or Ca2+ with subsequent activation of protein kinases A (PKA) and C (PKC) dependent pathways. CRH also modulates the activity of nuclear factor of kappa light polypeptide gene enhancer in B-cells (NF-kappaB), activator protein 1 (AP-1) and cAMP responsive element binding protein (CREB). The cellular functions affected by CRH depend on cell type and nutritional status and include modulation of differentiation program(s), proliferation, viability and immune activity. The accumulated evidence indicates that cutaneous CRH is also a component of a local structure organized similarly to the hypothalamo-pituitary-adrenal axis.

Corticotropin-releasing hormone-receptor 1 (CRH-R1) and CRH-binding protein (CRH-BP) are expressed in the gills and skin of common carp Cyprinus carpio L. and respond to acute stress and infection

We established that corticotropin-releasing hormone (CRH), CRH-binding protein (CRH-BP) and CRH-receptor 1 (CRH-R1) are expressed in the gills and skin of common carp Cyprinus carpio, an early vertebrate. Immunoreactive CRH was detected in macrophage-like cells in gills and skin, in fibroblasts in the skin and in endothelial cells in the gills. The involvement of the CRH system in gills and skin was investigated in response to infection and in an acute restraint stress paradigm. Carp were infected with the protozoan leech-transmitted blood flagellate Trypanoplasma borreliand subjected to acute restraint stress by netting for 24 h. The expression of CRH-BP and CRH-R1 genes in the gills and in the skin is downregulated after both infection and restraint. Thus the peripheral CRH system reacts to infection and stress. The gills and skin separate the internal from the external environment and are permanently exposed to stress and pathogens. Because of their pivotal role in maintaining the homeostatic equilibrium,these organs must act locally to respond to diverse stresses. Clearly, the CRH system is involved in the response of the integument to diverse stresses at the vulnerable interface of the internal and external milieu.

Problems in physiological experimental animal models investigated with factorial design

In the present study we investigated four variables using factorial design to decide if any of these could explain the variations in the control measurements of interstitial fluid pressure (P_if) in rat trachea that were experienced. This approach requires only a fraction of the animals normally needed when studying each factor separately. P_if in tracheal tissue was measured with the servocontrolled counterpressure system using sharpened micropipettes. The measurements were performed over a period of 60 min and are presented as mean for every 15 min period. The factors investigated in the study were: three strains of female rats (Strain) two brands of diets (Food); two breeder companies (Source); and finally two batches of the same set of animals to repeat the experiment twice (Week), using a total of 48 animals. There was a highly significant effect within Strain the first week (p=0.007), but this response was not observed the second week. The interaction between Strain×Week was significant (p=0.007) while the main effects Strain or Week alone were not significant. The response pattern for Strain and Food was inconsistent for the two experimental weeks studied. These experiments made it possible for us to simultaneously test several factors and exclude these factors as the reason for the observed changes in our experiments since the experiments did not allow the conclusion that one or several of these factors could explain the variation in P_if.

Neurogenic inflammation in mice deficient in heparin-synthesizing enzyme

Mast cell activation, or neurogenic inflammation, is known to induce lowering of interstitial fluid pressure (P(if)) and plasma protein extravasation (PPE) in several tissues from both rats and mice. To examine a possible role of connective tissue mast cells (CTMCs) in these inflammatory responses, we used mice with dysfunctional CTMCs due to lack of the N-deacetylase/N-sulfotransferase-2 enzyme (NDST-2(-/-)). P(if) and PPE were measured after challenge with compound 48/80 (C48/80), and P(if) alone was measured after treatment either with capsaicin, substance P (SP), or calcitonin gene-related peptide (CGRP). Measurements of P(if) in anesthetized (fentanyl/fluanison and midazolam, 1:1) mice were performed in paw skin with glass capillaries connected to a servo-controlled counterpressure system. PPE was measured with microdialysis by using hollow plasmapheresis fibers (cutoff at 3,000 kDa) placed subcutaneously on the back. Intravenous administration of C48/80 lowered P(if) significantly (P < 0.05) in NDST-2(-/-) mice (-1.67 +/- 0.42 mmHg) compared with vehicle (-0.57 +/- 0.17 mmHg) but the lowering was significantly (P < 0.05) less compared with that of the NDST-2(+/+) mice (-2.31 +/- 0.47 mmHg). PPE was increased 300% after treatment with C48/80 in NDST-2(+/+) mice, whereas there was no increase in PPE in NDST-2(-/-) mice. Capsaicin, SP, and CGRP lowered P(if) significantly (P < 0.05) compared with vehicle and to the same extent in both NDST-2(+/+) and NDST-2(-/-) mice. We can conclude that although NDST-2(-/-) mice demonstrate an altered response in P(if) after mast cell activation, there was no similar alteration after neurogenic inflammation. Therefore, we suggest that neurogenic inflammation in mouse skin is not exclusively dependent on intact CTMCs.

Regulation of nuclear factor-kappaB by corticotropin-releasing hormone in mouse thymocytes

CRH, a major mediator of the stress response, has been shown to exert potent immunomodulatory effects in vivo, through mechanisms that have not been elucidated yet. To determine the molecular pathways mediating the proinflammatory effects of peripheral CRH, we studied its role in the activation of nuclear factor-kappaB (NF-kappaB), a transcription factor crucial for the regulation of a variety of inflammatory mediator genes. Our studies demonstrate that, in mouse thymocytes, CRH induces the NF-kappaB DNA-binding activity in a time- and dose-dependent manner, with parallel degradation of its inhibitor protein inhibitor of NF-kappaB. The effect of CRH is not inhibited by dexamethasone and is mediated by the protein kinase A and protein kinase C signaling pathways. In vivo, we show that CRH-deficient mice respond to lipopolysaccharide administration by reduced activation of thymus NF-kappaB, despite their significantly elevated proinflammatory cytokine and their low corticosterone levels. These findings suggest a putative molecular pathway mediating the proinflammatory effects of peripheral CRH through induction of the NF-kappaB DNA binding activity.

The neurotensin fragment AcNT(8-13) inhibits lowering of interstitial fluid pressure in rat trachea

Injury to soft tissue results in the lowering of interstitial fluid pressure (P(if)), plasma protein extravasation, and increased total tissue volume. In this study, the effects of N-acetyl neurotensin(8-13) [AcNT(8-13)] on P(if) in rat trachea were examined after electrical stimulation (ES) of the vagus nerve. P(if) was measured with glass capillaries connected to a servocontrolled counterpressure system. In pentobarbital-anesthetized female Wistar rats, the P(if) after intravenous saline was -1.8 +/- 0.3 mmHg (means +/- SD) and decreased to -5.0 +/- 0.6 mmHg (P < 0.01, n = 9) after ES. AcNT(8-13) (10 microg/kg) blocked the fall in P(if) after ES (-2.5 +/- 2.3 mmHg, P < 0.01, n = 8). In tracheal tissue from animals pretreated with AcNT(8-13) at the same dose and immersed in phosphate-buffered saline (0.15 M, pH 7.4), the rate of fluid accumulation in excised tissues was significantly reduced after 2 h. The ability of AcNT(8-13) to modulate the fluid mechanics of tracheal interstitium after inflammation suggests that it may be a useful tool for studying cell adhesion and related factors that maintain structural integrity of connective tissue after injury.

Cutaneous expression of corticotropin-releasing hormone (CRH), urocortin, and CRH receptors

Studies in mammalian skin have shown expression of the genes for corticotropin-releasing hormone (CRH) and the related urocortin peptide, with subsequent production of the respective peptides. Recent molecular and biochemical analyses have further revealed the presence of CRH receptors (CRH-Rs). These CRH-Rs are functional, responding to CRH and urocortin peptides (exogenous or produced locally) through activation of receptor(s)-mediated pathways to modify skin cell phenotype. Thus, when taken together with the previous findings of cutaneous expression of POMC and its receptors, these observations extend the range of regulatory elements of the hypothalamic-pituitary-adrenal axis expressed in mammalian skin. Overall, the cutaneous CRH/POMC expression is highly reactive to common stressors such as immune cytokines, ultraviolet radiation, cutaneous pathology, or even the physiological changes associated with the hair cycle phase. Therefore, similar to its central analog, the local expression and action of CRH/POMC elements appear to be highly organized and entrained, representing general mechanism of cutaneous response to stressful stimuli. In such a CRH/POMC system, the CRH-Rs may be a central element.

Corticotropin releasing hormone and proopiomelanocortin involvement in the cutaneous response to stress

The skin is a known target organ for the proopiomelanocortin (POMC)-derived neuropeptides alpha-melanocyte stimulating hormone (alpha-MSH), beta-endorphin, and ACTH and also a source of these peptides. Skin expression levels of the POMC gene and POMC/corticotropin releasing hormone (CRH) peptides are not static but are determined by such factors as the physiological changes associated with hair cycle (highest in anagen phase), ultraviolet radiation (UVR) exposure, immune cytokine release, or the presence of cutaneous pathology. Among the cytokines, the proinflammatory interleukin-1 produces important upregulation of cutaneous levels of POMC mRNA, POMC peptides, and MSH receptors; UVR also stimulates expression of all the components of the CRH/POMC system including expression of the corresponding receptors. Molecular characterization of the cutaneous POMC gene shows mRNA forms similar to those found in the pituitary, which are expressed together with shorter variants. The receptors for POMC peptides expressed in the skin are functional and include MC1, MC5 and mu-opiate, although most predominant are those of the MC1 class recognizing MSH and ACTH. Receptors for CRH are also present in the skin. Because expression of, for example, the MC1 receptor is stimulated in a similar dose-dependent manner by UVR, cytokines, MSH peptides or melanin precursors, actions of the ligand peptides represent a stochastic (predictable) nonspecific response to environmental/endogenous stresses. The powerful effects of POMC peptides and probably CRH on the skin pigmentary, immune, and adnexal systems are consistent with stress-neutralizing activity addressed at maintaining skin integrity to restrict disruptions of internal homeostasis. Hence, cutaneous expression of the CRH/POMC system is highly organized, encoding mediators and receptors similar to the hypothalamic-pituitary-adrenal (HPA) axis. This CRH/POMC skin system appears to generate a function analogous to the HPA axis, that in the skin is expressed as a highly localized response which neutralizes noxious stimuli and attendant immune reactions.

Cutaneous expression of CRH and CRH-R. Is there a "skin stress response system?"

The classical neuroendocrine pathway for response to systemic stress is by hypothalamic release of corticotropin releasing hormone (CRH), subsequent activation of pituitary CRH receptors (CRH-R), and production and release of proopiomelanocortin (POMC) derived peptides. It has been proposed that an equivalent to the hypothalamic-pituitary-adrenal axis functions in mammalian skin, in response to local stress (see Reference 1). To further define such system we used immunocytochemistry, RP-HPLC separation, and RIA techniques, in rodent and human skin, and in cultured normal and malignant melanocytes and keratinocytes. Production of mRNA for CRH-R1 was documented in mouse and human skin using RT-PCR and Northern blot techniques; CRH binding sites and CRH-R1 protein were also identified. Addition of CRH to immortalized human keratinocytes, and to rodent and human melanoma cells induced rapid, specific, and dose-dependent increases in intracellular Ca2+. The latter were inhibited by the CRH antagonist alpha-helical-CRH(9-41) and by the depletion of extracellular calcium with EGTA. CRH production was enhanced by ultraviolet light radiation and forskolin (a stimulator for intracellular cAMP production), and inhibited by dexamethasone. Thus, evidence that skin cells, both produce CRH and express functional CRH-R1, supports the existence of a local CRH/CRH-R neuroendocrine pathway that may be activated within the context of a skin stress response system.

D-amino acid-substituted analogs of corticotropin-releasing hormone (CRH) and urocortin with selective agonist activity at CRH1 and CRH2beta receptors

The activities of corticotropin-releasing hormone (CRH)-related peptides and several analogs were examined in cells transfected with either CRH1 or CRH2beta receptors, in suppression of heat-induced rat paw edema in pentobarbital-anesthetised animals and in stimulation of release of immunoreactive corticotropin (ir-ACTH) from rat anterior pituitary tissue in vitro. The peptides tested were human/rat (h/r)-CRH, r-urocortin, h-urocortin, white sucker fish or maggy sole urotensin I and some analogs of these peptides substituted with D-amino acids at residues 4 (urocortin), 5 (CRH and urotensin I) and 20 (CRH). In cells transfected with CRH1 receptors, these peptides were similar in potency in stimulation of cAMP accumulation. By contrast, at CRH2beta receptors peptides of the urocortin and urotensin series were more potent than h/r-CRH while [D-Glu20]-h/r-CRH was 6.5-fold less active than h/r-CRH. I.v. administration of h/r-CRH or related peptides 10 min prior to a thermal stimulus produced a significant dose-dependent inhibition of rat paw edema formation. Comparison of the ED50's showed that urocortins ([D-Ser4]-h-urocortin, h-urocortin, [D-Pro4]-r-urocortin, r-urocortin) were approximately 2 to 3 times more active than h/r-CRH, but [D-Glu20]-h/r-CRH was 18.5-fold less active. In the assay for ir-ACTH release, the activity of h/r-CRH and [D-Glu20]-h/r-CRH was similar but [D-Pro5]-h/r-CRH and [D-Pro4]-r-urocortin was less potent than the native peptide. These results provide further evidence that D-amino acid substitution at residue 20 reduces the potency of h/r-CRH at endogenous (anti-edema effect) and transfected (cAMP accumulation) CRH2beta receptors whilst activity at the CRH1 receptor is retained (ACTH-release and cAMP accumulation). On the other hand substitutions at residues 4 or 5 in r-urocortin or h/r-CRH respectively appear to decrease activity at CRH1 but not CRH2beta receptors The modified CRH and urocortin analogs described here may provide clues for the further design of receptor selective ligands.