Marked suppression of gastric ulcerogenesis and intestinal responses to stress by a novel class of drugs

When exposed to prolonged stress, rats develop gastric ulceration, enhanced colon motility with depletion of its mucin content and signs of physiological and behavioral arousal. In this model, we tested whether antidepressants (fluoxetine and bupropion), anxiolytics (diazepam and buspirone) or the novel nonpeptide corticotropin-releasing hormone (CRH) type-1 receptor (CRH-R1) antagonist, antalarmin, modify these responses. Fluoxetine, bupropion, diazepam and antalarmin all suppressed stress-induced gastric ulceration in male Sprague-Dawley rats exposed to four hours of plain immobilization. Antalarmin produced the most pronounced anti-ulcer effect and additionally suppressed the stress-induced colonic hypermotility, mucin depletion, autonomic hyperarousal and struggling behavior. Intraperitoneal CRH administration reproduced the intestinal but not the gastric responses to stress while vagotomy antagonized the stress-induced gastric ulceration but not the intestinal responses. We conclude that brain CRH-R1 and vagal pathways are essential for gastric ulceration to occur in response to stress and that peripheral CRH-R1 mediates colonic hypermotility and mucin depletion in this model. Nonpeptide CRH-R1 antagonists may therefore be prophylactic against stress ulcer in the critically ill and therapeutic for other pathogenetically related gastrointestinal disorders such as peptic ulcer disease and irritable bowel syndrome.

The development of a potential single photon emission computed tomography (SPECT) imaging agent for the corticotropin-releasing hormone receptor type

A high-affinity radioligand for CRHR1 has been prepared that can serve as a template for the development of SPECT imaging agents. The 5-chloro-N-cyclopropylmethyl-N-(2,6-dichloro-4-iodophenyl)-2-methyl-N-propylpyrimidine-4,6-diamine (6b, Ki = 14 nM), and the corresponding 4-bromophenyl analogue (6a, Ki = 21 nM), were synthesized in four steps from compound 3.

Oral administration of a corticotropin-releasing hormone receptor antagonist significantly attenuates behavioral, neuroendocrine, and autonomic responses to stress in primates

We evaluated the effects of the lipophilic nonpeptide corticotropin-releasing hormone (CRH) type 1 receptor antagonist antalarmin on the behavioral, neuroendocrine, and autonomic components of the stress response in adult male rhesus macaques. After oral administration, significant antalarmin concentrations were detected in the systemic circulation and the cerebrospinal fluid by a mass spectrometry-gas chromatography assay developed specifically for this purpose. Pharmacokinetic and dose-response studies suggested that an oral dose of 20 mg/kg was optimal for behavioral and endocrine effects. We then administered this dose in a double-blind, placebo-controlled fashion to monkeys exposed to an intense social stressor: namely, placement of two unfamiliar males in adjacent cages separated only by a transparent Plexiglas screen. Antalarmin significantly inhibited a repertoire of behaviors associated with anxiety and fear such as body tremors, grimacing, teeth gnashing, urination, and defecation. In contrast, antalarmin increased exploratory and sexual behaviors that are normally suppressed during stress. Moreover, antalarmin significantly diminished the increases in cerebrospinal fluid CRH as well as the pituitary-adrenal, sympathetic, and adrenal medullary responses to stress. We conclude that CRH plays a broad role in the physiological responses to psychological stress in primates and that a CRH type 1 receptor antagonist may be of therapeutic value in human psychiatric, reproductive, and cardiovascular disorders associated with CRH system hyperactivity.

Synthesis and biological activity of fluoro-substituted pyrrolo[2,3-d]pyrimidines: the development of potential positron emission tomography imaging agents for the corticotropin-releasing hormone type 1 receptor

A series of fluoro-substituted 4-(dialkylamino)pyrrolo[2,3-d]pyrimidines was synthesized and their binding affinity for corticotropin-releasing hormone type 1 receptor (CRHR1) was investigated. Compounds 11a and 11b possessed very high CRHR1 affinity (Ki=3.5, 0.91 nM, respectively). They are promising candidates for the development of 18F-containing nonpeptide PET radioligands for CRHR1.

Chronic administration of the non-peptide CRH type 1 receptor antagonist antalarmin does not blunt hypothalamic-pituitary-adrenal axis responses to acute immobilization stress

Antalarmin is a pyrrolopyrimidine compound that antagonizes corticotropin-releasing hormone (CRH) type 1 receptors (CRHR1). In order to assess the effects of antalarmin treatment on hypothalamic-pituitary-adrenal (HPA) function we measured the plasma concentrations of adrenocorticotropic hormone (ACTH) and corticosterone in animals treated with either antalarmin or vehicle for 1 week or for 8 weeks. We found that antalarmin treatment for 1 week did not affect basal concentrations of ACTH or corticosterone. In contrast, treatment for 8 weeks significantly lowered basal ACTH and corticosterone concentrations and also significantly decreased the basal corticosterone to ACTH ratio, indicating decreased basal adrenocortical responsiveness to ACTH. However, immobilization stress resulted in ACTH and corticosterone concentrations that were the same in animals treated with vehicle or antalarmin for either 1 or 8 weeks. We conclude that even though 8-week antagonism of CRHR1 by the non-peptide antalarmin blunts basal concentrations of ACTH and corticosterone, and affects the adrenal responsiveness to ACTH, it does not blunt the HPA response to acute stress, and it does not appear to cause stress-induced adrenal insufficiency.

Stress, corticotropin-releasing hormone, glucocorticoids, and the immune/inflammatory response: acute and chronic effects

Corticotropin-releasing hormone (CRH) influences the immune system indirectly, through activation of the hypothalamic-pituitary-adrenal axis and sympathetic system, and directly, through local modulatory actions of peripheral (immune) CRH. We recently demonstrated that catecholamines and histamine potently inhibited interleukin (IL)-12 and stimulated IL-10, whereas glucocorticoids suppressed IL-12, but did not affect IL-10 production ex vivo. Thus, both glucocorticoids and catecholamines, the end products of the stress system, and histamine, a product of activated mast cells, may selectively suppress cellular immunity and favor humoral immune responses. We localized immunoreactive CRH in experimental carrageenin-induced aseptic inflammation and, in humans, in inflamed tissues from patients with several autoimmune disease. In addition, we demonstrated that CRH activated mast cells via a CRH receptor type 1-dependent mechanism, leading to release of histamine and hence vasodilatation and increased vascular permeability. Thus, activation of the stress system, through direct and indirect effects of CRH, may influence the susceptibility of an individual to certain autoimmune, allergic, infectious or neoplastic diseases. Antalarmin, a novel nonpeptide CRH antagonist, prevented several proinflammatory effects of CRH, thus revealing its therapeutic potential in some forms of inflammation.

Urocortin and inflammation: confounding effects of hypotension on measures of inflammation

Urocortin, a newly isolated 40-amino-acid mammalian peptide homologous to corticotropin-releasing hormone (CRH), activates both CRH type 1 and 2 receptors, but may be an endogenous ligand for CRH receptor type 2. Urocortin given systemically inhibited heat-induced paw edema in the rat, and was therefore ascribed anti-inflammatory properties. We examined the effects of urocortin in the carrageenin-induced subcutaneous inflammation model. Rats were treated with urocortin 200 (n = 6) or 20 nmol/kg (n = 6); inflammatory exudates were reduced by approximately 30% compared to controls (n = 7) at both doses. However, since subcutaneous urocortin has been shown to reduce arterial blood pressure, we tested the hypothesis that its antiedema and antiextravasatory effects were secondary to arterial hypotension. Therefore, we examined the parallel effects of urocortin- and hydralazine-induced hypotension on acute inflammation induced by carrageenin in the rat. Rats were treated with subcutaneous carrageenin and control injections (n = 8), carrageenin and urocortin (20 nmol/kg, n = 9), or carrageenin and intraperitoneal hydralazine (10 mg/kg, n = 8). Mean arterial blood pressure was measured hourly for 7 h in 12 animals, and after 2 h, the nadir of treatment, in a further 13 animals. Rats were then sacrificed, and the inflammatory exudate volume and leukocyte count were measured. Mean exudate volumes were reduced from 4.8 +/- 0.5 ml (controls) to 2.4 +/- 0.3 ml (p = 0.004) and 2.9 +/- 0.6 ml (p = 0.007) in urocortin- and hydralazine-treated animals, respectively. Urocortin and hydralazine both produced a significant fall in blood pressure compared to controls, with mean arterial pressure 2 h after carrageenin injection falling to 51.0 +/- 4.1 (p < 0.001) and 34.6 +/- 4.6 (p < 0.001) vs. 92.9 +/- 3.7 mm Hg in controls, respectively. A significant positive correlation was noted between blood pressure and inflammatory exudate volume (r = 0. 52, p = 0.007). As both hydralazine and urocortin lowered blood pressure and inflammatory exudate volume, we suggest that the anti-inflammatory effects of urocortin and related neuropeptides may be nonspecific, acting through hypotension rather than through direct anti-inflammatory mechanisms. The use of inflammatory models which rely on extravasation may be inappropriate for the study of substances that produce hypotension.

A corticotropin-releasing hormone type I receptor antagonist delays parturition in sheep

In sheep, corticotropin-releasing hormone (CRH) can stimulate the fetal release of ACTH to produce a cortisol surge which leads to the onset of parturition. We tested the hypothesis that fetal CRH is a primary factor in the onset of parturition in sheep by using a Type I CRH receptor antagonist, antalarmin, to block the endogenous action of CRH. Pregnant ewes were cannulated at 130-135 days of gestation. Five catheters were placed into the amniotic sac, fetal femoral artery, fetal tarsal vein, maternal jugular vein and carotid artery. After 5 days' recovery, blood samples from maternal and fetal vessels were collected at the following times: a day before the start of infusion, at [-1, 0, 1, 2, 4, 8 and 24]h, on the first day of infusion, and thereafter daily throughout a 10-day infusion. Animals (n=6 per group) received infusions into a fetal vein of either a vehicle comprising 1:1 mixture of ethanol and polyethoxylated castor oil (Cremophor EL) or antalarmin (50 g/L) in the vehicle at a rate of 0.3 mL/h. The plasma samples were assayed for ACTH and cortisol using commercial RIA kits. Fetuses infused with vehicle delivered at a mean gestational age of 141.8 +/- 0.9 days compared with antalarmin-infused sheep at 148.8 +/- 1.6 days (P = 0.0036, unpaired Student's t-test). Fetal ACTH and cortisol did not change in the antalarmin-infused sheep after 3 days' infusion compared to significant increases in vehicle-infused sheep (P=0.004 and P = 0.016 respectively, ANOVA). These data show that CRH receptor antagonism in the fetus can delay the onset of parturition. It supports the hypothesis that hypothalamic CRH drives fetal production of ACTH and is essential for the onset of parturition triggered by a surge in fetal cortisol.

Corticotropin-releasing hormone and inflammation

Corticotropin-releasing hormone (CRH) is a major regulator of the hypothalamic-pituitary-adrenal axis (HPA) and principal coordinator of the stress response. As in stress, intracerebroventricular administration of CRH suppresses the immune system indirectly, via glucocorticoid and/or sympathetic system-mediated mechanisms. Also, during inflammatory stress, the cytokines TNF alpha, IL-1, and IL-6 stimulate hypothalamic CRH and/or vasopressin secretion as a way of preventing the inflammatory reaction from overreacting. Recently, CRH receptors were described in peripheral sites of the immune system, and CRH was found to promote several immune functions in vitro. We demonstrated a direct role of CRH in the inflammatory immune process in vivo, by first studying the effect of systemic CRH immunoneutralization in an experimental model of carrageenin-induced aseptic inflammation in Spague-Dawley rats. We extended these observations to other forms of experimental inflammation, including streptococcal cell wall polysaccharide- and adjuvant-induced arthritides and peptide R16 (epitope of the interphotoreceptor retinoid-binding protein)-induced uveitis in Lewis rats. We also studied human disease states, including rheumatoid arthritis, Hashimoto thyroiditis, and ulcerative colitis. Inflamed tissues contained large amounts of IR CRH, reaching levels similar to those observed in the hypophyseal portal system. We also demonstrated the presence of CRH mRNA and CRH receptors in inflammatory cells and identified the mast cells as a major immune target for CRH. In addition to production by immune cells, the peripheral nervous system, including the postganglionic sympathetic neurons and the sensory fibers type C, appears to contribute to IR CRH production in inflammatory sites. The production of CRH from the postganglionic sympathetic neurons may be responsible for the stress-induced activation of allergic/autoimmune phenomena, such as asthma and eczema, via mast cell degranulation. Antalarmin, a novel nonpeptide CRH receptor antagonist, displaced 125I-labeled ovine CRH binding in rat pituitary, frontal cortex, and cerebellum, but not heart, consistent with antagonism at the CRHR1 receptor. In vivo antalarmin significantly inhibited CRH-stimulated ACTH release and carrageenin-induced subcutaneous inflammation in rats. Thus, antalarmin and other related compounds that antagonize CRH at the level of its own receptor have therapeutic potential in some forms of inflammation directly mediated by type 1 CRH receptors and promise to enhance our understanding of the many roles of CRH in immune/inflammatory reactions.

Chronic effects of a nonpeptide corticotropin-releasing hormone type I receptor antagonist on pituitary-adrenal function, body weight, and metabolic regulation

CRH, the principal regulator of the hypothalamic-pituitary-adrenal axis and modulator of autonomic nervous system activity, also participates in the regulation of appetite and energy expenditure. Antalarmin, a pyrrolopyrimidine compound, antagonizes CRH type 1 receptor-mediated effects of CRH, including pituitary ACTH release, stress behaviors, and acute inflammation. We administered antalarmin chronically to evaluate its effects on hypothalamic-pituitary-adrenal axis function and metabolic status. Adult male rats were treated twice daily with 20 mg/kg of i.p. antalarmin or placebo over 11 days. The animals were weighed; plasma ACTH, corticosterone, leptin, and blood glucose levels were determined; and morphometric analyses were performed to determine adrenal size and structure, including sizing, histochemistry, immunohistochemistry, and electron microscopy. Leptin messenger RNA expression in peripheral fat was analyzed by Northern blot. Antalarmin decreased plasma ACTH (mean +/- SD, 2.62 +/- 0.063 pg/ml) and corticosterone concentrations (10.21 +/- 1.80 microg/dl) compared with those in vehicle-treated rats [respectively, 5.3 +/- 2.0 (P < 0.05) and 57.02 +/- 8.86 (P < 0.01)]. Antalarmin had no significant effect on body weight, plasma leptin, or blood glucose concentrations or fat cell leptin messenger RNA levels. The width of the adrenal cortex of animals treated with antalarmin was reduced by 31% compared with that in controls without atrophy of the gland. On the ultrastructural level, adrenocortical cells were in a hypofunctional state characterized by reduced vascularization, increased content of lipid droplets, and tubulovesicular mitochondria with fewer inner membranes. The apoptotic rate was increased in the outer zona fasciculata of animals treated with the antagonist (26.6 +/- 3.58%) compared with that in placebo-treated controls (6.8 +/- 0.91%). We conclude that chronic administration of antalarmin does not affect body weight, carbohydrate metabolism, or leptin expression, whereas it reduces adrenocortical function mildly, without anatomical, clinical, or biochemical evidence of causing adrenal atrophy. These results are promising for future uses of such an antagonist in the clinic.

The role of corticotropin-releasing hormone in neuroendocrine-immune interactions

Neuroendocrine-immune interactions are profoundly regulated by corticotropin-releasing hormone (CRH) indirectly, through activation of a global stress response, and directly, through pro-inflammatory actions on peripheral immune functions. The indirect effects of stress on immune/inflammatory responses occur via the stress-induced activation of the hypothalamic-pituitary-adrenal (HPA) axis and the sympathetic/adrenomedullary system. We have demonstrated that glucocorticoids and catecholamines favor T helper 2 (TH2) over T helper 1 (TH1) immune cells and mediators, by controlling the production of specific key regulatory cytokines. This could explain the influences of chronic stress on the development, course, and pathology of certain allergic, autoimmune/inflammatory, infectious, and neoplastic diseases. We have also shown that 'immune CRH' is secreted peripherally and plays a direct immunomodulatory role as an autocrine or paracrine mediator of inflammation. Upon release from immune cells and peripheral sensory afferent and/or postganglionic sympathetic nerves, CRH acts locally to elicit pro-inflammatory responses. This would explain the triggering or exacerbation of certain allergic or vasokinetic states by acute stress.

In vivo and in vitro characterization of antalarmin, a nonpeptide corticotropin-releasing hormone (CRH) receptor antagonist: suppression of pituitary ACTH release and peripheral inflammation

Corticotropin-releasing hormone (CRH) secreted from the hypothalamus is the major regulator of pituitary ACTH release and consequent glucocorticoid secretion. CRH secreted in the periphery also acts as a proinflammatory modulator. CRH receptors (CRH-R1, R2alpha, R2beta) exhibit a specific tissue distribution. Antalarmin, a novel pyrrolopyrimidine compound, displaced 12SI-oCRH binding in rat pituitary, frontal cortex and cerebellum, but not heart, consistent with antagonism at the CRHR1 receptor. In vivo antalarmnin (20 mg/kg body wt.) significantly inhibited CRH-stimulated ACTH release and carageenin-induced subcutaneous inflammation in rats. Antalarmin, or its analogs, hold therapeutic promise in disorders with putative CRH hypersecretion, such as melancholic depression and inflammatory disorders.

Immunoreactive corticotropin-releasing hormone and its binding sites in the rat ovary

Corticotropin-releasing hormone (CRH), the principal neuropeptide regulator of pituitary ACTH secretion, is also produced at peripheral inflammatory sites, where it acts as a proinflammatory cytokine, and by the Leydig cell of the testis, where it exerts autocrine inhibition of testosterone biosynthesis. Because key ovarian functions, such as ovulation and luteolysis, represent aseptic inflammatory responses, and because the theca cell is the functional equivalent of the Leydig cell, we explored the CRH presence in the ovary, first, by specific CRH immunohistochemistry of adult cycling female Sprague-Dawley rat ovaries. We detected cytoplasmic immunoreactive CRH (IrCRH) in theca and stromal cells and in cells within the corpora lutea, at all phases of the estrous cycle. Using a specific radioimmunoassay, we measured IrCRH in extracts of rat ovaries (0.042-0.126 pmol/g wet tissue). The mobility of the ovarian IrCRH molecule was similar to that of rat/human CRH by reverse phase HPLC. To investigate the CRH action in the ovary, we identified, characterized, and localized CRH receptors in the rat ovary. Binding was linear with increasing tissue concentration, saturable, and of high affinity. Scatchard analysis of 125I-Tyr-ovine CRH competitive displacement curves indicated a high affinity binding site with a Kd of approximately 6 nM and a Bmax value of approximately 61 fM/mg protein. Autoradiographic studies revealed CRH receptors primarily in ovarian theca and stroma. We conclude that IrCRH and CRH receptors are present in rat ovaries, suggesting that this neuropeptide may play a regulatory role in this gonad, perhaps through its proinflammatory properties and/or by participating in the auto/paracrine regulation of steroid biosynthesis. Functional studies are necessary to define the role(s) of CRH in the ovary.

Expression and sequence of the gene for tissue inhibitor of metalloproteinases in patients with abdominal aortic aneurysms

PURPOSE

The tissue inhibitors of metalloproteinases (TIMPs) are major inhibitors of several enzymes that are destructive to connective tissue, and TIMP-1 has been reported to be deficient in the wall of abdominal aortic aneurysms. This deficiency could represent failure of expression resulting from either local tissue conditions or mutation in the primary structure of the gene (or one of its regulatory elements).

METHODS

Southern blotting techniques were used to examine the possibility of global deletions or inserts in the gene (14 patients); Northern blot techniques were performed to examine the expression of the mRNAs in cultured fibroblasts under basal conditions (six patients); and sequence analysis of the cDNA derived from fibroblast mRNAs was done after amplification by polymerase chain reaction (six patients).

RESULTS

The Southern blots revealed a normal distribution of the known alleles of the gene without unique restriction-length polymorphisms. Fibroblast expression of TIMP mRNA was normal under basal conditions. Sequence analysis of the cDNAs revealed an identical-point polymorphism in two of the six patients (a single base pair substitution of C-->T at the third position in codon 101), but the amino acid was conserved.

CONCLUSION

The studies reported here do not support the hypothesis that deficiency of TIMP-1 in specimens of aorta of patients with abdominal aortic aneurysms results from a primary genetic defect.

Local secretion of corticotropin-releasing hormone in the joints of Lewis rats with inflammatory arthritis

Corticotropin-releasing hormone (CRH), the principal regulator of the hypothalamic-pituitary-adrenal axis, is also secreted in peripheral inflammatory sites, where it acts as a local proinflammatory agent. Arthritis-susceptible LEW/N rats have profoundly deficient hypothalamic CRH responses to inflammatory stimuli and other stressors. Arthritis-resistant F344/N rats, on the other hand, have a robust increase in hypothalamic CRH in response to the same stimuli. Contrasting with these hypothalamic CRH responses, we now show that CRH expression is markedly increased in the joints and surrounding tissues of LEW/N rats with streptococcal cell wall- and adjuvant-induced arthritis, whereas it is not increased in similarly treated F344/N rats and is only transiently increased in congenitally athymic nude LEW.rnu/rnu rats. Glucocorticoid treatment suppressed, but did not eliminate, CRH immunoreactivity in the joints of LEW/N rats. CRH mRNA was present in inflamed synovia, as well as in spinal cord, and inflamed synovia also expressed specific CRH-binding sites. We compared CRH expression in inflamed joints with another well-characterized proinflammatory neuropeptide, substance P (SP), and found that SP immunoreactivity paralleled that of CRH. In summary, although LEW/N rats have deficient hypothalamic CRH responses to inflammatory stimuli compared with F344/N rats, they express relatively high levels of CRH at the site of inflammation. Analogous to SP, CRH may be delivered to the inflammatory site by peripheral nerves and/or synthesized at the inflammatory site. These data provide further support for the concept that CRH not only triggers the pituitary-adrenal antiinflammatory cascade, but also functions as an antithetically active local mediator of acute and chronic inflammatory arthritis. These data also illustrate the complex interrelationships of the nervous, endocrine, immune, and inflammatory systems.

Upregulation of interleukin-1 receptors in mouse AtT-20 pituitary tumor cells following treatment with corticotropin-releasing factor

Treatment of AtT-20 cell cultures with increasing concentrations of rat/human corticotropin-releasing factor (r/hCRF) for 24 h resulted in a dose-dependent 2-3 fold increase in specific 125I-labelled recombinant human IL-1 alpha (125I-IL-1 alpha) binding that was paralleled by a 70-80% decrease in 125I-Tyro-ovine CRF binding. Saturation analysis of 125I-IL-1 alpha binding in control and CRF-treated cultures indicated that CRF produced an increase in the density (Bmax) of IL-1 receptors without altering their affinity (KD). The CRF-induced upregulation of IL-1 receptors appears to be mediated through specific membrane receptors for CRF since the CRF receptor antagonist, alpha-helical oCRF (9-41), blocked the CRF-induced upregulation of IL-1 receptors without producing any effect on 125I-IL-1 alpha binding by itself. In summary, these data demonstrate complex interactions between CRF and IL-1 at the pituitary level and identify potential novel mechanisms for cytokines to alter neuroendocrine function.

Corticotropin-releasing factor receptors in mouse spleen: identification of receptor-bearing cells as resident macrophages

CRF is a primary integrator of the organism's coordinated neuroendocrine, autonomic, behavioral, and immune responses to stress. In the present study the identity of the cell type(s) expressing CRF receptors in mouse spleen was determined using a combination of cell fractionation and receptor-binding techniques. Autoradiographic studies of the distribution of [125I]Tyro-ovine CRF [( 125I]oCRF)-binding sites in spleen localized CRF receptors primarily to the red pulp and marginal zones. The distribution pattern of [125I]oCRF-binding sites closely resembled the pattern of India ink accumulated in phagocytic cells in the same sections. To identify the specific cell type(s) expressing CRF receptors, [125I]oCRF-binding activity was evaluated in splenic cell populations fractionated on the basis of their physical and functional properties. Macrophages were identified in each fraction by their phagocytosis of polystyrene beads and membrane labeling with MONTS-4, a monoclonal antibody specific for resident macrophages. Spleen cells were fractionated by adherence to glass bead or Sephadex G-10 columns, phagocytosis of carbonyl iron particles, and centrifugation on discontinuous Percoll gradients. By all fractionation methods, there was a significant correlation of [125I]oCRF binding with both phagocytic activity (r = 0.75; P less than 0.001) and MONTS-4 staining (r = 0.84; P less than 0.001), strongly suggesting that CRF receptors are primarily expressed on resident splenic macrophages. However, there was essentially no specific binding of [125I]oCRF to either resident or elicited peritoneal macrophages or to several monocyte/macrophage, B-cell, or T-cell lines. While these results suggest that the expression of CRF receptors may be restricted to a population of splenic macrophages, they do not exclude the possibility that CRF receptors may be induced on resident macrophages in spleen and other immune system-related tissues by factors present in the microenvironment.

Functional corticotropin-releasing factor (CRF) receptors in mouse spleen: evidence from adenylate cyclase studies

Radioligand binding studies have previously identified a high affinity, magnesium-dependent, guanine nucleotide-sensitive binding site for corticotropin-releasing factor (CRF) in mouse spleen. In order to determine the functional nature of these CRF binding sites, we examined the effects of CRF on adenylate cyclase activity in mouse spleen homogenates. The stimulation of adenylate cyclase activity was dependent on time, tissue protein concentration, and guanine nucleotides. CRF-stimulated adenylate cyclase activity was evident in the presence of guanosine-5'-triphosphate (GTP) and its precursor guanosine-5'-diphosphate (GDP) but was not detected in the presence of the hydrolysis-resistant GTP analogs, guanyl-5'-imidodiphosphate [Gpp(NH)p] and guanosine-5'-gamma-thiotriphosphate (GTP-gamma-S). The rank order of potency for CRF analogs and fragments in stimulating adenylate cyclase activity was comparable to their affinities for CRF binding sites in mouse spleen homogenates. The putative receptor antagonist, alpha helical ovine CRF(9-41), did not stimulate adenylate cyclase activity but did attenuate the stimulation by various concentrations of rat/human CRF. In summary, these data demonstrate the functional nature of CRF receptors in mouse spleen as evidenced by CRF stimulation of cAMP production and suggest that this peptide may play a physiological role in regulating immune function.

Corticotropin-releasing factor receptors in mouse spleen: identification, autoradiographic localization, and regulation by divalent cations and guanine nucleotides

The radioligand [125I-Tyro]ovine CRF [( 125I] oCRF) was used to identify, characterize, and localize CRF receptors in a crude homogenate of mouse spleen. The binding was linear with increasing membrane protein concentration, saturable, and of high affinity. Scatchard analysis of [125I]oCRF saturation curves revealed a high affinity component with an apparent dissociation constant of 0.26 nM and a maximum receptor concentration of 8.74 fmol/mg protein. The relative affinities of various CRF-related and unrelated peptides at the [125I]oCRF-binding site in spleen correlate well with their reported potencies in eliciting ACTH release from the pituitary and their relative affinities for CRF receptors in brain. Consistent with a coupling of splenic CRF receptors to a guanine nucleotide regulatory protein, the binding of [125I]oCRF was increased by magnesium ions and decreased by guanine nucleotides in both mouse spleen and brain. Saturation analysis of [125I]oCRF binding at 0, 1, and 10 mM MgCl2, 10 mM MgCl2 plus 200 microM GTP, and 10 mM MgCl2 plus 50 microM 5'-guanylimidodiphosphate indicated that high affinity [125I]oCRF binding in both brain and spleen requires Mg2+; however, subtle differences were observed in the degree of sensitivity and mechanisms by which Mg2+ and guanine nucleotides regulated specific binding of [125I]oCRF to brain and spleen. Autoradiographic studies indicated that [125I]oCRF-binding sites were primarily localized to the red pulp and marginal zone regions of the spleen, which are known to contain high concentrations of macrophages. The absence of [125I]oCRF-binding sites in the periarteriolar and peripheral follicular white pulp regions suggests that neither T nor B lymphocytes have specific CRF-binding sites. In summary, we have identified a high affinity, magnesium-dependent, and guanine nucleotide-sensitive binding site for CRF in mouse spleen which appears to be localized primarily in splenic macrophages.

Characterization of corticotropin-releasing factor receptor-mediated adenylate cyclase activity in the rat central nervous system

We report here that corticotropin-releasing factor (CRF) stimulates adenylate cyclase activity in the rat central nervous system (CNS). In frontoparietal cortex homogenates, the stimulation by CRF was dependent on time, temperature, tissue protein concentration, and guanine nucleotides. The rank order of potency for CRF analogs and fragments in stimulating adenylate cyclase activity [(Nle21,38) rat CRF greater than rat CRF approximately equal to acetyl ovine CRF (4-41) approximately equal to alpha helical ovine CRF greater than ovine CRF much greater than ovine CRF (1-39) approximately equal to ovine CRF (7-41)] was consistent with their affinities for CRF receptors in the brain and their relative potencies in stimulating pituitary adrenocorticotropic hormone secretion in vitro. The putative CRF receptor antagonist, alpha helical ovine CRF (9-41), did not stimulate adenosine 3',5'-cyclic monophosphate (cAMP) production but was able to attenuate the stimulation by various concentrations of rat CRF. The regional distribution of 125I-Tyr(o)-ovine CRF binding (olfactory bulb greater than frontoparietal cortex approximately equal to cerebellum greater than hypothalamus greater than striatum greater than or equal to midbrain greater than hippocampus greater than or equal to spinal cord) did not correspond with the regional degree of CRF receptor-mediated stimulation of adenylate cyclase (frontoparietal cortex greater than olfactory bulb greater than or equal to cerebellum greater than midbrain greater than or equal to hippocampus greater than striatum greater than or equal to hypothalamus greater than spinal cord). In addition, marked differences were observed in the ability of forskolin to potentiate CRF-stimulated cAMP production in the various brain areas examined. In summary, these data demonstrate that at least one of the second-messenger systems mediating the effects of CRF in the CNS involves stimulation of cAMP production and provides further support for a neurotransmitter role for this neuropeptide in the brain. Significant differences in the regulation of CRF-stimulated cAMP production and the disparity between CRF receptor number and receptor-mediated adenylate cyclase activity in discrete regions of the rat CNS suggest that some populations of CRF receptors in the brain may be functionally coupled to alternative signal transduction mechanisms.

Neonatal treatment with monosodium glutamate does not alter grooming behavior induced by novelty or adrenocorticotropic hormone

The increased grooming behavior observed in a novel environment has been attributed to release of peptides derived from proopiomelanocortin (POMC), such as ACTH, alpha-melanocyte-stimulating hormone (alpha-MSH), or beta-endorphin, which themselves can elicit grooming. This is because novelty-induced grooming is attenuated both by hypophysectomy and by antiserum to ACTH injected into the cerebral ventricles. Administration of monosodium glutamate (MSG) to neonatal rats destroys neurons in the arcuate nucleus of the hypothalamus, depleting the brain of POMC peptides, and also hypothalamic dopamine and choline acetyl-transferase activity. Neonatal MSG treatment did not significantly alter the grooming scores of adult rats in either home or novel environments compared to saline-treated animals. There were also no differences between MSG-and saline-treated rats in the grooming scores observed following graded doses of ACTH1-24 (0.2-1.0 micrograms) administered intracerebroventricularly. Thus if increased grooming in the novel environment is due to release into the ventricles of ACTH, alpha-MSH, beta-endorphin, these peptides more likely derive from the pituitary rather than from brain cells, although the failure of the MSG treatment to produce quantitative depletions of cerebral POMC peptides, especially in the brain stem, leaves open the latter possibility.

Evidence that taste aversion learning induced by l-5-hydroxytryptophan is mediated peripherally

Rats learned to avoid a saccharin solution if their initial consumption of it was followed by intraperitoneal (IP) administration of 25 mg/kg l-5-hydroxytryptophan (l-5-HTP); this taste aversion learning did not occur in rats pretreated with 50 mg/kg (IP) of the aromatic l-amino acid decarboxylase inhibitor RO 4-4602 (benserazide). RO 4-4602 antagonized the l-5-HTP-induced elevation of 5-hydroxytryptamine (5-HT) in the mesentery but significantly increased the l-5-HTP-induced elevation of 5-HT in the brain. These results indicate that l-5-HTP-induced taste aversion is correlated with peripheral, but not central, elevation of 5-HT.