Synthetic competitive antagonists of corticotropin-releasing factor: effect on ACTH secretion in the rat

Constrained corticotropin-releasing factor antagonists with i-(i + 3) Glu-Lys bridges

Hypothesis driven and systematic structure-activity relationship (SAR) investigations have resulted in the development of effective central nervous system (CNS) antagonists of corticotropin (ACTH)-releasing factor (CRF) such as alpha-helical CRF(9-41) and analogues of our assay standard [DPhe12,Nle21,38]hCRF(12-41). On the other hand, equally potent CRF antagonists that block the hypothalamic/pituitary/adrenal (HPA) axis had not been described until recently. Predictive methods, physicochemical measurements (nuclear magnetic resonance spectrometry and circular dichroism spectroscopy), and SAR studies suggest that CRF and its family members (urotensins and sauvagine) assume an alpha-helical conformation when interacting with CRF receptors. To further test this hypothesis, we have systematically scanned the hCRF(9-41) or hCRF(12-41) sequences with an i-(i + 3) bridge consisting of the Glu-Xaa-Xbb-Lys scaffold which we and others had shown could maintain or enhance alpha-helical structure. From this series we have identified seven analogues that are either equipotent to, or 3 times more potent than, the assay standard; in addition, as presented earlier cyclo(30-33)[DPhe12,-Nle21,38,Glu30, Lys33]hCRF(12-41) (astressin) is 32 times more potent than the assay standard in blocking ACTH secretion in vitro (rat pituitary cell culture assay). In vivo, astressin is also significantly more potent than earlier antagonists at reducing hypophysial ACTH secretion in intact stressed or adrenalectomized rats. Since the corresponding linear analogues that were tested are significantly less potent, our interpretation of the increased potency of the cyclic analogues is that the introduction of the side chain to side chain bridging element (Glu30-Lys33, and to a lesser extent that of Glu14-Lys17, Glu20-Lys23, Glu23-Lys26, Glu26-Lys29, Glu28-Lys31, Glu29-Lys32, and Glu33-Lys36) induces and stabilizes in the receptor environment a putative alpha-helical bioactive conformation of the fragment that is not otherwise heavily represented. The effect of the introduction of two favored substitutions [(cyclo(20-23) and cyclo(30-33)] yielded 37 with a potency 8 times that of the assay standard but actually 12 times less than expected if the effect of the two cycles had been multiplicative. These results suggest that the pituitary CRF receptor can discriminate between slightly different identifiable conformations, dramatically illustrating the role that secondary and tertiary structures play in modulating biological signaling through specific protein-ligand interactions.

The CRF1 receptor mediates the excitatory actions of corticotropin releasing factor (CRF) in the developing rat brain: in vivo evidence using a novel, selective, non-peptide CRF receptor antagonist

Corticotropin releasing factor (CRF) is the key coordinator of the neuroendocrine and behavioral responses to stress. In the central nervous system, CRF excites select neuronal populations, and infusion of CRF into the cerebral ventricles of infant rats produces severe age-dependent limbic seizures. These seizures, like other CRF effects, result from activation of specific receptors. Both of the characterized members of the CRF receptor family (CRF1 and CRF2), are found in the amygdala, site of origin of CRF-induced seizures, and may therefore mediate these seizures. To determine which receptor is responsible for the excitatory effects of CRF on limbic neurons, a selective, non-peptide CRF1 antagonist was tested for its ability to abolish the seizures, in comparison to non-selective inhibitory analogues of CRF. Pretreatment with the selective CRF1 blocker (NBI 27914) increased the latency and decreased the duration of CRF-induced seizures in a dose-dependent manner. The higher doses of NBI 27914 blocked the behavioral seizures and prevented epileptic discharges in concurrent electroencephalograms recorded from the amygdala. The selective CRF1 blocker was poorly effective when given systemically, consistent with limited blood-brain barrier penetration. Urocortin, a novel peptide activating both types of CRF receptors in vitro, but with preferential affinity for CRF2 receptors in vivo, produced seizures with a lower potency than CRF. These limbic seizures, indistinguishable from those induced by CRF, were abolished by pretreatment with NBI 27914, consistent with their dependence on CRF1 activation. In summary, CRF induces limbic seizures in the immature rat, which are abolished by selective blocking of the CRF1 receptor. CRF1-messenger RNA levels are maximal in sites of seizure origin and propagation during the age when CRF is most potent as a convulsant. Taken together, these facts strongly support the role of the developmentally regulated CRF1 receptor in mediating the convulsant effects of CRF in the developing brain.

Adrenocorticotropic hormone-releasing activity of urotensin I and its fragments in vitro

Adrenocorticotropic hormone (ACTH)-releasing activity of synthetic carp Urotensin I (UI) and its ten synthetic fragments were examined using cultured rat pituitary cells. Both UI(1-41) and rat CRF (rCRF) increased ACTH release in a similar fashion at a concentration range from 10 pM to 100 nM. The potency of UI(1-41) was about one seventh that of rCRF on a molar basis. Four of ten UI fragments, UI(1-36), UI(4-36), UI(6-36) and UI(1-19) showed relatively strong ACTH-releasing activity, whereas both UI(9-36) and UI(17-36) showed extremely weak ACTH-releasing activity. However, all these fragments showed the activity in a dose-dependent manner parallel with that of UI(1-41). The activity of UI(1-36) was weaker than UI(1-41), suggesting that the C-terminal 37-41 sequence is required to express the full ACTH-release activity, although each of four C-terminal fragments, UI(24-36), UI(24-41), UI(29-36) and UI(29-41), exhibited no activity. In summary, the 4-19 amino acid sequence of UI(is important to exhibit ACTH-releasing activity and the C-terminal 37-41 sequence will be necessary to express the full activity.

Enhancement of tachykinin-induced contractions of guinea pig isolated bronchus by corticotropin-releasing factor

The effect of corticotropin-releasing factor (CRF) on contractions of guinea pig isolated airways in response to electrical or chemical stimulation of tachykinergic nerve fibers was studied. CRF (1 microgram/ml) caused a 70% enhancement of the peak magnitude of the response to electrical field stimulation (EFS). CRF had a similar effect on contractions of the isolated bronchus evoked by capsaicin. CRF also potentiated contractions evoked by exogenously applied substance P. This effect was selective, as CRF has no effect on contractions evoked by neurokinin A or the substance P analog ASMSP. The potentiation of the substance P-induced contractions of airway smooth muscle was blocked by the CRF receptor antagonist alpha helical (9-41) CRF. These data support the hypothesis that CRF enhances the airway smooth muscle response to stimulation of tachykinin-containing nerve fibers and that this effect is due to a post-junctional mechanism of action.

Corticotropin-releasing factor-like peptides increase cytosolic [Ca2+] in human epidermoid A-431 cells

This study investigated whether sauvagine and urotensin I change [Ca2+]i in human epidermoid A-431 cells and whether these changes are correlated with their anti-edema properties in vivo. A-431 cells were used because they possess the corticotropin-releasing factor (CRF) receptor 2. Treatment with either sauvagine or urotensin I led to an immediate increase in [Ca2+]i, the magnitude of which depended on the concentration of the drug. Sauvagine was more effective than urotensin I, with a median effective concentration (EC50) of 1.4 +/- 0.2 fM, compared to an EC50 of 66 +/- 7 fM for urotensin I. Both were more effective at stimulating increases in [Ca2+]i than CRF (EC50 of 6.8 +/- 0.1 pM). There was a correlation between the EC50 for increasing [Ca2+]i and the median effective dose (ED50) for inhibiting edema induced by heating rat paw (r = 0.99). Removal of extracellular Ca2+ or incubation with La3+ eliminated the increase in [Ca2+]i stimulated by either peptide. Pretreatment with a CRF receptor antagonist reduced the increase in [Ca2+]i by these peptides. This occurred in an antagonist concentration-dependent manner, with median inhibitory concentrations (IC50) of 1.99 +/- 0.04 nM and 0.85 +/- 0.04 nM, respectively. Both pertussis toxin (an inhibitor of G proteins) and U-73122 (an inhibitor for inositol trisphosphate (InsP3) production) partially inhibited the increases. InsP3 was measured to determine whether these peptides mobilized Ca2+ from an InsP3-sensitive store. Both sauvagine and urotensin I increased InsP3. The InsP3 increases were inhibited by U-73 122 and CRF antagonist, but not by removal of external Ca2+. Both peptides elevated protein tyrosine phosphorylation. In summary, these peptides increase [Ca2+]i as a result of Ca2+ influx via CRF receptor-operated Ca2+ channels coupled to pertussis toxin-sensitive G proteins and a Ca2+ mobilization from InsP3-sensitive Ca2+ pools. Their in vivo effectiveness at inhibiting edema is related to their respective capacities to stimulate elevations of [Ca2+]i, supporting a role for intracellular Ca2+ in this process.

Synthesis and oral efficacy of a 4-(butylethylamino)pyrrolo[2,3-d]pyrimidine: a centrally active corticotropin-releasing factor1 receptor antagonist

The syntheses of a centrally active nonpeptide CRF1 receptor antagonist 2, butylethyl[2,5-dimethyl-7-(2,4,6-trimethylphenyl)-7H-pyrrolo [2,3-d]pyrimidin-4-yl]amine (CP-154,526), and its analogs 11-14 and [3H]-2 are reported. The in vitro CRF1 receptor binding affinity in the series 2, the pharmacokinetic properties of 2 in rats, and the anxiolytic-like effects of orally administered 2 are presented.

Environmental stress as a developmental cue: corticotropin-releasing hormone is a proximate mediator of adaptive phenotypic plasticity in amphibian metamorphosis

Environmentally induced phenotypic plasticity allows developing organisms to respond adaptively to changes in their habitat. Desert amphibians have evolved traits which allow successful development in unpredictable environments. Tadpoles of these species can accelerate metamorphosis as their pond dries, thus escaping mortality in the larval habitat. This developmental response can be replicated in the laboratory, which allows elucidation of the underlying physiological mechanisms. Here I demonstrate a link between a classical neurohormonal stress pathway (involving corticotropin-releasing hormone, CRH) and the developmental response to habitat desiccation. Injections of CRH-like peptides accelerated metamorphosis in western spadefoot toad tadpoles. Conversely, treatment with two CRH antagonists, the CRH receptor antagonist alpha-helical CRH(9-41) and anti-CRH serum, attenuated the developmental acceleration induced by habitat desiccation. Tadpoles subjected to habitat desiccation exhibited elevated hypothalamic CRH content at the time when they responded developmentally to the declining water level. CRH injections elevated whole-body thyroxine, triiodothyronine, and corticosterone content, the primary hormonal regulators of metamorphosis. In contrast, alpha-helical CRH(9-41) reduced thyroid activity. These results support a central role for CRH as a neurohormonal transducer of environmental stimuli into the endocrine response which modulates the rate of metamorphosis. Because in mammals, increased fetal/placental CRH production may initiate parturition, and CRH has been implicated in precipitating preterm birth arising from fetal stress, this neurohormonal pathway may represent a phylogenetically ancient developmental regulatory system that allows the organism to escape an unfavorable larval/fetal habitat.

Corticotropin-releasing factor and systemic capsaicin-sensitive afferents are involved in abdominal surgery-induced Fos expression in the paraventricular nucleus of the hypothalamus

We previously reported that abdominal surgery induces Fos expression in specific hypothalamic and medullary nuclei and also causes gastric stasis. The gastric ileus is reduced by systemic capsaicin and abolished by central injection of corticotropin-releasing factor (CRF) antagonist. We studied the influence of systemic capsaicin and intracerebroventricular (i.c.v.) injection of the CRF antagonist, alpha-helical CRF9-41, on Fos expression in the brain 1 h after abdominal surgery in conscious rats using immunocytochemical detection. In control groups (vehicle s.c. or i.c.v.), abdominal surgery (laparotomy with cecal manipulation) performed under 7-8 min of enflurane anesthesia induced Fos staining in neurons of the spinal trigeminal, C1/A1 group, ventrolateral medulla, central amygdala, parabrachial nucleus, cuneate nucleus, nucleus tractus solitarii (NTS), paraventricular nucleus of the hypothalamus (PVN) and supraoptic nucleus (SON). Capsaicin (125 mg/kg s.c., 2 weeks before) or alpha-helical CRF9-41 (50 microg i.c.v., before surgery) reduced the number of Fos-positive cells by 50% in the PVN while not modifying the number of Fos-labelled cells in the other nuclei. These results indicate that capsaicin-sensitive primary afferents and brain CRF receptors are part of the pathways and biochemical coding through which abdominal surgery activates PVN neurons 1 h post surgery.

Neurotensin stimulates CRH and ACTH release by rat adrenal medulla in vitro

Neurotensin (NT) is a 13-amino acid peptide, widely distributed in the central and peripheral nervous system, which is able to stimulate the activity of the hypothalamo-pituitary CRH-ACTH system. We investigated by RIA the effect of NT on the release of CRH and ACTH immunoreactivities (ir) by rat adrenal medulla in vitro. NT enhanced the release of both CRH-ir and ACTH-ir, the maximal effective concentration being 10(-8) M. [D-Trp11]-NT, a specific NT receptor antagonist, abrogated the effects of NT. The stimulatory effect of 10(-8) M NT on ACTH-ir release was blocked by alpha-helical-CRH (an antagonist of CRH receptors), thereby suggesting that the enhancement in ACTH secretion is consequent to the stimulation of CRH release. These findings suggest that NT is a stimulator not only of the central (hypothalamo-pituitary), but also of the peripheral (intramedullary), branch of the CRH-ACTH system.

Presence of functional receptors for corticotropin releasing hormone in caecal circular smooth muscle cells of guinea pig

The presence of specific binding sites for corticotropin releasing hormone (CRH) in caecal circular smooth muscle cells of guinea pig was investigated by binding and pharmacological studies. The specific binding of 125I-CRH to these muscle cells reached an equilibrium after 90 minutes. Several peptides structurally unrelated to CRH did not affect the specific binding of 125I-CRH to these muscle cells. Unlabeled CRH completely inhibited the specific binding of 125I-CRH in a concentration-dependent manner, with an IC50 value of 13.5 nM. A CRH receptor antagonist, alpha-helical CRH (9-41), inhibited the specific binding of 125I-CRH in a concentration-dependent manner with a lower affinity than CRH. In pharmacological study, CRH inhibited the contractile response of these muscle cells to 1 nM cholecystokinin-octapeptide in a concentration-dependent manner, with an IC50 value of 14.1 nM. A CRH receptor antagonist, alpha-helical CRH (9-41), significantly antagonized this inhibitory effect produced by CRH. These results strongly suggest the presence of functional receptors for CRH that mediate relaxation of caecal circular smooth muscle cells of guinea pig.

Neuropeptide K and neurokinin A stimulate CRH and ACTH release by rat adrenal medulla in vitro

Tachykinins are a family of peptides that are able to modulate the activity of the hypothalamo-pituitary CRH-ACTH system. Mammalian tachykinins include neurokinin A (NKA), neurokinin B (NKB), neuropeptide K (NPK), and substance P (SP). We investigated by RIA the effects of tachykinins on the release of CRH and ACTH by rat adrenal medulla in vitro. NKA and NPK concentration-dependently enhanced the release of both CRH and ACTH, NPK being more active than NKA. NKB exerted only a minor stimulatory action exclusively on CRH release, and SP was ineffective. The stimulatory effect of both NKA and NPK on ACTH release was blocked by the CRH receptor antagonist alpha-helical-CRH, thereby suggesting that the increase in ACTH secretion is consequent to the stimulation of CRH release. These findings indicate that NKA and NPK are stimulators not only of the central (hypothalamo-pituitary), but also of the peripheral (intramedullary) branch of the CRH-ACTH system.

Arginine-vasopressin stimulates CRH and ACTH release by rat adrenal medulla, acting via the V1 receptor subtype and a protein kinase C-dependent pathway

Arginine-vasopressin (AVP) is a hypothalamic hormone that, like CRH, stimulates the pituitary release of ACTH, thereby activating adrenal glucocorticoid secretion. Evidence indicates that rat adrenal medulla contains a CRH-ACTH system duplicating that existing at the hypothalamo-pituitary level and involved in the paracrine stimulation of the cortex secretion. Therefore, we investigated by RIA the effect of AVP on the release of CRH and ACTH immunoreactivities (IR) by rat adrenal medulla in vitro. AVP concentration-dependently enhanced the release of both CRH-IR and ACTH-IR, and the effect was blocked by a selective antagonist of the V1 subtype of AVP receptors. The CRH receptor antagonist alpha-helical-CRH partially reversed AVP-evoked rise in ACTH-IR release, without altering either CRH response or basal secretions of CRH and ACTH. The specific inhibitors of protein kinase C Ro31-8220 and calphostin C abolished both CRH and ACTH responses to AVP. In conclusion, our present findings suggest that AVP stimulates intramedullary the CRH-ACTH system, acting via V1 receptors and activating protein kinase C.

Use of animal models in peptic ulcer disease

Considerable progress has been made in the understanding of the formation of gastric erosions by the use of animals. The role of gastric acid secretion in their pathogenesis has been clarified. Gastric erosions are associated with the presence of acid in the stomach and slow gastric contractions. With several different experimental procedures, the animal's body temperature falls; preventing the fall averts erosions. A fall in body temperature or exposure to cold are associated with the secretion of thyrotropin-releasing hormone (TRH), and both increased and decreased concentration of corticotropin-releasing factor (CRH) in discrete regions of rat brains. Thyrotropin-releasing hormone when injected into specific sites in the brain produces gastric erosions and increases acid secretion and slow contractions, whereas CRH has the opposite effects. One of the major sites of interaction of the two peptides is in the dorsal motor complex of the vagus nerve. Thyrotropin-releasing hormone increases serotonin (5-HT) secretion into the stomach. Serotonin counter-regulates acid secretion and slow contractions. Many other peptides injected into discrete brain sites stimulate or inhibit gastric acid secretion.

Synthesis and characterization of a photoactivatable analog of corticotropin-releasing factor for specific receptor labeling

A novel photoactivatable analog of ovine corticotropin-releasing factor (ovine photoCRF) has been synthesized and characterized. A diazirine group, the 4-(1-azi-2,2,2-trifluoroethyl)benzoyl residue, was covalently bound to the amino terminus of ovine CRF (oCRF), which was N-terminally extended by a tyrosyl residue for radioactive labeling with 125I. Under mild conditions, photolysis yielded highly reactive carbenes, responsible for the formation of covalent bonds to the CRF receptor. Ovine photoCRF was shown to bind to the high-affinity site of the CRF receptor with a similar Kd value as oCRF. When radioactively iodinated ovine photoCRF (ovine 125I-photoCRF) was covalently linked to rat CRF receptor, type 1 (rCRFR1), permanently transfected into human embryonic kidney (HEK) 293 cells, a highly glycosylated 75-kDa protein was identified with SDS/PAGE. The specificity of ovine 125I-photoCRF was demonstrated by the finding that this analog could be displaced from the receptor by oCRF, but not other unrelated peptides such as vasoactive intestinal peptide. The observed size of the 75-kDa cross-link was in agreement with the molecular weight reported earlier for native CRFR1 from rat brain. Deglycosylation of the 75-kDa cross-link with peptide:N-glycosidase (PNGase) yielded a 46-kDa protein, in agreement with the molecular weight estimated from cDNA coding for rat CRFR1. The developed CRF analog, photoCRF, is expected to facilitate future biochemical and physiological analysis of CRF receptors and--by analogous strategies--of other peptide receptors.

A single-point slight alteration set as a tool for structure-activity relationship studies of ovine corticotropin releasing factor

In order to determine which amino acid side chains of ovine corticotropin releasing factor (oCRF) are most sensitive to alterations with respect to receptor binding and activation, we synthesized a single-point replacement set by replacing each residue by a similar, preferably proteinogenic amino acid, maintaining a minimal change of character at each position (Ser by Thr, Gln by Asn, Glu by Asp, Arg by Lys, and vice versa, Pro by N-MeAla, Ile by Leu, Leu by Nle, Phe by Trp, His by Ala, Val by Leu, Met by Nle, Ala by Leu). In general, any loss in the biological potency by a single-point substitution in oCRF parallels a decrease in receptor binding, indicating that, in contrast to previous suggestions, there is no specific side chain in the peptide that is more responsible for receptor activation than for receptor binding. In addition to Arg(16), Ala(31), and Arg(35), amino acid residues in the N-terminal sequence (5-14) were found to be sensitive to alteration, demonstrating their particular importance for the receptor interaction of CRF agonists. Most of the analogs tested exhibited agonistic potencies in an in vitro pituitary cell culture assay at a concentration of 0.3 nM, and all analogs showed full agonistic potency at 1 microM. In contrast to the results of an alanine replacement study, the strongest decrease in receptor binding and biological potency was observed for analogs with substitutions of hydrophilic amino acids Ser(7), Arg(16), Glu(17), or Asn(34). In the case of Ser(7) and Arg(16), side chain specific interactions with the receptor may be required for high affinity. Alanine replacements at positions 17 or 34 resulted in analogs that were as potent as oCRF, while replacement of Glu(17) by Asp or Asn(34) by Gln caused a dramatic loss in potency, thereby suggesting an important effect at sterically or conformationally sensitive positions. In contrast to corresponding alanine analogs which exhibited a significant loss in biological potency, slight alterations of lipophilic side chains at positions 6, 12, or 38 did not cause a significant reduction of receptor binding and activation, indicating that it is not specific side chains but rather lipophilicity which is essential at these positions. Indeed, replacement of Phe(12) by Trp provides an agonist with significantly increased receptor binding and biological potency.

A non peptidic corticotropin releasing factor receptor antagonist attenuates fever and exhibits anxiolytic-like activity

The multiple actions of corticotropin-releasing factor (CRF) on neuroendocrine and behavioural functions can now be examined using new, high affinity, non peptidic antagonists which exhibit central activity upon systemic application. We have shown that compound CP 154,526 (butyl-ethyl-[2,5-dimethyl-7-(2,4,6-trimethylphenyl)-7H-pyrrolo [2,3-d]pyrimidin-4-yl]amine) displaces [125I][Tyr0]CRF from rat hippocampal CRF receptors (IC50 = 0.5 nM) and from pituitary CRF receptors (IC50 = 0.04 nM). The same compound inhibits in a concentration-dependent manner the ovine CRF (0.1 microM)-stimulated adenylate cyclase activity in membranes of a mouse pituitary adenoma cell line, AtT20, with an IC50 value of 50 nM. Systemic application of the CRF receptor antagonist (0.16 mg/kg i.p.) blocked recombinant human interleukin-1 beta 5 micrograms/kg i.p.) induced fever in rats. The CRF receptor antagonist CP 154,526 (1 mg/kg i.p.) also exhibited signs of anxiolytic-like activity in the elevated plus-maze test in rats.

Dexamethasone rapidly increases hypothalamic neuropeptide Y secretion in adrenalectomized ob/ob mice

A single intracerebroventricular injection of dexamethasone (DEX) rapidly (within 30 min) suppresses brown adipose tissue thermogenesis and increases plasma insulin concentrations in adrenal-ectomized (ADX) ob/ob mice but not in ADX lean mice. Intracerebroventricular neuropeptide Y (NPY) administered intracerebroventricularly causes these same metabolic changes within 30 min in both ob/ob and lean ADX mice. We therefore hypothesized that DEX exerts these rapid-onset metabolic actions in ob/ob mice via a phenotype-specific enhancement of NPY secretion within the central nervous system. In support of this hypothesis, DEX (a type II glucocorticoid receptor agonist) administered intracerebroventricularly selectively lowered NPY concentrations in the whole hypothalamus of ADX ob/ob mice by 35% and in the arcuate nucleus region by approximately 70% within 30 min but not in the brain stem or hippocampus or in any of these regions of lean mice. DEX also functioned in vitro to enhance depolarization-dependent release of NPY from hypothalamic blocks of ADX ob/ob mice but not of ADX lean mice. Thus DEX acts in the hypothalamus of ob/ob mice in a phenotype-specific manner to evoke rapid transport of NPY from cell bodies within the arcuate nucleus to terminal regions including the dorsomedial and ventromedial hypothalamic regions for release.

[D-Pro5]Corticotropin-releasing factor analogs as selective agonists at corticotropin-releasing factor receptors

Corticotropin-releasing factor (CRF) acts on at least two types of CRF receptors. To search for selective CRF receptor agonists, 37 ovine CRF analogs, systematically substituted with D-amino acids, were tested for inhibitory activity on edema induced in the pentobarbital-anesthetized rat paw by heat (immersion in 58 degrees C water for 1 min). The activity of each analog, administered 21 nmol/kg i.v. 10 min before heat, was compared to published data on the analog's potency in stimulating adrenocorticotropin (ACTH) release from cultured rat pituitary cells. In general, a positive rank correlation was found between the anti-edema and neuroendocrine activities of these analogs, however, one outlier, [D-Pro5]ovine CRF, exhibited greater selectivity for anti-edema activity. The human/rat analog of [D-Pro5]CRF was synthesized and found to be equipotent to human/rat CRF for suppression of heat-edema. In cells transfected with two types of cloned CRF receptors, the intracellular cAMP response to [D-Pro5]human/rat CRF was equipotent to human/rat CRF in the heart-muscle CRF (CRF2 beta) receptor assay but was five times less potent than human/rat CRF in the pituitary-central nervous system CRF (CRF1) receptor assay. We conclude that changing residue Pro5 in the CRF molecule from a L- to a D-configuration confers selectivity by decreasing second messenger activation at the CRF1 receptor whilst retaining full potency at the CRF2 beta receptor.

Urocortin, a corticotropin-releasing factor-related mammalian peptide, inhibits edema due to thermal injury in rats

Urocortin is a recently characterized mammalian peptide which appears to be an endogenous ligand for corticotropin-releasing factor (CRF) receptors, in particular CRF receptor type 2. The effect of rat urocortin on protein extravasation and edema, produced by immersion of the paws of anesthetized rats in 58 degrees C water for 5 min, was compared to that of rat/human CRF. Urocortin administered i.v. dose-dependently inhibited the leakage of Evans blue dye into the skin of the footpad and the increase in paw weight, with a potency 6.6-6.7 times greater than CRF. alpha-Helical CRF-(9-41), a more potent antagonist of type 2 than type 1 CRF receptors, completely reversed the inhibition of edema produced by either CRF or urocortin, at a dose (200 nmol/kg) that did not affect adrenocorticotropin secretion induced by either peptide. These data indicate that urocortin is a potent inhibitor of heat-induced edema, and that this action is mediated by CRF receptors, most likely CRF receptor type 2.

Conformational differences of ovine and human corticotropin releasing hormone. A CD, IR, NMR and dynamic light scattering study

The differences in the conformational properties of ovine (o) and human (h) CRH in aqueous solution, structure-inducing TFE and in the presence of detergent micelles and lipid vesicles have been investigated by circular dichroism, Fourier transform infrared spectroscopy, NMR and dynamic light scattering. o-CRH was found to exist as a monomer with little regular structure in dilute aqueous solution. Association at concentrations higher than 10-3 mol/L results predominantly in dimers. The induction of a substantial amount of intermolecular beta-structure seems to be the result of interactions of the C-terminal hexapeptide and the N-terminal region 6-12 of o-CRH chains in antiparallel orientation. In contrast, h-CRH exhibits a high tendency of association which is highly sensitive to the pH. The formation of tetramers at millimolar peptide concentration is related to a helical content of ca. 50%. The potentially helical, highly hydrophobic region 6-20 enlarged by more hydrophobic residues in position 23 and 25 is proposed to stabilize the h-CRH associates. In the presence of structure inducing TFE (> 40% v) both CRH peptides exist as monomers. o-CRH reveals about 72% helicity, in h-CRH the formation of about 85% helix is observed. The differences in helicity of the two CRH molecules are located in the C-terminal heptapeptide, as concluded on the basis of NMR studies. Both peptides bind to detergent micelles at pH 4 as well as 7.4 associated with an increase in the alpha-helical content. Interaction of the two peptides with DMPC vesicles was found exclusively at pH 4. Above the phase transition temperature of DMPC the alpha-helical content in h-CRH increases slightly; however, o-CRH reveals a substantial amount of beta-type structure. The intramolecular type of beta-structure is associated with a deeper insertion of the o-CRH region 6-12 into the hydrophobic region of the lipid bilayer, whereas the corresponding region of h-CRH is kept in the bilayer surface. The higher helicity of h-CRH might explain to some extent its higher affinity to the CRH receptor, CRH antibodies and the CRH binding protein.

Stimulation of 5-HT2A receptors in the paraventricular hypothalamus attenuates neuropeptide Y-induced hyperphagia through activation of corticotropin releasing factor

The effect of 5-HT1 and 5-HT2 receptor agonists administered into the paraventricular hypothalamus was studied on the hyperphagia caused by neuropeptide Y (NPY) injected into the same area. The 5-HT2A/2C receptor agonist DOI (10-20 nmol/0.5 microliter) significantly reduced NPY overeating while the 5-HT1A/1B receptor agonist RU 24969 (3.5-14 nmol/0.5 microliter) and the 5-HT1B/2C receptor agonist mCPP (5-20 nmol/0.5 microliter) had no such effect. The 5-HT2A receptor antagonist spiperone (5 microgram/0.5 microliter) and the corticotropin releasing factor antagonist alpha-helical-CRF9-41 (0.5-1 micrograms/0.5 microliter) completely antagonized the effect of 10 nmol DOI.

Neuropeptides implicated in the control of diuresis in insects

Primary urine production in insect Malpighian tubules is stimulated by two classes of neuropeptides, CRF-related diuretic peptides and insect kinins. The CRF-related peptide of the locust, Locusta migratoria, has a hormonal role in the control of postfeeding diuresis, but the functional role of the kinins has yet to be defined. The two classes of peptide act synergistically to stimulate tubule secretion, and the kinins may therefore have a modulatory action in the control of diuresis. The peptides differ in their effects on Malpighian tubule ion transport, and this could be important for the regulation of hemolymph volume and composition.

The role of CRF in behavioral aspects of stress

CRF in the central nervous system appears to hve activating properties on behavior and to coordinate behavioral responses to stressors. These behavioral effects of CRF appear to be independent of the pituitary-adrenal axis and can be reversed by CRF antagonists. CRF antagonist administration reverses not only decreases in behavior associated with stress, but also increases in behavior associated with stress, thus suggesting that the role of CRF is stress dependent and not intrinsic to a given behavioral response. Further, microinjection of alpha-helical CRF 9-41 and immunotargeting of CRF neurons in separate brain compartments reveal a link between the anatomical sites that contain CRF and the nature of the behavioral response to stressors that can be modified by suppression of endogenous CRF activity therein. These actions of CRF in coordinating coping responses to stress at several bodily levels are consistent with a role for CRF similar to the dual role of other hypothalamic releasing factors in integrating hormonal and neural mechanisms by acting both as secretagogues for anterior pituitary hormones and as extrapituitary peptide neurotransmitters. Moreover, dysfunction in such a fundamental homeostatic system may be the key to a variety of pathophysiological conditions including mental disorders.

Corticotropin-releasing hormone is involved in conditioned stimulus-induced reduction of natural killer cell activity but not in conditioned alterations in cytokine production or proliferation responses

Research from our laboratory has demonstrated that the presentation of an aversive conditioned stimulus produces pronounced suppression of several in vitro measures of immune status. The present study was designed to evaluate the role of central corticotropin-releasing hormone (CRH) in the mechanisms mediating these conditioned effects. The aversive conditioned stimulus was a distinct environment that had previously been associated with electric footshock. Lewis rats received intraventricular administration of either buffered saline or a dose of the CRH-selective receptor antagonist alpha-helical CRH(9-41) (0, 0.5, 5, or 50 micrograms) prior to exposure to the aversive conditioned stimulus or home cage control treatment. The aversive conditioned stimulus produced decreases in splenic natural killer cell activity, splenocyte responsiveness to the mitogens concanavalin A (ConA), phytohemagglutinin (PHA), lipopolysaccharide (LPS), and the combination of ionomycin and phorbol myristate acetate (PMA), blood leukocyte responsiveness to ConA and PHA, and the production of interleukin-2 and interferon-gamma by activated splenocytes. The conditioned stimulus also produced an increase in plasma levels of corticosterone. Pretreatment with alpha-helical CRH(9-14) completely blocked the conditioned stimulus-induced suppression of natural killer cell activity. The CRH antagonist had no attenuative effect on the conditioned suppression of splenocyte or blood leukocyte proliferation in response to mitogens, or the production of interleukin-2 or interferon-gamma by activated splenocytes. There was also no effect of alpha-helical CRH(9-14) on the conditioned stimulus-induced increase in plasma corticosterone. These findings suggest that conditioned stimulus-induced suppression of natural killer cell activity is mediated by a mechanism that involves activity at central CRH receptors, and that this conditioned modulation is independent of HPA activation. Furthermore, these results indicate that the mechanisms involved in conditioned stimulus-induced suppression of proliferative or cytokine production responses are distinct from those involved in the modulation of natural killer cell activity.

Potent, structurally constrained agonists and competitive antagonists of corticotropin-releasing factor

Predictive methods, physicochemical measurements, and structure activity relationship studies suggest that corticotropin-releasing factor (CRF; corticoliberin), its family members, and competitive antagonists (resulting from N-terminal deletions) usually assume an alpha-helical conformation when interacting with the CRF receptor(s). To test this hypothesis further, we have scanned the whole sequence of the CRF antagonist [D-Phe12,Nle21,38]r/hCRF-(12-41) (r/hCRF, rat/human CRF; Nle, norleucine) with an i-(i + 3) bridge consisting of the Glu-Xaa-Xaa-Lys scaffold. We have found astressin [cyclo(30-33)[D-Phe12,Nle21,38,Glu30,Lys33]r/ hCRF(12-41)] to be approximately 30 times more potent than [D-Phe12,Nle21,38]r/hCRF-(12-41), our present standard, and 300 times more potent than the corresponding linear analog in an in vitro pituitary cell culture assay. Astressin has low affinity for the CRF binding protein and high affinity (Ki = 2 nM) for the cloned pituitary receptor. Radioiodinated [D-125I-Tyr12]astressin was found to be a reliable ligand for binding assays. In vivo, astressin is significantly more potent than any previously tested antagonist in reducing hypophyseal corticotropin (ACTH) secretion in stressed or adrenalectomized rats. The cyclo(30-33)[Ac-Pro4,D-Phe12,Nle21,38,Glu30,Lys33++ +]r/hCRF-(4-41) agonist and its linear analog are nearly equipotent, while the antagonist astressin and its linear form vary greatly in their potencies. This suggests that the lactam cyclization reinstates a structural constraint in the antagonists that is normally induced by the N terminus of the agonist.

Nizatidine accelerates gastric emptying of a solid meal in rats

Nizatidine, a new histamine-2-receptor antagonist, stimulates gastrointestinal motility in dogs and gastric emptying of liquids in rats. Effect of nizatidine on gastric emptying of a solid meal was investigated using a novel gastric emptying model in rats. Male Wistar rats (weighing 200-300 g) were supplied with powdered food containing 30 w/w% barium 14 hr before the beginning of the experiment and x-ray photography of rat stomach was taken under light ether anesthesia. Gastric emptying was assessed by percentage of a decrease in area 30 min after drug was injected intraperitoneally. There was a positive correlation between the area of the gastric outline and the weight of the gastric contents (r = 0.94, P < 0.01). Ether anesthesia itself did not affect gastric emptying. Nizatidine increased gastric emptying dose-dependently (emptied percentage; vehicle: 4.9 +/- 1.5%, 1 mg/kg: 7.2 +/- 0.4%, 3 mg/kg: 10.4 +/- 2.0%, 10 mg/kg: 16.7 +/- 4.9%, 30 mg/kg: 25.7 +/- 7.4%). N-Desmethyl nizatidine (NDM) also stimulated gastric emptying, but nizatidine S-oxide, cimetidine, an famotidine had no significant effects on gastric emptying. Nizatidine and neostigmine, but not NDM, at a subthreshold dose accelerated gastric emptying treated with a low dose of acetylcholine (0.1 mg/kg). Atropine (2 mg/kg, -30 min) did not modulate the gastroprokinetic action of nizatidine, but blocked that of NDM. These findings suggest that this noninvasive method may allow measurement of gastric emptying of solids accurately and that nizatidine and NDM facilitate gastric emptying probably mediated by a direct and/or an indirect (acetylcholinesterase inhibition) cholinergic mechanism.

Corticotropin releasing factor decidualizes human endometrial stromal cells in vitro. Interaction with progestin

Decidualization of endometrial cells is a hormone-dependent process of differentiation which occurs during the menstrual cycle and pregnancy. Recent in vitro studies have revealed that cAMP and its generators induce decidualization of stromal cells isolated from proliferative endometrium and that progestins enhance the effect of cAMP. Since corticotropin releasing factor (CRF) generates cAMP and prostaglandins in other organs, in the present study the effect of CRF, a hypothalamic factor also produced by decidua and fetal membranes, on in vitro decidualization of endometrial stromal cells was evaluated. The addition of CRF to a culture medium of stromal cells induced in vitro decidualization, as indicated by morphologic changes from elongated fibroblast-like cells into larger and round cells and by the release of prolactin in the medium. The effect of CRF on stromal cells and on prolactin release was significantly augmented by the coincubation in the presence of medroxyprogesterone acetate. This observation indicates CRF as a novel factor of decidualization and confirms that progestins act as enhancers of the expression of decidual products.

Bacterial lipopolysaccharide stimulates glucocorticoid secretion in hypophysectomized rats

The effect of an i.p. bolus injection of 200 micrograms.kg-1 bacterial lipopolysaccharide (LPS) on the plasma concentrations of ACTH and corticosterone (B) were studied in intact and hypophysectomized/ACTH replaced (Hx) rats. Hormonal blood levels were measured by RIA, 30, 60, 120, 180 and 240 min after the injection. The stress evoked by the vehicle i.p. injection provoked significant rises in ACTH and B blood levels at 30 and 60 min in intact rats, but not in Hx animals. In intact rats, LPS enhanced (over the respective control value) ACTH plasma level at 60, 120 and 180 min, and B plasma concentration at 120, 180 and 240 min. In Hx rats, LPS did not affect ACTH blood level, but raised B plasma concentration at 60, 120 and 180 min. B response to LPS at 120 min was completely annulled, in both intact and Hx rats, by the simultaneous administration of 25 nmol.kg-1 alpha-helical-CRH and corticotropin-inhibiting peptide that are competitive inhibitors of CRH and ACTH, respectively. The hypothesis is advanced that LPS may activate hypothalamo-pituitary adrenal axis in rats, by stimulating not only the central (hypothalamo-pituitary), but also the peripheral (intra-adrenal) branch of the CRH/ACTH system.

Interaction of an amphiphilic peptide with a phospholipid bilayer surface by molecular dynamics simulation study

Corticotropin-releasing factor (CRF) is the principal neuroregulator of adrenocorticotropic hormone (ACTH) secretion. Previous experiments have demonstrated that CRF binds avidly to the surface of single egg phosphatidylcholine vesicles and its amphiphilic secondary structure might play an important role in the function. In this study, the interaction of the residues 13-41 in human CRF with the surface of a DOPC bilayer was investigated by molecular dynamics (MD) simulation in order to understand the role of the membrane surface in the formation of the amphiphilic alpha helix as well as to determine the effects of the peptide on the lipid bilayer. The model used included 60 DOPC molecules, 1 helical peptide (CRF13-41) on the bilayer surface, and explicit waters of solvation in the lipid polar head group regions, together with constant-volume periodic boundary conditions in three dimensions. The MD simulation was carried out for 510 ps. In addition, CRF13-41, initially in a helical form, was simulated in vacuo as a control. The results indicate that while it was completely unstable in vacuo, the peptide helical form was generally maintained on the bilayer surface, but with distortions near the terminal ends. The peptide was confined to the bilayer headgroup/water region, similar to that reported from neutron diffraction measurement of tripeptides bound to the phosphatidylcholine bilayer surface (Ref 1). The amphiphilicity of the peptide matched that of the bilayer headgroup environment, with the hydrophilic side oriented toward water and the hydrophobic side making contact with the bilayer hydrocarbon core. These results support the hypothesis that the amphiphilic environment of a membrane surface is important in the induction of peptide amphiphilic alpha-helical secondary structure. Two major effects of the peptide on the lipids were found: the first CH2 segment in the lipid chains was significantly disordered and the lipid headgroup distribution was broadened towards the water region.

Stress-induced behavioral responses and multiple opioid systems in the brain

Various stressor produce a wide range of behavioral responses such as analgesia, catalepsy and motor suppression, which are sensitive to opioid receptor antagonists. These behavioral responses in stress are accompanied by changes in the contents of opioid peptides, the mRNAs encoding their precursors and opioid receptor binding in the brain. In the present article, experimental data concerning stress-induced analgesia and motor suppression is reviewed and discussed in relation to a possible involvement of different opioid systems in the various observed behavioral responses in stress. Pharmacological studies with subtype-selective antagonists have demonstrated that not only mu- but also delta- and/or kappa-opioid receptors are involved in opioid-mediated stress-induced analgesia. There are two types of stress-induced analgesia referred to as opioid-mediated and non-opioid mediated forms. It has been proposed that the intensity and temporal pattern of stressor may be a critical factor determining the nature of stress-induced analgesia. Accumulated evidence demonstrate that these two forms of pain inhibitory systems interact each other according to a collateral inhibition model. Recent studies show that parallel activation of multiple opioid receptors mediates non-opioid froms of stress-induced analgesia. Dynorphins, by acting at kappa-opioid receptors, may play a pivotal role in the expression of stress-induced motor suppression, whereas enkephalins may act to attenuate this response.

Stimulation of CRH-mediated ACTH secretion by central administration of neurotensin: evidence for the participation of the paraventricular nucleus

Central administration of neurotensin (NT) stimulates hypothalamic-pituitary-adrenal (HPA) activity in freely-moving rats. Increases in adrenocorticotropin hormone (ACTH) and corticosterone (B) were observed 15 min following central NT administration and remained elevated for up to 4 h. Of the two NT fragments tested, NT1-8 and NT8-13, only NT8-13 was found to significantly elevate ACTH and B levels. Moreover, NT8-13 activated the HPA axis with a temporal profile similar to NT1-13, suggesting an interaction with the pharmacologically and molecularly characterized NT receptor. Animals pre-treated intravenously with the corticotropin-releasing hormone (CRH) antagonist, alpha-helical CRH, showed attenuated plasma ACTH and B responses to central NT administration. This indicates that CRH receptor activation is necessary for the stimulatory effects of NT on HPA function. Bilateral lesions of the paraventricular nucleus (PVN) of the hypothalamus significantly reduced NT-induced stimulation of ACTH and B release suggesting that the PVN is essential for NT's stimulatory action. Median eminence content studies indicated that acute central NT administration stimulates CRH, but not arginine vassopressin (AVP), release in animals examined 60 min following NT injection. Taken together, these findings suggest that the stimulatory effects of NT on HPA activity occur via specific NT receptors and that one site of action of NT is likely at the level of the PVN where NT elicits the release of CRH.

Cloning and characterization of a functionally distinct corticotropin-releasing factor receptor subtype from rat brain

The present study reports the isolation of a cDNA clone that encodes a second member of the corticotropin-releasing factor (CRF) receptor family, designated as the CRF2 receptor. The cDNA was identified using oligonucleotides of degenerate sequence in a PCR paradigm. A PCR fragment obtained from rat brain was utilized to isolate a full-length cDNA from a rat hypothalamus cDNA library that encoded a 411-amino acid protein with approximately 70% identity to the known CRF1 receptor over the entire coding region. When expressed in mouse Ltk- cells, this receptor stimulates cAMP production in response to CRF and known CRF-like agonists. CRF and the nonmammalian CRF-related peptides sauvagine and urotensin I stimulate adenylate cyclase activity in a dose-dependent manner with a rank order of potency different from that of the CRF1 receptor: sauvagine > urotensin > or = rat/human CRF > ovine CRF. Tissue distribution analysis of the mRNAs by reverse transcriptase-PCR shows CRF2 receptor mRNA is present in rat brain and detectable in lung and heart. In situ hybridization studies indicate specific expression within the brain in the ventromedial nuclei of the hypothalamus, the lateral septum, the amygdala, and entorhinal cortex, but there is unremarkable expression in the pituitary. An additional splice variant of the CRF2 receptor with a different N-terminal domain has been identified by PCR, encoding a putative protein of 431 amino acids. Thus, the data demonstrate the presence of another functional CRF receptor, with significant differences in the pharmacological profile and tissue distribution from the CRF1 receptor, which would predict important functional differences between the two receptors.

Corticotropin-releasing hormone involvement in stressor-induced alterations in sleep and in the regulation of waking

Sleep responds to a variety of stressors, but the precise mechanisms whereby these alterations occur are not known. Ample evidence, however, testifies to corticotropin-releasing hormone (CRH) being uniquely situated to contribute to stressor-induced alterations in sleep. Behavioral responses to most stressors include periods of increased arousal and waking, regardless of whether the stressor is psychological in nature or results in physical insult. Furthermore, a large body of evidence suggests that CRH may also contribute to the regulation and maintenance of physiological waking. In this paper we hypothesize that CRH mediates waking, particularly after periods of exposure to acute stressors. The complex interactions of multiple systems determine the behavioral response to a particular stressor. As such, many factors determine the time course and duration of response, including stressor type, and the status of a particular system at the time of stressor presentation. We briefly review data indicating that CRH mediates physiological and behavioral responses to stressors, and present new data supporting the hypothesis that CRH may also be involved in the physiological regulation of waking.

Cross reactivity studies of CRF-related peptides on insect Malpighian tubules

Manduca sexta diuretic peptide II (Mas-DPII) stimulates fluid secretion by adult Malpighian tubules and cyclic AMP production by larval proximal and adult tubules of M. sexta in a dose-dependent manner. Mas-DPII has no effect on fluid transport across the larval cryptonephric complex. M. sexta diuretic hormone (Mas-DH) and CRF-related insect diuretic peptides from Acheta domesticus, Locusta migratoria, and Periplaneta americana also cause similar increases in the production of cyclic AMP by the Malpighian tubules of both larval and adult M. sexta. Insect CRF-related diuretic peptides exhibit varying degrees of potency when assayed on Malpighian tubules from L. migratoria and A. domesticus. Sauvagine, bovine-CRF, and human-CRF have only a small, but significant, effect on cyclic AMP production by M. sexta Malpighian tubules. However, sauvagine, bovine-CRF, and sucker fish urotensin-I have no effect on L. migratoria tubules. Stimulation of cyclic AMP production by M. sexta Malpighian tubules could potentially be used as a screening assay to identify other insect CRF-related diuretic peptides.

Corticotropin-releasing factor administered into the locus coeruleus, but not the parabrachial nucleus, stimulates norepinephrine release in the prefrontal cortex

Previous studies have indicated that intracerebroventricular application of corticotropin-releasing factor (CRF) activates noradrenergic neurons in the brain stem locus coeruleus (LC) and norepinephrine (NE) metabolism in several brain regions. To assess whether CRF has direct effects on LC noradrenergic neurons, CRF was infused into the LC and concentrations of NE and its metabolites were measured in microdialysates collected from the medial prefrontal cortex (PFM). Infusion of 100 ng of CRF into the LC significantly increased dialysate concentrations of NE and of its catabolite MHPG in the ipsilateral PFM, whereas no significant changes were observed following infusion of artificial CSF. No response was observed when the infusions of CRF occurred outside of the LC, including those in the parabrachial nucleus. Although CRF administered into the LC slightly increased dialysate concentrations of NE in the contralateral PFM, this effect was not statistically significant. The effect of CRF injected into the LC on dialysate NE was prevented by combination with a 10-fold excess of the CRF antagonist alpha-helical CRF9-41, indicating some specificity in the response. These results are consistent with anatomical and electrophysiological evidence suggesting that CRF may directly activate noradrenergic neurons in or close to the LC.

Effects of neuromedin U-8 on the secretory activity of the rat adrenal cortex: evidence for an indirect action requiring the presence of the zona medullaris

The acute effect of increasing concentrations (from 10(-8) to 10(-6) M) of neuromedin U-8 (NMU-8) on steroid secretion of rat adrenal gland was investigated in vitro by high-pressure liquid chromatography. The production of the following steroids was measured: pregnenolone (PREG), progesterone (PROG), 11-deoxycorticosterone (DOC), corticosterone (B), 18-hydroxy-11-deoxycorticosterone (18OH-DOC), 18-hydroxycorticosterone (18OH-B) and aldosterone (ALDO). NMU-8 had no effects on either dispersed adrenocortical cells or fragments of adrenocortical autotransplants lacking medullary chromaffin cells. Conversely, NMU-8 exerted concentration-dependent secretagogue effects on adrenal slices, including both cortex and medulla. At all concentrations tested, NMU-8 increased the production of both PREG and total post-PREG steroids. The increase in total post-PREG steroid output induced by low concentrations of NMU-8 (10(-8) M) was due to similar rises in the production of non-18-hydroxylated steroids (PROG, DOC and B) and 18-hydroxylated hormones (18OH-DOC, 18OH-B and ALDO); conversely, that provoked by higher concentrations of the neuropeptide (10(-7) to 10(-6) M) was almost exclusively caused by the rise in the yield of 18-hydroxylated steroids. The stimulating effect of NMU-8 on PREG output was blocked by both alpha-helical-CRH and corticotropin-inhibiting peptide, which are competitive inhibitors of CRH and ACTH, respectively. The following conclusions have been drawn: (1) NMU-8 affects adrenal steroid secretion indirectly by acting on the medullary chromaffin cells, which in turn may paracrinally stimulate the cortical ones; (2) at all concentrations tested, NMU-8, by stimulating the intramedullary CRH/ACTH system, causes a net rise in the activity of the early rate-limiting step of steroidogenesis, with the consequent increase in the output of the entire spectrum of post-PREG steroids; and (3) at higher concentrations (over 10(-8) M), NMU-8 also elicits the release from chromaffin cells of a factor (not yet known) that specifically enhances 18-hydroxylase activity.

Neuropeptide K enhances glucocorticoid release by acting directly on the rat adrenal gland: the possible involvement of zona medullaris

Neuropeptide K (NPK), a member of the kassinin-like tachykinin family, is contained in the rat hypothalamus and is known to stimulate pituitary ACTH release. The intraperitoneal bolus administration of NPK dose-dependently enhanced corticosterone blood level not only in intact rats, but also in hypophysectomized/ACTH replaced animals. NPK did not affect corticosterone secretion of dispersed rat adrenocortical cells; however, it concentration-dependently raised basal corticosterone production by decapsulated adrenal quarters (including both cortical and medullary tissues). Minimal and maximal effective concentrations were 10(-9) and 10(-8) M, respectively. 10(-8) M NPK potentiated corticosterone response of adrenal quarters elicited by 10(-12) M ACTH, but not that evoked by higher concentrations of ACTH. The direct corticosterone secretagogue effect of 10(-8) M NPK is annulled by 10(-6) M alpha-helical-CRH or corticotropin-inhibiting peptide, competitive inhibitors of CRH and ACTH, respectively. In light of these findings, the hypothesis is advanced that NPK exerts a direct stimulatory action on adrenocortical secretion and that the mechanism underlying this effect of NPK may involve the activation of the intra-medullary CRH/ACTH system.

Elevation of plasma ACTH concentration in rabbits made febrile by systemic injection of bacterial endotoxin

This study was carried out to investigate the adrenocorticotropic hormone (ACTH) response in rabbits made febrile by systemic injection of lipopolysaccharide (LPS, Salmonella typhosa endotoxin). Intravenous (i.v.) injection of LPS (0.1 microgram/kg and 1.0 microgram/kg) increased rectal temperature (biphasic fever) and the plasma concentration of ACTH (ACTH response) in a dose-related manner. These responses were suppressed by pretreatment with indomethacin (20 mg/kg, subcutaneously). Intracerebroventricular (i.c.v.) administration of indomethacin (400 micrograms) had no effect on the ACTH response to LPS, although it significantly suppressed febrile response. Small increases in plasma concentration of ACTH and significant fevers followed i.c.v. administration of prostaglandin E2 (2 micrograms) or F2 alpha (2 micrograms). I.v. administration of corticotropin releasing factor (CRF) antagonist [alpha-helical CRF (9-41) (200 micrograms/kg)] partly suppressed the ACTH increase induced in plasma by i.v. LPS. These results suggest that prostaglandins synthesized outside the blood-brain barrier play an important role in the ACTH response and that the mechanism for induction of the ACTH response is not exactly the same as that for the febrile response, although prostaglandins are involved in both responses.

Effect of corticotropin-releasing factor antagonist on behavioral and neuroendocrine responses during exposure to defensive burying paradigm in rats

Defensive burying behavior is a coping strategy in rodents in response to an aversive stimulus where fear will facilitate burying and treatment with anxiolytics will result in less burying. To test the hypothesis that endogenous corticotropin-releasing factor (CRF) is involved in the defensive burying response, the effects of an ICV CRF antagonist were tested on defensive burying behaviors as well as the plasma adrenocorticotropic hormone (ACTH) and plasma corticosterone response. Rats were allowed to self-administer one mild electric shock (1.0 mA) through a probe mounted on the wall of the home cage by briefly touching it. Following this shock, control rats typically display burying behavior, as defined as moving the bedding material toward and/or over the shock probe. A CRF antagonist, alpha-hel CRF9-41, was administered ICV (1, 5, and 25 micrograms) 1 min after they received the shock. The 5 micrograms dose of the CRF antagonist significantly attenuated the time spent in defensive burying compared to vehicle-treated controls. The 5 and 25 micrograms doses of alpha-hel CRF9-41 increased the latency to display defensive burying. However, the enhanced release of plasma ACTH and plasma corticosterone concentrations in the stressed animals was not significantly modified over the 15-min period by either of the three doses of CRF antagonist. The results suggest that endogenous CRF is involved in the expression of defensive burying behavior and that the brain CRF receptors modulating the behavioral response may be different from the CRF receptors modulating the hormonal response of defensive burying.

Corticotropin-releasing factor increases [Ca2+]i via receptor-mediated Ca2+ channels in human epidermoid A-431 cells

Corticotropin-releasing factor (CRF) has been shown to attenuate vascular leakage in injured skin, mucous membrane, muscle, and brain. Calcium is thought to play an important role in many of the physiological responses to CRF, but there has been little characterization of how calcium is involved in process by which CRF protects damaged tissues. The goal of this study was to characterize changes in cytosolic free calcium concentrations ([Ca2+]i) in human epidermoid A-431 cells exposed to human/rat-CRF and to investigate the mechanisms by which these changes occur. The resting [Ca2+]i in normal cells at 37 degrees C was 66 +/- 4 nM (n = 32). When cells were treated with CRF, [Ca2+]i increased immediately. The increase depended on CRF concentration, with a median effective concentration of 11 pM. This increase in [Ca2+]i depended on external Ca2+ but not Na+, Mg2+, or K+. La3+ (10 microM) and Co2+ (10 microM) inhibited the CRF-induced [Ca2+]i increase, whereas verapamil and nifedipine tested at concentrations up to 1 mM did not. alpha-Helical CRF-(9-41), a synthetic CRF receptor antagonist, and pertussis toxin blocked the increase in [Ca2+]i induced by CRF, which suggests that the entry of extracellular Ca2+ is mediated by receptor-operated Ca2+ channels coupled with pertussis toxin-sensitive G proteins. Although 420 pM CRF stimulated an immediate increase in [Ca2+]i, inositol trisphosphate and cellular cAMP levels did not change within 1 min either in the presence or absence of external Ca2+.(ABSTRACT TRUNCATED AT 250 WORDS)

Water-avoidance stress-induced c-fos expression in the rat brain and stimulation of fecal output: role of corticotropin-releasing factor

Immunohistochemical detection of the immediate-early gene c-fos was used to determine the pattern of neuronal activity in the rat brain after exposure to water-avoidance stress known to stimulate fecal output in rats. Avoidance to water for 1 h by standing on a small platform increases pellet output and induces numerous Fos-positive cells in the parvocellular part of the paraventricular nucleus of the hypothalamus (PVN), locus coeruleus (LC) and, to a lesser extent, in the bed nucleus of the stria terminalis, lateral septum, dorsal raphe nucleus and A5 and A1 noradrenergic neurons. The corticotropin-releasing factor (CRF) antagonist, alpha-helical CRF9-41 (50 micrograms i.c.v.) reduced water-avoidance stress-induced c-fos expression mainly in the PVN and the LC (44 and 60%, respectively) and decreased by 60% the stimulated fecal output. These data indicate that water-avoidance stress activates PVN and LC neurons through CRF pathways which contribute to the stimulation of colonic motor function.

Corticotropin-releasing factor and schedule-induced polydipsia

Two experiments examined the effects of ICV-administered corticotropin-releasing factor (CRF) and alpha-helical CRF (9-41), a CRF antagonist, on the performance of schedule-induced polydipsia (SIP). Infusions of CRF into the lateral ventricle dose-dependently (0.02, 0.1, and 0.5 micrograms) attenuated both the volume of water consumed and licking on a fixed-time 60-s schedule. This effect of CRF on schedule-induced drinking was accompanied by a reduction in the number of nose pokes made into the food tray, suggesting that CRF may attenuate SIP through an action on appetitive motivation. Neither the temporal distribution of responding nor the locomotor activity induced by the schedule was affected by CRF. In marked contrast to these effects of exogenous CRF on the performance of SIP, infusions of alpha-helical CRF (1, 5, and 25 micrograms) into the lateral ventricle did not affect the performance of schedule-induced polydipsia. The implications of these results for the hypothesis that SIP is a coping response to stress are discussed.

A novel macromolecular structure is a target of the promyelocyte-retinoic acid receptor oncoprotein

Acute promyelocytic leukemia (APL) is associated with a t(15;17) translocation that creates the promyelocyte-retinoic acid receptor alpha (PML-RAR alpha) fusion gene. Immunohistochemistry demonstrates that PML is a part of a novel macromolecular organelle (including at least three other nuclear proteins) referred to as PML oncogenic domains (PODs). In APL cells, the POD is disrupted into a microparticulate pattern as a consequence of the expression of the PML-RAR oncoprotein. RA treatment of APL cells triggers a reorganization of PML to generate normal-appearing PODs. We propose that PML-RAR is a dominant negative oncoprotein that exerts its putative leukomogenic effect by inhibiting assembly of the POD. According to this proposal, not only is the POD a novel structure, but it can be ascribed an imputed function such that its disruption leads to altered myeloid maturation; this may represent a novel oncogenic target.

Benzodiazepines antagonize central corticotropin releasing hormone-induced suppression of natural killer cell activity

Benzodiazepines have anxiolytic properties and attenuate behavioral stress responses induced by corticotropin releasing hormone (CRH). To evaluate the effect of benzodiazepines on CRH-induced immune suppression, potent centrally acting benzodiazepines were administered prior to central infusion of CRH (i.c.v.; 1.0 microgram). CRH induced a significant (P < 0.01) reduction of splenic natural killer cell activity which was completely antagonized by pretreatment with either diazepam or alprazolam.

Inducibility and negative autoregulation of CREM: an alternative promoter directs the expression of ICER, an early response repressor

cAMP-responsive element modulator (CREM) expression is tissue specific and developmentally regulated. Here we report that CREM is unique within the family of cAMP-responsive promoter element (CRE)-binding factors since it is inducible by activation of the cAMP signaling pathway. The kinetic of expression is characteristic of an early response gene. The induction is transient and cell specific, does not involve increased transcript stability, and does not require protein synthesis. Significantly, the subsequent decline in CREM expression requires de novo protein synthesis. The induced transcript encodes a novel repressor, inducible cAMP early repressor (ICER), and is generated from an alternative intronic promoter. A cluster of four CREs in this promoter directs cAMP inducibility. ICER binds to these elements and thereby represses the activity of its own promoter, thus constituting a negative autoregulatory loop.

Primary structure and functional expression of mouse pituitary and human brain corticotrophin releasing factor receptors

Corticotrophin-releasing factor (CRF) is the principal hypothalamic factor governing the pituitary-adrenal axis, but the wide extra-pituitary distribution of CRF and its receptors suggest a major role for this neuropeptide in the integration of the overall physiological and behavioral responses of an organism to stress. We have cloned a CRF receptor complementary DNA (cDNA) by expression in COS-7 cells of a cDNA library from the AtT20 mouse pituitary tumour cell line. The cloned mouse cDNA was then as a probe to isolate a human CRF receptor cDNA from a human brain cDNA library. The mouse and human cDNAs both encode 415 amino acid proteins that are 97% identical, containing seven putative transmembrane domains characteristic of G protein-coupled receptors. The CRF receptor shows homology with the receptors for growth hormone-releasing factor, vasoactive intestinal peptide, secretin, parathyroid hormone, and calcitonin. COS-7 cells transfected with the mouse CRF receptor cDNA bind radiolabelled ovine CRF with high affinity and respond specifically to CRF by accumulation of intracellular cAMP. A 2.7 kb mRNA coding for the CRF receptor could be detected in AtT20 cells and human cortex tissue. PCR analysis also detected the receptor transcript in human pituitary, brainstem, and testis.

TCDD alters pituitary-adrenal function. II: Evidence for decreased bioactivity of ACTH

The present study assessed the ability of primary cultures of rat anterior pituitary cells to secrete bioactive ACTH in the presence of 2, 3, 7, 8-tetrachlorodibenzo-p-dioxin (TCDD). The bioactivity of the secreted pituitary cell ACTH was determined by its ability to stimulate secretion of corticosterone from primary cultures of rat adrenal cells. ACTH from basal or CRH stimulated pituitary cells treated with TCDD was found to be less capable of stimulating corticosterone secretion from primary rat adrenal cell cultures than equimolar concentrations of ACTH purchased from a commercial supplier. Corticosterone secretion from adrenal cell cultures treated with ACTH from basal or CRH stimulated pituitary cell cultures exposed to TCDD was decreased by 60 and 70%, respectively. The decreased ability to stimulate corticosterone secretion can be overcome when extracts of ACTH from pituitary cell cultures treated with TCDD are supplemented with commercial ACTH. These findings indicate that TCDD may alter the bioactivity of secreted ACTH from the anterior pituitary gland.