Biomedical subjects

Jean Rivier

Publications and source records attributed to Jean Rivier.

At least 19 recordsLinked to original sources

PubMed2006

CRF receptors in the rodent and human cardiovascular systems: species differences.

CRF has powerful receptor-mediated cardiovascular actions. To evaluate the precise distribution of CRF receptors, in vitro CRF receptor autoradiography with (125)I-[Tyr(0), Glu(1), Nle(17)]-sauvagine or [(125)I]-antisauvagine-30 was performed in the rodent and human cardiovascular system. An extremely high density of CRF(2) receptors was detected with both tracers in vessels of rodent lung, intestine, pancreas, mesenterium, kidney, urinary bladder, testis, heart, brain, and in heart muscle. In humans, CRF(2) receptors were detected with (125)I- antisauvagine-30 at low levels in vessels of kidneys, intestine, urinary bladder, testis, heart and in heart muscle, while only heart vessels were detected with (125)I-[Tyr(0), Glu(1), Nle(17)]-sauvagine. This is the first extensive morphological study reporting the extremely wide distribution of CRF(2) receptors in the rodent cardiovascular system and a more limited expression in man, suggesting a species-selective CRF receptor expression.

Animals↗

PubMed2006

Novel sst2-selective somatostatin agonists. Three-dimensional consensus structure by NMR.

The 3D NMR structures of six octapeptide agonist analogues of somatostatin (SRIF) in the free form are described. These analogues, with the basic sequence H-DPhe/Phe2-c[Cys3-Xxx7-DTrp8-Lys9-Thr10-Cys14]-Thr-NH2 (the numbering refers to the position in native SRIF), with Xxx7 being Ala/Aph, exhibit potent and highly selective binding to human SRIF type 2 (sst2) receptors. The backbone of these sst2-selective analogues have the usual type-II' beta-turn reported in the literature for sst2/3/5-subtype-selective analogues. Correlating the biological results and NMR studies led to the identification of the side chains of DPhe2, DTrp8, and Lys9 as the necessary components of the sst2 pharmacophore. This is the first study to show that the aromatic ring at position 7 (Phe7) is not critical for sst2 binding and that it plays an important role in sst3 and sst5 binding. This pharmacophore is, therefore, different from that proposed by others for sst2/3/5 analogues.

Humans↗

PubMed2006

Novel analogues of degarelix incorporating hydroxy-, methoxy-, and pegylated-urea moieties at positions 3, 5, 6 and the N-terminus. Part III.

Novel degarelix (Fe200486) analogues were screened for antagonism of GnRH-induced response (IC(50)) in a reporter gene assay. Inhibition of luteinizing hormone release over time was measured in the castrated male rat. N(omega)-Hydroxy- and N(omega)-methoxy-carbamoylation of Dab and Dap at position 3 (3-6), and N(omega)-hydroxy-,N(omega)-methoxy-carbamoylation and pegylation of 4Aph at positions 5 and 6 (7-10, 15-17, 22-25) were carried out. Modulation of hydrophobicity was achieved using different acylating groups at the N-terminus (11-14, 18-21, 26-28). Analogues 8, 15-17, 22, and 23 were equipotent to acyline (IC(50) = 0.69 nM) and degarelix (IC(50) = 0.58 nM) in vitro. Analogues 7, 17, and 23 were shorter acting than acyline, when 9, 11, 13, 15, 16, and 22 were longer acting. Only 9 and 14 were inactive at releasing histamine. No analogue exhibited a duration of action comparable to that of degarelix. Analogues with shorter and longer retention times on HPLC (a measure of hydrophilicity) than degarelix were identified.

Acylation↗

PubMed2006

Definition and characterization of the short alphaA-conotoxins: a single residue determines dissociation kinetics from the fetal muscle nicotinic acetylcholine receptor.

We report the definition and characterization of a conotoxin subfamily, designated the short alphaA-conotoxins (alphaA(S)) and demonstrate that all of these share the unique property of selectively antagonizing the fetal subtype of the mammalian neuromuscular nicotinic acetylcholine receptor (nAChR). We have characterized newly identified alphaA(S)-conotoxins from Conus pergrandis and have conducted a more detailed characterization of alphaA-conotoxins previously reported from additional Conus species. Among the results, the characterization of the short alphaA-conotoxins revealed diverse kinetics of a block of the fetal muscle nAChR, particularly in dissociation rates. The structure-function relationships of native alphaA(S)-conotoxins and some analogues revealed a single amino acid locus (alternatively either His or Pro in native peptides) that is a critical determinant of the dissociation kinetics. The unprecedented binding selectivity for the fetal muscle nAChR, coupled with the kinetic diversity, should make alphaA(S)-conotoxins useful ligands for a diverse set of studies. The rapidly reversible peptides may be most suitable for electrophysiological studies, while the relatively irreversible peptides should be most useful for binding and localization studies.

Amino Acid Sequence↗

PubMed2006

Identification of new gonadotrophin-releasing hormone partial agonists.

GnRH agonists or antagonists are currently utilized as therapeutic agents in a number of diseases. A side-effect of prolonged treatment with GnRH analogues is hypoestrogenism. In this study, we tested the in vitro potency of different GnRH analogues originally found to be partial agonists (i.e. analogues with decreased efficacy for activating or stimulating their cognate receptor) as well as novel analogues, to identify compounds that might potentially be useful for partial blockade of gonadotrophin release. Cultured COS-7 cells transiently expressing the rat or human GnRH receptor (GnRHR) were exposed to increasing concentrations (10(-8) to 10(-5) M) of GnRH analogues (c(4-10)[Asp4,DNal6,Dpr10]-GnRH; c(4-10) [Dpr4,DNal6,Asp10]-GnRH; c(4-10)[Cys(4,10),DNal6]-GnRH; c[Eaca1,DNal6]-GnRH; c[Gly1,DNal6]-GnRH; c[betaAla1,DTrp6]-GnRH; c[Dava1,DNal6]-GnRH; c[Gaba1, DNal6]-GnRH), and the ability of these analogues to provoke or antagonize GnRH-stimulated inositol phosphate production was assessed. With both human and rat GnRHRs, c[Eaca1,DNal6]-GnRH, c[Gly1,DNal6]-GnRH, c[betaAla1,DTrp6]-GnRH and c[Dava1,DNal6]-GnRH exhibited partial agonist activity (35-87% of the maximal efficacy shown by 10(-6) M GnRH), whereas c[Gaba1,DNal6]-GnRH behaved as a partial agonist with the human GnRHR and as full agonist with the rat GnRHR. c(4-10)[Asp4, DNal6,Dpr10]-GnRH and c(4-10)[Dpr4,DNal6,Asp10]-GnRH exhibited full antagonist activity with both GnRHRs, and c(4-10) [Cys(4,10),DNal6]-GnRH was a weak, partial agonist with the human GnRHR and a full antagonist with the rat GnRHR. With the exception of c[Gaba1,DNal6]-GnRH stimulation of the human GnRHR, and c[Dava1,DNal6]-GnRH and c[Gaba1, DNal6]-GnRH stimulation of the rat GnRHR, all partial agonists also exhibited antagonist activity in the presence of the exogenous full agonist. The results demonstrate that structurally similar analogues display variable potencies and efficacies in vitro for a specific GnRHR as well as for the human versus the rat GnRHR. Their ultimate in vivo usefulness to treat clinical conditions in which complete suppression of gonadotroph activity is not required remains to be investigated.

Animals↗

PubMed2005

Bifunctional gonadotropin-releasing hormone antagonist-progesterone analogs with increased efficacy and duration of action.

GnRH peptide analogs are widely used to treat diverse clinical conditions. However, they have poor oral activity and exhibit rapid metabolic clearance, thus requiring injection and depot formulation. Because steroid hormones are bound to plasma proteins, we explored the possibility of conjugating hydroxylated progesterones to GnRH analogs to reduce metabolic clearance of the peptides. Conjugation of [D-Lys6]GnRH agonist to the alpha11-hydroxyl of alpha11-hydroxyl progesterone via a hemi-succinate bridge increased the plasma half-life after iv injection in rabbits by 3.6-fold while retaining high binding affinity, thus providing proof of concept. Five GnRH antagonists were then synthesized with 21-hydroxyprogesterone conjugated via C21-hydroxyl to positions six (conjugates A and B) and position seven (conjugates C and D) of GnRH antagonists. In the fifth compound the NH2 terminus of a GnRH antagonist lacking the first two amino acids was conjugated via the C21-hydroxyl to 21-hydroxyprogesterone (conjugate E). All five analogs bound to guinea pig progesterone binding globulin with relatively high affinities (264-1020 nM). Moreover, all five conjugates retained high progestogenic activity in stimulating a progesterone-response-element-driven chloramphenicol acetyltransferase reporter gene in the T47D breast cancer cell line. Conjugation via the epsilon-amino function of D-Lys6 (conjugates A and B) produced compounds with high binding affinity for the human GnRH receptor (15 and 7 nM) comparable to that of the unconjugated GnRH antagonists (4 and 26 nM). Conjugation via the epsilon-amino function of Lys7 (conjugates C and D) or the NH2 terminus of an N-terminally truncated antagonist (conjugate E) produced compounds of low binding affinity. Conjugates A and B also exhibited high functional antagonism of GnRH stimulation of inositol phosphate production in COS-7 cells expressing the human GnRH receptor (2.6 and 16 nM) compared with the unconjugated antagonists (1.3 and 122 nM). In accordance with their poor receptor binding affinity, conjugates C, D, and E had poor functional antagonism. Preliminary dose-finding studies in female marmosets showed transitory progesterone inhibition by 0.25 mg and prolonged suppression of 12 and 17 d by 0.5- and 1.0-mg doses. Injection of conjugate A in adult male marmosets (0.5 mg sc) rapidly suppressed plasma testosterone levels, which remained suppressed for at least 3 d. In contrast, the unconjugated parent antagonist alone or with progesterone suppressed testosterone for only 8 h to 1 d. The findings demonstrate that conjugation of progesterone to GnRH antagonists conveys plasma binding and progestogenic properties and increases their efficacy and duration of action in vivo. These new GnRH antagonists show promise as therapeutic agents for hormone-dependent diseases and as contraceptives.

Animals↗

PubMed2005

Iterative approach to the discovery of novel degarelix analogues: substitutions at positions 3, 7, and 8. Part II.

Degarelix (FE200486, Ac-d-2Nal(1)-d-4Cpa(2)-d-3Pal(3)-Ser(4)-4Aph(l-Hor)(5)-d-4Aph(Cbm)(6)-Leu(7)-ILys(8)-Pro(9)-d-Ala(10)-NH(2)) is a potent and very long acting antagonist of gonadotropin-releasing hormone (GnRH) after subcutaneous administration in mammals including humans. Analogues of degarelix were synthesized, characterized, and screened for the antagonism of GnRH-induced response in a reporter gene assay in HEK-293 cells expressing the human GnRH receptor. The duration of action was also determined in the castrated male rat assay to measure the extent (efficacy and duration of action) of inhibition of luteinizing hormone (LH) release. Structurally, this series of analogues has novel substitutions at positions 3, 7, and 8 and N(alpha)-methylation at positions 6, 7, and 8 in the structure of degarelix. These substitutions were designed to probe the spatial limitations of the receptor's cavity and to map the steric and ionic boundaries. Some functional groups were introduced that were hypothesized to influence the phamacokinetic properties of the analogues such as bioavailability, solubility, intra- or intermolecular hydrogen bond forming capacity, and ability to bind carrier proteins. Substitutions at positions 3 ([N(beta)-(2-pyridyl-methyl)d-Dap(3)]degarelix, IC(50) = 2.71 nM) (5), 7 ([Pra(7)]degarelix, IC(50) = 2.11 nM) (16), and 8 ([N(delta)-(IGly)Orn(8)]degarelix, IC(50) = 1.38 nM) (20) and N-methylation ([N(alpha)-methyl-Leu(7)]degarelix, IC(50) = 1.47 nM) (32) yielded analogues that were equipotent to degarelix (2) in vitro (IC(50) = 1.64 nM) but shorter acting in vivo. Out of the 33 novel analogues tested for the duration of action in this series, two analogues ([N(epsilon)-cyclohexyl-Lys(8)]degarelix, IC(50) = 1.50 nM) (23) and ([N(beta)-(IbetaAla)Dap(8)]degarelix, IC(50) = 1.98 nM) (26) had antagonist potencies and duration of action similar to that of azaline B {inhibited LH (>80%) release for >72 h after sc injection to castrated male rats at a standard dose of 50 mug/rat in 5% mannitol}. Under similar conditions analogues ([N(gamma)-(IGly)Dab(8)]degarelix, IC(50) = 1.56 nM) (21) and ([IOrn(8)]degarelix, IC(50) = 1.72 nM) (18) had a longer duration of action {inhibited LH (>96 h) release} than azaline B; however they were shorter acting than degarelix. Hydrophilicity of these analogues, a potential measure of their ability to be formulated for sustained release, was determined using RP-HPLC at neutral pH yielding analogues with shorter as well as longer retention times. No correlation was found between retention times and antagonist potency or duration of action.

Animals↗

PubMed2005

Definition of the M-conotoxin superfamily: characterization of novel peptides from molluscivorous Conus venoms.

Most of the >50,000 different pharmacologically active peptides in Conus venoms belong to a small number of gene superfamilies. In this work, the M-conotoxin superfamily is defined using both biochemical and molecular criteria. Novel excitatory peptides purified from the venoms of the molluscivorous species Conus textile and Conus marmoreus all have a characteristic pattern of Cys residues previously found in the mu-, kappaM-, and psi-conotoxins (CC-C-C-CC). The new peptides are smaller (12-19 amino acids) than the mu-, kappaM-, and psi-conotoxins (22-24 amino acids). One peptide, mr3a, was chemically synthesized in a biologically active form. Analysis of the disulfide bridges of a natural peptide tx3c from C. textile and synthetic peptide mr3a from C. marmoreus showed a novel pattern of disulfide connectivity, different from that previously established for the mu- and psi-conotoxins. Thus, these peptides belong to a new group of structurally and pharmacologically distinct conotoxins that are particularly prominent in the venoms of mollusc-hunting Conus species. Analysis of cDNA clones encoding the novel peptides as well as those encoding mu-, kappaM-, and psi-conotoxins revealed highly conserved amino acid residues in the precursor sequences; this conservation in both amino acid sequence and in the Cys pattern defines a gene superfamily, designated the M-conotoxin superfamily. The peptides characterized can be provisionally assigned to four distinct groups within the M-superfamily based on sequence similarity within and divergence between each group. A notable feature of the superfamily is that two distinct structural frameworks have been generated by changing the disulfide connectivity on an otherwise conserved Cys pattern.

Amino Acid Sequence↗

PubMed2005

Synthesis, in vivo and in vitro biological activity of novel azaline B analogs.

Several azaline B analogs (2-10) were synthesized and evaluated for their ability to antagonize GnRH in vitro and for duration of action in inhibiting luteinizing hormone secretion in a castrated male rat assay in vivo. Analogs, 8 (IC(50) = 1.85 nM), and 9 (IC(50) = 1.78 nM), are equipotent with azaline B (1, IC(50) = 1.36 nM) in vitro. Whereas 9 is short acting, 8 is as long acting as azaline B. Other analogs have IC(50) greater than 2.0 nM and are all short acting.

Animals↗

PubMed2005

Receptor signaling and endocytosis are differentially regulated by somatostatin analogs.

Upon hormone stimulation, the sst2 somatostatin receptor couples to adenylyl cyclase through G(i/o) proteins and undergoes rapid endocytosis via clathrin-coated pits. In this study, we determined the relationship between the ability of ligands to induce sst2 receptor internalization and inhibit adenylyl cyclase. Immunocytochemical studies demonstrated that peptide agonists [such as somatostatin-14, cortistatin-17, octreotide, vapreotide, KE108 (Tyr0-cyclo[d-diaminobutyric acid-Arg-Phe-Phe-d-Trp-Lys-Thr-Phe]), and SOM230 (cyclo[diaminoethylcarbamoyl-hydroxyproline-phenylglycine-d-Trp-Lys-(4-O-benzyl)-l-Tyr-Phe])] and nonpeptide agonists (such as L-779,976), stimulated the rapid endocytosis of sst2 receptors in human embryonic kidney 293 and CHO-K1 cells. In contrast, two antagonists did not induce receptor endocytosis by themselves and completely blocked agonist stimulation. Using a quantitative enzyme-linked immunosorbent assay to measure sst2 receptor sequestration, we found that peptide agonists varied by more than 100-fold in their potencies but exhibited the same efficacy as somatostatin14. In contrast, L-779,976 did not induce maximal receptor internalization. It is interesting that although betaarrestin-2 was recruited to cell surface sst2 receptors after stimulation with either somatostatin14 or L-779,976, the betaarrestin-receptor complex dissociated earlier in the endocytic pathway with the nonpeptide ligand. Although all agonists, including L-779,976, produced the same maximal inhibition of cyclic AMP, the potency ratio for inhibition of cyclic AMP and stimulation of receptor endocytosis varied by 15-fold. In general, native peptides showed similar potencies for cyclic AMP inhibition and receptor endocytosis, whereas short therapeutic analogs were substantially more potent at inhibiting cyclic AMP synthesis. These results demonstrate that the activity of somatostatin analogs to regulate receptor endocytosis and signaling are not tightly linked and provide compelling evidence for the induction of agonist specific states of the sst2 receptor.

Animals↗

PubMed2005

Peripheral injection of sauvagine prevents repeated colorectal distension-induced visceral pain in female rats.

We investigated the effects of peripheral injection of sauvagine, a CRF2>CRF1 receptor (corticotropin-releasing factor) agonist compared with CRF, on two sets of tonic colorectal distension (CRDs 30, 40, 50 mmHg, 3-min on/off)-induced visceromotor response (VMR) measured as area under the curve (AUC) of abdominal muscle contraction in conscious female rats. Sauvagine (10 or 20 microg/kg, s.c.) abolished the 226.7+/-64.3% and 90.4+/-38.1% increase in AUC to the 2nd CRD compared with the 1st CRD (performed 30 min before) in female Fisher and Sprague-Dawley (SD) rats, respectively. CRF had no effect while the CRF1 antagonist, antalarmin (20 mg/kg, s.c.), alone or with sauvagine, blocked the enhanced response to the 2nd CRD, performed 60 min after the 1st CRD, and reduced further the AUC by 33.5+/-23.3% and 63.5+/-7.2%, respectively in Fisher rats. These data suggest that peripheral CRF2 receptor activation exerts antinociceptive effects on CRD-induced visceral pain, whereas CRF1 contributes to visceral sensitization.

Abdominal Pain↗

PubMed2005

A uniquely selective inhibitor of the mammalian fetal neuromuscular nicotinic acetylcholine receptor.

We have purified and characterized a novel conotoxin from the venom of Conus obscurus, which has the unique property of selectively and potently inhibiting the fetal form of the mammalian neuromuscular nicotinic acetylcholine receptor (nAChR) (alpha1beta1gammadelta-subunits). Although this conotoxin, alphaA-conotoxin OIVB (alphaA-OIVB), is a high-affinity antagonist (IC50 of 56 nm) of the fetal muscle nAChR, it has >1800-fold lower affinity for the adult muscle nAChR (alpha1beta1epsilondelta-subunits) and virtually no inhibitory activity at a high concentration on various neuronal nAChRs (IC50 > 100 microm in all cases). The peptide (amino acid sequence, CCGVONAACPOCVCNKTCG), with three disulfide bonds, has been chemically synthesized in a biologically active form. Although the neuromuscular nAChRs are perhaps the most extensively characterized of the receptors/ion channels of the nervous system, the precise physiological roles of the fetal form of the muscle nAChR are essentially unknown.alphaA-OIVB is a potentially important tool for delineating the functional roles ofalpha1beta1gammadelta receptors in normal development, as well as in various adult tissues and in pathological states. In addition to its potential as a research tool, alphaA-OIVB may have some direct biomedical applications.

Adult↗

PubMed2005

Chronic cocaine administration switches corticotropin-releasing factor2 receptor-mediated depression to facilitation of glutamatergic transmission in the lateral septum.

Corticotropin-releasing factor (CRF) and urocortin (Ucn I) are endogenous members among a family of CRF-related peptides that activate two different and synaptically localized G-protein-coupled receptors, CRF1 and CRF2. These peptides and their receptors have been implicated in stress responses and stress with cocaine abuse. In this study, we observed significant alterations in excitatory transmission and CRF-related peptide regulation of excitatory transmission in the lateral septum mediolateral nucleus (LSMLN) after chronic cocaine administration. In brain slice recordings from the LSMLN of control (saline-treated) rats, glutamatergic synaptic transmission was facilitated by activation of CRF1 receptors with CRF but was depressed after activation of CRF2 receptors with Ucn I. After acute withdrawal from a chronic cocaine administration regimen, CRF1 activation remained facilitatory, but CRF2 activation facilitated rather than depressed LSMLN EPSCs. These alterations in CRF2 effects occurred through both presynaptic and postsynaptic mechanisms. In saline-treated rats, CRF1 and CRF2 coupled predominantly to protein kinase A signaling pathways, whereas after cocaine withdrawal, protein kinase C activity was more prominent and likely contributed to the CRF2-mediated presynaptic facilitation. Neither CRF nor Ucn I altered monosynaptic GABA(A)-mediated IPSCs before or after chronic cocaine administration, suggesting that loss of GABAA-mediated inhibition could not account for the facilitation. This switch in polarity of Ucn I-mediated neuromodulation, from a negative to positive regulation of excitatory glutamatergic transmission after chronic cocaine administration, could generate an imbalance in the brain reward circuitry associated with the LSMLN.

Animals↗

PubMed2005

Novel gonadotropin-releasing hormone antagonists with substitutions at position 5.

Gonadotropin-releasing hormone (GnRH) antagonists with high potency and improved duration of action are needed for potential clinical applications. We synthesized four new antagonists (2-5) of GnRH homologues to Azaline B (1), with a common core sequence of [Aph(X)5, D-Aph(Cbm)6]Azaline B. In these analogs, (X) contains hydrophobic aromatic moieties (like homoveratoyl in 2, homovanillyl in 3, 2,5-dimethoxyphenylacetyl in 4, and 3,5-dimethoxyphenylacetyl in 5) designed to improve the duration of action over that of Azaline B. These analogs were tested in vitro for their ability to antagonize the GnRH receptor and in vivo for duration of action in a castrated male rat assay. Analogs 2, 4, and 5 were potent in vitro, but were found to be short acting in vivo. However, analog 3 [Aph(Hvn)5,D-Aph(Cbm)6]Azaline B is a potent human GnRH receptor antagonist in vitro (IC50 1.47 nM) and exhibits a longer duration of action than azaline B.

Amino Acid Substitution↗

PubMed2004

Colocalization of urocortin and neuronal nitric oxide synthase in the hypothalamus and Edinger-Westphal nucleus of the rat.

Different lines of studies suggest that both the corticotropin-releasing hormone-related peptide Urocortin I (Ucn) and the neuromodulator nitric oxide (NO) are involved in the regulation of the complex mechanisms controlling feeding and anxiety-related behaviors. The aim of the present study was to investigate the possible interaction between Ucn and NO in the hypothalamic paraventricular nucleus (PVN), an area known to be involved in the modulation of these particular behaviors. Therefore, we mapped local mRNA and peptide/protein presence of both Ucn and the NO producing neuronal NO synthase (nNOS). This investigation was extended to include the hypothalamic supraoptic nucleus (SON) and the Edinger-Westphal nucleus area (EW), the latter being one of the major cellular Ucn-expressing sites. Furthermore, we compared the two predominantly used laboratory rat strains, Wistar and Sprague-Dawley. Ucn mRNA and immunoreactivity were detected in the SON and in the EW. A significant difference between Wistar and Sprague-Dawley rats was found in mRNA levels in the EW. nNOS was detected in all brain areas analyzed, showing a significantly lower immunoreactivity in the PVN and EW of Sprague-Dawley versus Wistar rats. Contrary to some previous reports, no Ucn mRNA and only a very low immunoreactivity were detectable in the PVN of either rat strain. Interestingly, double-labeling immunofluorescence revealed that in the SON approximately 75% of all cells immunoreactive for Ucn were colocalized with nNOS, whereas in the EW only approximately 2% of the Ucn neurons were found to contain nNOS. These findings suggest an interaction between Ucn and NO signaling within the SON, rather than the PVN, that may modulate the regulation of feeding, reproduction, and anxiety-related behaviors.

Animals↗

PubMed2004

Cocaine- and amphetamine-regulated transcript activates the hypothalamic-pituitary-adrenal axis through a corticotropin-releasing factor receptor-dependent mechanism.

Cocaine- and amphetamine-regulated transcript (CART) is a highly expressed hypothalamic transcript that is concentrated in areas associated with the stress response. There is evidence for a role of CART in the regulation of the hypothalamic-pituitary-adrenal (HPA) axis. However, it is not clear whether CART regulates activity of the HPA axis by directly stimulating ACTH release from pituitary corticotropes or through interaction with hypothalamic factors. To address this issue, the effects of central and peripheral administration of CART on the HPA axis were compared. Central administration of CART(55-102) (1 microg) significantly increased circulating levels of ACTH (481 +/- 122 vs. 93 +/- 14 pg/ml; CART vs. vehicle) and corticosterone (460 +/- 29 vs. 179 +/- 62 ng/ml; CART vs. vehicle). In contrast, iv injection of CART(55-102) (0.09-9.0 nmol/kg) did not significantly affect circulating levels of ACTH or corticosterone. The corticotropin-releasing factor (CRF) receptor antagonist Astressin B was used to determine whether CART(55-102) elicits ACTH secretion via a CRF receptor-dependent mechanism. Injection of Astressin B (50 microg/kg, iv) inhibited CART(55-102)-induced ACTH and corticosterone responses. The effects of CART(55-102) on CRF and arginine vasopressin (AVP) expression were also examined in static hypothalamic explants. RT-PCR analysis revealed a significant up-regulation of CRF and AVP mRNA levels after CART(55-102) (10 nm and 1 microm) treatment. Last, the effects of CART(55-102) on CRF- and AVP-mediated ACTH release was investigated in dispersed rat anterior pituitary cells. Incubation of CART(55-102) (10-100 nm) did not significantly affect ACTH release from anterior pituitary cells. Findings from the present study suggest that CART regulates activity of the HPA axis through a CRF-dependent central mechanism and not by means of direct interaction with pituitary corticotropes.

Adrenocorticotropic Hormone↗

PubMed2004

Corticotropin-releasing factor and Urocortin I modulate excitatory glutamatergic synaptic transmission.

Corticotropin-releasing factor (CRF)-related peptides serve as hormones and neuromodulators of the stress response and play a role in affective disorders. These peptides are known to alter complex behaviors and neuronal properties, but their receptor-mediated effects at CNS synapses are not well described. Here we show that excitatory glutamatergic transmission is modulated by two endogenous CRF-related peptide ligands, corticotropin-releasing factor [CRF rat/human (r/h)] and Urocortin I (Ucn I), within the central nucleus of the amygdala (CeA) and the lateral septum mediolateral nucleus (LSMLN). These limbic nuclei are reciprocally innervated, are involved in stress and affective disorders, and have high densities of the CRF receptors CRF1 and CRF2. Activation of these receptors exerts diametrically opposed actions on glutamatergic transmission in these nuclei. In the CeA, CRF(r/h) depressed excitatory glutamatergic transmission through a CRF1-mediated postsynaptic action, whereas Ucn I facilitated synaptic responses through presynaptic and postsynaptic CRF2-mediated mechanisms. Conversely, in the LSMLN, CRF caused a CRF1-mediated facilitation of glutamatergic transmission via postsynaptic mechanisms, whereas Ucn I depressed EPSCs by postsynaptic and presynaptic CRF2-mediated actions. Furthermore, antagonists of these receptors also affected glutamatergic neurotransmission, indicating that endogenous ligands tonically modulated synoptic activity at these synapses. These data show that CRF receptors in CeA and LSMLN synapses exert and maintain a significant synaptic tone and thereby regulate excitatory glutamatergic transmission. The results also suggest that CRF receptors may provide novel targets in affective disorders and stress.

Amygdala↗

PubMed2004

The cardiovascular physiologic actions of urocortin II: acute effects in murine heart failure.

Corticotropin-releasing factor (CRF) and its paralogues urocortin (Ucn)I, -II, and -III signal by activating their receptors, CRF receptors (CRFR)1 and -2, to maintain homeostasis through endocrine, autonomic, and behavioral responses. CRFR2 is found in cardiomyocytes and in endothelial and smooth muscle cells of the systemic vasculature. Echocardiography and cardiac catheterization were used in mice to assess the physiologic effects of i.v. UcnII and CRFR2 deficiency on left ventricular function and the systemic vasculature. UcnII treatment augmented heart rate, exhibited potent inotropic and lusitropic actions on the left ventricle, and induced a downward shift of the diastolic pressure-volume relation. UcnII also reduced systemic arterial pressure, associated with a lowering of systemic arterial elastance (end-systolic pressure/stroke volume) and systemic vascular resistance. CRFR2-deficient mice showed no alteration in cardiac contractility or blood pressure in response to UcnII administration, suggesting that the effects of UcnII are specific to CRFR2 function. Pretreatment with a beta-adrenergic receptor antagonist, esmalol, had no effect on the inotropic or lusitropic effects of UcnII in vivo, indicating that its actions are independent of beta-adrenergic receptors. Single i.v. bolus administration of UcnII to a heart failure model (muscle-specific LIM protein-deficient mice) produced significant enhancement of inotropic and lusitropic effects on left ventricular function and improved cardiac output. These results demonstrate the potent cardiovascular physiologic actions of UcnII in both wild-type and cardiomyopathic mice and support a potential beneficial use of this peptide in therapy of congestive heart failure.

Animals↗