Sequence analysis of rat hypothalamic corticotropin-releasing factor with the o-phthalaldehyde strategy

Corticotropin-releasing factor peptide antagonists: design, characterization and potential clinical relevance

Elusive for more than half a century, corticotropin-releasing factor (CRF) was finally isolated and characterized in 1981 from ovine hypothalami and shortly thereafter, from rat brains. Thirty years later, much has been learned about the function and localization of CRF and related family members (Urocortins 1, 2 and 3) and their 2 receptors, CRF receptor type 1 (CRFR1) and CRF receptor type 2 (CRFR2). Here, we report the stepwise development of peptide CRF agonists and antagonists, which led to the CRFR1 agonist Stressin1; the long-acting antagonists Astressin2-B which is specific for CRFR2; and Astressin B, which binds to both CRFR1 and CRFR2.This analog has potential for the treatment of CRF-dependent diseases in the periphery, such as irritable bowel syndrome.

Reduction of reperfusion injury edema with corticotropin-releasing factor (CRF): a pilot study

Regulation of capillary permeability with ischemic reperfusion injury is a complex interaction between vascular endothelium and circulating blood factors. Corticotropin-releasing factor (CRF), a 41 -amino acid peptide CNS neurotransmitter known to modulate the pituitary-adrenal axis during stress response, has been shown to affect capillary leakage after thermal injury in peripheral tissue. When administered prior to ischemic reperfusion injury in a pedicled rat hindlimb model, CRF (80 mcg/kg) reduced limb weight gain to approximately 50% of saline control, suggesting a role for CRF in control of vascular permeability. The characteristics of CRF are reviewed.

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.

Comparison of hCRF and oCRF effects on cardiovascular responses after central, peripheral, and in vitro application

Three assays have been used to show that the neuropeptides human corticotropin-releasing factor (hCRF) and the ovine analogue oCRF produced substantial dose-dependent cardiovascular responses. The assays included intracerebroventricular (ICV) and intravenous (IV) administration in conscious rats, and also in vitro experiments with resistance arteries. Central administration of the peptides (0.1-10 micrograms, ICV) caused an increase in blood pressure and heart rate, whereas peripheral administration (0.75-750 micrograms/kg, IV) produced a decrease in blood pressure and tachycardia. Isometric ring preparations of mesenteric resistance arteries (diameter 200 microns) relaxed in response to both peptides (1-100 nM). In all cases, the effects were more pronounced for hCRF compared to compared to oCRF. Furthermore, all effects were inhibited by the CRF analogue alpha-helical CRF(9-41), the effect of the analogue being most potent against oCRF. The results of all three assays indicate that the difference in structure between hCRF and oCRF produces differences in biological activity.

Predicted primary and antigenic structure of canine corticotropin releasing hormone

Although the dog has been recognized as a useful model for the study of the cerebrospinal and peripheral actions of corticotropin releasing hormone (CRH) the exact amino acid composition of canine CRH is still unknown. In the present study the structure of canine CRH was predicted from the partial sequence of the gene encoding canine CRH. The CRH gene was amplified from genomic DNA obtained from white blood cells by a polymerase chain reaction and subsequently sequenced using the dideoxy method. The likely structure of canine CRH is: SEEPPISLDLTFHLLREVLEMARAEQLAQQAHSNRKLMEII-NH2, which is identical to the structure of human, rat and equine CRH. PEPSCAN analysis of 3 different CRH antisera predicted an antiserum raised against a conjugate of human CRH and CNBr -activated thyroglobulin to be the antiserum of choice for the measurement of CRH in the dog. Preliminary data confirmed the existence of the highest cross-reactivity of a canine hypothalamus extract, known to have a high content of CRH, with antisera directed against human, rat CRH. As a result of the present study immunological tools for CRH estimations are characterized. Also, a homologous DNA probe for in situ hybridizations has become available for further investigations.

Corticotropin-releasing factor stimulates catecholamine release in hypothalamus and prefrontal cortex in freely moving rats as assessed by microdialysis

In vivo microdialysis was used to measure changes in extracellular concentrations of catecholamines and indoleamines in freely moving rats in response to administration of corticotropin-releasing factor (CRF). Dialysis probes were placed stereotaxically in either the medial hypothalamus or the medial prefrontal cortex. We used a repeated-measures design in which each rat received artificial CSF or one dose of CRF 3-4 h apart, and each subject was retested with the same treatments in the reverse order 5-7 days later. With the dialysis probe in the hypothalamus, intracerebroventricular administration of CRF (17 or 330 pmol) dose-dependently increased dialysate concentrations of norepinephrine (NE), dopamine (DA), and all their measurable catabolites except normetanephrine. The effects on NE were substantially greater than those on DA. Dialysate concentrations of serotonin could not be measured reliably, but those of its catabolite, 5-hydroxyindoleacetic acid, were also elevated. Concentrations of NE and DA were elevated within the first one or two (20 min) collection periods, with a peak response at approximately 1-2 h. Dialysate concentrations of catecholamines and metabolites normally returned to baseline within 3 h. Similar data were obtained with dialysis probes in the medial prefrontal cortex after intracerebroventricular administration of 17 or 167 pmol of CRF, except that the increases in DA exceeded those of NE in this region. Intraperitoneal administration of CRF (1 nmol) similarly elevated dialysate concentrations of NE, DA, 5-hydroxyindoleacetic acid, and all catecholamine catabolites except normetanephrine in both medial hypothalamus and medial prefrontal cortex. These results support earlier neurochemical data suggesting that CRF administered both centrally and peripherally stimulates the release of both DA and NE in the brain.

A vasotocin-like peptide in Aplysia kurodai ganglia: HPLC and RIA evidence for its identity with Lys-conopressin G

The presence of a vasopressin (VP)- or vasotocin (VT)-like peptide in the central nervous system of the gastropod mollusc Aplysia has been indicated previously. In the case of Aplysia californica, HPLC and RIA evidence suggested the peptide was VT-like but not identical with the nonmammalian vertebrate peptide [Arg8]VT (AVT). In the present study, anterior ganglia extracts from the related species Aplysia kurodai were analyzed by HPLC followed by RIA. Further analysis of the major AVT-IR peak showed it to be indistinguishable, in three distinct solvent systems, from the sea snail venom peptide Lys-conopressin G, but to be different from the vertebrate peptides [Arg8]VP (AVP), [Lys8]VP (LVP), AVT, oxytocin (OT), mesotocin, isotocin, aspargtocin, glumitocin, and valitocin, from the sea snail venom peptide Arg-conopressin S, and from the peptides [Lys8]VT and [Gln8]OT. In addition, the carboxymethylated (CM) A. kurodai peptide had the same HPLC retention time as CM-Lys-conopressin G. The HPLC/RIA results suggest that (i) based on the properties of the solvent systems used, the A. kurodai peptide has two basic amino acids (like the conopressins but unlike the vertebrate peptides), and (ii) there is a high probability that the A. kurodai peptide is identical with Lys-conopressin G.

Immunoglobulin variable-region-like domains of diverse sequence within the major histocompatibility complex of the chicken

The highly polymorphic B-G antigens are considered to be part of the major histocompatibility complex (MHC) of the chicken, the B system of histocompatibility, because they are encoded in a family of genes tightly linked with the genes encoding MHC class I and class II antigens. To better understand these unusual MHC antigens, full-length B-G cDNA clones were isolated from B21 embryonic erythroid cell cDNA library, restriction-mapped, and sequenced. Five transcript types were identified. Analysis of the deduced amino acid sequences suggests that the B-G polypeptides are composed of single extracellular domains that resemble immunoglobulin domains of the variable-region (V) type, single membrane-spanning domains typical of integral membrane proteins, and long cytoplasmic tails. Sequence diversity among the five transcript types was found in all domains, notably including the B-G immunoglobulin V-like domains. The cytoplasmic tails of the B-G antigens are made up entirely of units of seven amino acid residues (heptads) that are typical of an alpha-helical coiled-coil conformation. The heptads vary in number and sequence between the different transcripts. The presence within B-G polypeptides of polymorphic immunoglobulin V-like domains warrants further investigations to determine the degree and nature of variability within this domain in these unusual MHC antigens.

Isolation, Amino-Acid Sequence, Synthesis and Biological Properties of Urotensin I from Hippoglossoides elassodon

Abstract A 41-residue urotensin I neuropeptide (H-UI) was isolated from urophyses of the marine teleost Hippoglossoides elassodon (the flathead sole). The peptide was recognized by its partial cross-reactivity in a radioimmunoassay developed for Catostomus (sucker) Ul (S-UI), and was purified by reversed-phase high-performance liquid chromatography. The amino-acid sequence was shown to be H-Ser-Glu-Glu-Pro-Pro-Met-Ser-lle-Asp-Leu-Thr-Phe-His-Met-Leu-Arg-Asn-Met-lle-His-Arg-Ala-Lys-Met-Glu-Gly-Glu-Arg-Glu-Gln-Ala-Leu-lle-Asn-Arg-Asn-Leu-Leu-Asp-Glu-Val-NH(2). H-UI is 66% homologous with S-UI and 63% homologous with Cyprinus (carp) Ul (C-UI). Like S- and C-UI, H-UI is about 50% homologous with the frog skin peptide sauvagine and with Catostomus and mammalian corticotropin-releasing factors. H-UI had similar vasodilatory effects in mammals, and similar adrenocorticotropin-releasing effects (in rat and goldfish) to S-UI, C-UI, sauvagine and the corticotropin-releasing factors, but had relatively low potency (e.g. 10% to 30% of the vasodilatory potency of S- and C-UI) in all the bioassay systems studied.

Human class 1 heparin-binding growth factor: structure and homology to bovine acidic brain fibroblast growth factor

The structure of the major class 1 heparin-binding growth factor from human brain has been analyzed. Edman degradation performed on the native mitogen and on fragments generated by chemical and enzymatic cleavage allows the sequence to be described by four nonoverlapping segments. The sum of the amino acids of the four segments is in excellent agreement with the experimentally determined amino acid composition of the mitogen itself, suggesting that, jointly, they account for the entire molecule. The four segments can be aligned into a presumptive complete sequence that shows 92% identity with that of bovine acidic brain fibroblast growth factor. The data indicate that the human mitogen has the following sequence: Phe1-Asn-Leu-Pro-Pro-Gly-Asn-Tyr-Lys-Lys-Pro-Lys-Leu-Leu-Try15+ ++-Cys- Ser-Asn-Gly-Gly-His-Phe-Leu-Arg-Ile-Leu-Pro-Asp-Gly-Thr30-Val-Asp- Gly-Thr-Arg- Asp-Arg-Ser-Asp-Gln-His-Ile-Gln-Leu-Gln45-Leu-Ser-Ala-Glu-Ser-Val- Gly-Glu-Val- Tyr-Ile-Lys-Ser-Thr-Glu60-Thr-Gly-Gln-Tyr-Leu-Ala- Met-Asp-Thr-Asp-Gly-Leu-Leu-Tyr-Gly75-Ser-Gin-Thr-Pro-Asn-Glu-Glu- Cys-Leu-Phe- Leu-Glu-Arg- Leu-Glu90-Glu-Asn-His-Tyr-Asn-Thr-Tyr-Ile-Ser-Lys-Lys-His-Ala-Glu- Lys105-Asn- Trp-Phe-Val-Gly- Leu-Lys-Lys-Asn-Gly-Ser-Cys-Lys-Arg-Gly120-Pro-Arg-Thr-His-Tyr-Gly -Gln-Lys-Ala- Ile-Leu-Phe-Leu- Pro-Leu135-Pro-Val-Ser-Ser-Asp140.

Purification and characterization of an FSH releasing protein from porcine ovarian follicular fluid

A variety of hypophysiotropic peptides or proteins have been reported to be present in mammalian gonads. Inhibin, a hormone that under most circumstances selectively suppresses the secretion of follicle-stimulating hormone (FSH) but not luteinizing hormone (LH), has been isolated from the gonadal fluids of several species and characterized as a heterodimeric protein consisting of alpha- and beta-polypeptides associated by disulphide bonds. The complete amino-acid sequences of the precursors of porcine and human inhibin alpha-subunits and two distinct porcine inhibin beta-subunits (beta A and beta B) have been deduced from complementary DNA sequences. Gonadotropin releasing peptides have also been found in the gonad and have generally been shown to be active in radioreceptor assays for gonadotropin releasing hormone (GnRH) but to exhibit different chromatographic and immunological characteristics from those of GnRH. During our purification of inhibin from porcine follicular fluid, we noted fractions that could stimulate the secretion of FSH by cultured anterior pituitary cells. We report here the purification of an FSH releasing protein (FRP) and its characterization by SDS-polyacrylamide gel electrophoresis under non-reducing and reducing conditions and by partial sequence analysis. Our results indicate that porcine gonadal FRP is a homodimer consisting of two inhibin beta A-chains linked by disulphide bonds. FRP is highly potent (50% effective concentration (EC50) approximately 25 pM) in stimulating the secretion and biosynthesis of FSH but not of LH or any other pituitary hormone. In contrast to the effects of GnRH and other reported gonadal gonadotropin releasing fractions, the action of FRP is not mediated by GnRH receptors.

Purification and characterization of peptides with corticotropin-releasing factor activity from porcine hypothalami

Ten polypeptides that stimulated the release of corticotropin from superfused rat pituitary cells and that are structurally related to porcine corticotropin-releasing factor were isolated from porcine hypothalami. The purification was carried out by gel filtration followed by reversed-phase HPLC using trifluoroacetic acid or heptafluorobutyric acid as the ion-pairing agent in water/acetonitrile solvent systems. The purified peptides were homogeneous by chromatography and by sequence analysis. One major polypeptide was characterized. Its structure is -H-Ser-Glu-Glu-Pro-Pro-Ile-Ser-Leu-Asp-Leu-Thr-Phe-His-Leu-Leu-Arg-Gl u-Val -Leu-Glu-Met-Ala-Arg-Ala-Glu-Gln-Leu-Ala-Gln-Gln-Ala-His-Ser-Asn-Arg-Lys -Leu-Met-Glu-Asn-Phe-NH2 [Patthy, M., Horvath, J., Mason-Garcia, M., Szoke, B., Schlesinger, D. H. & Schally, A. V. (1985) Proc. Natl. Acad. Sci. USA 82, 8762-8766]. This 41-amino acid sequence is thought to represent porcine corticotropin-releasing factor. Based on automated gas-phase sequencing of the intact and CNBr-cleaved peptides, amino acid analysis, and carboxypeptidase Y digestion, the other nine polypeptides were found to be structurally similar to this 41-amino acid sequence. Modifications of this structure include deamidation of glutamine at position 26 or 29, oxidation of methionine at positions 21 and/or 38, a blocked N terminus, and deletion of phenylalanine amide at the C terminus. Eight of these nine modified peptides retained significant corticotropin-releasing factor activity as shown by the stimulation of corticotropin release from superfused rat and pig pituitary cells. Some of these peptides may be present in pig hypothalami, while the others could have been produced during the isolation.

Isolation and amino acid sequence of corticotropin-releasing factor from pig hypothalami

A polypeptide was isolated from acid extracts of porcine hypothalami on the basis of its high ability to stimulate the release of corticotropin from superfused rat pituitary cells. After an initial separation by gel filtration on Sephadex G-25, further purification was carried out by reversed-phase HPLC. The isolated material was homogeneous chromatographically and by N-terminal sequencing. Based on automated gas-phase sequencing of the intact and CNBr-cleaved peptide and on carboxypeptidase Y digestion, the primary structure of this 41-residue polypeptide was determined to be Ser-Glu-Glu-Pro-Pro-Ile-Ser-Leu-Asp-Leu-Thr-Phe-His-Leu-Leu-Arg-Glu-Val -Leu-Glu-Met-Ala-Arg-Ala-Glu-Gln-Leu-Ala-Gln-Gln-Ala-His-Ser-Asn-Arg-Lys -Leu-Met-Glu-Asn-Phe-NH2. Porcine corticotropin-releasing factor (CRF) shares a common amino acid sequence (residues 1-39) with rat and human CRF and differs from these only in positions 40 and 41. However, isoleucine was also present at position 40 in porcine CRF, but in a smaller percentage than asparagine. The sequence of porcine CRF shows 83% homology with ovine CRF. Porcine CRF markedly stimulated the release of corticotropin from superfused rat and pig pituitary cells. The biological activity and close structural relationship to CRFs of other species indicate that the peptide isolated represents porcine CRF.

Role of cyclic AMP in corticotropin releasing factor mediated ACTH release

To elucidate the role of cAMP in the secretion of ACTH, the effect of (1) three phosphodiesterase inhibitors, (2) forskolin, and (3) 8Bromo-cAMP, on CRF mediated ACTH release was studied in rat pituitary cell culture. The action of glucocorticoids on CRF induced cAMP accumulation and ACTH release was investigated. Isobutyl-methylxanthine (IBMX), caffeine, and forskolin augmented the release of ACTH induced from CRF 1.0 nM by 17%, 39%, and 20%, respectively. Also IBMX and caffeine potentiated CRF 10 nM stimulated ACTH release by 32% and 20%. Doses of forskolin and 8Bromo-cAMP, which alone stimulate large amounts of ACTH release, did not increase the amount of ACTH released from CRF 100 nM stimulated cells. Cortisol (500 nM) and corticosterone (500 nM) inhibited CRF induced intracellular cAMP by 39% and 26% while inhibiting pituitary ACTH release by 40% and 52%. In conclusion, cAMP plays an important role in the mechanism of ACTH secretion and it appears the final intracellular mechanism of CRF stimulated ACTH is via cAMP. Also, glucocorticoids exert their inhibitory influence prior to cAMP generation.

Distribution of corticotropin releasing factor-like immunoreactivity in the rat brain by immunohistochemistry and radioimmunoassay: comparison and characterization of ovine and rat/human CRF antisera

The distribution of corticotropin releasing factor (CRF)-like immunoreactivity in the rat brain has been demonstrated by immunohistochemistry and radioimmunoassay using 4 different antisera. Two antisera were directed against synthetic ovine CRF, two antisera were directed against synthetic rat/human CRF. Immunohistochemistry revealed that there are discrete regions where CRF immunoreactive cell bodies are seen with all 4 antisera (e.g., the paraventricular nucleus, the dorsolateral tegmental nucleus) whereas there are cells observed only with one rat CRF antiserum (e.g., in the cortex) or terminal fields observed only with ovine CRF antisera (e.g., the spinal trigeminal tract, the substantia gelatinosa, the spinal cord). Radioimmunoassay showed different cross reactivity of the antisera with synthetic ovine or rat/human CRF and sauvagine, however, there was no cross reactivity with a variety of other peptides. Tissue values of CRF obtained by RIA of micropunched brain nuclei with the 4 antisera were frequently dissimilar suggesting that different antisera recognize different substances. High performance liquid chromatography and radioimmunoassay of brain tissue samples, revealed that there is more than one form of CRF-like immunoreactivity present. There is indirect evidence that there exists at least one peptide in the rat brain, prominent in the medulla and the spinal cord, which cross reacts with antisera directed to ovine CRF only.

Anglerfish pancreatic islets produce two forms of somatostatin-28

It has been predicted on the basis of cDNA sequence analysis that anglerfish pancreatic islets contain at least two different preprosomatostatins (I and II). The C-terminal amino acid sequences of preprosomatostatin I and II were predicted to be identical to mammalian hypothalamic somatostatin-14 (SS-14) and its analog [Tyr7, Gly10]SS-14, respectively. That SS-14 is expressed in anglerfish pancreatic islets, has been shown earlier in pulse-chase experiments and by chemical characterization. However, it was observed that [Tyr7, Gly10]SS-14 was not expressed as such, but as part of larger polypeptides. Pulse-chase experiments combined with reverse-phase high pressure liquid chromatography, amino acid analysis with two different chromatographic systems, and complete Edman degradation indicated that preprosomatostatin II is processed in anglerfish islets to two different forms of somatostatin-28 (SS-28). The primary structure of the major form containing hydroxylysine (Hyl) was determined to be: H-Ser-Val-Asp-Ser-Thr-Asn-Asn-Leu-Pro-Pro-Arg- Glu-Arg-Lys-Ala-Gly-Cys-Lys-Asn-Phe-Tyr-Trp-Hyl-Gly-Phe-Thr-Ser-Cys-OH. The amino acid sequence of the minor form differs only at residue 23 by substitution of lysine for hydroxylysine. This is the first time that hydroxylysine, an amino acid which characteristically occurs in collagen or collagen-like structures has been identified in a potential regulatory peptide. It can be speculated that this amino acid is formed by post-translational hydroxylation of a lysine C-terminally linked to a glycine residue and thus modified at a site which has been recognized as hydroxylation site in collagen or collagen-like structures. The biological consequences of this unusual modification are being investigated.

Processing of an anglerfish somatostatin precursor to a hydroxylysine-containing somatostatin 28

A novel 28-residue somatostatin (SS) has been isolated from anglerfish pancreatic islets and characterized by complete Edman degradation, peptide mapping, and amino acid analysis. The primary structure of this anglerfish SS-28 (aSS-28) containing hydroxylysine (Hyl) was established to be H-Ser-Val-Asp-Ser-Thr-Asn-Asn-Leu-Pro-Pro-Arg-Glu-Arg-Lys-Ala-Gly-Cys- Lys-Asn-Phe-Tyr-Trp-Hyl-Gly-Phe-Thr-Ser-Cys-OH. This sequence (with the exception of hydroxylysine-23, which is replaced by lysine) is identical to the sequence of the COOH-terminal 28 residues of prepro-SS II predicted on the basis of cDNA analysis [Hobart, P., Crawford, R., Shen, L., Pictet, R. & Rutter, W. J. (1980) Nature (London) 288, 137-141]. This is the first instance in which hydroxylysine (to date characteristically observed in collagen or collagen-like structures) has been found in a potential regulatory peptide. Chromatographic characterization of peptides, radiolabeled in islet culture, revealed that aSS-28 contained 10-12% of the radioactivity incorporated into the 8000- to 1000-dalton SS-like polypeptides, whereas 88-90% of this radioactivity was detected in anglerfish SS-14. It appears probable that aSS-28 represents the predominant primary cleavage product derived from prepro-SS II by cleavage at the COOH-terminal side of a single arginine. Based on knowledge of the collagen biosynthesis, it is speculated that hydroxylation may take place as an early post-translational event.

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

Polypeptide analogs of the known members of the corticotropin-releasing factor (CRF) family were synthesized and tested in vitro and in vivo for enhanced potency or competitive antagonism. Predictive methods and physicochemical measurements had suggested an internal secondary alpha-helical conformation spanning about 25 residues for at least three members of the CRF family. Maximization of alpha-helix-forming potential by amino acid substitutions from the native known sequences (rat/human and ovine CRF, sauvagine, and carp and sucker urotensin 1) led to the synthesis of an analog that was found to be more than twice as potent as either of the parent peptides in vitro. In contrast, certain amino-terminally shortened fragments, such as alpha-helical CRF or ovine CRF residues 8 to 41, 9 to 41, and 10 to 41, were found to be competitive inhibitors in vitro. Selected antagonists were examined and also found to be active in vivo.

Arginine vasopressin potentiates adrenocorticotropin release induced by ovine corticotropin-releasing factor

Arginine vasopressin (AVP) stimulates ACTH release in man and acts synergistically with synthetic ovine corticotropin-releasing factor (oCRF) in vitro. This study was designed to examine in man the combined effects of synthetic AVP (10 U intramuscularly) and oCRF (1 micrograms/kg intravenously) on ACTH release. Five normal male volunteers participated in five separate experiments: (a) AVP alone; (b) oCRF alone; (c) AVP followed by oCRF 15 min later; (d) simultaneous AVP and oCRF; and (e) insulin-induced hypoglycemia. Plasma immunoreactive ACTH (IR-ACTH) and IR-cortisol were measured for 4 h after injection of each hormone; basal levels for all subjects were less than or equal to 9 +/- 1.2 pg/ml and 4.9 +/- 0.4 micrograms/dl (mean +/- SE), respectively. AVP and oCRF, when given individually, caused rapid rises in IR-ACTH to similar peak levels of 25 +/- 6.6 and 33 +/- 4.6 pg/ml, respectively. AVP given 15 min before oCRF caused a 2.6-fold potentiation of the oCRF response, with a peak IR-ACTH of 85 +/- 4.6 pg/ml. AVP given at the same time as oCRF produced a fourfold potentiation of the peak IR-ACTH response to 132 +/- 11 pg/ml. These ACTH responses were far greater than those previously observed after 30-fold greater doses of oCRF alone. By way of comparison, insulin-induced hypoglycemia caused a peak IR-ACTH of 169 +/- 20 pg/ml. IR-ACTH returned to base line at 60-90 min after AVP alone, whereas the prolonged effect of oCRF was apparent whether it was given alone or in combination with AVP. The mean peak IR-cortisol responses to AVP, oCRF, and AVP given 15 min before oCRF were similar (16.5 +/- 0.9, 16.4 +/- 2.3, and 18.5 +/- 0.8 micrograms/dl, respectively), but the peak IR-cortisol responses to AVP and oCRF given simultaneously and to insulin-induced hypoglycemia were 1.5 and 1.7 times greater, respectively. IR-cortisol returned to base line within 2-3 h after AVP alone, but remained elevated for at least 4 h after oCRF alone or in combination with AVP. These results indicate that AVP acts synergistically with oCRF to release ACTH in man and suggest that AVP may play a physiologic role in modulating the ACTH response mediated by corticotropin-releasing factor.