Biomedical subjects

J M Conlon

Publications and source records attributed to J M Conlon.

At least 253 records · Page 14Linked to original sources

PubMed1988

Sulphated CCK-8-like peptides in the neural ganglion of the protochordate Ciona intestinalis.

Immunochemical studies were carried out on extracts of the neural ganglion from the ascidian Ciona intestinalis in order to the characterize the peptide(s), which react with antibodies against the C-terminal sequence common for the mammalian hormones, cholecystokinin (CCK) and gastrin. Radioimmunoassays specific for the sulphotyrosyl-containing N-terminus of CCK-8, for the common alpha-carboxyamidated C-terminus and for gastrin were used to monitor gel chromatography and reverse-phase HPLC of the extracts. Only neutral extracts contained immunoreactive material (634 (524-785) pmol eqv.CCK-8/g) (mean and range, n = 4)). HPLC revealed a small peak eluting almost like CCK-8 and a larger peak eluting earlier. By subsequent gel chromatography the larger peak eluted in the same position as sulphated CCK-8. The material was recognized almost equally by the N- and C-terminal CCK radioimmunoassays, whereas the specific C-terminal gastrin radioimmunoassay did not measure the peptides. Treatment with arylsulphatase removed the binding to the antiserum specific for the sulphotyrosyl-containing sequence of CCK. The results indicate that the ganglion of Ciona intestinalis contains a tyrosyl-sulphated peptide resembling mammalian CCK-8.

Amino Acid Sequence↗

PubMed1988

Measurement and partial characterization of the C-terminal flanking peptides from bovine preprotachykinins in extracts of brain and gut.

Sequence analysis of bovine cDNAs has shown that the biosynthetic precursors of the tachykinins (alpha-, beta- and gamma-preprotachykinins) contain a common amino acid sequence [AYERSVMQDYERRRK] in the C-terminal flanking region. Using an antiserum raised against the synthetic peptide [YERSVMQDYE] in a specific radioimmunoassay, preprotachykinin C-terminal flanking peptide (C-PPT)-like immunoreactivity was measured in extracts of bovine corpus striatum, cerebral cortex and small intestine in concentrations that were equimolar with substance P. Consistent with the presence of two amino acid substitutions in the C-terminal flanking region of human and rat preprotachykinins, the antiserum did not detect immunoreactivity in extracts of human and rat tissues. Chromatographic analysis of the extracts identified two major immunoreactive components. It is proposed that they represent the 16-amino acid residue C-terminal flanking peptide derived from beta- and gamma-preprotachykinins and the 37-amino acid residue C-terminal flanking peptide derived from alpha-preprotachykinin. Treatment of tissue extracts with carboxypeptidase B did not result in a change in C-PPT-like immunoreactivity or in a change in chromatographic properties of the C-terminal flanking peptides suggesting that the C-terminal basic tetrapeptide (RRRK) had already been removed from the primary transcript of the preprotachykinin mRNAs by the action of endogenous processing enzymes.

Amino Acid Sequence↗

PubMed1988

Binding sites for peptide-histidine-isoleucine (PHI) on rat insulinoma-derived RINm5F cells.

Specific binding sites for 125I-labelled rat peptide-histidine-isoleucine (PHI) were identified on rat insulinoma-derived RINm5F cells. The concentrations of peptides producing half-maximal displacement of label were rat PHI, 0.36 +/- 0.14 nM, vasoactive intestinal polypeptide (VIP), 0.38 +/- 0.13 nM and secretin, approximately 0.2 microM. Glucagon and glucagon-like peptide-1(7-36)amide were without effect on binding. PHI and VIP produced dose-dependent increases in cAMP production in the cells that were significantly (P less than 0.05) above unstimulated rates for ligand concentrations between 10(-8) and 10(-6) M. Both PHI and VIP produced a small but significant (P less than 0.05) enhancement in the rate of release of immunoreactive insulin from the cells but the effect was not dose dependent.

Adenoma, Islet Cell↗

PubMed1988

Insulin and other islet hormones (somatostatin, glucagon and PP) in the neuroendocrine system of some lower vertebrates and that of invertebrates--a minireview.

Onto- and phylogenetical studies of the evolution of cells, producing regulatory peptides, belonging to the "hormone families" of insulin, somatostatin, glucagon, and PP (the pancreatic polypeptide), have shown that the islets of Langerhans in vertebrates form a substantial part of the large neuroendocrine system (NES). The NES consists of three major parts, viz. (i) neuronal cells of the central and peripheral nervous systems, (ii) disseminated cells in the mucosa of the alimentary tract (and that of other hollow organs), (iii) the parenchymal cells of the classical endocrine glands. In the NES of coelenterates no evidence of islet hormone production has been obtained, so far. In invertebrates, belonging to the protostomian evolution line, the neuronal parts of the NES predominate markedly, and in the most highly developed phyla, such as artropods and molluscs, clear-cut evidence has been obtained for the presence of cells producing members of the islet hormone families. A "brain-gut axis" for all the four islet hormones is well established in the NES of the pro-craniates, i.e. in the invertebrates of the deuterostomian evolution line. Here, the gut endocrine cells are cells of the disseminated type in the epithelium of the mucosa. A separate islet organ does not occur in the NES until the appearance of the first vertebrates, viz. the Agnatha, some 500 million years ago. Here, a grossly visible islet organ exists, free from exocrine, acinar, pancreatic parenchyma. It is a two-hormone organ with insulin and somatostatin cells only.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

PubMed1988

Circulating bradykinin-like immunoreactivity and the pentagastrin-induced carcinoid flush.

Bradykinin and structurally related peptides are potent vasodilators and a role for these kinins in the aetiology of the carcinoid flush has been proposed. Using an antiserum directed against the COOH-terminal region of bradykinin in radioimmunoassay, the concentrations of bradykinin-like immunoreactivity in extracts of peripheral blood were compared in patients with carcinoid syndrome (n = 11) and healthy subjects (n = 6). In the fasted state, the concentrations of bradykinin-like immunoreactivity in the patients (10 +/- 5 ng/l) were not significantly different from the concentrations in healthy subjects (6 +/- 3 ng/l). An intravenous injection of pentagastrin (0.6 micrograms/kg) provoked a flush of differing degrees of severity in all patients. In four patients, the flush was concurrent with large rises (277-, 26-, 11- and 10-fold over mean basal values) in bradykinin-like immunoreactivity that was resolved by high performance liquid chromatography into lysyl-bradykinin and bradykinin (approximate ratio 1:2). In two patients, small rises in immunoreactivity (2.4- and 1.7-fold) occurred after the flush and in the remaining five patients no rise in bradykinin-like immunoreactivity was measured. In the healthy subjects, the pentagastrin injection did not provoke a flush and no rises in bradykinin-like immunoreactivity were observed. The data support earlier results obtained using bioassays that the carcinoid flush in some patients is associated with the appearance in blood of bradykinin-related peptides. It has been shown, however, that these kinins cannot be the sole causative agent of the flush. It is suggested, therefore, that the aetiology of the flush is probably multi-factorial.

Aged↗

PubMed1988

Circulation of a fragment of haemoglobin alpha-chain during a pentagastrin-induced flush in patients with metastatic carcinoid tumours.

Intravenous injection of pentagastrin (0.6 microgram/kg body wt) into two patients with metastatic carcinoid tumours evoked a severe carcinoid flush. Analysis by reverse-phase HPLC of acetone-extracts of peripheral blood taken from the patients during the flush indicated the presence of a peptide identified as the residues (1-33) fragment of the alpha-chain of haemoglobin. The peptide was not detected in blood taken from the patients immediately before stimulation of the flush or in the blood of healthy subjects after pentagastrin injection. The observation is interpreted as evidence that the pentagastrin-induce carcinoid flush is associated with the activation and possible release of a tumour protease that result in damage to erythrocytes.

Adult↗

PubMed1988

Primary structure of neuromedin U from the rat.

The primary structure of neuromedin U from the rat ileum was established as: Tyr-Lys-Val-Asn-Glu5-Tyr-Gln-Gly-Pro-Val10-Ala-Pro-Ser-Gly-+ ++Gly15-Phe-Phe-Leu- Phe-Arg20-Pro-Arg-Asn.NH2. There was no evidence for microheterogeneity. This amino acid sequence contains two deletions and nine substitutions compared with the neuromedin U-25 from the pig. In particular, the replacement of the Arg16-Arg17 processing site in the porcine peptide by Gly14-Gly15 in the rat means that a peptide corresponding to neuromedin U-8 was not found in the rat intestine.

Amino Acid Sequence↗

PubMed1988

Neuropeptide-gamma: a peptide isolated from rabbit intestine that is derived from gamma-preprotachykinin.

The neurokinin A-like immunoreactivity in an extract of rabbit small intestine was resolved into two molecular forms by gel permeation chromatography. These components were purified to apparent homogeneity by reverse-phase HPLC. The primary structure of the larger component was established as the following: Asp-Ala-Gly-His-Gly-Gln-Ile-Ser-His-Lys-Arg-His-Lys-Thr-Asp-Ser-Phe-Val- Gly-Leu - Met.NH2. This amino acid sequence represents residues (72-92) of gamma-preprotachykinin, as predicted from the nucleotide sequence of a cloned cDNA from the rat. The peptide, termed neuropeptide-gamma, lacks residues (3-17) of neuropeptide K, and this segment is specified exactly by exon 4 in the preprotachykinin gene. The smaller form of neurokinin A-like immunoreactivity was identical to neurokinin A. Neuropeptide K was not present in the extract, demonstrating that the pathways of post-translational processing of beta- and gamma-preprotachykinins in the rabbit gut are different.

Amino Acid Sequence↗

PubMed1988

Primary structures of somatostatins from the islet organ of the hagfish suggest an anomalous pathway of posttranslational processing of prosomatostatin-1.

The cyclostomes represent the first class of vertebrate in evolution to develop an endocrine pancreas. Two peptides with somatostatin-like immunoreactivity were isolated from the islet organ of one such cyclostome, the Atlantic hagfish (Myxine glutinosa). The primary structure of the more abundant peptide was established as: Ala-Val-Glu-Arg-Pro5-Arg-Gln-Asp-Gly-Gln10-Val-His-Glu-Pro- Pro15-Gly-Arg-Glu-Arg-Lys20-Ala-Gly-Cys-Lys-Asn25-Phe- Phe-Trp-Lys-Thr30-Phe-Thr-Ser-Cys. The second peptide, comprising 27% of the total immunoreactivity in the islet extract, was identical to mammalian somatostatin-14. The pathway of posttranslational processing of prosomatostatin in the hagfish islet differs markedly from the pathway in the higher vertebrates. In the mammalian pancreas, prosomatostatin is cleaved at the site of the single arginyl residue (corresponding to position 6 in hagfish somatostatin-34) and at the arginine-lysine site (corresponding to positions 19 and 20 in the hagfish peptide) to generate somatostatin-14 and somatostatin-28(1-12)-peptide. In the hagfish islet, Arg6 is not used as a cleavage site and cleavage at Arg19-Lys20 represents only a minor pathway of processing. The data provide further evidence of the strong evolutionary pressure to conserve the complete amino acid sequence of somatostatin-14.

Amino Acid Sequence↗

PubMed1988

Preferential release of proinsulin relative to insulin in non-insulin-dependent diabetes mellitus.

A radioimmunoassay, using an antiserum that is specific for human proinsulin, has been used to study the response of serum proinsulin to low (25 g) and high (75 g) oral glucose loads in non-obese patients with non-insulin-dependent diabetes mellitus (NIDDM). Diabetic patients were treated by diet only (N = 8) or were receiving oral anti-hyperglycemic agents (N = 8) and therapy was not interrupted during the study. In the fasted state, proinsulin concentrations were higher (P less than 0.05) in the drug-treated patients (31 +/- 3 pmol/l (SEM)) compared with age- and weight-matched healthy subjects (22 +/- 2 pmol/l; N = 10), but concentrations in the diet-treated patients 25 +/- 3 pmol/l) were not significantly different. Following 25 g and 75 g glucose loads, the rises in serum immunoreactive insulin and C-peptide concentrations in both groups of diabetic patients were impaired and delayed relative to those in the control subjects. The responses of serum proinsulin, however, were not significantly different in the NIDDM patients compared with controls at any time point up to 180 min except in the case of drug-treated patients receiving 25 g of glucose who had elevated (P less than 0.05) proinsulin concentrations at 150 min and 180 min after ingestion. It is concluded that NIDDM is not associated with an exaggerated release of proinsulin in response to glucose compared with healthy subjects, but the islets have maintained the ability to release proinsulin better than the ability to release insulin.

Adult↗

PubMed1988

Receptors for glucagon-like peptide-1(7-36) amide on rat insulinoma-derived cells.

Specific binding of 125I-labelled glucagon-like peptide-1(7-36)amide (GLP-1(7-36)amide) to rat insulinoma-derived RINm5F cells was dependent upon time and temperature and was proportional to cell concentration. Binding of radioactivity was inhibited in a concentration-dependent manner by GLP-1(7-36) amide consistent with the presence of a single class of binding site with a dissociation constant (Kd) of 204 +/- 8 pmol/l (mean +/- S.E.M.). Binding of the peptide resulted in a dose-dependent increase in cyclic AMP concentrations (half maximal response at 250 +/- 20 pmol/l). GLP-1(1-36)amide was approximately 200 times less potent than GLP-1(7-36)amide in inhibiting the binding of 125I-labelled GLP-1(7-36)amide to the cells (Kd of 45 +/- 6 nmol/l). Binding sites for GLP-1 (7-36)amide were not present on dispersed enterocytes from porcine small intestine.

Adenoma, Islet Cell↗

PubMed1988

Isolation and structural characterization of thymosin-beta 4 from a human medullary thyroid carcinoma.

An extract of a tumour metastases from a human medullary thyroid carcinoma contained a high concentration (at least 2.9 nmol/g wet weight) of the immunoregulatory peptide, thymosin-beta 4. The peptide was isolated as a mixture of two components with free and blocked NH2-terminal amino acid residues, the latter form predominating (approximately 98% of the total). The primary structure of the peptide was established by automated Edman degradation after cleavage with cyanogen bromide. The amino acid sequence of human thymosin-beta 4 was identical to thymosin-beta 4 previously isolated from calf thymus. Further studies are warranted to determine whether thymosin-beta 4 production is a useful marker for thyroid and other tumours.

Adult↗

PubMed1987

Characterization of three peptides derived from prosomatostatin [prosomatostatin-(1-63)-, -(65-76)- and -(79-92)-peptides] in a human pancreatic tumour.

By using only reverse-phase h.p.l.c., three fragments of prosomatostatin were isolated from an extract of a human pancreatic neuroendocrine tumour that produced somatostatin, vasoactive intestinal polypeptide and gastrin-releasing peptide. The amino acid composition of the peptides indicated that they represented prosomatostatin-(1-63)-peptide, prosomatostain-(65-76)-peptide and prosomatostatin-(79-92)-peptide (somatostatin-14). The identity of prosomatostatin-(1-63)-peptide was confirmed by characterization of the products of digestion with Armillaria mellea (honey fungus) proteinase. Partial micro-sequencing of prosomatostatin-(1-63)-peptide showed that the Gly24-Ala25 bond of preprosomatostatin was the site of cleavage of the signal peptide. Thus human prosomatostatin is a protein of 92 amino acid residues that is proteolytically cleaved in a pancreatic tumour at the site of a dibasic-residue (arginine-lysine) processing site and at a single-monobasic-residue (arginine) processing site.

Amino Acids↗

PubMed1987

Structural characterization of peptides derived from prosomatostatins I and II isolated from the pancreatic islets of two species of teleostean fish: the daddy sculpin and the flounder.

The primary structures of three peptides from extracts from the pancreatic islets of the daddy sculpin (Cottus scorpius) and three analogous peptides from the islets of the flounder (Platichthys flesus), two species of teleostean fish, have been determined by automated Edman degradation. The structures of the flounder peptides were confirmed by fast-atom bombardment mass spectrometry. The peptides show strong homology to residues (49-60), (63-96) and (98-125) of the predicted sequence of preprosomatostatin II from the anglerfish (Lophius americanus). The amino acid sequences of the peptides suggest that, in the sculpin, prosomatostatin II is cleaved at a dibasic amino acid residue processing site (corresponding to Lys61-Arg62 in anglerfish preprosomatostatin II). The resulting fragments are further cleaved at monobasic residue processing sites (corresponding to Arg48 and Arg97 in anglerfish preprosomatostatin II). In the flounder the same dibasic residue processing site is utilised but cleavage at different monobasic sites takes place (corresponding to Arg50 and Arg97 in anglerfish preprosomatostatin II). A peptide identical to mammalian somatostatin-14 was also isolated from the islets of both species and is presumed to represent a cleavage product of prosomatostatin I.

Amino Acid Sequence↗

PubMed1987

Effects of guinea pig neurotensin ([Ser7]neurotensin) on gastrointestinal smooth muscle.

Guinea pig neurotensin differs from other mammalian neurotensin by the substitution of proline by serine at position 7. [Ser7]neurotensin produced a concentration-dependent contraction of the guinea pig oesophagus and rat fundus, a biphasic effect (initial relaxation followed by more sustained contraction) on the guinea pig stomach corpus, duodenum and longitudinal muscle of the ileum and a relaxation of the guinea pig colon and rat ileum. The potencies (EC50) and % maximum contraction compared with the maximum effect produced by either histamine or acetylcholine of [Ser7]neurotensin and neurotensin were not significantly different in any tissue studied.

Animals↗

PubMed1987

A glucagon-like peptide, structurally related to mammalian oxyntomodulin, from the pancreas of a holocephalan fish, Hydrolagus colliei.

The pancreatic islets of the holocephalan fishes contain, in addition to A-, B- and D-cells, X-cells, which are immunoreactive towards antisera directed against the N-terminal region of glucagon but not towards antisera directed against the C-terminal region. A 36-amino-acid-residue peptide was isolated from the pancreas of a holocephalan fish, the Pacific ratfish (Hydrolagus colliei), that shows homology (69%) to mammalian glucagon in its N-terminal region and is reactive towards an N-terminally directed antiserum. Reactivity towards C-terminally directed antisera is prevented by the presence of a 7-residue C-terminal extension to the glucagon sequence that shows limited homology to the C-terminal region of glucagon-37 (oxyntomodulin). It is proposed that this peptide represents a major storage product of the islet X-cell.

Amino Acids↗

PubMed1987

Catabolism of neurotensin in the epithelial layer of porcine small intestine.

The mammalian small intestine is both a source and a site of degradation of neurotensin. Metabolites produced by incubation of the peptide with dispersed enterocytes from porcine small intestine were isolated by high-performance liquid chromatography and identified by amino-acid analysis. The principal sites of cleavage were at the Tyr-11-Ile-12 bond, generating neurotensin-(1-11), and at the Pro-10-Tyr-11 bond, generating neurotensin-(1-10). The corresponding COOH-terminal fragments, neurotensin-(11-13) and -(12-13) were metabolized further. Formation of neurotensin-(1-11) and -(1-10) was completely inhibited by phosphoramidon (Ki = 6 nM), an inhibitor of endopeptidase 24.11, but not by captopril, an inhibitor of peptidyl dipeptidase A. Incubation of neurotensin with purified endopeptidase 24.11 from pig stomach also resulted in cleavage of the Tyr-11-Ile-12 and Pro-10-Tyr-11 bonds. A minor pathway of cell-surface-mediated degradation was the phosphoramidon-insensitive cleavage of the Tyr-3-Glu-4 bond, generating neurotensin-(1-3) and neurotensin-(4-13). No evidence for specific binding sites (putative receptors) for neurotensin was found either on the intact enterocyte or on vesicles prepared from the basolateral membranes of the cells. Neurotensin-(1-8), the major circulating metabolite, was not formed when neurotensin(1-13) was incubated with cells, but represented a major metabolite (together with neurotensin-(1-10] when neurotensin-(1-11) was used as substrate. The study has shown that degradation of neurotensin in the epithelial layer of the small intestine is mediated principally through the action of endopeptidase 24.11, but this enzyme is probably not responsible for the production of the neurotensin fragments detected in the circulation.

Animals↗

PubMed1987

Primary structure of glucagon from the gut of the common dogfish (Scyliorhinus canicula).

The primary structure of glucagon isolated from the intestine of the common dogfish, Scyliorhinus canicula, was established as H S E G T F T S D Y S K Y M D N R R A K D F V Q W L M N T. The peptide shows four substitutions compared with human glucagon: Glu-3 for Gln, Met-14 for Leu, Asn-16 for Ser and Lys-20 for Gln. Glucagon represented the predominant molecular form of the glucagon-like immunoreactivity in the dogfish gut extracts demonstrating that the pathway of posttranslational processing of proglucagon in the gut of this fish differs markedly from the pathway in the mammalian gut.

Amino Acid Sequence↗