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Query: UNIPROT:P01275 (glucagon)
 26,492 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

The effects of L-leucine, D-leucine, and L-isoleucine upon the secretion of glucagon and insulin were investigated using the isolated, perfused rat pancreas. All experiments were conducted in the presence of 5.6 mM D-glucose. Ten-minute perfusions of 2, 5, and 10 mM L-leucine induced the release of glucagon and insulin in a dose-related manner. The removal of L-leucine was followed by renewed release of insulin ("off-response") but not of glucagon. The magnitude of the off-response was greater when L-leucine was perfused over longer periods. L-Isoleucine evoked the release of both glucagon and insulin. When L-leucine was administered during perfusion of L-isoleucine, L-leucine-induced release of glucagon was inhibited, that of insulin was augmented, and the insulin off-response prevailed. When the perfusion of L-leucine immediately preceded that of L-isoleucine, L-isoleucine-induced release of glucagon was abolished and that of insulin was augmented. D-Leucine evoked the release of glucagon but not of insulin, and no off-response occurred. When the perfusion of D-leucine followed that of L-leucine, D-leucine-induced glucagon release was inhibited; the insulin off-response to L-leucine was not altered. We reached the following conclusions. 1) Glucagon release induced by L-leucine, D-leucine, or L-isoleucine is likely to be related to the occupancy by these analogous amino acids of transport and/or receptor sites which they share. 2) The insulin off response to L-leucine seems to be evoked by events which take place during the period of administration of L-leucine; these events are not likely to be the release of insulin that occurs during perfusion of L-leucine or the transport of L-leucine into or out of the beta cell. 3) Structurally or chemically similar compounds which are secretagogues both for glucagon and insulin affect the release of these hormones in different ways; these differences are likely to be due to dissimilar mechanisms governing the secretion of the two hormones.
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PMID:L-Leucine-induced secretion of glucagon and insulin, and the "off-response" to L-leucine in vitro. I. Characterization of the dynamics of secretion. 74 40

Transplantation of human pancreatic islets to diabetic patients may require that donor islets be kept viable in vitro for extended time periods before transfer to the recipient. We have maintained isolated pancreatic islets obtained from the human cadaveric pancreas in tissue culture for 1-3 wk, after which we studied the structure and function of the islets. Electron micrographs of the cultured islets showed a satisfactory preservation of both beta-cells and alpha 2-cells. After culture for 1 wk, the islet oxygen uptake proceeded at a constant rate at a low glucose concentration (3.3 mM) and was significantly enhanced by raising the glucose concentration to 16.7 mM. Likewise, after culture for 1 wk, the islets responded with an increased insulin release when exposed to 16.7 mM glucose with or without added theophylline (10 mM). Islets cultured for 1-3 wk were able to incorporate [3H]leucine into proinsulin, as judged by gel filtration of acid-alcohol extracts. Glucagon release from the cultured islets was reduced significantly by 16.7 mM glucose alone, but stimulated by glucose (16.7 mM) plus theophylline (10 MM). It is concluded that viable pancreatic islets can be isolated from the pancreas of adult human donors and maintained in tissue culture for at least 1 wk without loss of the specific functions of the alpha 2- and beta-cells. It remains to be established whether such islets will survive and remain functionally competent after transplantation to human recipients.
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PMID:Survival of isolated human islets of Langerhans maintained in tissue culture. 77 May 4

The biosynthesis of glucagon was studied in microdissected pigeon pancreatic, islets. [3H]-Tryotophan and [3H]leucine were incorporated into big and little glucagon. No precursor-product relationship was evident between big and little glucagon after radioactive pulsechase and immunoreactive chase incubations. Radioactive and immunoreactive little glucagon and immunoreactive big glucagon were actively secreted and the synthesis of both glucagons was inhibited by high concentrations of glucose. [3H]Tryptophan and [3H]leucine were incorporated into an islet protein of about 20000mol.wt. Gel filtration of extracts of turkey pancreas revealed the presence of an immunoreactive peak of mol.wt. approx. 20000. This glucagon-immunoreactive component was also present in dog and ox pancreas and was stable to chaotropic agents and elution at various pH values. A similar-sized glucagon-immunoreactive species was present in the dog circulation. These results are discussed in the light of the presently accepted mechanisms of glucagon biosynthesis.
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PMID:Studies on the biosynthesis of pancreatic glucagon in the pigeon (Columba livia). 78 50

To evaluate the effect of insulin-saline-bicarbonate therapy on amino acid metabolism in diabetic ketoacidosis, arterial and venous blood samples as well as cerebrospinal fluid (CSF) were obtained from six patients before and after initiation of corrective therapy. Levels of CSF glutamine were decreased while alanine alpha-amino-n-butyrate, valine, isoleucine and leucine were increased significantly compared to a control group composed of six normal, postabsorptive adults free of any neurologic disease. Following therapy, CSF levels of alanine, alpha-amino-n-butyrate, valine, isoleucine, and leucine declined while glutamine levels did not change. Admission arterial plasma levels of the glycogenic amino acids were lower than normal while the branched-chain amino acids were elevated. Plasma alanine and glutamine arterio-venous (A-V) differences across forearm tissue were larger. After four hours of corrective therapy, arterial plasma levels of most of the amino acids had declined sharply and A-V differences for glutamine and alanine were markedly reduced (p smaller than.025 and p smaller than.01, paired t, respectively). Coincident with the decrease in A-V amino acid differences, plasma glucagon and free fatty acid levels declined significantly. These data suggest that the effect exerted by insulin-saline-bicarbonate therapy on amino acid metabolism is manifested by diminished A-V plasma alanine and glutamine differences across forearm tissue. Thus, the role played by the splanchnic bed both before and following corrective measures may be secondary to substrate availability.
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PMID:Plasma and cerebrosponal fluid amino acid levels in diabetic ketoacidosis before and after corrective therapy. 80 76

A novel manual method for protein-sequence analysis is described. Three peptides, the hexapeptide (Leu-TRP-Met-Arg-Phe-Ala), insulin A chain and glucagon were used to test this technique. Peptides (1 or 2 nmol) were hydrolysed with acid and their qualitative amino acid compositions were confirmed by reacting with 4-NN-dimethylaminoazobenzene-4'-sulphonylchloride and 4-NN-dimethylaminoazobenzene 4'-isothiocyanate. Sequence determination of 20-200 nmol of peptide was then performed by the combined use of phenyl isothiocyanate and 4-NN-dimethylaminoazobenzene 4'-isothiocyanate, a new procedure that is analogous to the dansyl-Edman method with the replacement of dansyl chloride by 4-NN-dimethylaminoazobenzene 4'-isothiocyanate as the N-terminal residue determination reagent. On t.l.c. this new N-terminal reagent gave brightly coloured 4-NN-dimethylaminoazobenzene-4-thiohydantoins of amino acids and showed the following advantages: (1) the detection sensitivity is in the pmol range; (2) u.v. observation is not required; (3) there is no destruction of acid-labile amino acids; (4) two-dimensional t.l.c. separation is adequate to identify 24 amino acids, except leucine and isoleucine (this pair of amino acids can be resolved by using 4-NN-dimethylaminoazobenzene-4'-sulphonyl chloride); (5) the determination of a new N-terminal residue (from coupling to t.l.c. identification) takes only 3 h; (6) the colour difference beteen isothiocyanate, thiocarbamoyl and thiohydantoin derivatives facilitates the identifications.
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PMID:A novel manual method for protein-sequence analysis. 82 42

The alpha-ketoanalogues of the branched-chain amino acids were administered to fasting subjects to determine whether or not they promoted nitrogen sparing. Two fasting studies were carried out in each subject. During the first week of one of the two fasts 4.7 g of a mixture of the alpha-ketoanalogues of valine, leucine, and isoleucine were infused daily. No infusions were administered during the other fast, which served as a control. Urinary urea and calculated total urinary nitrogen were significantly lower during both the week of infusions and the ensuing week of fasting after the infusions were discontinued. Immediately after ketoacid infusions, plasma branched-chain amino acids, including allosioleucine, rose, while alanine and several other amino acids (but not glutamine) fell. There were no differences between the two fasts with respect to ketone bodies, free fatty acids, glucose, insulin, or glucagon concentrations. We conclude that branched-chain ketoacids spare nitrogen early in fasting and that this effect persists after they are metabolized.
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PMID:Nitrogen sparing induced early in starvation by infusion of branched-chain ketoacids. 83 56

A protein with glucagon-like immunoreactivity has been isolated from porcine intestine in a highly purified form. The isoelectric point is 6.8-6.9, and the molecular weight is 11,625, as calculated from its amino acid composition: this estimate has been confirmed by S.D.S. gel electrophoresis. The partial sequence so far elucidated is from the N-terminal: Arg-Ser-Leu-Gin-Asn-Thr-Glx-Glx-Lys-Ala-Arg-Ser-Phe-, and from the C-terminal: -Ile-Ala, both differing from those of porcine pancreatic glucagon. On a molar basis the protein has the same immunoreactivity as porcine glucagon when assayed with some anti-glucagon sera, while the activity is less than 0.2% using other anti-glucagon sera.
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PMID:Purification and characterization of a protein from porcine gut with glucagon-like immunoreactivity. 97 35

Insulin release was studied in vitro using pieces of pancreas from rabbits of between 24 days gestational age and 6 weeks postnatal age. When allowance was made for the fraction of pancreas which was endocrine, 16-5mM-glucose caused increasing stimulation of insulin release as development advanced and 3-3 mM-glucose caused a similar rate of secretion at all ages. Secretion was not significantly influenced by insulin destruction in the incubation medium. Glucagon (5 mug/ml) did not stimulate insulin secretion from 24-day foetal pancreas but did so postnatally. Theophylline (1 mmol/1) stimulated insulin release at all ages and was equipotent on 24-day foetal pancreas in 3-3 or 16-5 mM-glucose. The stimulation of insulin release from 24-day foetal pancreas by 1 mM-theophylline occurred in the absence of extracellular glucose, pyruvate, fumarate and glutamate and in the presence of mannoheptulose and 2-deoxyglucose (each 3 mg/ml). Adrenaline (1 mumol/1) and diazoxide (250 mug/ml) abolished or attenuated the stimulation of insulin release by glucose, leucine plus arginine or theophylline from 24-day foetal, 1 day and 6 weeks postnatal pancreas. The stimulation of insulin release from 6-week-old pancreas by 1mM-barium was blocked by adrenaline and diazoxide but the effect became less with increasing immaturity. The experimental results illustrate some of the ways in which insulin secretion by the rabbit beta cell changes as a function of development and draw attention to the importance of glucose and cyclic adenosine monophosphate in this process.
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PMID:Development of pathways of insulin secretion in the rabbit. 109 Jun 94

Tumoral secretions and pathophysiology of diarrhea were studied in 1 patient with pancreatic cholera. High concentrations of vasoactive intestinal peptide were found in both systemic blood and tumoral extracts, together with increased plasma levels of calcitonin and protaglandins E and Falpha. Gastric inhibitory peptide and gastrointestinal and pancreatic hormones were absent from the tumor, except for small amounts of glucagon, and their blood levels were normal. Decreased basal but normal pentagastrin-stimulated gastric acid secretion, normal basal and secretin-stimulated pancreatic secretion, increased volume of gallbladder bile with high bicarbonate, and low bile salt concentrations were observed, but the electrolyte content and flow rate of fluid passing the duodenojejunal junction were within normal limits. Small intestine was found to be the origin of the water and electrolyte fasting losses. Jejunum was the site of bicarbonate secretion. Jejunal glucose and leucine-stimulated water and sodium transports were also strikingly decreased, whereas the absorption rates of the sugar and amino acid were normal. Colon reabsorbed high amounts of water and sodium but increased potassium losses. Biological effects of vasoactive intestinal peptide may explain most of the patient's upper digestive secretion abnormalities and small intestinal function impairments, whereas secondary aldosteronism might explain the modified colonic function.
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PMID:Pancreatic cholera. Sudies on tumoral secretions and pathophysiology of diarrhea. 109 88

Lectins from Agaricus bisporus and Agaricus campestris stimulate insulin and glucagon release from isolated rat islets in the presence of 2 mM glucose. In the case of insulin release, maximal stimulation was observed at lectin concentrations above 58 mug. per milliliter (approximately 1 muM).A. bisporus PHA-B-stimulated insulin release was independent of a source of metabolic energy but was abolished by deuterium oxide. The lectin did not alter islet glucose oxidation to CO2 or incorporation of [3H] leucine into trichloracetic acid-precipitable material nor did it modify rates of insulin secretion induced by 20 mM glucose. None of nine other lectins tested stimulated insulin release, whereas stimulation of fat cell glucose oxidation was a general property of the lectins. Binding of 125I-labeled A. bisporus PHA-B to islets increased with time up to one hour and after attainment of equilibrium was very slowly reversible. Binding was directly proportional to islet number and the estimated Kdiss of the binding reaction was 17 mug per milliliter. The total number of A. bisporus PHA-B binding sites per islet was approximately 2 times 10(10). Binding of A. bisporus PHA-B to the islets and A. bisporus PHA-B-stimulated insulin release were inhibited in parallel by a glycopeptide containing the oligosaccharide receptor for the lectin, suggesting that lectin binding is essential for the expression of insulin-releasing activity. It is proposed that the specific interaction between mushroom lectin and its receptors may lead to conformational changes in the structure of the membranes of the islet A2- and B-cells that facilitate exocytosis.
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PMID:Effect of lectins on hormone release from isolated rat islets of langerhans. 109 48


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