Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: UNIPROT:P01275 (glucagon)
 26,492 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Increasing evidence suggests that ethanol-induced changes in cyclic AMP (cAMP) signal transduction play a critical role in the acute and chronic effects of ethanol. Here we have investigated the effects of ethanol on cAMP signal transduction in primary cultures of rat hepatocytes. Acute exposure to ethanol had a biphasic effect on glucagon-receptor-dependent cAMP production in intact cells: 25-50 mM-ethanol decreased cAMP, whereas treatment with 100-200 mM-ethanol increased cAMP. After chronic exposure to 50-200 mM-ethanol for 48 h in culture, glucagon-receptor-dependent cAMP levels were increased, but no change in glucagon receptor number was observed. These effects of ethanol were independent of ethanol oxidation. Chronic ethanol treatment also increased adenosine-receptor- and forskolin-stimulated cAMP production. Increased cAMP production was also observed upon stimulation of adenylate cyclase with glucagon, forskolin and F- in membranes isolated from cells cultured with 100 mM-ethanol for 48 h. However, no differences were observed in basal and MnCl2-stimulated adenylate cyclase activity. The quantity of alpha i protein was decreased by 35% after chronic ethanol treatment, but no change in the quantity of alpha s protein was detected. Decreased alpha i protein was associated with a decrease in G(i) function, as assessed by the ability of 0.1 nM-guanosine 5'-[beta gamma-imido]triphosphate and 1 microM-somatostatin to inhibit forskolin-stimulated adenylate cyclase activity. Taken together, these results suggest that chronic exposure to ethanol increases receptor-dependent cAMP production in hepatocytes by decreasing the quantity of alpha i protein at the plasma membrane and thereby decreasing the inhibitory effects of G(i) on adenylate cyclase activity.
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PMID:Ethanol increases receptor-dependent cyclic AMP production in cultured hepatocytes by decreasing G(i)-mediated inhibition. 135 61

This paper reports the synthesis and the biological activities of six new glucagon analogues. In these compounds N-terminal modifications of the glucagon sequence were made, in most cases combined with changes in the C-terminal region which had been shown previously to enhance receptor affinity. The design of these analogues was based on [Lys17,18,Glu21]glucagon,1 a superagonist, which binds five times better than glucagon to the glucagon receptor, and on the potent glucagon antagonist [D-Phe4,Tyr5,Arg12]glucagon, which does not stimulate adenylate cyclase system even at very high concentrations. The N-terminal modifications involved substitution of His1 by the unnatural conformationally constrained residue, 4,5,6,7-tetrahydro-1H-imidazo[c]pyridine-6-carboxylic acid (Tip) and by desaminohistidine (dHis). In addition we prepared two analogues (6 and 7), in which we deleted the Phe6 residue, which was suggested to be part of a hydrophobic patch and involved in receptor binding. The following compounds were synthesized: [Tip1, Lys17,18,Glu21]glucagon (2); [Tip1,D-Phe4,Tyr5,Arg12,Lys17,18,Glu21]glucagon (3); [dHis1,D-Phe4,Tyr5,Arg12,Lys17,18,Glu21]glucagon (4); [dHis1,Asp3,D-Phe4,Tyr5,Arg12,Lys17,18,Glu21+ ++]glucagon (5); des-Phe6-[Tip1,D-Phe4,Tyr5,Arg12,Glu21]glucagon (6); des-Phe6-[Asp3,D-Phe4,Tyr5,Arg12,Glu21]glucagon (7). The binding potencies of these new analogues relative to glucagon (= 100) are 3.2 (2), 2.9 (3), 10.0 (4), 1.0 (5), 8.5 (6), and 1.7 (7). Analogue 2 is a partial agonist (maximum stimulation of adenylate cyclase (AC) approximately 15% and a potency 8.9% that of glucagon, while the remaining compounds 3-7 are antagonists unable to activate the AC system even at concentrations as high as 10(-5) M. In addition, in competition experiments, analogues 3-7 caused a right-shift of the glucagon stimulated adenylate cyclase dose-response curve.(ABSTRACT TRUNCATED AT 250 WORDS)
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PMID:Synthetic glucagon antagonists and partial agonists. 166 20

Recent studies on the glucagon antagonist des-His1-[Glu9]glucagon amide have resulted in pure inhibitors of the hormone, suggesting that the inhibitory properties may be centered around position 9. The present study was designed to investigate the chemical characteristics of substitutions in position 9 of glucagon that determine binding affinity and biological activity. Twenty replacement analogs of position 9 of glucagon were synthesized and assessed for their ability to bind to the glucagon receptor in rat hepatocyte membranes and to activate adenylate cyclase. Any substitution of aspartic acid 9 was accompanied by a severely diminished capacity to transmit the biological signal, while retaining receptor binding affinity. These results are an indication of an uncoupling of receptor binding and biological activity at this locus and define a central role of aspartic acid 9 in glucagon activity. Single replacement or deletion of either His1 or Asp9 in glucagon caused a 20- to 50-fold decrease in cyclase activity, whereas these same changes made in tandem caused virtually complete loss of activity, with decreases of 10(4)-to 10(6)-fold. These observations have led us to speculate that, at the molecular level, the region of glucagon required for transduction of the biological response may be distinct from the binding region and is mediated by a coupled interaction between His1 and Asp9 of the hormone and a complementary functional site of the glucagon receptor.
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PMID:Position 9 replacement analogs of glucagon uncouple biological activity and receptor binding. 184 33

The hydrodynamic behavior of G alpha s, the alpha subunit of the stimulatory guanine nucleotide-binding regulatory protein (G protein), in octyl glucoside extracts of rat liver membranes was investigated. As was previously shown for G proteins similarly extracted from brain synaptoneurosomes, G alpha s behaved as polydisperse structures with S values higher than that of heterotrimeric G proteins. At concentrations of guanosine 5'-[gamma-thio]triphosphate (GTP[gamma S]) greater than 100 microM, incubation with membranes led to smaller structures having S values in the range of 4-5 S. Incubation of liver membranes with glucagon also caused a marked increase in structures having these S values; glucagon action required the presence of low concentrations of GTP[gamma S] (maximal, 10 microM), was rapid (within 10 sec), and was not observed with vasopressin, angiotensin II, or glucagon-(19-29). When G alpha s in its membrane-bound form was [32P]ADP-ribosylated by cholera toxin and the treated membranes were extracted with octyl glucoside, greater than 35% of the labeled G alpha s was found in material that sedimented through sucrose gradients and contained relatively low levels of immunoreactive G alpha s. Glucagon selectively converted the apparently large molecular weight structures to the 4-5 S structures in the presence of GTP[gamma S], even at 1 mM (the maximal effect of the nucleotide alone), when incubated with the toxin-treated membranes. These findings suggest that the glucagon receptor selectively interacts with polymer-like structures of G alpha s and that activation by GTP[gamma S] results in disaggregation. The role of the beta and gamma subunits of G proteins in the hormone-induced process is not clear since the polymer-like structures extracted with octyl glucoside are devoid of beta and gamma subunits.
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PMID:Glucagon induces disaggregation of polymer-like structures of the alpha subunit of the stimulatory G protein in liver membranes. 190 89

We have investigated the interactions of ligand with the canine hepatic glucagon receptor. Whereas time courses for radiolabeled glucagon binding to receptor and dissociation from receptor revealed fast and slow components at both 30 and 4 degrees C, time courses of ligand dissociation revealed a third component of irreversibly cell-associated (nondissociable) ligand only at the higher temperature. Related experiments identified that (a) the initial rate of formation of nondissociable ligand was slower than that of dissociably bound hormone; (b) the fraction of ligand bound to nondissociable sites achieved a plateau during extended incubations, whereas that bound to dissociable sites was seen to rise and then slowly to fall; (c) the kinetics of formation of a nondissociable ligand was consistent with linked, sequential reactions; (d) dissociable ligand-receptor complexes formed at 4 degrees C were converted to nondissociable complexes during subsequent incubation at 30 degrees C, and (e) nondissociable sites were filled by prior incubation of cells with unlabeled ligand. Analysis of receptor-bound hormone resulting from the incubation of cells with 125I-labeled glucagon and selected concentrations of either glucagon or [[127I]iodo-Tyr10]glucagon at steady state revealed in each case four components of receptor-bound ligand: those corresponding to high and low affinity components of dissociably bound ligand and to high and low affinity components of nondissociably bound ligand. Implications of these findings are considered in terms of mechanisms for the formation of irreversibly bound hormone and for the distribution of hormone among the various components of hepatic glucagon-binding sites.
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PMID:Analysis of glucagon-receptor interactions on isolated canine hepatocytes. Formation of reversibly and irreversibly cell-associated hormone. 215 69

Pancreatic glucagon receptor radioassay has been developed with rat liver cell plasma membrane prepared with sucrose gradient centrifugation. 125I-glucagon was prepared in this laboratory and the separation of B/F was done by low speed centrifugation with addition of PEG (W/V, 20%) and normal human serum. The specific binding of 125I-glucagon was 25%-35% and nonspecific binding was less than 5%. Reproducibility within and between- assay was 6.83% and 8.40% (CV%), respectively. Binding characteristics of glucagon receptor of normal and streptozotocin-induced diabetic rats were determined by using two methods, receptor dilution and conventional competitive binding assay. The results showed that there were no marked differences concerning high and low binding affinities between normal and diabetic rats, but the concentration of binding sites for both high and low affinity receptors was significantly higher for diabetic rats than normal rats. The possible mechanisms for the above results have been discussed.
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PMID:[Pancreatic glucagon receptor radioassay with liver cell plasma membrane in normal and streptozotocin-induced diabetic rats]. 216 72

Four monoclonal antibodies, designated 4H11, 6E10, 2C5, and 3E9 were prepared against partially purified rat hepatic glucagon receptor. These antibodies were characterized by their ability to recognize the glucagon receptor in target tissues using immunoblot and immunoprecipitation procedures. The antibodies recognized a 62-kDa receptor band in rat liver, kidney, and adipose tissue but not in lung, adrenals, and erythrocytes, indicating a high degree of specificity. These antibodies recognize different antigenic determinants; the 6E10 and 2C5 bind protein epitopes, while 4H11 and 3E9 bind carbohydrate epitopes. Furthermore, proteolytic mapping of the glucagon receptor established that monoclonal antibodies 6E10 and 2C5 recognize different domains of the receptor molecule. These antibodies were used to study the immunochemical similarities among the receptors from different species and to assess the topological location of the ligand-binding site. By combining the techniques of affinity cross-linking, proteolytic mapping, and antibody binding, we have identified the location of the glucagon-binding site near to the COOH-terminal domain of the receptor.
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PMID:Characterization of the glucagon receptor and its functional domains using monoclonal antibodies. 217 41

The studies described here were undertaken to characterize the hepatic insulin and glucagon receptors of control (C), pinealectomized (Pn), and melatonin-treated pinealectomized (Pn + Mel) rats. Compared with C rats, an increase in plasma glucose and glucagon levels and a reduction in circulating concentrations of insulin in Pn animals were observed. Melatonin treatment of Pn rats reverses all three parameters toward the normal values. In liver membranes, insulin binding was lower in Pn than in C rats, and glucagon binding was greater in Pn than in C animals; in Pn + Mel rats both insulin and glucagon binding reverse toward the normal values that were observed in C rats. The modifications in hormone binding reflect changes in the number of receptors but not in the affinity constants. The time courses of hormone association and dissociation from liver membranes were similar in all three experimental groups. The degradation of both hormones by liver membranes was similar in all three groups. Insulin receptor degradation also was similar in the three groups, while glucagon receptor degradation was similar in the liver membranes of C and Pn rats but smaller in Pn + Mel animals. These findings suggest that the pineal gland may modulate the circulating levels and liver receptor concentrations of insulin and glucagon. In addition, our results indicate that insulin and glucagon did not induce a down-regulation of liver receptors in Pn rats.
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PMID:Effect of pinealectomy on liver insulin and glucagon receptor concentrations in the rat. 253 98

We have examined the effect on rat liver glucagon receptors and adenylate cyclase activity of a high saturated fat diet (butter fat), a high n-6 polyunsaturated fat diet (corn oil), and a high n-3 polyunsaturated fat diet (menhaden fish oil) with or without additional cholesterol. The number and affinity of the glucagon receptors were unaffected by diet. The glucagon-stimulated adenylate cyclase activity from fish oil-fed animals exhibited the greatest stimulation, followed by corn oil-fed animals. Butter fat-fed and all cholesterol-supplemented groups showed a depression in stimulation. The pattern of adenylate cyclase activity with fluoride stimulation was similar to that observed with glucagon. The effect of dietary fat on forskolin stimulation was similar to glucagon and fluoride for the groups without added cholesterol. However, the cholesterol-supplemented groups did not exhibit a decreased activity. It is suggested that the effect of dietary lipid on glucagon-stimulated adenylate cyclase is not due to changes in the glucagon receptor, but rather due to changes in signal transduction, the Gs-protein or the catalytic unit.
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PMID:Effect of dietary fat and cholesterol supplements on glucagon receptor binding and adenylate cyclase activity of rat liver plasma membrane. 253 45

The studies described in this paper were undertaken to characterize the circulating and hepatic insulin and glucagon receptor concentrations of control (C), diabetic (Db), and pinealectomized-diabetic (Pn + Db) rats. Compared with C rats, an increase in plasma glucose and glucagon levels and a reduction in circulating insulin concentrations in Db animals was observed; these differences were greater in Pn + Db rats. In liver membranes, insulin binding was lower in Db and in Pn + Db than in C rats, and glucagon binding was greater in Db and in Pn + Db than in C rats. The modifications in hormone binding did not reflect changes in the affinity constants. The time courses of hormone association and dissociation from liver membranes were similar in all three experimental groups. The degradation of both hormones and their receptors was similar in all three groups. These findings indicate that in either pinealectomized-diabetic or diabetic rats there were significant changes in the circulating and liver insulin and glucagon receptor concentrations and that the changes in the circulating levels of both pancreatic hormones were more pronounced in pinealectomized-diabetic animals. In addition, the absence in Db and in Pn + Db rats of the insulin and glucagon down-regulation of their own receptors could further modify metabolic activities in these animals.
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PMID:Effect of pinealectomy and of diabetes on liver insulin and glucagon receptor concentrations in the rat. 254 6


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