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)

[des-His1, des-Phe6,Glu9]Glucagon-NH2 is a newly designed glucagon antagonist. This analog has a binding IC50 of 48 nM (compared to glucagon IC50 of 1.5 nM) and demonstrates pure antagonism in an adenylate cyclase assay. Although the number of glucagon antagonists has grown rapidly recently, closer examination suggested that many of these antagonists retained very low, almost imperceptible levels of cAMP accumulation that were sufficient to elicit an in vivo biological response. To investigate more carefully this secondary biological signal, we measured cAMP accumulation in a revised assay using isolated hepatocytes in the presence of the phosphodiesterase (PDE) inhibitor Rolipram. The PDE inhibitors Rolipram and isobutyl-1-methylxanthine (IBMX) increased the sensitivity of the cAMP accumulation assay from approximately 10-fold for the native hormone to 35-fold above basal levels. On the other hand, amrinone, another PDE inhibitor, did not affect the cAMP accumulation caused by glucagon. The use of PDE inhibitors indicated that three glucagon analogs that had previously been reported to have strong antagonist properties in classical adenylate cyclase assays were actually weak partial agonists in this new assay system. [N alpha-Trinitrophenyl-His1, homo-Arg12]glucagon, [des-amino-His1,D-Phe4,Tyr5, Arg12, Lys17,18,Glu21]glucagon, and [des-His1,Glu9]glucagon-NH2 demonstrated 233%, 21%, and 5.5% cAMP accumulation relative to the native hormone in the presence of 25 microM Rolipram. On the other hand, [des-His1,des-Phe6,Glu9]glucagon-NH2, a newly designed glucagon antagonist, did not activate adenylate cyclase in the presence of Rolipram up to a maximal physiological concentration of 1 microM, indicating that it was a pure antagonist of glucagon-induced adenylate cyclase activity and also the first one in this class. This compound and others were tested in a glycogen phosphorylase assay. As [des-His1,des- Phe6,Glu9]glucagon-NH2 did not activate phosphorylase activity, it was chosen as our candidate for in vivo testing in streptozotocin-induced diabetic rats. An initial dose of 0.75 mg/kg was found to cause the greatest lowering of blood glucose levels (to 63% of the initial levels in 15 min) when the bolus was followed by continuous infusion of 25 micrograms/kgxmin for 1 h.
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PMID:Low level cyclic adenosine 3',5'-monophosphate accumulation analysis of [des-His1, des- Phe6, Glu9] glucagon-NH2 identifies glucagon antagonists from weak partial agonists/antagonists. 875 57

Five new glucagon analogues have been designed, synthesized, characterized and their biological activities tested. The investigation was centered on modifications in the N-terminal region in particular, residues at Thr5, Phe6 and Tyr10 positions, with the goal of obtaining pure glucagon antagonists in our newly developed high sensitivity cAMP accumulation assay. The structures of the designed compounds are: [des-His1, des-Phe6, Glu9] glucagon-NH2 (1); [des-His1, des-Phe6, Glu9, Phe10]glucagon-NH2 (2); [des-His1, Tyr5, des-Phe6, Glu9]glucagon-NH2 (3); [des-His1, Phe5, des-Phe6, Glu9]glucagon-NH2 (4) and [des-His1, des-Phe6, Glu9, D-Arg18]glucagon-NH2 (5). The binding potencies IC50 values in (nM) were 48.0, 27.4, 26.0, 20.0 and 416.0, respectively. All of these analogues when tested in the classical adenylate cyclase assay demonstrate antagonist properties, and in competition experiments, all caused a rightward-shift of the glucagon stimulated adenylate cyclase dose-response curve. The pA2 values for these analogues were 8.20 (1); 6.25 (2); 6.10 (3); 6.25 (4); and 6.08 (5), respectively. A newly revised assay has been developed to determine the intracellular cAMP accumulation levels in hepatocytes at the highest possible sensitivity. Four of the five glucagon analogues in this report (analogues 1, 2, 4 and 5), did not activate the adenylate cyclase in the presence of Rolipram up to a maximal physiological concentration of 1 microM, and thus are pure antagonists.
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PMID:Pure glucagon antagonists: biological activities and cAMP accumulation using phosphodiesterase inhibitors. 921 55

Various phosphodiesterase (PDE) 3,4 and 5 inhibitors have been compared with glucagon for their effectiveness at increasing hepatocyte cAMP, glycogenolysis and gluconeogenesis. Preincubation of isolated hepatocytes with PDE 3 and 4 inhibitors (50 microM) for 2 h induced significant increases in cellular cAMP level. The order of effectiveness was: glucagon (78%), V11294A (42%), rolipram (40%), milrinone (36%), CDP-840 (33%), R(0) 20-1724 (31%), papaverine (27%), isobutylmethylxanthine (28%), isoliquiritigenin (25%), theophylline (22%), and amrinone (22%). The PDE 5 inhibitors dipyridamol and sildenafil had only a slight effect on cAMP levels. Glucose formation was increased as a result of increased glycogenolysis in the following order of effectiveness: glucagon (89%), V11294A (63%), rolipram (61%), milrinone (50%), CDP-840 (46%), R(0) 20-1724 (45%), sildenafil (34%), dipyridamol (31%), papaverine (30%), isobutylmethylxanthine (29%), theophylline (20%), amrinone (20%), and isoliquiritigenin (20%). Rolipram and milrinone, selective PDE 4 and PDE 3 inhibitors respectively, stimulated the gluconeogenesis of alanine, lactate + pyruvate, or fructose in hepatocytes isolated from fasted rats. On the other hand, selective cGMP specific phospodiesterase inhibitors, sildenafil and dipyridamol inhibited alanine-induced gluconeogenesis. All PDE inhibitors increased hepatocyte susceptibility to cyanide toxicity (3-4 fold) which was prevented by fructose whereas PDE 5 inhibitors did not significantly increase hepatocyte susceptibility.
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PMID:Effects of phosphodiesterase 3,4,5 inhibitors on hepatocyte cAMP levels, glycogenolysis, gluconeogenesis and susceptibility to a mitochondrial toxin. 1457 94

Glucagon increases cardiac contractility through G(s) protein-coupled glucagon receptors, but the inotropic responses fade. The fade could be due to receptor desensitisation or to the action of phosphodiesterases (PDE), or to both mechanisms. We investigated the effects of the PDE4 inhibitor rolipram (1 microM) on the inotropic and cAMP-responses to glucagon in paced right ventricular strips of the rat heart. Responses to the partial agonist dobutamine, mediated through beta(1)-adrenoceptors, were studied for comparison. Glucagon increased contractility (-logEC(50)M=7.3 for maximum responses with E(max)=32% of the response to 9 mM Ca(2+)), but the responses tended to fade (-logEC(50)M=7.1 for faded responses with E(max)=11.5%). Dobutamine (-logEC(50)M=5.8, E(max)=56%) produced positive inotropic effects that did not fade. Rolipram did not affect basal contractility and cAMP levels. Rolipram enhanced the contractile responses to glucagon and reduced fade (-logEC(50)M=7.5 and 7.3 with E(max)=74% and 45% for maximum and faded responses respectively). The response to glucagon (0.1 microM) completely faded in the absence of rolipram, but only partially faded and then remained stable in the presence of rolipram (1 microM). Rolipram enhanced contractile responses to dobutamine (-logEC(50)M=6.0, E(max)=75%). Dobutamine (3 microM), but not glucagon (0.1 microM), increased tissue levels of cAMP. Consistent with the inotropic data, rolipram caused glucagon to augment cAMP and enhanced the effects of dobutamine. Thus, PDE4 activity limits the responses mediated through both glucagon receptors and beta(1)-adrenoceptors. PDE4-catalysed hydrolysis of cAMP contributes to the inotropic tachyphylaxis of glucagon.
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PMID:Rolipram reduces the inotropic tachyphylaxis of glucagon in rat ventricular myocardium. 1545 86