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)

Hepatocytes isolated from the liver of the common goldfish Carassius auratus L. with crude bacterial collagenase maintained ATP levels for at least 2 h. Glycogenolysis was maximally activated by 1 X 10(-6) M epinephrine and 5.8 X 10(-9) M glucagon. In liver cells incubated in calcium-free buffer containing 1 mM ethylene glycol-bis-(beta-aminoethylether)-N,N'-tetraacetic acid, basal glycogenolysis was enhanced by the addition of 1-4 mM calcium but the elevation of cyclic AMP and glycogenolysis due to epinephrine was unaffected by calcium. The divalent cation ionophore A23187 did not alter basal or hormone-stimulated glycogenolysis. Isoproterenol was approximately as potent as epinephrine but phenylephrine was glycogenolytic only at very high concentrations. l-Propranolol competitively inhibited the increased glycogenolysis due to catecholamines but phentolamine was ineffective as a blocking agent. Isoproterenol and epinephrine stimulated glycogenolysis at lower concentrations than those required to elevate cyclic AMP accumulation. Phenylephrine was without effect on cyclic AMP. Propranolol competitively inhibited both epinephrine- and isoproterenol-stimulated cyclic AMP accumulation, but phentolamine did not block either response. Catecholamine-stimulated glycogenolysis in goldfish liver is apparently a beta-adrenergic effect. However, low concentrations of epinephrine enhance glycogenolysis without affecting total cyclic AMP.
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PMID:Hormone-stimulated glycogenolysis in isolated goldfish hepatocytes. 18 9

Parenchymal rat liver cells were isolated by the collagenase method and incubated in Krebs-Henseleit buffer containing 0.5% gelatin. The basal level of cyclic AMP in isolated cells was 0.52 nmol per g liver wet wt. Glucagon (10(-10)-10(-6) M) caused a significant increase in the level of cyclic AMP. Maximum levels were obtained 2-15 min after addition of glucagon. Repeated administration of glucagon caused a new increase in cyclic AMP, but the response was lesser than after the first addition of glucagon, indicating refractoriness to glucagon. The rate of albumin secretion was 4.6 mug/min per g liver wet wt. This is about the rate found in the perfused liver, Glucagon (10(-8-10(-6) M) inhibited albumin secretion and the incorporation of 14C-leucine into albumin, into total proteins in the medium and into total proteins in the cell suspension. The effect of glucagon on albumin secretion is compatible with an effect on the rate of synthesis. A positive correlation existed between the maximal level of cyclic AMP after glucagon administration and the inhibition of both albumin secretion and the incorporation of 149leucine.
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PMID:Effect of glucagon on cyclic AMP, albumin metabolism and incorporation of 14C-leucine into proteins in isolated parenchymal rat liver cells. 18 84

Amino acid transport was studied in primary cultures of parenchymal cells isolated from adult rat liver by a collagenase perfusion technique and maintained as a monolayer in a serum-free culture medium. These cells carried out gluconeogenesis from three carbon precursors (alanine, pyruvate, and lactate) in response to glucagon addition. Amino acid transport was assayed by measuring the uptake of the nonmetabolizable amino acid, alpha-aminoisobutyric acid (AIB). Addition of insulin or glucagon to culture rat liver parenchymal cells resulted in an increased influx of AIB transport. The glucocorticoid, dexamethasone, when added alone to cultures did not affect AIB transport. However, prior or simultaneous addition of dexamethasone to glucagon-treated cells caused a strong potentiation of the glucagon induction of AIB transport. Kinetic analysis of the effects of insulin and glucagon demonstrated that insulin increased the Vmax for transport without changing the Km while glucagon primarily decreased the Km for AIB transport. The effect of dexamethasone was to increase the Vmax of the low Km system.
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PMID:Hormonal regulation of amino acid transport and gluconeogenesis in primary cultures of adult rat liver parenchymal cells. 18 35

Treatment of rat liver plasma membranes with various commercial preparations of crude collagenase from Clostridium histolyticum at concentrations as low as 1 mug/ml, resulted in activation of the adenylate cyclase system. Maximal activation occurred at 50 to 100 mug/ml of collagenase, and promoted a 2- to 3-fold increase in the basal activity as well as in the activities stimulated by catecholamines, glucagon, fluoride, or GTP. This was due to an increase in the maximal velocity of the cyclizing reaction without any increase in the affinity of the enzyme for its substrate. Treatment of plasma membranes with crude collagenase did not induce gross structural modifications as judged by electron microscopic examination. 5'-Nucleotidase activity was slightly inhibited and ATPase activity remained unaffected. The stimulatory substance was nondialyzable, thermolabile, and inhibited by both EDTA and -SH reagents, thus appearing to be a protein. The following observations suggest the effects observed were due to other protease(s) present in crude collagenase: (a) only crude collagenase was active on liver adenylate cyclase: treatment with purified collagenase from C. histolyticum or from Achromobacter iophagus gave no stimulation; (b) the stimulatory activity was irreversible since washing of the membranes after treatment was without effect; (c) crude collagenase contained no lecithinase or sphingomyelinase activity under our conditions of adenylate cyclase assay; (d) after chromatography on Sephadex G-100, the activator appeared as a peak in the 30,000-dalton region and was clearly separated from the collagenase and clostripain peaks, but coincident with elastolytic and caseinolytic activities; (e) the effect of crude collagenase could be prevented by addition of elastin in vitro and was mimicked by purified elastase from hog pancreas. It remains to be seen whether the effects observed result from an increase in the catalytic constant of adenylate cyclase, or an unmasking of new catalytic sites.
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PMID:Proteolytic activation of rat liver adenylate cyclase by a contaminant of crude collagenase from Clostridium histolyticum. 19 49

Glucose stimulation increased the cAMP content of collagenase-isolated rat pancreatic islets fourfold above baseline values. The elevation was transient, lasting about 5 min, and was dose-dependent. Insulin release continued at a constant rate throughout the incubation. Glucagon, in the absence of glucose, increased cAMP for about 1 min but only slightly, and had no effect on insulin release. In the presence of glucose, however, glucagon enhanced islet cAMP content 15-fold and increased the release of insulin. Glucagon was most effective at high glucose concentrations (16.6 and 25 mM). This indicates that glucagon is critically dependent on the presence of glucose in order to increase the islet cAMP content and to stimulate insulin release. The inability of glucagon to generate sufficient cAMP in the absence of glucose might be one of the reasons why the hormone is a potentiator rather than an initiator of insulin release.
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PMID:Permissive effect of glucose on the glucagon-induced accumulation of cAMP in isolated rat pancreatic islets. 19 21

A number of enzymatic methods have been developed to prepare hepatocytes using collagenase and hyaluronidase. However, best cell preparations are obtained by using only low concentrations of collagenase and exposing the liver to the enzyme for a very short period of time. These isolated cells with intact cell membranes and large numbers of microvilli on the cell surface respond to hormones at physiological concentrations suggesting that these microvilli contain hormone receptors. In addition, high glycogen content is essential to maintain the in vivo metabolic characteristics of the hepatocytes suggesting that intracellular glycogen plays an important role in the hormonal regulation of metabolism in hepatocytes. Studies with glucagon and insulin on carbohydrate metabolism show that the molar ratios of these hormones control gluconeogenesis and glycogenolysis. Furthermore, in vitro addition of insulin stimulates glycogen synthesis and activates glycogen synthase. Insulin also stimulates protein synthesis in cells containing high glycogen and maintains more normal parallel strands of polyribosomes. Studies with isolated hepatocytes from diabetic, hypophysectomized and adrenalectomized animals show a reduced glucagon response to glycogenolysis. This lack of glucagon response was not due to reduction in glycogen levels. Other hormones such as somatostatin and parathyroid also give rise to alterations in carbohydrate metabolism in isolated hepatocytes.
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PMID:Studies of hormonal regulation of metabolism using isolated hepatocytes. 19 66

In collagenase isolated rat pancreatic islets, CCK-PZ, SHG, secretin and glucagon stimulated the accumulation of cAMP, in physiological ranges. The resulting increment of cAMP showed a good correlation with insulin release stimulated by either glucagon or secretin, but not by SHG or CCK-PZ. In the same system, 14CO2 production from glucose-U-14C was significantly increased by either SHG or CCK-PZ. The results presented in this report are compatible with the hypothesis that insulin release by gastrointestinal hormones may be mediated by cAMP in the B-cell in the case of either glucagon or secretin; whereas, in the case of either SHG or CCK-PZ, it may presumably be mediated by an unknown mechanism in glucose metabolism, other than c-AMP.
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PMID:Stimulation by gastro-intestinal hormones of cyclic adenosine 3': 5'-monophosphate accumulation and insulin release in isolated pancreatic islets of the rat. 20 18

In this work we have investigated the effect of serotonin on glucagon release in mouse pancreatic islets isolated by the collagenase technique. Incubation of the islets with serotonin (4 X10(-3)mol/l) was associated with an inhibition of glucagon output both in the basal medium (3.3 mmol/l glucose) and in the presence of arginine (10 mmol/l). The inhibitory effect of serotonin on basal glucagon release was also apparent at concentrations of 2 X10(-3) mol/l, 10(-3)mol/l and 5 X 10(-4) mol/l. Addition of 5-hydroxytrypophan (4 X10(-3) mol/l) to the incubation medium was without effect on basal glucagon output while it significantly reduced arginine-induced glucagon release. In contrast, tryptophan (4 X10(-3) mol/l) provoked glucagon secretion. As inferred from our previous human studies, the present data indicate that serotonin is able to inhibit glucagon secretion. These findings provide further support for the participation of a serotoninergic mechanism in the control of A-cell function.
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PMID:Inhibition of glucagon release by serotonin in mouse pancreatic islets. 33 6

Islets were isolated by mild collagenase digestion and microdissection from rat fetuses 2 days before term and pups 1 or 2 days after birth and their insulin and glucagon secretion studied in vitro. Fetal B cells were stimulated by 16.7 mmol/l glucose, 20 mmol/l leucine or 20 mmol/l arginine. Fetal A cells were not affected by glucose or leucine, but were significantly stimulated by arginine. Somatostatin abolished the effect or arginine on both IRI and IRG output. Neonatal islets proportionally released more insulin and glucagon than their fetal counterparts, but reacted to the tested agents in a similar fashion. During the perinatal period, pancreatic insulin storage increased at a higher rate than that of glucagon. It is concluded that fetal B cells are equipped with sensors to a variety of agents and able to modulate their secretory rate according to the concentration of these agents. A cells are reactive to arginine 2 days before term but do not become glucose reactive until several days after birth.
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PMID:Insulin and glucagon secretion by islets isolated from fetal and neonatal rats. 36 57

(Pro-)Insulin biosynthesis ([3H]leucine incorporation) and insulin secretion were studied in collagenase-isolated rat islets incubated for 3 hours at 1 and 2 mg/ml glucose in the presence of gastric inhibitory polypeptide (GIP). GIP augmented [3H]leucine incorporation and release of insulin at both glucose concentrations. In a second series of experiments it was found that an amino acid mixture was without influence on the insulotrophic action of GIP. Combined stimulation of insulin release by GIP and glucagon did not result in higher insulin output than observed in the presence of each substance alone. Thus GIP, in constrast to many other gastrointestinal peptides, however similar to glucagon, enhances not only release but also biosynthesis of insulin. This insulinotrophic action can be observed already at a glucose concentration of 1 mg/ml. The results underline the outstanding role which GIP appears to play in the regulation of beta-cell function.
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PMID:Stimulation of (Pro-)insulin biosynthesis and release by gastric inhibitory polypeptide in isolated islets of rat pancreas. 38 25


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