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

The interrelationships of calcium and glucagon, and calcium and Isuprel were investigated in spontaneous and paced isolated guinea pig atria. Positive force responses with glucagon were in part both frequency and [Ca+2]o-dependent. Negative inotropic responses were observed with high concentrations of glucagon (5.0 microgram/ml) and calcium (10.0 mM). Persistence of a positive inotropic response of the atria to Isuprel (1.0 microgram/ml) and high [Ca+2]o (10 mM) was seen. Catecholamines stimulate c-AMP production in guinea pig atria while glucagon may not. The negative inotropism produced via calcium-glucagon interaction is consistent with the known inhibitory action of high calcium concentration on adenylyl cyclase and stimulation of phosphodiesterase. It is hypothesized that since glucagon does not activate c-AMP in this tissue then the combined action of high calcium and glucagon leads to degeneration of contractility; with Isuprel and high calcium, atrial contractility is maintained via Isuprel's c-AMP activation.
 ...
PMID:Paradoxical effects of calcium-glucagon interaction on cardiac muscle contractility of isolated guinea pig atria. 20 43

The ability of isoproterenol, glucagon, PGE1 and cholera toxin to stimulate the synthesis of cAMP and protein kinase activity in line of liver cells (BRL) and a line of rat hepatoma cells (H35) has been determined. The concentration of cAMP in BRL cells (approximately 10 pmoles/mg protein) is in the range reported for other cultured cell lines but H35 cells contain extraordinarily low amounts of this cyclic nucleotide (approximately 0.05 pmoles/mg protein). Isoproterenol and PGE1 caused an increase in cAMP content, and protein kinase activation in BRL cells, although glucagon was ineffective. H35 cells, in contrast, were completely insensitive to all hormonal agonists. Despite this fact, cholera toxin was able to produce a marked increase in cAMP content, adenylate cyclase activity and protein kinase activation in H35 cells. binding studies with [125 I]-iodohydroxybenzylpindolol, a specific beta-adrenergic receptor antagonist, revealed that each H35 cell possesses fewer than 10 beta-adrenergic receptors whereas BRL cells contain 2-5,000 receptors per cell. The low level of cAMP in H35 cells appears to result from a combination of totally unstimulated adenylate cyclase and apparently elevated phosphodiesterase activities.
 ...
PMID:Studies of cAMP metabolism in cultured hepatoma cells: presence of functional adenylate cyclase despite low cAMP content and lack of hormonal responsiveness. 20 52

1. The effects of changes in the cytoplasmic [NADH]/[NAD+] ratio on the efficacy of glucagon to alter rates of metabolism in isolated rat hepatocytes were examined. 2. Under reduced conditions (with 10mM-lactate), 10nM-glucagon stimulated both gluconeogenesis and urea synthesis in isolated hepatocytes from 48h-starved rats; under oxidized conditions (with 10mM-pyruvate), 10nM-glucagon had no effect on either of these rates. 3. The ability of glucagon to alter the concentration of 3':5'-cyclic AMP and the rates of glucose output, glycogen breakdown and glycolysis in cells from fed rats were each affected by a change in the extracellular [lactate]/[pyruvate] ratio; minimal effects of glucagon occurred at low [lactate]/[pyruvate] ratios. 4. Dose-response curves for glucagon-mediated changes in cyclic AMP concentration and glucose output indicated that under oxidized conditions the ability of glucagon to alter each parameter was decreased without affecting the concentration of hormone at which half-maximal effects occurred. 5. The phosphodiesterase inhibitor 3-isobutyl-1-methylxanthine (0.05 mM) significantly reversed the inhibitory effects of pyruvate on glucagon-stimulated glucose output. 6. For exogenously added cyclic [3H]AMP(0.1 mM), oxidized conditions decreased the stimulatory effect on glucose output as well as the intracellular concentration of cyclic AMP attained, but did not alter the amount of cyclic [3H]AMP taken up. 7. The effects of lactate, pyruvate, NAD+ and NADH on cyclic AMP phosphodiesterase activities of rat hepatocytes were examined. 8. NADH (0.01--1 MM) inhibited the low-Km enzyme, particularly that which was associated with the plasma membrane. 9. The inhibition of membrane-bound cyclic AMP phosphodiesterase by NADH was specific, reversible and resulted in a decrease in the maximal velocity of the enzyme. 10. It is proposed that regulation of the membrane-bound low-Km cyclic AMP phosphodiesterase by nicotinamide nucleotides provides the molecular basis for the effect of redox state on the hormonal control of hepatocyte metabolism by glucagon.
 ...
PMID:Responsiveness to glucagon by isolated rat hepatocytes controlled by the redox state of the cytosolic nicotinamide--adenine dinucleotide couple acting on adenosine 3':5'-cyclic monophosphate phosphodiesterase. 21 54

Parathyroid hormone (PTH) and glucagon increase the urinary fractional excretion of phosphate, but insulin administration is associated with a decreased fractional excretion of phosphate. It was the purpose of this study to determine whether insulin will antagonize the effects of PTH and glucagon on cAMP levels and protein kinase activation of rat renal cortex. In situ incubation studies were performed on rat renal cortical slices exposed to insulin, PTH, and glucagon. Insulin alone did not affect the tissue cAMP and cGMP levels or the state of protein kinase activation. Preincubation of slices with insulin, however, did significantly inhibit increases in protein kinase activation induced by both PTH and glucagon. Insulin also significantly inhibited PTH-stimulated increases in tissue cAMP levels, but did not blunt the elevations of cAMP levels induced by glucagon. Insulin (10(-9) M) had no effect on either the in vitro activity of adenylate cyclase, basal or PTH-stimulated, or on the activities of low Km cytosolic or membrane-bound cAMP phosphodiesterase. The data show that insulin antagonizes activation of protein kinase by both PTH and glucagon in renal cortex. Separate mechanisms are probably involved for PTH and glucagon interaction. The antiphosphaturic effect of insulin in vivo may result in part from this antagonism at the cellular level.
 ...
PMID:Insulin inhibition of hormone-stimulated protein kinase systems of rat renal cortex. 22 Aug 84

The antitumour agent 5-(3,3-dimethyl-1-triazeno)imidazole-4-carboxamide (DTIC) was found to inhibit competitively the low-Km cyclic AMP phosphodiesterase activity in an ammonium-sulphate-precipitable fraction of the 2,000g supernatant of rat liver. With substrate concentration at 0.25 microM, I50 was 790 microM for DTIC and 350 microM for theophylline. DTIC at 2 mM more than doubled the cAMP response to glucagon in hepatocytes and to adrenaline in MH1C1 hepatoma cells, indicating that it also exerts its inhibitory effect on the phosphodiesterase in intact cells. The possible contribution of the phosphodiesterase inhibition to the growth-inhibitory and cytotoxic effects of DTIC is discussed.
 ...
PMID:The antitumour agent 5-(3,3-dimethyl-1-triazeno) imidazole-4-carboxamide (DTIC) inhibits rat liver cAMP phosphodiesterase and amplifies hormone effects in hepatocytes and hepatoma cells. 22 92

Non-nucleated red blood cells from rats contain adenyl cyclase, the activity of which is predominantly localized in the reticulocytes. Basal enzyme activities in membrane preparations from reticulocyte-rich blood (pretreatment of rats with acetyl-phenylhydrazide: about 60% reticuloytes) are about 5 times higher than in preparations from reticulocyte-poor blood (untreated animals: 2-3% reticulocytes). The enzyme activities are stimulated 10-fold by sodium fluoride (10(-2)M) and 6 to 8-fold by isoprenaline (10(-4)M). Adenyl cyclase activities in membrane preparations from reticulocyte-rich and reticulocyte-poor blood can be ascribed to identical enzymes since identical apparent Km (ATP; 3 times 10(-4)M, Ka (isoprenaline; 3 times 10(-6)M) and Ki (propranolol vs. isoprenaline; 3 times 10(-7)M) values were obtained in both preparations. Besides NaF, only phenylethanolamine derivatives with beta-adrenergic receptor stimulant properties were effective as stimulators of adenyl cyclase activity. The affinities (apparent Ka values) of the investigated compounds decreased in the order isoprenaline--hexoprenaline--fenoterol--salbutamol--adrenaline--terbutalin--noradrenaline--phenylephrine. For maximal intrinsic activity, the catechol structure was essential; the relative intrinsic activities of resorcinol derivatives did not exceed 0.6. The isoprenaline-stimulated adenyl cyclase activities in erythrocyte membrane preparations were competitively inhibited by beta-adrenergic blocking drugs, the affinities (apparent Ki values) decreasing in the order prindolol--penbutolol--propranolol--practolol. The dextrorotatory enantiomers of penbutolol and propranolol were 1/100 to 1/200 as active as the resp. levorotatory enantiomers. From experiments with alpha-adrenergic agonists (e.g. phenylephrine) and antagonists (e.g. phentolamine), it is concluded that alpha-adrenergic receptors do not interfere with the beta-adrenergically-mediated cAMP formation in these particular membranes. A variety of hormones and drugs known to stimulate denyl cyclase activities in various tissues, e. g. ACTH, glucagon, STH, erythropoietin, prostaglandin E1 etc. did not affect adenyl cyclase activity in reticulocyte-rich erythrocyte membrane preparations. In contrast to adenyl cyclase activity, phosphodiesterase activities in erythrocyte membrane and cytoplasmic fractions were only twice as high in reticulocyte-rich as in reticulocyte-poor preparations. From the experiments described, it is obvious that the adenyl cyclase of the rat reticulocyte is subject to monovalent-hormonal, i.e. beta-sympathomimetic stimulation. Moreover, the premature red blood cell provides a useful model for quantitative studies of the interaction of drugs with the beta-adrenergic receptor.
 ...
PMID:The beta-adrenergic receptor-adenyl-cyclase system of rat reticulocytes: effects of adrenergic stimulants and inhibitors. 24 Jan 35

Fetal mouse hearts develop tachycardia in response both to norepinephrine and to glucagon, but although adenylate cyclase is stimulated and adenosine 3':5'-monophosphate (cyclic AMP) elevated by norepinephrine, no measurable changes are produced by glucagon. To test further the possible independence of glucagon chronotropy from the cyclic AMP system, the effects of a phosphodiesterase inhibitor were evaluated. The dose-response curve to norepinephrine was shifted to the left by the phosphodiesterase inhibitor 4-(3,4-dimethoxybenzyl)-2-imidazolidinone (Ro7-2956), but the dose-response curve to glucagon was unaltered. Thus, 10(-6) M norepinephrine produced an increase of 40 +/- 5 beats/min in hearts pretreated with Ro7-2956, as compared to an increase of 22 +/- 3 in control hearts (P less than .01). In contrast, 10(-6) M glucagon produced a rate increase of 25 +/- 4 beats/min in treated hearts vs. 26 +/- 4 beats/min in controls. These data are compatible with the hypothesis that adenylate cyclase and cyclic AMP are involved in the chronotropic response of the fetal mouse heart to norepinephrine but not to glucagon.
 ...
PMID:Influence of a phosphodiesterase inhibitor on the chronotropic effects of glucagon and norepinephrine in fetal mouse hearts. 57 59

The temperature optimum for the positive inotropic response of guinea-pig isolated atria to single submaximal doses of isoprenaline was 25 degrees C. This was well separated from that for rate responses (37.5 degrees C). This separation was not due to changes in catechol-0-methyl-transferase or phosphodiesterase activity since it occurred with orciprenaline alone and in the presence of theophylline. The rate optima for aminophylline, histamine, glucagon, ouabain, calcium chloride and dibutyryl cAMP were essentially the same as for isoprenaline. The temperature-dependences therefore lie at a common ultimate pathway leading to the rate response. The site of temperature-dependence of the inotropic response to isoprenaline is not at the common contractile mechanisms since its optimum differed from those of ouabain and CaCl2. Activity of cAMP and its production were also eliminated as possible sites from differing optima of aminophylline, histamine and dibutyryl cAMP. The temperature-dependence may lie at the beta-adrenoceptor itself, possibly adenyl cyclase. This may be shared by glucagon although tachyphaylaxis made its optimum difficult to determine.
 ...
PMID:Possible sites of temperature-dependent changes in sensitivity of the positive inotropic and chronotropic responses to sympathomimetic amines by comparisons of the temperature optima for a range of agonists. 64 19

Gamma irradiation of rat liver plasma membranes leads to a decrease of the adenylcyclase activities stimulated by glucagon and fluoride. The observed inhibition is more important for the activity stimulated with glucagon. The 5'-nucleotisade activity is not changed by irradiation. When the phosphodiesterase system is submitted to gamma irradiation, the radiosensibility of enzymatic complex is more important.
 ...
PMID:[Effect of gamma irradiation on the production and degradation system of the second hormonal messenger (author's transl)]. 100 9

To determine whether somatostatin inhibits glucagon secretion directly at the pancreatic level and to study quantitatively the relative effects of somatostatin on glucagon and insulin secretion, the effects of various concentrations of somatostatin on glucagon and insulin release from the in vitro perfused rat pancreas in response to arginine (14.2 mM), isoproterenol (2 mg/ml) and theophylline (10 MM) were studied. Glucagon and insulin responses to arginine were progressively inhibited by somatostatin over a concentration range from 0.1-100 ng/ml. At all doses, somatostatin caused greater inhibition of glucagon secretion than of insulin secretion. Approximately 4 ng/ml somatostatin reduced glucagon responses 50%, whereas 90 ng/ml was required to produce comparable inhibition of insulin responses. Glucagon responses to isoproterenol, an activator of adenylate cyclase, and to theophylline, a phosphodiesterase inhibitor, were completely abolished by 100 ng/ml somatostatin. Isoproterenol did cause insulin release in this system, but insulin responses to theophylline were diminished by somatostatin. The present studies thus indicate that somatostatin is a potent inhibitor of both glucagon and insulin secretion and indicate that it acts directly on the pancreatic alpha and beta cells. Glucagon secretion is approximately 20 times more sensitive to the inhibitory effects of somatostatin than is insulin secretion. Furthermore, the present results suggest that somatostatin may act by modifying cAMP-dependent systems rather than by altering cAMP levels.
 ...
PMID:Inhibition by somatostatin of glucagon and insulin release from the perfused rat pancreas in response to arginine, isoproterenol and theophylline: evidence for a preferential effect on glucagon secretion. 111 81


<< Previous 1 2 3 4 5 6 7 8 9 10 Next >>