Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: UNIPROT:P01185 (vasopressin)
23,126 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Activation of glycogen phosphorylase by hormones was examined in hepatocytes isolated from euthyroid and hypothyroid female rats and incubated by Ca2+-free buffer containing 1 mM-EGTA. Basal glycogen phosphorylase activity was decreased in Ca2+-free buffer. However, the activation of hepatocyte glycogen phosphorylase, in the absence of extracellular Ca2+, in response to adrenaline, glucagon or phenylephrine was slightly lower, whereas that by vasopressin was abolished. The activation of glycogen phosphorylase by phenylephrine, adrenaline or isoproterenol (isoprenaline) in hepatocytes from euthyroid rats incubated in the absence of Ca2+ was not accompanied by any detectable increase in total cyclic AMP. The log-dose/response curves for activation of phosphorylase by phenylephrine or low concentrations of adrenaline were the same in hepatocytes from hypothyroid as compared wit euthyroid rats, whereas the response to isoproterenol was greater in hepatocytes from hypothyroid rats. However, the increases in total cyclic AMP accumulation caused by adrenaline or isoproterenol were greater in hepatocytes from hypothyroid rats than in hepatocytes from euthyroid rats. The increases in cyclic AMP accumulation caused by adrenaline or isoproterenol in Ca2+-depleted hepatocytes from hypothyroid rats were blocked by propranolol, a beta-adrenergic antagonist. In contrast, propranolol was only partially effective asan inhibitor of the activation of glycogen phosphorylase by phenylephrine or adrenaline in hepatocytes from hypothyroid rats and ineffective on phosphorylase activation in cells from euthyroid rats. These data indicate that the alpha-adrenergic activation of glycogen phosphorylase is not affected by the absence of extracellular Ca2+, and the extent to which total cyclic AMP was increased by adrenergic amines did not correlate with glycogen phosphorylase activation.
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PMID:Hormonal stimulation of cyclic AMP accumulation and glycogen phosphorylase activity in calcium-depleted hepatocytes from euthyroid and hypothyroid rats. 625 57

Perfusion of livers from fed rats with medium containing glucagon (2 x 10(-10) or 1 x 10(-8) M) resulted in both time- and concentration-dependent inactivation of glycogen synthase phosphatase. Expected changes occurred in cAMP, cAMP-dependent protein kinase, glycogen synthase, and glycogen phosphorylase. The effect of glucagon on synthase phosphatase was partially reversed by simultaneous addition of insulin (4 x 10(-8) M), an effect paralleled by a decrease in cAMP. Addition of arginine vasopressin (10 milliunits/ml) resulted in a similar inactivation of synthase phosphatase and activation of phosphorylase, but independent of any changes in cAMP or its kinase. Phosphorylase phosphatase activity was unaffected by any of these hormones. Synthase phosphatase activity, measured as the ability of a crude homogenate to catalyze the conversion of purified rat liver synthase D to the I form, was no longer inhibited by glucagon or vasopressin when phosphorylase antiserum was added to the phosphatase assay mixture in sufficient quantity to inhibit 90-95% of the phosphorylase a activity. These data support the following conclusions: 1) hepatic glycogen synthase phosphatase activity is acutely modulated by hormones, 2) hepatic glycogen synthase phosphatase and phosphorylase phosphatase are regulated differently, 3) the hormone-mediated changes in synthase phosphatase cannot be explained by an alteration of the synthase D molecule affecting its behavior as a substrate, and 4) glycogen synthase phosphatase activity is at least partially controlled by the level of phosphorylase a.
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PMID:Hormonal regulation of hepatic glycogen synthase phosphatase. 625 45

The effects of hypothyroidism on the hepatic alpha 1-receptor system were studied in isolated rat liver cells. Phenylephrine and vasopressin caused concentration-dependent activation of glycogen phosphorylase and release of 45Ca from 45Ca-loaded cells in either normal or thyroidectomized rats. However, the magnitude of both responses to phenylephrine was markedly suppressed after thyroidectomy and could be restored to near normal levels by in vivo treatment with 1-triiodothyronine (0.25 mg/kg/day) for 4 days. The potency of vasopressin to induce phosphorylase activation and 45Ca release was only slightly reduced by thyroidectomy. Binding of [3H]prazosin to putative alpha 1-receptors in purified liver plasma membranes revealed that the above changes were accompanied by a decrease in the density of binding sites from 567 +/- 51 fmol/mg of protein in controls to 326 +/- 51 fmol/mg in thyroidectomized rats and a return to 498 +/- 23 fmol/mg in thyroidectomized rats treated with 1-triiodothyronine. The affinity of binding sites for [3H]prazosin or for alpha-receptor agonists was the same in the three groups of rats and affinity for epinephrine was unaffected by the presence of guanyl-5'-yl imidodiphosphate (30-100 microM). From these findings, it appears that a reduction in the number of hepatic alpha 1-receptors is responsible for the selective decrease in alpha-adrenergic responses in the hypothyroid rat liver. These changes are opposite to those previously reported for hepatic beta-receptors.
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PMID:Decreased alpha 1-adrenoceptor responsiveness and density in liver cells of thyroidectomized rats. 627 32

Recent studies have demonstrated that angiotensin II, catecholamines, and vasopressin can stimulate the phosphorylation of hepatic cytosolic proteins via a Ca2+-linked cyclic AMP-independent mechanism. The present study used high resolution, two-dimensional gel electrophoresis to determine if the proteins phosphorylated in response to the Ca2+-linked hormones were distinct from those affected by glucagon acting via the cyclic AMP-dependent pathway. Intact hepatocytes labeled with [32P]PO4(3-) were stimulated with glucagon, angiotensin II, l-norepinephrine, and vasopressin and over 100 phosphorylated proteins resolved by two-dimensional electrophoresis and autoradiography. Six important enzymes known to be regulated through covalent modification were positively identified, including phosphorylase, phosphofructokinase, pyruvate kinase, fructose-6-phosphate, 2-kinase, phenylalanine hydroxylase, and fructose-1,6-bisphosphatase. Computer analysis of the autoradiograms from control and hormone-treated cells demonstrated that glucagon increased the phosphorylation state of 12 phosphoproteins and reduced the phosphorylation of one protein with a Mr = 21,000 and a pI = 5.9. The Ca2+-linked hormones stimulated the phosphorylation of 7 phosphoproteins and also reduced the phosphorylation state of the 21,000-dalton protein. Angiotensin II, l-norepinephrine, and vasopressin had equivalent effects on protein phosphorylation. There were six protein substrates uniquely affected by glucagon and one phosphoprotein uniquely stimulated by the Ca2+-linked hormones. Seven substrates were affected by stimulation of the cell with either glucagon or the Ca2+-linked hormones. These results demonstrate that, while there is overlap in the substrates affected by glucagon and the Ca2+-linked hormones, each pathway is able to affect the phosphorylation of unique substrates. This finding suggests that the two types of hormones may have some distinct effects on hepatic function.U
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PMID:Glucagon and the Ca2+-linked hormones angiotensin II, norepinephrine, and vasopressin stimulate the phosphorylation of distinct substrates in intact hepatocytes. 629 Apr 94

Incubation of isolated hepatocytes containing normal Ca2+ levels with angiotensin II, vasopressin or A23187 caused significant inhibition of the cAMP response to glucagon. Angiotensin II also inhibited cAMP accumulation induced by either glucagon or epinephrine in Ca2+-depleted hepatocytes. When submaximal doses of hormone were employed such that cell cAMP was elevated only 3-4-fold (approximately 2 pmol cAMP/mg wet wt cells) inhibition by angiotensin II was correlated with a decrease in phosphorylase activation. The data demonstrate that inhibition of hepatic cAMP accumulation results in reduced metabolic responses to glucagon and epinephrine and do not support the contention that the hepatic actions of glucagon are independent of cAMP.
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PMID:Angiotensin II inhibits hepatic cAMP accumulation induced by glucagon and epinephrine and their metabolic effects. 629 10

Hepatocyte phosphatidylinositol 4,5-bisphosphate (4,5-P2), phosphatidylinositol 4-phosphate (4-P), and phosphatidylinositol were labeled with 3H when rats were injected intraperitoneally with 200 microCi of [2-3H] myo-inositol 18 h previously. Phosphatidylinositol 4,5-P2 and phosphatidylinositol 4-P accounted for 0.84 +/- 0.06 and 7.48 +/- 0.36%, respectively, of the total [3H] myo-inositol containing phospholipids. The breakdown of phosphatidylinositol 4,5-P2 was stimulated transiently (maximum effect seen at 15 s) and in a Ca2+-dependent manner by 10(-8) M vasopressin. Phosphatidylinositol 4-P breakdown was enhanced to a smaller, but longer, extent by vasopressin, whereas no changes in phosphatidylinositol were detected up to 120 s. Subcellular fractionation studies also showed no preferential breakdown of phosphatidylinositol in plasma membranes at 5-20 min. Only doses of vasopressin (10(-8) and 10(-7) M) in excess of those producing maximum effects on phosphorylase activation and Ca2+ efflux (10(-9) M) were effective at stimulating phosphatidylinositol 4,5-P2 breakdown. It is concluded that phosphatidylinositol 4,5-P2 breakdown induced by vasopressin in rat hepatocytes is not responsible for the mobilization of Ca2+ which leads to the activation of phosphorylase. On the contrary, it is Ca2+-dependent and appears to require the occupation of more receptors than are required for Ca2+ mobilization and phosphorylase activation.
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PMID:Stimulation of phosphatidylinositol 4,5-bisphosphate hydrolysis in hepatocytes by vasopressin. 629 3

In in vitro cultures of liver from Ambystoma mexicanum glycogenolysis was stimulated by adrenaline, glucagon, and vasopressin in a dose-dependent manner. Maximum activity was seen at 10(-6) M hormone while 10(-9) M was without effect. Dibutyryl cyclic AMP (10(-3) M) stimulated glycogenolysis maximally although 10(-5) M had no effect. The glucose release brought about by adrenaline was blocked by the beta-adrenergic antagonist propranolol but not by prazosin or yohimbine which are alpha 1- and alpha 2-adrenergic antagonists. Cyclic AMP concentrations in liver were elevated within 1 min of administration of adrenaline and remained elevated for at least 60 min. Phosphorylase a activity was elevated 10 min after addition of adrenaline and remained elevated for at least 6 hr. The rise in hepatic cyclic AMP concentration and phosphorylase a activity was largely blocked by propranolol. These findings are consistent with adrenaline acting via a beta-adrenergic receptor in A. mexicanum. Glycogenolysis in A. mexicanum liver was stimulated by isoprenaline and phenylephrine and in each case the stimulation was reduced in the presence of propranolol but unaffected by phentolamine. High concentrations of methoxamine, a specific alpha 1-agonist, had no effect upon glycogenolysis. These findings suggest that alpha-adrenergic receptors play no role in regulation of glycogenolysis in A. mexicanum.
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PMID:Hormonal control of glycogenolysis and the mechanism of action of adrenaline in amphibian liver in vitro. 630 36

Rat hepatocytes rapidly incorporate [32P]Pi into phosphatidylinositol 4-phosphate (PtdIns4P) and phosphatidylinositol 4,5-bisphosphate [PtdIns(4,5)P2]; their monoester phosphate groups approach isotopic equilibrium with the cellular precursor pools within 1 h. Upon stimulation of these prelabelled cells with Ca2+-mobilizing stimuli (V1-vasopressin, angiotensin, alpha 1-adrenergic, ATP) there is a rapid fall in the labelling of PtdIns4P and PtdIns(4,5)P2. Pharmacological studies suggest that each of the four stimuli acts at a different population of receptors. Insulin, glucagon and prolactin do not provoke disappearance of labelled PtdIns4P and PtdIns(4,5)P2. The labelling of PtdIns4P and PtdIns(4,5)P2 in cells stimulated with vasopressin or angiotensin initially declines at a rate of 0.5-1.0% per s, reaches a minimum after 1-2 min and then returns towards the initial value. The dose-response curves for the vasopressin- and angiotensin-stimulated responses lie close to the respective receptor occupation curves, rather than at the lower hormone concentrations needed to evoke activation of glycogen phosphorylase. Disappearance of labelled PtdIns4P and PtdIns(4,5)P2 is not observed when cells are incubated with the ionophore A23187. The hormone-stimulated polyphosphoinositide disappearance is reduced, but not abolished, in Ca2+-depleted cells. These hormonal effects are not modified by 8-bromo cyclic GMP, cycloheximide or delta-hexachlorocyclohexane. The absolute rate of polyphosphoinositide breakdown in stimulated cells is similar to the rate previously reported for the disappearance of phosphatidylinositol [Kirk, Michell & Hems (1981) Biochem. J. 194, 155-165]. It seems likely that these changes in polyphosphoinositide labelling are caused by hormonal activation of the breakdown of PtdIns(4,5)P2 (and may be also PtdIns4P) by the action of a polyphosphoinositide phosphodiesterase. We therefore suggest that the initial response to hormones is breakdown of PtdIns(4,5)P2 (and PtdIns4P?), and that the simultaneous disappearance of phosphatidylinositol might be a result of its consumption for the continuing synthesis of polyphosphoinositides.
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PMID:Rapid breakdown of phosphatidylinositol 4-phosphate and phosphatidylinositol 4,5-bisphosphate in rat hepatocytes stimulated by vasopressin and other Ca2+-mobilizing hormones. 630 53

Calcium efflux from rat liver perfused with nonrecirculating medium was observed at 1.4 s following 10(-6) M (-)epinephrine infusion, when the perfusate Ca2+ was 60 microM. Net calcium efflux was also seen in livers perfused with 1.3 microM Ca2+ at approximately 8 s. In isolated rat hepatocytes, phosphorylase, a cytosolic enzyme, was activated significantly at 3 s and maximally at approximately 15 s by phenylephrine (10(-5) M), epinephrine (10(-6) M), and vasopressin (10(-8) M). Hexose phosphates were elevated at between 3 and 6 s with vasopressin. Phenylephrine and vasopressin stimulated hepatocyte respiration relatively slowly. The effects took 10 s to become evident, were dependent on the presence of Ca2+, and were probably the result of increased total cellular reduced pyridine nucleotide observed at 5 s. The slowness of the increase in respiration indicates that it cannot be the cause of the Ca2+ mobilization, but is more likely to be a consequence of it. From these studies, it is proposed that, following binding of catecholamines to alpha 1-adrenergic receptors, Ca2+ is first mobilized from the plasma membrane resulting in an elevation of the free Ca2+ ion concentration in the cytosol (Charest, R., Blackmore, P. F., Berthon, B., and Exton, J. H. (1983) J. Biol. Chem. 258, 8769-8773) which stimulates phosphorylase kinase and, hence, phosphorylase. These events begin to occur within the first 2 to 3 s. Following this, the concentration of reduced pyridine nucleotide(s) increases at 5 s resulting in the stimulation of respiration seen at 10 s. These events occur more slowly than the mobilization of cell Ca2+ and activation of phosphorylase, and may be secondary to the rise in cytosolic Ca2+. The time at which mitochondrial Ca2+ decreases is not known, but it accounts for most of the Ca2+ mobilized.
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PMID:Time course of alpha1-adrenergic and vasopressin actions on phosphorylase activation, calcium efflux, pyridine nucleotide reduction, and respiration in hepatocytes. 630 7

For the mechanism of glycogen metabolism in the liver hormonal action of epinephrine, norepinephrine, glucagon, vasopressin and angiotensin II is of importance. The potential importance of hormonal regulation for interpreting the changes in glycogen metabolism under conditions of stress is underlined. Own results show an acute increase of glycogen phosphorylase activity in stress within 1-2 minutes. 24 hours fasting decreases the sensibility of this enzyme towards the hormonal influence.
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PMID:[Hormonal activity control of liver glycogen phosphorylases with special reference to their significance within the scope of a stress reaction]. 631 84


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