Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts: Gene/Protein Disease Symptom Drug Enzyme Compound   Target Concepts: Gene/Protein Disease Symptom Drug Enzyme Compound

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Query: EC:3.1.4.1 (phosphodiesterase)
18,767 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

beta-Cell-rich pancreatic islets were microdissected from ob/ob-mice and used for studies of 45Ca uptake and washout. Irrespective of whether the experiments were performed at 21 or 37 degrees C both glucose and phosphate stimulated the net uptake of lanthanum-nondisplaceable 45Ca. The stimulatory effect of phosphate was additive to that produced by glucose. 45Ca incorporated in response to phosphate differed from that taken up in the presence of 20 mM glucose in being easily washed out although it was not affected by the glucose concentration of the washing medium. The efflux of 45Ca was reduced after introducing phosphate into a medium used to perifuse islets which had accumulated 45Ca in response to 20 mM glucose. This suggests that the outward calcium transport can be influenced also by intracellular trapping of the cation. The glucose-stimulated insulin release was inhibited by phosphate; an effect reversed by the phosphodiesterase inhibitor 3-isobutyl-1-methylxanthine. It is concluded that a common effect of glucose and phosphate is to trap calcium in the pancreatic beta-cells but that there are fundamental differences between their effects on intracellular distribution of calcium and on insulin release.
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PMID:Calcium and pancreatic beta-cell function. 4. Evidence that glucose and phosphate stimulate calcium-45 incorporation into different intracellular pools. 35 7

The efflux of radioactivity after loading with trace amounts of tritiated 5-hydroxytryptamine ([3H]5-HT) or 5-hydroxytryptophan ([3H]5-HTP) was studied in perifused beta-cell-rich pancreatic islets from ob/ob mice. Analysis of the effluent revealed that more than 90% of the radioactivity was released as [3H]5-HT after loading with [3H]5-HTP. Increasing the concentration of glucose in the perifusion medium from 3 to 20 mmol/l enhanced the efflux when islets from fed mice were used and this effect was potentiated by the phosphodiesterase inhibitor 3-isobutyl-1-methylxanthine (IBMX). Whereas 20 mM-glucose alone did not stimulate the efflux of 5-HT from islets isolated from mice starved for 3 days, a stimulatory effect was observed in the presence of IBMX. Stimulation of the efflux of radioactivity by glucose was inhibited if calcium was omitted from or adrenaline added to the medium. The results are consistent with the concept of exocytotic release of 5-HT occurring in response to stimulation of insulin secretion, although basal non-exocytotic transport must also be occurring across the beta-cell membrane.
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PMID:Association between 5-hydroxytryptamine release and insulin secretion. 35 42

Pharmacodynamic characteristics of pentoxyfylline (BL 191) related to insulin secretion by the isolated perfused rat pancreas are studied. The results obtained show that: 1) BL 191 (5 mM) is capable of stimulating insulin secretion, even in the presence of another stimulator; 2) BL 191 increases both phases of the secretion produced by constant arginine 20 mM/glucose 5 mM perfusion; 3) BL 191 significantly increases and turns biphasic the monophasic insulin secretion pattern produced by 1 microgram/ml glibenclamide; 4) the effects mentioned in points 2) and 3) are inhibited if the phosphodiesterase activator imidazole (300 mg/100 ml) is present in the perfusion medium; 5) the phosphodiesterase inhibitor theophylline has the same effects as BL 191, except for its inability to stimulate insulin release in the absence of another stimulator; 6) somatostatin (100 ng/ml) significantly inhibits insulin secretion produced by arginine/glucose or glibenclamide, as well as by arginine, glucose plus theophylline or BL 191, and by glibenclamide plus theophylline or BL 191, in both cases the inhibitory effect of somatostatin is reduced by the presence of BL 191 or theophylline.
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PMID:The influence of pentoxyfylline [1-(5-oxohexyl-) 3,7-dimethylxanthine] (BL 191) on the insulin secretion induced by glibenclamide and by arginine/glucose in the perfused pancreas. 41 15

The effect of insulin was examined with emphasis on the alteration in the force-frequency relation. The results show that insulin does not change the time to peak tension nor the time of contraction. The inotropic effect was significant and did not depend upon the frequency of stimulation. However, there was a definite dependence of the magnitude of the inotropic effect on temperature. Previous studies have indicated that the inotropic effect is not a result of increased substrate availability or changes in cAMP phosphodiesterase activity. These results and those reported here are consistant with the hypothesis that insulin's inotropic effect is due to increases in intracellular Ca++.
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PMID:Study of the characteristics of the inotropic effect of insulin in rabbit papillary muscle. 102 45

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.
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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

In cultured rat hepatocytes, transcription of the glucokinase gene is turned on by insulin and turned off by glucagon/cAMP, the latter being the dominant effector system. It is thus possible that in the absence of hormones the gene is maintained in a repressed state by the basal level of cAMP and that insulin turns on transcription by relieving cAMP repression, for instance via activation of a cyclic-nucleotide phosphodiesterase. Three inhibitors of this class of enzymes were tested for their effect on the insulin-dependent induction of the glucokinase gene in hepatocytes. Isobutyl methylxanthine, the prototype inhibitor, abrogated the gene response to insulin, as shown by run-on transcription assay. Among the drugs investigated, Ly186126, a preferential inhibitor of type-III phosphodiesterase, proved the most potent in inhibiting insulin-induced accumulation of glucokinase mRNA. Type-III phosphodiesterase is inhibited by cGMP. Induction of glucokinase mRNA was prevented in hepatocytes challenged with insulin in presence of 8-bromoguanosine-3',5'-phosphate. These results are consistent with the involvement of type-III phosphodiesterase in transduction of the insulin signal to the glucokinase gene. However, we were unable to detect significant decreases in total cellular cAMP level or cAMP-dependent-protein-kinase ratio after the addition of insulin to hepatocytes. Many effects of glucagon are mediated via cAMP-dependent protein-kinase phosphorylation of regulatory proteins and, conversely, insulin effects are often accompanied by protein dephosphorylation. A specific inhibitor of protein phosphatases PP1 and PP2A, okadaic acid, was shown to abolish the transcriptional response of the glucokinase gene to insulin. Thus, interference of insulin with the cAMP signal transduction pathway at several steps may be a critical aspect of insulin action on hepatic glucokinase gene expression. In addition, insulin induction of glucokinase mRNA was suppressed by inhibitors of protein synthesis. The underlying mechanism was a severe inhibition of the transcriptional effect of insulin, rather than mRNA destabilization, as demonstrated by run-on transcription assays with nuclei from cycloheximide-treated or pactamycin-treated cells. Transcription of the glucokinase gene may therefore depend on de novo synthesis of the product of an early-response gene induced by insulin, or may require a short-lived trans-acting or accessory factor of transcription. Alternatively, insulin signalling may be compromised in hepatocytes by a mechanism indirectly related to the arrest of protein synthesis.
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PMID:Insulin signalling and regulation of glucokinase gene expression in cultured hepatocytes. 128 Feb 18

The aim of this study was to evaluate the insulin (IRI) response to different stimuli and insulin sensitivity in Type 2 diabetic patients responsive to oral hypoglycaemic agents (OHA) and in Type 2 diabetic patients with secondary failure of OHA (SF), all patients being of normal body weight (relative body weight less than 120%), and the possible role of cyclic AMP in the reduced IRI release. SF patients, without islet cell antibodies (ICA), with hyperglycaemia lasting more than 3 months, underwent tests with i.v. tolbutamide (n = 21), i.v. glucose (n = 14), i.v. glucagon (n = 19), i.v. arginine infusion (n = 18); the arginine infusion was repeated in 12 patients during administration of aminophylline, an inhibitor of phosphodiesterase. The same tests were performed in groups of 8 to 15 OHA patients and in groups of 6 to 17 healthy subjects. During all the tests, blood glucose levels were higher in SF patients, than in OHA patients and in healthy subjects. Both SF patients and OHA patients had no IRI response to glucose; SF patients, in contrast to OHA patients, had a reduced IRI response to tolbutamide and to glucagon. The IRI response to arginine was not different in OHA, in SF patients and in healthy controls, but was significantly enhanced by aminophylline only in healthy controls. Insulin infusions (1.66 mU/Kg/min for 90 min) were performed in OHA patients and in SF patients at blood glucose levels of 150 and of 250 mg/dl: during the last 60 min, the amount of glucose metabolized (M), and the insulin sensitivity (M/I) index were greater in OHA than in SF patients.(ABSTRACT TRUNCATED AT 250 WORDS)
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PMID:Secondary failure of oral hypoglycaemic agents in lean patients with type 2 diabetes mellitus: insulin sensitivity, insulin response to different stimuli, and the role of cyclic-AMP. 131 98

We previously characterized human placental cytosolic cAMP phosphodiesterase (PDE) and found that two low K(m) cAMP PDE isoforms that were very sensitive to inhibition by cGMP and cilostamide were activated by insulin. As a first step toward understanding the mechanisms by which insulin activates this enzyme, we purified the cGMP-inhibited low K(m) cAMP PDE (cGI-PDE) from human placentas. The enzyme was purified 11,700-fold from a pool of 100,000 x g supernatant fractions of 10-15 placentas by ammonium sulfate precipitation, diethylaminoethyl-cellulose chromatography, and affinity chromatography, using an isothiocyanate derivative of cilostamide (CIT-agarose). The specific activity of the affinity-purified enzyme was 432 +/- 17 nmol/min.mg (mean +/- SD; n = 4). Gel permeation chromatography of the CIT-agarose eluates revealed one protein peak that coincided with PDE activity at an elution position of 135,000 daltons. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis analysis of this protein peak and CIT-agarose eluates revealed the same patterns, indicating that the purified PDE preparations contained multiple proteins with apparent mol wt of 138K, 83K, 72K, 67K, 63K, and 44K. The 138K form appears to be an intact enzyme; an analogous approximately 135K form has recently been identified in rat adipocyte particulate fractions by specific immunoprecipitation or Western immunoblots. In addition, other smaller forms eluted at 135,000 daltons on gel permeation chromatography, suggesting that, although proteolyzed, they must have been associated by either noncovalent interactions or disulfide bonds. All of the protein bands observed on the sodium dodecyl sulfate-polyacrylamide electrophoresis gel reacted with rabbit antibodies raised against human platelet cGI-PDE. Ten peptides from endoproteinase Lys-C-digests of the affinity-purified placental cGI-PDE were isolated and sequenced; sequences of eight peptides were identical to the deduced amino acid sequences in the C-terminal half of a human heart cGI-PDE cDNA, while those of two peptides were not found in the heart enzyme. The sequences of the eight peptides also matched peptide sequences derived from a purified human platelet cGI-PDE. These results provide evidence that the catalytic C-terminal half domain of the placental insulin-sensitive cGI-PDE shares homology with those of human heart and platelet cGI-PDEs. K(m) and maximum velocity values for cAMP and cGMP were 0.57 microM and 862 nmol/min.mg, and 15 microM and 467 nmol/min.mg, respectively. ED50 values for cGMP, cilostamide, and Ro 20-1724 were 0.12, 0.22, and 120 microM, respectively.(ABSTRACT TRUNCATED AT 400 WORDS)
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PMID:Purification and characterization of guanosine 3',5'-monophosphate-inhibited low K(m) adenosine 3',5'-monophosphate phosphodiesterase from human placental cytosolic fractions. 131 79

When isolated rat fat pads were incubated with vanadate, the low Michaelis-Menten constant (Km) cAMP phosphodiesterase (PDE) activity in the microsomal fraction was increased in a time- and dose-dependent manner with vanadate. 3',5'-Cyclic GMP inhibited the vanadate-stimulated PDE activity with similar profile to the insulin-stimulated one. The stimulatory effect of vanadate was inhibited by inhibitors of tyrosine kinases such as amiloride, biochanin A, and genistein to various extents. Vanadate and insulin both showed the full effect in the absence of either K+, N+, or Ca2+ in the medium, while preincubation of the fat pads with a chelator of intracellular Ca2+ inhibited the vanadate action in a dose-dependent manner. The insulin action was not inhibited by it at tested concentrations. These results suggest that the vanadate action, in contrast to the insulin one, is dependent on the intracellular level of Ca2+. Preincubation of the fat pads with inhibitors of protein kinase C such as 1-(5-isoquinoline sulfonyl)-2-methylpiperazine (H-7) and staurosporine inhibited, in part, the vanadate action but did not inhibit the insulin one. Furthermore, vanadate increased the protein kinase C activity in fat pads but insulin did not increase. H-7 and amiloride showed a significant inhibition of stimulation of protein kinase C activity by vanadate. These results suggest that vanadate stimulates, in part, the 3',5'-cyclic GMP-inhibited low Km cAMP PDE activity in the microsomal fraction of fat pads through the activation of tyrosine kinase and protein kinase C-mediated processes.
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PMID:Stimulatory effect of vanadate on 3',5'-cyclic guanosine monophosphate-inhibited low Michaelis-Menten constant 3',5'-cyclic adenosine monophosphate phosphodiesterase activity in isolated rat fat pads. 131 24

Preincubation of murine macrophage-like P388D1 cells with physiological amounts of insulin resulted in an increase in prostaglandin E2 binding to these cells, by approximately 2-fold, when compared to untreated cells. Scatchard analysis of the binding of PGE2 to insulin-treated cells indicated that the enhanced binding was due to an increase in receptor number (from 0.30 +/- 0.02 to 0.63 +/- 0.03 fmol/10(6) cells for the high affinity receptor binding sites, and from 2.4 +/- 0.31 to 5.0 +/- 0.41 fmol/10(6) cells for the low affinity receptor binding sites) rather than to an increase in the affinity of the binding sites. The insulin-stimulation of PGE2 binding appeared to be associated with a lowering of the cAMP level in these cells; treatment of cells with insulin lowered the cAMP level by increasing the cAMP phosphodiesterase activity of both the membrane and cytosolic fractions. However, enhanced PGE2 binding to the cells resulted in an increase in cAMP level in the cells. This increase in cAMP level may help to enhance the immunosuppressive action of this prostanoid, as PGE2 is known to suppress many steps in the immune response, including interleukin-1 expression, by raising cAMP levels via activation of receptor-linked adenylate cyclase. Our data suggest that insulin at physiological concentrations may enhance the immunosuppressive action of PGE2.
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PMID:Regulation of prostaglandin E2 binding to a murine macrophage cell line, P388D1, by insulin. 132 Apr 12


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