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)

To investigate the hypothesis that cyclic AMP (cAMP) regulates arachidonic acid metabolism in vascular tissue, we have studied the effects of forskolin (FSK), an activator of adenylate cyclase, and 3-isobutyl-1-methylxanthine (IBMX), a phosphodiesterase inhibitor, on hormone-stimulated prostacyclin (PGI2) synthesis in porcine aortic endothelial cells grown in culture. In these experiments, bradykinin (1 microgram/ml) and A23187 (0.2 microM) potently stimulated PGI2 biosynthesis (9- and 10-fold respectively). However, prostaglandin synthesis in response to either of these agents was not affected by FSK even though FSK elevated intracellular levels of cAMP 10-fold. IBMX failed to elevate basal cAMP levels when incubated with unstimulated cells. Stimulation of IBMX-treated (0.1 but not 1.0 or 4.0 mM) cells with bradykinin, however, did result in increased cAMP levels, presumably due to PGI2 formation and subsequent activation of adenylate cyclase. In addition to phosphodiesterase inhibition, IBMX inhibited PGI2 formation (72% at 1 mM) in a dose-dependent manner so that, at higher doses of IBMX, cAMP levels returned to baseline. Thus, prostacyclin synthesis inhibition by IBMX could not be attributed to elevated cAMP. In other experiments, IBMX (1 mM) was found to directly inhibit arachidonic acid release (32%) and arachidonic acid metabolism (65%) in endothelial cells and to inhibit arachidonic acid conversion to PGE2 by sheep seminal vesicle microsomes (65%). These data suggest that IBMX directly inhibits both phospholipase and cyclooxygenase activities. These experiments do not support the contention that cAMP regulates these enzymes in cultured aortic endothelial cells.
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PMID:Arachidonic acid metabolism in cultured aortic endothelial cells. Effect of cAMP and 3-isobutyl-1-methylxanthine. 257 80

The inhibition of platelet adhesion by nitric oxide (NO) and prostacyclin and their mechanism of action was studied. Platelet adhesion to collagen fibrils and endothelial cell matrix was inhibited completely by NO but only partially by prostacyclin. Adhesion of platelets to endothelial cell monolayers was inhibited by bradykinin. This effect of bradykinin was unaffected by aspirin, and was accounted for by the amounts of NO released by the endothelial cells. Inhibition of platelet adhesion by NO and prostacyclin was potentiated by selective inhibitors of cGMP phosphodiesterase, but not of cAMP phosphodiesterase, indicating that elevation of cGMP regulates platelet adhesion.
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PMID:The role of nitric oxide and cGMP in platelet adhesion to vascular endothelium. 282 88

Prostaglandin E1 (PGE1) at 1 nM inhibits arginine-vasopressin (AVP)-induced water reabsorption in the rabbit cortical collecting tubule (RCCT), while 100 nM PGE1, by itself, stimulates water reabsorption (Grantham, J. J., and Orloff, J. (1968) J. Clin. Invest. 47, 1154-1161). To investigate the basis for these two responses, we measured the effects of prostaglandins on cAMP metabolism in purified RCCT cells. In freshly isolated cells, PGE2, PGE1, and 16,16-dimethyl-PGE2 acting at high concentrations (0.1-10 microM) stimulated cAMP accumulation; however, one PGE2 analog, sulprostone (16-phenoxy-17,18,19,20-tetranor-PGE2 methylsulfonilamide), failed to stimulate cAMP accumulation or to antagonize PGE2-induced cAMP formation; PGD2, PGF2 alpha, and a PGI2 analog, carbacyclin (6-carbaprostaglandin I2), also failed to stimulate cAMP synthesis. These results suggest that there is a PGE-specific stimulatory receptor in RCCT cells which mediates activation of adenylate cyclase. Occupancy of this receptor would be anticipated to cause water reabsorption by the collecting tubule. At lower concentrations (0.1-100 nM) PGE2, PGE1, 16,16-dimethyl-PGE2, and, in addition, sulprostone inhibited AVP-induced cAMP accumulation by fresh RCCT cells in the presence of cAMP phosphodiesterase inhibitors. Pertussis toxin pretreatment of RCCT cells blocked the ability of both PGE2 and sulprostone to inhibit AVP-induced cAMP accumulation. In membranes prepared from RCCT cells, sulprostone prevented stimulation of adenylate cyclase by AVP. These results suggest that E-series prostaglandins (including sulprostone) can act through an inhibitory PGE receptor(s) coupled to the inhibitory guanine nucleotide regulatory protein, Gi, to block AVP-induced cAMP synthesis by RCCT cells. Occupancy of this receptor would be expected to cause inhibition of AVP-induced water reabsorption in the intact tubule. Curiously, after RCCT cells were cultured for 5-7 days, PGE2 no longer inhibited AVP-induced cAMP accumulation, but PGE2 by itself could still stimulate cAMP accumulation. In contrast to PGE2, epinephrine acting via an alpha 2-adrenergic, Gi-linked mechanism did block AVP-induced cAMP formation by cultured RCCT cells. This implies that some component of the inhibitory PGE response other than Gi is lost when RCCT cells are cultured.
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PMID:Regulation of cyclic AMP metabolism in rabbit cortical collecting tubule cells by prostaglandins. 283 64

The effect of cooling (at 27 degrees C) on the synthesis of prostacyclin (PGI2) by rat aortic rings, thromboxane A2 (TXA2) synthesis by human platelets and phosphodiesterase activity in human platelets was investigated. Cooling induced a significant reduction in both PGI2 synthesis by rat aortic rings and TXA2 synthesis by human platelets, but the inhibition of the former was proportionately greater. Platelet phosphodiesterase activity decreased, with a subsequent increase in intraplatelet c-AMP content. Diminished PGI2 synthesis/release associated with the previously described diminution in the sensitivity of platelets to PGI2 after cooling probably contributes to the hyperaggregability of platelets at lower temperatures. This occurs in spite of the potential antiaggregatory effect of diminished TXA2 synthesis by platelets and the increase in intraplatelet c-AMP. These observations are relevant to the pathogenesis of hyperaggregability of platelets in Raynaud's syndrome.
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PMID:The effect of cooling on in vitro vascular prostacyclin and platelet thromboxane A2 synthesis: relevance to cold-induced pathology. 283 26

Agents such as prostaglandins E1 and I2 which elevate cAMP levels in platelets also increase cAMP phosphodiesterase activity. Since much of the cAMP phosphodiesterase activity in human platelets is due to the cGMP-inhibited isozyme (Macphee, C. H., Harrison, S. A., and Beavo, J. A. (1986) Proc. Natl. Acad. Sci. U. S. A. 83, 6600-6663), we examined the regulation of this isozyme by prostaglandins E1 and I2 in intact platelets. Because this isozyme is a minor component of platelet protein, normally requiring several thousand-fold purification to achieve homogeneity, a specific monoclonal antibody (CGI-5) was utilized to identify and isolate the cGMP-inhibited phosphodiesterase activity. Treatment of intact platelets with the prostaglandins promoted an increase in the phosphorylation state of the cGMP-inhibited phosphodiesterase and a corresponding increase in phosphodiesterase activity. The effect on activity and phosphorylation of the cGMP-inhibited phosphodiesterase was observed within 2 min after intact platelets were exposed to the prostaglandins. The half-maximal effective dose for prostaglandin I2 (10 nM) was approximately 10-fold lower than that for prostaglandin E1. The phosphorylated, cGMP-inhibited isozyme migrated as a 110-kDa peptide following sodium dodecyl sulfate gel electrophoresis. Direct in vitro phosphorylation of the platelet cGMP-inhibited phosphodiesterase by the catalytic subunit of cAMP-dependent protein kinase caused a similar increase in phosphodiesterase activity. Treatment with PKI peptide, a specific inhibitor of cAMP-dependent protein kinase, blocked the phosphorylation and the effect on activity. Taken together, the data strongly suggest that the effects of prostaglandins E1 and I2 on platelet phosphodiesterase activity are mediated by a direct cAMP-dependent protein kinase-catalyzed phosphorylation of the cGMP-inhibited phosphodiesterase isozyme.
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PMID:Phosphorylation results in activation of a cAMP phosphodiesterase in human platelets. 283 85

A new in vitro bleeding time (BT) device was applied to various surgical patients. After setting the optimal assay condition, the normal in vitro bleeding time (T2) and volume (V2) were obtained from healthy volunteers, being 114.7 secs +/- 25.8 (SD) and 272.2 microliter +/- 69.1 (SD), respectively. When the T2 was below 210 secs, the platelet count was inversely proportional to the T2 and V2 of the in vitro BT with p less than 0.01. The value of the in vitro BT was not affected by heparin. Agents, which modify platelet functions, such as PGI2, DN9693 (an inhibitor of phosphodiesterase) and aspirin, prolonged the in vitro BT (T2, V2) dose-dependently. Administration of aspirin (660 mg) to volunteers prolonged the T2 from 108 to over 300 secs and the V2 from 253 to over 600 microliter but ticlopidine (500 mg/day for 3 days) had no effect. In 8 patients with liver cirrhosis who underwent hepatectomy, one patient with a prolonged T2 (260 secs) and a normal skin BT bled postoperatively, however, 3 patients with a prolonged skin BT (greater than 15 min) and a normal T2 had no hemorrhagic complications. From these observations it was concluded that in vitro BT is a convenient and useful tool to examine primary hemostasis or platelet function.
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PMID:Clinical application of a new in vitro bleeding time device on surgical patients. 284 75

The shape of the time-course of cyclic AMP formation by intact human platelets in response to the stable prostaglandin I2 analogue iloprost varied with the concentration of the prostaglandin. At low concentrations of iloprost, the time-course showed a rise to a plateau with little subsequent decrease in cyclic AMP level. At high concentrations of iloprost, the initial rate of cyclic AMP formation was more rapid than at low concentrations, but the curves showed a marked time-dependent fall in cyclic AMP level to values below those observed at lower prostaglandin concentration. By contrast, PGE1 gave a rise and marked fall in cyclic AMP level at all concentrations of the prostaglandin and the curves did not cross. The time- and concentration-dependent fall in cyclic AMP level in response to iloprost was still apparent in the presence of phosphodiesterase inhibitors, indicating that inhibition of adenylate cyclase, rather than activation of cyclic AMP phosphodiesterases, was responsible for the fall in cyclic AMP level. Activators of protein kinase C, which phosphorylates platelet Ni and impairs its function, abolished the time-dependent fall in cyclic AMP level, indicating that Ni may be involved in prostaglandin-induced inhibition of adenylate cyclase. Time-courses were analyzed using an equation derived by Barber et al. (Adv. Cyc. Nuc. Res. 9, 507-516 (1978)) to yield rate constants for activation and inhibition of adenylate cyclase. Because of the difference in prostaglandin dependence of the activation and inhibition rate constants we propose that activation of adenylate cyclase in platelets is mediated by a rapid-acting stimulatory receptor, while time-dependent inhibition (desensitization) is mediated through a separate, slow-acting inhibitory receptor. The stimulatory receptor has an affinity for prostaglandin greater than the putative inhibitory receptor in the case of iloprost (as well as PGI2 and PGD2), and a lower affinity than the inhibitory receptor in the case of PGE1 (and PGE2). Prostaglandin-induced inhibition may be mediated through Ni.
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PMID:Cyclic AMP turnover in response to prostaglandins in intact platelets: evidence for separate stimulatory and inhibitory prostaglandin receptors. 284 22

Cyclic AMP and cyclic GMP content and activities of cyclic nucleotide metabolic enzymes were determined in intima and media of atherosclerotic and unaffected human aorta obtained shortly after death due to myocardial infarction. Cyclic AMP content in fatty streaks and atherosclerotic plaques was lower by three- and five-fold, respectively, as compared with uninvolved intima. Cyclic GMP level in atherosclerotic lesions was estimated to be three-fold higher than in grossly normal area. Basal activity of adenylate cyclase in fatty streaks and plaques was two- to six-fold lower than in unaffected intima. Besides, the ability of adenylate cyclase to be stimulated by the stable analogue of prostacyclin, carbacyclin, was suppressed in plaques. Guanylate cyclase activity in fatty streaks was 1.5- to three-fold higher than in normal tissue. The thiol-reducing agent, dithiothreitol, decreased the enzyme activity to normal level, suggesting the oxidative nature of guanylate cyclase activation in the lesion zone. There were no significant changes in cyclic AMP phosphodiestease activity in the regions of the atherosclerotic lesion. Cyclic GMP phosphodiesterase activity in atherosclerotic plaques was two-fold lower than in the intima of unaffected areas. We did not find differences in the content of cyclic nucleotides or related enzyme activities in the media of uninvolved areas of human aorta nor in the media underlying atherosclerotic lesions. Our findings suggest that development of human atherosclerotic lesions is accompanied by dramatic changes in the cyclic nucleotide metabolism featuring gradual hormonal receptor uncoupling from adenylate cyclase, activation of guanylate cyclase in fatty streaks and inhibition of cyclic GMP phosphodiesterase in plaques.(ABSTRACT TRUNCATED AT 250 WORDS)
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PMID:Disorders in the system of cyclic nucleotides in atherosclerosis: cyclic AMP and cyclic GMP content and activity of related enzymes in human aorta. 288 18

PL2-49 is a murine monoclonal IgG1 antibody obtained after immunization of Balb/c mice with EDTA washed platelets. Binding could be detected on Zwa(+) as well as Zwa(-) platelets, but not on type I Glanzmann's thrombasthenia platelets using an ELISA screening test. Immunoprecipitation studies showed that PL2-49 bound to glycoprotein IIb when the glycoprotein IIb/IIIa complex dissociation was performed after the monoclonal antibody binding. Experiments with a human alloantibody against Zwa antigen were run in parallel to control the complex dissociation. Ascitic fluid, as well as the purified antibody, induced activation and aggregation of washed platelets and ATP release. PL2-49-induced aggregation did not require exogenous fibrinogen and was inhibited, partially, in the presence of aspirin, apyrase, isosorbide dinitrate. Raising intra-platelet cyclic AMP with a stable PGI2 analogue, iloprost, and/or a phosphodiesterase inhibitor, RA 233, suppressed the responses to PL2-49. F(ab')2 fragments did not induce aggregation of normal platelets but inhibited the response to the whole immunoglobulin. Finally PL2-49 was shown to induce aequorin-detected elevations in intraplatelet Ca++ levels. Thus PL2-49 seems to differ from monoclonal antibodies so far described, since it binds to glycoprotein IIb in a complex-dependent manner at least under our experimental conditions for immunoprecipitation studies, and it induces platelet Ca++ mobilization and platelet aggregation after a lag-time. These reactions depend both on Fab and Fc domains of the antibody and require neither complement nor exogenous fibrinogen.
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PMID:PL2-49, a monoclonal antibody against glycoprotein IIb which is a platelet activator. 291 29

The effects of inhibition of endogenous prostaglandin synthesis on the release of norepinephrine from sympathetic nerves and on postjunctional adrenergic responsiveness were studied in isolated canine left circumflex coronary arteries. In rings, suspended for isometric tension recording and contracted with prostaglandin F2 alpha, transmural electrical stimulation caused frequency-dependent relaxations, which were blocked by propranolol and augmented by indomethacin. In superfused strips, previously incubated with [3H]norepinephrine, electrical stimulation (2 Hz) increased the overflow of tritiated neurotransmitter; indomethacin did not influence basal or evoked [3H]norepinephrine overflow. Exogenous norepinephrine caused relaxations in rings contracted with prostaglandin F2 alpha, but increases in tension in potassium-depolarized tissues which could be abolished by phentolamine; isoproterenol induced relaxations in both cases. Indomethacin significantly augmented the relaxation in response to exogenous norepinephrine (during contractions with prostaglandin F2 alpha) and reversed norepinephrine-induced contractions (during potassium-depolarization) into relaxation. Other cyclooxygenase inhibitors had comparable effects. In the presence of propranolol, indomethacin did not diminish contractions evoked by norepinephrine in depolarized rings. Relaxations induced by sodium nitroprusside or acetylcholine during contractions caused by prostaglandin F2 alpha or potassium chloride were not affected by indomethacin. The augmentation of beta-adrenergic responsiveness by indomethacin was abolished by exogenous prostacyclin. The prostacyclin synthetase inhibitor tranylcypromine and exogenous prostaglandin E2 depressed beta-adrenergic responsiveness. Indomethacin did not affect the facilitatory action of phosphodiesterase inhibition on beta-adrenergic relaxation. The data suggest that endogenous prostaglandins (most probably prostacyclin and prostaglandin E2) exert a "braking" effect on beta-adrenergic responsiveness in coronary arterial smooth muscle.
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PMID:Inhibitors of prostaglandin synthesis augment beta-adrenergic responsiveness in canine coronary arteries. 298 46


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