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At least 55 records · Page 3Linked to original sources
PubMed1978

Cyclic AMP-dependent protein kinase mediates a cyclic AMP-stimulated decrease in ornithine and S-adenosylmethionine decarboxylase activities.

Incubation of S49 lymphoma cells with N6,O2'-dibutyryl cyclic AMP (Bt2cAMP) decreases the activities of ornithine decarboxylase (L-ornithine carboxy-lyase; EC 4.1.1.17) and S-adenosylmethionine decarboxylase (S-adenosyl-L-methionine carboxy-lyase; EC 4.1.1.50), the two principal enzymes in the pathway of polyamine synthesis. This decrease is dose-dependent, commences after a 3-hr delay, virtually abolishes the assayable activities of the two enzymes, and is not associated with a soluble inhibitor of the enzyme activities. Studies in mutant S49 clones that have altered protein kinase indicate that cAMP-dependent protein kinase mediates the decreases in enzyme activities. The dose-response pattern for the cAMP-stimulated decrease in enzyme activities parallels the pattern for the cAMP-stimulated, cell cycle-specific (G1) growth arrest of S49 cells. The activity of ornithine decarboxylase decreases faster than Bt2cAMP arrests wild-type S49 cells and, similarly, release of cells from the cAMP-stimulated arrest in G1 increases the activity of ornithine decarboxylase faster than cells exit from G1. These findings contrast with reports that cAMP induces ornithine decarboxylase in other cell types and further suggest that passage of cells through cell cycle is required for maintaining the activities of ornithine and S-adenosylmethionine decarboxylases.

Adenosylmethionine Decarboxylase↗
PubMed1977

Stimulation by alcohols of cyclic AMP metabolism in human leukocytes. Possible role of cyclic AMP in the anti-inflammatory effects of ethanol.

In this study ethanol and certain other short-chain aryl (benzyl and phenethyl) and aliphatic (methyl, propyl, butyl, and amyl) alcohols produced up to 10-fold increases in cyclic AMP (cAMP) concentrations in purified human peripheral blood lymphocytes. Ethanol concentrations as low as 80 mg/dl produced significant elevations in lymphocyte cAMP. Significant but less marked augmentation of cAMP in response to alcohols was observed in human platelets, human granulocytes, and rabbit alveolar macrophages. The mechanism of the alcohol-induced cAMP accumulation is probably secondary to membrane perturbation and consequent activation of adenylate cyclase, because ethanol directly stimulated this enzyme in lymphocyte membrane preparations but had no effect on lymphocyte phosphodiesterase activity. Lysosomal enzyme release, by phagocytosing human leukocytes, and aminoisobutyric acid transport in mitogen-stimulated human lymphocytes were shown to be inhibited by ethanol and other alcohols at concentrations which also elevate cAMP. In general, the magnitude of the inhibition of these inflammatory processes correlated with the ability of the alcohol to elevate cAMP concentrations. Lectin-and anti-thymocyte globulin-induced lymphocyte mitogenesis was inhibited or unaffected depending upon both the concentration and type of mitogenic stimulus and the concentration and type of alcohol utilized. Inflammatory mediator release from rat mast cells also was inhibited by ethanol and certain other alcohols, but whole cell cAMP was not increased. Ethanol may alter these inflammatory responses and other biologic processes at least in part by modulating cellular levels of cAMP.

Adenylyl Cyclases↗
PubMed1975

Direct effects of cyclic AMP and dibutyryl cyclic AMP on renal blood flow.

The direct effects of adenosine 3',5'-cyclic monophosphate (cAMP) and dibutyryl adenosine 3',5'-cyclic monophosphate (D-cAMP) on renal blood flow were studied in dogs under renal perfusion with constant pressure. Cyclic AMP caused a marked phasic decrease in renal blood flow in doses more than 1 mg, while D-cAMP produced a slight increase in that in doses more than 10 mg. The vasoconstrictive effect of cAMP was not blocked by the pretreatment with phenoxybenzamine, but was markedly depressed during the infusion of aminophylline. On the other hand, the vasodilative effect of D-cAMP was not affected either by the pretreatment with propranolol or during the infusion of aminophylline. These findings indicate that cAMP and D-cAMP have an opposite direct effect on the renal artery, independently of the adrenergic receptors. However, there may be a possibility that cAMP produces its vasoconstrictive effect on the renal artery partly through the action of its metabolites.

Aminophylline↗
PubMed1978

The concentration of cyclic AMP and the activity of cyclic AMP dependent protein kinase and an inhibitor in the adipose tissue of rats fed lard or glucose diets.

Measurements of tissue cyclic AMP (cAMP) concentration, the activity of cAMP-dependent protein kinase and the level of the enzyme's thermostable, macromolecular inhibitor were made on preparations of rat epididymal fat pad from animals fed high fat or high carbohydrate diets. The cAMP concentration from rats adapted to a high lard diet for 14-15 days was 153 +/- 17.8 pmoles/mg protein as opposed to 76 +/- 6.0 found with high glucose diet. No significant difference in total cAMP-dependent protein kinase activity was observed among rats fed high glucose, high lard or laboratory chow, although the enzyme's activity ratio (-cAMP)(+cAMP) was significantly elevated with lard feeding (0.49 +/- 0.02) as opposed to glucose feeding (0.43 +/- 0.01). Crude preparations from lard and glucose fed animals were equivalent in inhibitory activity when tested with enzyme from chow fed animals. Agarose column chromatography separated holoenzyme and C subunit forms of the protein kinase when 500 mM NaCl was present in the elution buffer. Absence of the salt allowed subunit reassociation to occur. Direct addition of NaCl greater than or equal to 75 mM significantly inhibited protein kinase activity. The results indicate that the adipose tissue of rats fed a high lard diet has a higher concentration of cAMP and an increased protein kinase activity ratio than tissue from rats fed a fat free, high glucose diet. Total cAMP-dependent protein kinase activity and the level of a thermostable macromolecular inhibitor remained unchanged.

Adipose Tissue↗
PubMed1979

Role of calcium dependent regulator protein (CDR) in inhibition of 3',5'-c AMP-phosphodiesterase by influenza virus. I. Isolation and purification of CDR and CDR-dependent 3',5'-c' AMP-phosphodiesterase from chick embryos.

Calcium-dependent regulator protein (CDR) and CDR-dependent 3',5'-c AMP-phosphodiesterase were isolated and partially purified from 12-day chick embryos. Some basic properties of the preparations obtained were described. Native (infectious) but not noninfectious (heat-inactivated) influenza virus in the presence of CDR and ATP reduced the activity of CDR-dependent phosphodiesterase.

3',5'-Cyclic-AMP Phosphodiesterases↗
PubMed1976

Sequential alterations in the hepatic content and metabolism of cyclic AMP and cyclic GMP induced by DL-ethionine: evidence for malignant transformation of liver with a sustained increase in cyclic AMP.

There is evidence than adenosine 3',5'-monophosphate (cAMP) and guanosine 3',5'-monophosphate (cGMP) may have antagonistic actions on cell growth, with cAMP inhibiting and cGMP stimulating this process. However, reductions in cAMP and increases in cGMP are not charactersitic of all neoplastic tissues. Thus, benign and malignant tissues from hepatoma-bearing rats exposed to the hepatic carcinogen DL-ethionine have elevated rather than depressed cAMP, compared to control liver, and parenteral administration of this drug increases hepatic cAMP within hours. In the present study, the effects of ethionine ingestion on the hepatic content and metabolism of both cAMP and cGMP were examined sequentially in rats at 2 and then 6 wk intervals, from the initiation of drug administration until the development of hepatomas. After 2 wk, cAMP content of quick-frozen liver from rats receiving ethionine (E) was significantly increased (826 +/- 91 pmole/g wet weight) above that of liver from pair-fed controls (C, 415 +/- 44), whether calculated by tissue wet weight, protein, or DNA content. In benign tissue from E, higher cAMP was still evident after in vitro incubations of slices with 2 mM 1-methyl-3-iso-butylxanthine (MIX) and was associated with enhanced adenylate cyclase and unchanged high or low Km cAMP-phosphodiesterase activities. These findings are compatible with accelerated cAMP generation in liver from E. Protein kinase activity ratios were significantly increased in frozen liver from E (0.52 +/- 0.04 versus 0.36 +/- 0.03 in C), and the percent glycogen synthetase in the I form was clearly reduced (19% +/- 2% in E versus 47% +/- 5% in c). incubation of hepatic slices from E or C with MIX and/or 10 muM glucagon further increased cAMP and protein kinase activity ratios, data which imply higher effective, as well as total, cellular cAMP in E. Changes in cAMP metabolism and action observed at 2 wk persisted throughout the 38-wk period of drug ingestion. Adenylate cyclase activity, cAMP content, and protein kinase activity ratios of ethionine-induced hepatomas exceeded those of both the surrounding liver from tumor-bearing rats and that of control liver, but alterations in these parameters were qualitatively similar in both tissues from E. By contrast, while cGMP in quick-frozen surrounding liver from tumor-bearing rats (36 +/- 4 pmole/g wet weight) did not differ from that of control liver (30 +/- 3), cGMP in the hepatomas was increased. This change was evident in both frozen tumor (89 +/- 10) and in tumor slices incubated in vitro with MIX (C, 90 +/- 11; surrounding liver, 85 +/- 10; hepatoma 231 +/- 29). These results indicate that malignant conversion can occur in liver with a sustained elevation of both total and effective cAMP during the premalignant phase. The increase in cGMP detected in ethionine-induced hepatomas could also be a key determinant of malignant transformation in the model, although premalignant changes in cGMP were not apparent.

3',5'-Cyclic-AMP Phosphodiesterases↗
PubMed1978

A new extragenic suppressor of cya mutation. Mutant cyclic AMP receptor protein with an increased affinity for cyclic AMP.

A strain bearing an extragenic suppressor of cya mutation was isolated as a second-site revertant of an adenylate cyclase deficient strain. The mutant was unable to synthesize cAMP but showed normal fermentation profiles and growth properties on a variety of carbon sources. The site of reversion was mapped in, or near, the structural gene for the cAMP receptor protein. Structural alteration of the protein was directly demonstrated by the following biochemical observations: (i) A 10-fold decrease in the dissociation constant for cAMP, (ii) an acidic shift in the isoelectric point, and (iii) the altered binding properties to lambdah80dlac ps DNA.

Carbohydrate Metabolism↗
PubMedDate not supplied

[Effect of cortisol on adenylate cyclase and 3',5'-AMP phosphodiesterase activity and 3',5'-AMP concentration in tissues and biological fluids in experimental atherosclerosis].

Administration of hydrocortisone into healthy rabbits activated adenilate cyclase and phosphodiesterase in liver tissue; activity of the enzymes was normalized within 5 days after the treatment. The hormone, administered into animals with experimental cholesterol-induced atherosclerosis, caused an activation of adenilate cyclase and inhibition of phosphodiesterase; due to the phenomenon more distinct and long-term increase in cAMP concentration was observed in kidney, liver and fatty tissues. Concentration of cAMP exceeded considerably its initial content in the tissues within 5 days after the hydrocortisone administration. Hydrocortisone inhibited the adenilate cyclase system activity in adrenal cortex of experimental and control animals at early period of the experiment. In health rabbits content of cAMP was increased in adrenal cortex within 5 days after the hormone administration. As the similar effect was not found in animals with experimental atherosclerosis these data suggest that the hypophysis-adrenal cortex system under the experimental conditions studied was inhibited.

3',5'-Cyclic-AMP Phosphodiesterases↗
PubMed1978

Possible participation of glucocorticoid in elevation of 3',5'-cyclic AMP levels through inhibition of cyclic AMP phosphodiesterase.

Administration of prednisolone and cholate to rats elevated levels of cAMP (adenosine 3',5'-cyclic monophosphate) by 1.5- to 2.0-fold. Compounds such as prednisolone, hydrocortisone, cholate, and deoxycholate were found to be potent inhibitors of partially purified cAMP phosphodiesterase prepared from rat liver. Kinetic analysis showed that the prednisolone inhibition was noncompetitive with a Ki of 8.9 x 10(-4) M. These results suggest that in addition to increasing DNA-dependent RNA polymerase activity in vivo, a large application of glucocorticoid may incur elevation of intracellular cAMP levels.

3',5'-Cyclic-AMP Phosphodiesterases↗