Interaction between cyclic adenosine monophosphate and cyclic gunaosine monophosphate in guinea pig ventricular myocardium.

The purpose of this study was to examine the mechanisms underlying adrenergic-cholinergic antagonism in ventricular myocardium. Myocardial contractility, cyclic adenosine monophosphate (AMP) levels, and cyclic guanosine monophosphate (GMP) levels were measure in isolated guinea pig ventricles after treatment with various inotropic agents given alone and simultaneously with acetylcholine. Acetylcholine alone markedly elevated cyclic GMP levels but did not substantially change myocardial contractility. However, the same concentration of acetylcholine significantly attenuated the inotropic effect of isoproterenol and histamine, two drugs that may act by increasing myocardial levels of cyclic AMP. The decrease in the inotropic response to isoproterenol did not appear to be due to a decrease in the generation of cyclic AMP, because cyclic AMP levels were similar in hearts receiving isoproterenol alone and those receiving isoproterenol with acetylcholine. Dibutyryl cyclic GMP also antagonized the intropic action of isoproterenol. Acetylcholine did not alter the inotropic effects of ouabain, an agent that increases myocardial contractility without changing cyclic AMP levels. These results suggest that cyclic GMP mediates the antiadrenergic effects of acetylcholine by specifically antagonizing the inotropic actions of cyclic AMP.     

Effect of angiotensin II on cyclic guanosine monophosphate and cyclic adenosine monophosphate in human plasma.

Infusion of alpha-adrenergic catecholamines increases plasma cyclic guanosine monophosphate (pcGMP), raising the possibility that the pressor effect of these agents may be mediated by cyclic GMP. We infused pressor doses of angiotensin II in 10 studies in 8 normal subject and measured pcGMP and plasma cyclic adenosine monophosphate (pcAMP) by radioimmunoassay. After 120 minutes of infusion, mean pcGMP was 128 +/- 31% (SE) higher than baseline values (P less than 0.01) while pcAMP was increased 30 +/- 10% (P less than 0.05).     

Dissociations between changes in myocardial cyclic adenosine monophosphate and contractility.

The relationship between changes in the myocardial concentration of adenosine 3':5'-cyclic monophosphate (cyclic AMP) and cardiac contractility was studied in guinea pig and rat myocardium. When isolated perfused guinea pig heart were perfused with 10-5-M papaverine, a potent inhibitor of cyclic AMP phosphodiesterase activity, myocardial cyclic AMP concentration increased significantly from 1.7 plus and minus 0.2 (SE) pmoles/mg protein (N equal 12) to 3.3 plus and minus 0.2 pmoles/mg protein (N equal 12), and the percent of phosphorylase aual 6) (P less than 0.01). However, perfusion with papaverine had no effect on contractility in the absence or the presence of exogenous epinephrine. In perfused rat hearts, 10-5 M glucagon increased myocardial cyclic AMP concentration from 1.5 plus and minus 0.1 pmoles/mg protein (N equal 12) to 2.6 plus and minus 0.1 pmoles/mg protein (N equal 12) (P less than 0.001). In contrast, cyclic AMP levels did not increase detectably in guinea pig heart perfused with glucagon. Glucagon increased adenylate cyclase activity more than twofold in rat myocardial broken cell preparations but failed to stimulate the enzyme in preparations from guinea pigs. Despite these differences, the positive inotropic effects of glucagon on rat and guinea pig hearts were very similar over a wide dose range. Thus, with both papaverine and glucagon, changes in cardiac contractility were dissociated from stimulation of adenylate cyclase activity, increases in myocardial cyclic AMP levels, and conversion of phosphorylase b to phosphorylase a in perfused hearts.     

Dibutyryl cyclic adenosine monophosphate inhibits pulmonary vasoconstriction

The effects of the cell-permeable dibutyryl derivative of cyclic AMP on the vascular reactivity of isolated perfused rat lungs were examined. In lungs perfused with homologous blood, pulmonary arterial infusion of db-cAMP (30μg/min) inhibited hypoxia-induced vasoconstriction (IC₅₀=6.3×10⁻⁵ M) and vasoconstriction due to bolus injection of angiotensin II (IC₅₀=8.2×10⁻⁵ M). Cyclic AMP phosphodiesterase inhibition by aminophylline acted synergistically with db-cAMP in the reduction of hypoxia-induced vasoconstriction. Somatostatin, an inhibitor of adenylate cyclase, prevented the decay of hypoxic vasoconstriction typically observed in isolated lungs, suggesting that a rise in intracellular cAMP may occur during hypoxic vasoconstriction as a consequence of activation of the adenylate cyclase. In lungs perfused with cell and protein-free salt solution, db-cAMP inhibited both initial and prolonged vasoconstriction following bolus injection of 2μg leukotriene C₄. Thus, db-cAMP inhibited pulmonary vascular reactivity nonspecifically.     

Dibutyryl cyclic adenosine monophosphate inhibits pulmonary vasoconstriction

The effects of the cell-permeable dibutyryl derivative of cyclic AMP on the vascular reactivity of isolated perfused rat lungs were examined. In lungs perfused with homologous blood, pulmonary arterial infusion of db-cAMP (30 micrograms/min) inhibited hypoxia-induced vasoconstriction (IC50 = 6.3 X 10(-5) M) and vasoconstriction due to bolus injection of angiotensin II (IC50 = 8.2 X 10(-5) M). Cyclic AMP phosphodiesterase inhibition by aminophylline acted synergistically with db-cAMP in the reduction of hypoxia-induced vasoconstriction. Somatostatin, an inhibitor of adenylate cyclase, prevented the decay of hypoxic vasoconstriction typically observed in isolated lungs, suggesting that a rise in intracellular cAMP may occur during hypoxic vasoconstriction as a consequence of activation of the adenylate cyclase. In lungs perfused with cell and protein-free salt solution, db-cAMP inhibited both initial and prolonged vasoconstriction following bolus injection of 2 microgram leukotriene C4. Thus, db-cAMP inhibited pulmonary vascular reactivity nonspecifically.     

alpha-Adrenergic reduction of cyclic adenosine monophosphate concentrations in rat myocardium.

We determined the effect of alpha-adrenergic receptor stimulation on cyclic adenosine monophosphate (cyclic AMP) concentrations in isolated myocytes derived from adult rat hearts and in isolated perfused rat hearts. Activation of alpha-adrenergic receptors with either phenylephrine (10(-8) M to 10(-6) M) or epinephrine (10(-8) M to 10(-6) M) plus propranolol (10(-6) M) resulted in a reduction in cyclic AMP levels in isolated myocytes. The action of phenylephrine was antagonized by phentolamine (10(-6) M). Phenylephrine (10(-5)M attenuated cyclic AMP generation in response to isoproterenol (10(-8) M and 10(-5) M). However, this effect of phenylephrine was not antagonized by phentolamine. Elevation of cyclic AMP concentrations produced by glucagon and by theophylline in isolated myocytes was attenuated by phenylephrine and by epinephrine plus propranolol and the attenuation was antagonized by phentolamine. In isolated perfused rat hearts epinephrine (10(-6) M), when given with propranolol, diminished the rate of development of tension and also reduced tissue levels of cyclic AMP. Epinephrine alone, as well as isoproterenol, increased contractility and myocardial cyclic AMP concentrations as expected. These results indicate that catecholamines may increase or decrease cyclic AMP levels in rat myocardium, depending on the intensity of stimulation of receptor types. Increases are mediated by beta-adrenergic receptors, whereas decreases appear to by mediated by alpha-adrenergic receptors.     

Variations of plasmatic cyclic nucleotides in the asthmatic patient (cyclic adenosine monophosphate and cyclic guanosine monophosphate) (author's transl)

The present paper studies in asthmatic patients the variations of the plasmatic levels of cAMP and cGMP as control of an eventual adrenergic beta receptors trouble. The first part includes the study of relations of the plasmatic level of nucleotides with the parameters: age, sex, time of sampling in a population of normal subjects (n = 91) and asthmatic patients (n = 203). There is a significant correlation between the age and the level of plasmatic cAMP in normal subject (r = 0.63) as well as in asthmatic patients (r = 0.73). Age for age, there is no difference between the plasmatic levels of controls and the asthmatic patients. The cGMP level is stable, identical in asthmatic (18 p mu +/- 1.74/ml) and in normal subjects (16.84 p mu +/- 2.77 p mu/ml). No nycthemeral rhythm has been revealed. The second part examines the variations of plasmatic levels of cyclic nucleotids during pharmacodynamic assay: methylcholine, beta blocking drugs, spray and subcutaneous sympathomimetics, corticotherapy. No variation of cAMP and cGMP was shown after inhalation of methylcholine or injection of beta blocking drugs able to induce or to reveal a bronchospasm. On the other hand the sympathomimetic drugs, whatever mean of introduction, bring a significant increase of the average level of cAMP going from 40 p mu/ml +/- 5.09 to 101 p mu/ml +/- 4.67 in healthy subject and of 49.42 p mu/ml +/- 10.10 to 74.38 p mu/ml +/- 13.7 in asthmatic patients. The difference in variation amplitude between asthmatic and control subjects is significant, the asthmatic patients responding less to a beta adrenergic stimulation. The plasmatic cGMP remains unchanged during the assay. Corticotherapy does not modify the initial level of cAMP but restores the response to a beta adrenergic stimulation. Inhalation of cAMP dibutyryl restores the bronchial permeability. The study of the variations of plasmatic levels of cAMP reveals a hyposensitivity of the whole of beta adrenergic receptors in asthmatic patients. The former varies in time and can be normalized either spontaneously or by corticotherapy.     

Renal cyclic adenosine monophosphate: an accurate index of parathyroid function.

Measurement of total urine cyclic 3':5'-adenosine monophosphate (cyclic AMP) only incompletely discriminates between normal, hyperparathyroid, and nonparathyroid hypercalcemic patients. Only a fraction of total urine cyclic AMP is contributed by parathyroid hormone (PTH) action on the proximal nephron (renal cyclic AMP); the remainder is derived from plasma by glomerular filtration. We dtermined total urine and plasma cyclic AMP and PTH (by carboxy-terminal specific radioimmunoassay) in control, hyperparathyroid, nonparathyroid hypercalcemic, and surgically hypoparathyroid patients. Renal cyclic AMP was calculated as total urine cyclic AMP minus the filtered component. Of these determinations, only renal cyclic AMP segregated normal from hyperparathyroid, and hyperparathyroid from nonparathyroid hypercalcemic patients with complete accuracy. These data suggest that measurement of renal cyclic AMP provides an accurate index of parathyroid activity and allows clinical discrimination and appropriate treatment of the sub-groups of patients with malignancy and nonparathyroid hypercalcemia from those with hyperparathyroidism.     

3,5 cyclic adenosine monophosphate mediates the salmon calcitonin-induced increase in hypothalamic tyrosine hydroxylase activity.

This study examined the effect of salmon calcitonin (sCT) on hypothalamic tyrosine hydroxylase (TH) activity and evaluated the cellular signaling mechanisms involved in the response. Fetal hypothalamic cells were cultured in a defined medium and treated with sCT and/or specific protein kinase inhibitors on day 14 in vitro. sCT (0.1-10 nM) increased both TH activity and cellular cAMP content in a concentration-dependent manner. sCT (10 nM) increased TH activity to 150-175% of control values and resulted in a 10-fold increase in cellular cAMP content. Both the C1a and C1b CT receptor isoforms were present in the cultures, as assessed by RT-PCR. Rp-adenosine 3',5'-cyclic monophosphothioate (Rp-cAMPS), a cAMP antagonist, and H-8, a cyclic nucleotide kinase inhibitor, blocked the sCT-induced increase in TH activity, with complete abolition of the response observed at concentrations of 1 mM and 5 microM, respectively. sCT (10 nM) increased radiolabeled phosphate incorporation into TH protein to 169% of control values and 1 mM Rp-cAMPS completely blocked this effect. In contrast, neither Calphostin C, a protein kinase C inhibitor, nor U-73122, a phospholipase C inhibitor, significantly altered the ability of sCT to increase TH activity. Likewise, the sCT-induced increase in TH activity was observed after pretreating the cells with either BAPTA/AM, an intracellular calcium chelator, or thapsigargin, an inhibitor of the endoplasmic reticulum calcium pump. These data indicate that sCT has a profound stimulatory effect on TH activity in fetal hypothalamic cells and that enhanced phosphorylation of TH coincides with the sCT-induced increase in enzyme activity. Moreover, CT receptors, which are linked to cAMP production, are expressed in the hypothalamic cells and a cAMP-dependent mechanism mediates the sCT-induced activation and phosphorylation of TH.     

Beta-adrenergic receptor agonists and cyclic nucleotide phosphodiesterase inhibitors: shifting the focus from inotropy to cyclic adenosine monophosphate.

Clinical trials of beta-adrenergic receptor agonists and cyclic nucleotide phosphodiesterase inhibitors in heart failure have demonstrated a reduction in survival in treated patients despite initial inotropic responses. These findings have led many to infer that activation of the mechanisms through which contractility is increased has deleterious effects on failing myocardium. It should be remembered, however, that these agents act proximately by raising intracellular cyclic adenosine monophosphate (cAMP) content and stimulating protein phosphorylation by cAMP-dependent protein kinase, and that the proteins whose phosphorylation contributes to the inotropic responses may be different from the proteins whose phosphorylation contributes to the reduction in survival. Evidence in support of the latter interpretation is presented, and potential therapeutic approaches through which the phosphorylation of different proteins might be selectively affected are considered.     

Effects of pH and cyclic adenosine monophosphate on ileal electrolyte transport in the rat and rabbit.

Alterations in extracellular pH cause reciprocal changes in NaCl absorption in the rat and rabbit ileum. The presence of cholera toxin-induced secretion does not affect pH action measured by in vivo perfusion of the rat ileum. We examined the interaction of pH and cyclic adenosine monophosphate-induced secretion in the rabbit ileum. We found that alterations in arterial pH did not affect ileal absorption in the rabbit in the presence of cholera toxin-induced secretion. This was true whether transport was studied during in vivo ileal perfusion of anesthetized rabbits or by measuring Na+ and Cl- fluxes across isolated, short-circuited tissues in the Ussing chamber. The effects of pH also were blocked when normal rabbit ileum was exposed to 1 mmol/L dibutyryl cyclic adenosine monophosphate in vitro. By contrast, alterations in bathing solution pH affected ileal absorption in the rat in the presence and absence of cyclic adenosine monophosphate. Similarly, exposure to cyclic adenosine monophosphate did not affect the response of the rat colon to PCO2. These findings suggest that the apparently independent effects of pH and cyclic adenosine monophosphate in the rat ileum are not universal. In tissues such as the rabbit ileum, the mechanisms of pH and cyclic adenosine monophosphate action may have biochemical or physiological pathways in common.     

Expression of cyclic adenosine monophosphate response-element binding protein in acute leukemia

Cyclic adenosine monophosphate response-element binding protein (CREB) is a nuclear protein that regulates expression of genes that control cell proliferation, differentiation, and survival. To analyze CREB expression in leukemia cells, we conducted Western blot analysis of bone marrow cells obtained from patients with acute lymphoblastic leukemia, patients with acute myeloid leukemia, and patients without active leukemia. CREB was expressed at a higher frequency in bone marrow cells from patients with acute lymphoid or myeloid leukemia than in patients with leukemia remission or without leukemia. Our results indicate that CREB expression could be a useful marker for leukemia in patients with acute disease and suggest a role for CREB in leukemogenesis.     

Contrasting effects of hypoglycemia on plasma renin activity and cyclic adenosine 3',5'-monophosphate (cyclic AMP) in low renin and normal renin essential hypertension.

Insulin-induced hypoglycemia previously has been shown to provoke a beta-adrenergic response that normally results in an increase in plasma renin activity (PRA). In our study, hypoglycemia induced definite increases in PRA in a group of five patients with normal renin essential hypertension but failed to do so in a group of six patients with low renin essential hypertension. In both groups, plasma cyclic adenosine 3',5'-monophosphate (cyclic AMP; cAMP) increased more than 2-fold during hypoglycemia, but the response in the low renin group was significantly less than that previously observed in normal subjects under the same conditions. Plasma cortisol increased to an equal extent in both groups of hypertensive patients during hypoglycemia. Infusion of the phosphodiesterase inhibitor, theophylline, resulted in definite increases of PRA in patients with normal renin hypertension but not in patients with low renin hypertension. Because changes in the level of plasma cAMP during hypoglycemia have been thought to reflect adrenal catecholamine release, our finding of a blunted increase in plasma cAMP during hypoglycemia in patients with low renin hypertension may suggest that there is a generalized alteration in adrenergic responsiveness in this condition.     

Thyrotropin regulation of cyclic adenosine monophosphate production in human coronary artery smooth muscle cells.

Thyroid disease has been associated with the occurrence of pathophysiologic changes in the vasculature that may result in part from altered serum thyroid hormone and serum lipid levels. Thyrotropin (TSH) levels are also altered in thyroid disease, but a direct effect of TSH on vascular smooth muscle has not previously been considered. In the present study, human coronary artery smooth muscle cells (CASMC) were induced into two morphologically distinct forms by culturing in either (1) growth factor supplemented, 0.5% serum medium (SmGM-3) or (2) basal medium (SmBM) plus 10% fetal bovine serum (FBS). Intracellular cyclic adenosine monophosphate (cAMP) accumulation was determined by radioimmunoassay after exposure to increasing doses of bovine TSH. Cells grown in SmBM/10% FBS for 3 days exhibited a dose-dependent increase in intracellular cAMP that reached a level 10 times higher than baseline at the highest dose examined (100 mIU/mL). In contrast, cells grown in SmGM-3 medium exhibited no change in intracellular cAMP on exposure to increasing TSII. Low serum (0.5% FBS) reduced the ability of TSH to stimulate cAMP above the control value in CASMC. Pretreatment of CASMC with either transforming growth factor-beta1 (TGF-beta1) or tumor necrosis factor-alpha (TNF-alpha) lowered basal levels of cAMP production, but did not inhibit the ability of TSH to stimulate cAMP production. Human, but not rat aortic smooth muscle cells in culture also responded to TSH with a significant increase in cAMP. The results of this study suggest that TSH may exert direct effects on vascular smooth muscle mediated by adenylate cyclase activation that could conceivably affect the progression of vascular disease associated with thyroid dysfunction.     

Platelet cyclic adenosine monophosphate phosphodiesterases: targets for regulating platelet-related thrombosis

Platelets contain two cyclic adenosine monophosphate (cAMP) phosphodiesterases (PDEs) that regulate the level of cAMP, the major inhibitor of platelet activation pathways. PDE3A hydrolyzes cAMP to 5' AMP with a low K (m). PDE3A is inhibited by cyclic guanosine monophosphate (cGMP), which provides a feedback control and controls basal levels of cAMP. In contrast, PDE2A hydrolyzes both cAMP and cGMP with a high K (m), is allosterically stimulated by cGMP at moderate levels, and may control the stimulated levels of cAMP. Using affinity labeling, chemical modification, and site-directed mutagenesis of highly conserved amino acids, the amino acids required for catalytic activity and/or metal binding are H752 and H756. The singular binding sites for cAMP include N845, E971, and F972, whereas the unique amino acids interacting with cGMP are Y751, H836, H849, and D950. Residues E866 and F1004 are present in both the overlapping cGMP and cAMP sites. Two inhibitors of PDE3A are used in clinical medicine: milrinone and cilostazol. Three amino acids, Y751, D950, and F1004, show decreased sensitivity to both inhibitors (increased K (i)). These inhibitors mimic cGMP as an inhibitor of PDE3A rather than compete for cAMP binding. New nonhydrolyzable affinity labels inactivate PDE3A and are protected by Sp-cAMPS, a nonhydrolyzable substrate of the enzyme. These compounds have the potential to identify amino acids that are unique for PDE3A. An inhibitor of platelet PDE2A increases cAMP more than inhibitors of PDE3A but has much less effect on platelet activation, suggesting that these enzymes are present in different compartments of the cell.