Changes In Cyclic Nucleotide Concentrations Research Articles

Alteration in Cngb1 Expression upon Maternal Immune Activation in a Mouse Model and Its Possible Association with Schizophrenia Susceptibility.

ObjectiveThe cyclic nucleotide-gated channel (Cng) regulates synaptic efficacy in brain neurons by modulating Ca2＋ levels in response to changes in cyclic nucleotide concentrations. This study investigated whether the expression of Cng channel, cyclic nucleotide-gated channel subunit beta 1 (Cngb1) exhibited any relationship with the pathophysiology of schizophrenia in an animal model and whether genetic polymorphisms of the human gene were associated with the progression of schizophrenia in a Korean population.MethodsWe investigated whether Cngb1 expression was related to psychiatric disorders in a mouse model of schizophrenia induced by maternal immune activation. A case-control study was conducted of 275 schizophrenia patients and 410 controls with single-nucleotide polymorphisms (SNPs) in the 5′-near region of CNGB1.ResultsCngb1 expression was decreased in the prefrontal cortex in the mouse model. Furthermore, the genotype frequency of a SNP (rs3756314) of CNGB1 was associated with the risk of schizophrenia.ConclusionOur results suggest that CNGB1 might be associated with schizophrenia susceptibility and maternal immune activation. Consequently, it is hypothesized that CNGB1 may be involved in the pathophysiology of schizophrenia.

Cyclic Nucleotide-Activated Currents in Cultured Olfactory Receptor Neurons of the HawkmothManduca sexta

Moth pheromones cause rises in intracellular Ca(2+) concentrations that activate Ca(2+)-dependent cation channels in antennal olfactory receptor neurons. In addition, mechanisms of adaptation and sensitization depend on changes in cyclic nucleotide concentrations. Here, cyclic nucleotide-activated currents in cultured olfactory receptor neurons of the moth Manduca sexta are described, which share properties with currents through vertebrate cyclic nucleotide-gated channels. The cyclic nucleotide-activated currents of M. sexta carried Ca(2+) and monovalent cations. They were directly activated by cyclic adenosine monophosphate (cAMP) and cyclic guanosine monophosphate (cGMP), modulated by Ca(2+)/calmodulin, and inhibited by lanthanum. M. sexta cyclic nucleotide-activated currents developed in an all-or-none manner, which suggests that the underlying channels are coupled and act coordinately. At least one cAMP- and two cGMP-activated nonselective cation currents could be distinguished. Compared with the cAMP-activated current, both cGMP-activated currents appeared to conduct more Ca(2+) and showed a stronger down-regulation by Ca(2+)/calmodulin-dependent negative feedback. Furthermore, both cGMP-activated currents differed in their Ca(2+)-dependent inhibition. Thus M. sexta olfactory receptor neurons, like vertebrate sensory neurons, appear to express nonselective cyclic nucleotide-activated cation channels with different subunit compositions. Besides the nonselective cyclic nucleotide-activated cation currents, olfactory receptor neurons express a cAMP-dependent current. This current resembled a protein kinase-modulated low-voltage-activated Ca(2+) current.

Real-time monitoring of phosphodiesterase inhibition in intact cells

Phosphodiesterases (PDEs) are hydrolytic enzymes, which convert cyclic AMP (cAMP) and cyclic GMP (cGMP) into their corresponding monophosphates. PDE-dependent hydrolysis shape gradients of these second messengers in cells, which may form the basis of their compartmentation and play a key role in a vast number of physiological and pathological processes.Here, we present a novel approach for real-time monitoring of local cAMP and cGMP levels associated with particular PDEs. We used HEK 293 cells expressing genetic constructs encoding a PDE of interest (PDE3A, PDE4A1 or PDE5A) fused to cAMP and cGMP sensors, which allow to directly visualize changes in cyclic nucleotide concentrations in the vicinity of PDE molecules by fluorescence resonance energy transfer (FRET). FRET was detected by imaging of single cells on 96-well plates and demonstrated specific effects of PDE inhibitors on local cyclic nucleotide levels. In addition, this approach reported physiological regulation of PDE3A activity, its activation by PKA-dependent phosphorylation and inhibition by cGMP.In conclusion, our assay provides a unique and highly sensitive method to analyze PDE activity in living cells. It allows to sense cAMP gradients around particular PDE molecules and to study the pharmacological effects of selective inhibitors on localized cAMP signalling.

Novel N7- and N1-Substituted cGMP Derivatives Are Potent Activators of Cyclic Nucleotide-Gated Channels

Cyclic nucleotide-gated (CNG) channels, key players in olfactory and visual signal transduction, generate electrical responses to odorant- and light-induced changes in cyclic nucleotide concentration. Previous work suggests that substitutions are tolerated solely at the C8 position on the purine ring of cGMP. Our studies with C8, 2'-OH, and 2-NH2-modified cGMP derivatives support this assertion. To gain further insight into determinants important for CNG channel binding and activation, we targeted previously unexplored positions. Modifications at N7 of 8-SH-cGMP (6) are well tolerated by olfactory and retinal rod CNG channels. Toleration of a very large substituent, a 3400 molecular weight PEG, at either N7 or C8 argues for broad accommodation at these positions in the binding site. Modification at N1 of cGMP reduces the apparent affinity for the channel; however, when combined with 8-parachlorophenylthio derivatization, the resulting cGMP analogue is more potent than cGMP itself. These studies establish the N7 and N1 positions of cGMP as targets for modification in the design of novel CNG channel agonists.

Combined phosphodiesterase inhibition and beta-blockade in the GI104313, decreases ischemia-induced arrhythmias in the rat.

The purpose of the present study was to evaluate the effects of GI104313, a chimeric molecule containing a phosphodiesterase inhibiting pyradazinone and a blocking phenoxpropanolamine, on ischemia-induced arrhythmias in anesthetized rats. The coronary artery was occluded 15 min after commencing drug administration and myocardial ischemia was maintained for 30 min during which the heart rate and mean blood pressure were recorded. Cyclic AMP and GMP were determined by radio-immunoassay. GI104313 (0.1 micromol x kg(-1) plus 0.01 micromol x kg(-1) x min(-1) or 1 micromol x kg(-1) plus 0.1 micromol x kg(-1) x min(-1)) decreased the incidence of ventricular tachycardia (86% and 75%), ventricular fibrillation (28%, P <0.01 and 12%, P <0.001) and premature ventricular beats (164 +/- 27.0 and 114 +/- 28.5, P <0.05) following coronary artery ligation, resulting in a decrease in mortality (29% and 12%, P <0.05). Changes in cyclic nucleotide concentrations have been implicated in the genesis of ischemia-induced arrhythmias. However, in the present study GI104313 did not change the concentrations of adenosine 3':5'-cyclic monophosphate (cyclic AMP) (1.0 +/- 0.07 pmol x mg(-1), 1.0 +/- 0.05 pmol x mg(-1)) or guanosine 3':5'-cyclic monophosphate (cyclic GMP) (0.025 +/- 0.008 pmol x mg(-1) protein, 0.017 +/- 0.004 pmol x mg(-1) protein) in the left ventricle during ischemia-induced arrhythmias in anesthetized rats compared to saline (0.9 +/- 0.1 pmol x mg(-1) and 0.013 +/- 0.002 pmol x m(-1), respectively). Our results demonstrate that, in rats, GI104313 induced a decrease in both incidence of arrhythmias and mortality which was not associated with changes in ventricular cyclic nucleotide content.

Carbon dioxide and the cerebral circulation.

Carbon dioxide and the cerebral circulation.

Functional Expression of the Heteromeric “Olfactory” Cyclic Nucleotide-Gated Channel in the Hippocampus: A Potential Effector of Synaptic Plasticity in Brain Neurons

Cyclic nucleotide-gated (cng) channels are important components of signaling systems mediating sensory transduction. In vertebrate photoreceptors, light activates a signaling cascade that causes a decrease in intracellular cGMP concentrations, closing retinal cng channels. Signal transduction in olfactory receptor neurons is believed to proceed via G-protein-mediated elevation of intracellular cAMP in response to odorant binding by 7-helix receptors. cAMP opens the olfactory cng channel, which is highly permeable to Ca2+. Here we demonstrate by in situ hybridization and immunohistochemistry with subunit-specific antibodies that both subunits of the heteromeric rat olfactory cng channel are also widely expressed in the brain. Expression of the retinal rod cng channel, however, can be detected only in the eye. In the adult hippocampus, the olfactory cng channel is expressed on cell bodies and processes of CA1 and CA3 neurons. In cultured embryonic hippocampal neurons, the channel is localized to a subset of growth cones and processes. We recorded conductances with the electrophysiological characteristics of the heteromeric olfactory cng channel in excised inside-out patches from these cultured neurons. We also show that Ca2+ influx into hippocampal neurons in response to cyclic nucleotide elevation can be detected using fura-2 imaging. Cyclic nucleotide elevation has been implicated in several mechanisms of synaptic plasticity in the hippocampus, and these mechanisms also require elevation of intracellular Ca2+. Our results suggest that the "olfactory" cng channel could regulate synaptic efficacy in brain neurons by modulating Ca2+ levels in response to changes in cyclic nucleotide concentrations.

Localization of nitric oxide synthase and haemoxygenase, and functional effects of nitric oxide and carbon monoxide in the pig and human intravesical ureter

The distribution of nitric oxide synthase (NOS)-immunoreactive (IR) and haemoxygenase (HO)-IR nerves was investigated in the pig and human intravesical ureter (IVU). NOS activity was measured by monitoring the conversion of [3H]-arginine to [3H]-citrulline. Effects of NO and resulting changes in cyclic nucleotide concentrations were assessed in vitro. The effects of carbon monoxide (CO) on IVU motility was also tested. Immunohistochemistry revealed an abundant overall innervation of the IVU and numerous NOS-IR nerves. Nerve trunks were also found expressing immunoreactivity for HO-1, one of the enzymes synthetising CO. Similar profiles of nerve structures expressing immunoreactivities for NOS and tyrosine-hydroxylase (TH), as well as NOS and vasoactive intestinal peptide (VIP) were demonstrated. In the pig IVU, measurement of NOS activity revealed a moderate calcium-dependent catalytic activity. NO and the NO-donor SIN-1 reduced in a concentration-dependent manner serotonin-induced contractions of pig and human IVU, and the spontaneous contractions of pig IVU. In pig IVU strips precontracted with the thromboxane analogue U-46619, tetrodotoxin-sensitive relaxations were abolished by the NOS inhibitor NG-nitro-L-arginine. CO exerted no significant effect on spontaneous or induced contractions in the pig and human IVU. In precontracted strips of the pig and human IVU exposed to SIN-1 or No, significant increases of cyclic GMP levels were measured in comparison to control preparations. The results suggest that the L-arginine/NO/cyclic GMP pathway may play a role in the regulation of the valve function in the uretero-vesical junction (UVJ). A role for CO in the UVJ has yet to be established. Neurourol. Urodynam. 16:209–227, 1997. © 1997 Wiley-Liss, Inc.

Localization of nitric oxide synthase and haemoxygenase, and functional effects of nitric oxide and carbon monoxide in the pig and human intravesical ureter.

The distribution of nitric oxide synthase (NOS)-immunoreactive (IR) and haemoxygenase (HO)-IR nerves was investigated in the pig and human intravesical ureter (IVU). NOS activity was measured by monitoring the conversion of [3H]-arginine to [3H]-citrulline. Effects of NO and resulting changes in cyclic nucleotide concentrations were assessed in vitro. The effects of carbon monoxide (CO) on IVU motility was also tested. Immunohistochemistry revealed an abundant overall innervation of the IVU and numerous NOS-IR nerves. Nerve trunks were also found expressing immunoreactivity for HO-1, one of the enzymes synthetising CO. Similar profiles of nerve structures expressing immunoreactivities for NOS and tyrosine-hydroxylase (TH), as well as NOS and vasoactive intestinal peptide (VIP) were demonstrated. In the pig IVU, measurement of NOS activity revealed a moderate calcium-dependent catalytic activity, NO and the NO-donor SIN-1 reduced in a concentration-dependent manner serotonin-induced contractions of pig and human IVU, and the spontaneous contractions of pig IVU. In pig IVU strips precontracted with the thromboxane analogue U-46619, tetrodotoxin-sensitive relaxations were abolished by the NOS inhibitor NG-nitro-L-arginine. CO exerted no significant effect on spontaneous or induced contractions in the pig and human IVU. In precontracted strips of the pig and human IVU exposed to SIN-1 or NO, significant increases of cyclic GMP levels were measured in comparison to control preparations. The results suggest that the L-arginine/NO/cyclic GMP pathway may play a role in the regulation of the valve function in the uretero-vesical junction (UVJ). A role for CO in the UVJ has yet to be established.

The effects of aluminum on agonist-induced alterations in cyclic AMP and cyclic GMP concentrations in rat brain regions in vivo

Aluminum administered intracerebroventricularly (icv) (1 μmol) caused a significant decrease in cyclic GMP in the cortex after 3 days and a significant increase in cyclic AMP in the cortex after 14 days. Pilocarpine administration to untreated rats elevated cyclic AMP and cyclic GMP levels in specific brain regions. These pilocarpine-induced increases in the cyclic nucleotide concentrations were significantly attenuated in rats that had been treated with aluminum 14 days previously. Isoproterenol administration to control rats did not alter cyclic AMP concentrations; however, cyclic AMP concentrations were significantly reduced in the cortex of aluminum-treated animals after isoproterenol administration. Apomorphine elevated cyclic GMP concentrations in the cerebellum, hippocampus, and striatum of naive rats. This apomorphine-induced elevation in cyclic GMP concentrations was significantly potentiated in aluminum-treated rats.These results indicate that: (1) cyclic AMP synthesis in the cortex is most sensitive to aluminum; (2) agonist-stimulated changes in cyclic nucleotide concentrations can be altered by pretreatment with aluminum; (3) effects of aluminum persist for at least 2 weeks after central administration; and (4) modulation of the metabolism of cyclic nucleotides may play a role in the neurotoxic effects of aluminum.

Cholinergic modulation of the synaptic transmission in the frog spinal cord

It was found during experiments on isolated frog spinal cord involving extracellular recording from the dorsal roots (sucrose bridging) and intracellular recording from motoneurons by microelectrodes that 10 mM of the M-cholinomimetic arecoline produces motoneuronal depolarization which is matched by depolarizing electronic ventral root potentials and a rise in motoneuronal input resistance. Arecoline changes synaptic transmission by increasing the amplitude of postsynaptic potentials during intracellular recording and that of motoneuronal reflex discharges in the ventral roots but reduces the duration of dorsal root potentials. In the presence of arecoline, L-glutamate-induced motoneuronal response increases. Facilitation of synaptic transmission produced by arecoline in the spinal cord is bound up with cholinergic M2- activation, since it is suppressed by atropine but not by low concentrations of pirenzipine; it is also coupled with a reduction in adenylcyclase activity. When motoneuronal postsynaptic response has been suppressed, as in the case of surplus calcium or theophylline, arecoline produces an inhibitory effect on the amplitude of motoneuronal monosynaptic reflex discharges which is suppressed by pirenzipine at a concentration of 1×10−7 M. This would indicate the presence at the primary afferent terminals of presynaptic cholinergic M1 receptors which mediate its inhibition of impulses of transmitter release. This effect is independent of changes in cyclic nucleotide concentration.

Biochemistry and Regulation of Signal Transduction by Neuronal Acetylcholine Receptors

This chapter focuses on the muscarinic acetylcholine receptors of neurons, which is an important receptor system of the central nervous system (CNS). The chapter discusses cellular responses mediated by muscarinic receptors, muscarinic receptor regulation, and the assembly of the muscarinic system. Specific blockade of CNS muscarinic receptors can lead to dreamless sleep, profound disorientation, hallucinations, and amnesia. Recent work has emphasized the relationship of muscarinic activity to memory processes and to states of arousal. After binding acetylcholine, muscarinic receptor systems mediate a variety of cellular responses, including changes in cyclic nucleotide concentrations, altered phospholipid turnover, and various cell-specific changes in membrane potential. Muscarinic receptors accelerate the turnover of phosphatidylinositol (PI) through stimulation of phospholipase C activity. Accelerated turnover typically has been measured by uptake of 32P into PI, an assay facilitated by the rapid isolation of PI. In homogeneous populations of cloned cells, muscarinic stimulation gives both a PI response and adenylate cyclase inhibition, consistent with the idea that a single class of muscarinic receptors mediates multiple responses.

Cyclic Nucleotide Immunohistochemistry

It has been reported that cyclic nucleotide immunohistochemistry fails to localize all pools of cyclic nucleotides and to detect the changes in cyclic nucleotide concentration when applied to unfixed brain tissue sections. Losses of cyclic nucleotides during antibody incubations have been demonstrated, but it has not been determined whether such losses are due entirely to extraction or if phosphodiesterase activity contributes to the loss. We also found that cyclic nucleotides are extracted during the incubations required by the procedure but report that the phosphodiesterase inhibitor 3-isobutyl-1-methylxanthine (IBMX) reduces cyclic nucleotide losses.The application of the unlabelled antibody-enzyme technique and the inclusion of IBMX in incubation solutions permitted the detection of cyclic GMP in all layers of rat cerebellar cortex. The administration of ethanol (4g/kg, per os) ubiquitously reduced cyclic GMP staining.

The effect of first-dose doxorubicin on the cyclic nucleotide levels of the human myocardium

This study investigated changes in cyclic nucleotide concentration in human myocardium during the first 24 hr after the initial injection of doxorubicin. Ten patients with a normal cardiac status and no previous radiation or chemotherapy received 44.5 ± 3.5 mg/m 2 ( X ± SEM ) of doxorubicin. Cyclic nucleotide analysis of endomyocardial biopsy tissue removed at baseline and 4 and 24 hr after injection of doxorubicin demonstrated no change of cyclic AMP, but did show a fall of cyclic GMP at both 4 ( p < 0.01) and 24 hr ( p < 0.02) and a consequent rise of the cyclic AMP: cyclic GMP ratio. These changes in cyclic GMP levels in the myocardium of patients receiving doxorubicin may reflect injury induced by free radicals.

Effects of isolated heat-stable enterotoxin produced by Escherichia coli on fluid secretion and cyclic nucleotide levels in the jejunum of the weanling pig

Fluid secretory responses and associated changes in cyclic nucleotide concentration caused by the heat-stable enterotoxin of Escherichia coli (ST) have been investigated in the jejunum of weanling pigs. Effects associated with ST treatment have been compared with the actions of cholera toxin (CT) in the same experimental model. Positive correlations were obtained for the log of the ST dose correlating with net fluid secretion and with mucosal cyclic GMP (cGMP) concentration. Net fluid secretion rates could be predicted by mucosal cGMP concentration except for a brief interval when secretion was returning to control levels following ST removal from loops. Secretion rates in this post-ST period correlated more closely with the ratio of cGMP to cAMP concentration than with cGMP levels alone. Attempts to decrease the cGMP concentration and the secretory rate by combining CT and ST treatment were not successful. We conclude that the previously observed lack of cAMP response to CT in the pig may not be due to major differences in secretory control in that species. The pig is similar to other animal models where changes in mucosal cGMP concentration are associated with net jejunal fluid secretion induced by ST.

Cyclic nucleotide metabolism during lymphocyte transformation: I. Enzymatic mechanisms in changes in cAMP and cGMP concentration in Balb/c mice

Balb/c mouse spleen lymphocytes incubated from 0 to 30 min with the mitogen, lipopolysaccharide (LPS), were examined for alterations in concentration of cGMP and cAMP using radioimmunoassay. An optimal concentration of LPS, 10 μg/10 6 cells/ml, caused an increase in the cGMP concentration which reached a maximum of 53% above control values 10 min after the addition of LPS. cAMP concentration also increased, showing two peaks, the first after 5 min to 32% above control values and the second after 30 min to 52% above control values. Although these changes in cyclic nucleotide concentration are small in comparison with other studies, they demonstrate that consistent and statistically significant data are obtained following transformation by a mitogen at its optimal concentration rather than at a concentration that causes maximum cyclic nucleotide changes. Enzymatic mechanisms were also investigated in order to explain the changes in cyclic nucleotide concentration during Balb/c mouse splenocyte transformation that were reported earlier. In cells incubated with LPS, the specific activity of adenylate cyclase increased more than twofold within 10 min, while there was no change in guanylate cyclase activity. Furthermore, cyclic nucleotide phosphodiesterase activity for both cAMP and cGMP increased by more than 20% over control values. These results explain the observed increase in cAMP, but not cGMP. It was demonstrated that cAMP was capable of inhibiting cGMP degradation by cyclic nucleotide phosphodiesterase by as much as 70%. The same is true for the effect of cGMP on cAMP degradation. LPS tended to inhibit the latter with no effect on the former. The relative affect was shown to be dependent on the cGMP/cAMP ratio. Therefore, it is proposed that the elevation in cGMP concentration observed early in lymphocyte activation occurs as a consequence of the inhibition by each cyclic nucleotide on the hydrolysis of the other.

Role of cyclic GMP in the action of heat-stable enterotoxin of Escherichia coli

ENTEROTOXIGENIC strains of Escherichia coli elaborate two enterotoxins, a heat-labile toxin (LT) and a heat-stable toxin (ST), which cause diarrhoeal disease in humans1; ST-producing E. coli cause diarrhoea in adult volunteers2 and have been associated with epidemic diarrhoea in a nursery for the newborn3 and with sporadic adult diarrhoea among North American tourists to Latin America4 and the Navajo people in Arizona5. LT-producing strains are identified by the ability of culture filtrates to cause fluid accumulation in rabbit ileal loops at 18 h (ref. 6) or by morphological alteration of Chinese hamster ovary (CHO) cells7 or of Y-l adrenal cells8. ST-producing strains are identified by the ability of culture filtrates to cause earlier fluid accumulation in rabbit ileal loops (peak accumulation at 6 h (ref. 6), or by fluid accumulation in the gut of the suckling mouse at 3 h (refs 9, 10). LT acts in a manner similar to cholera toxin (CT) by activating adenylate cyclase11. The mechanism of action of ST is unknown, however. Culture filtrates of a strain of E. coli that produced both LT and ST caused immediate net fluid secretion in canine jejunal segments without the 1-h delay characteristic of the response to CT12,13. In addition, culture filtrates caused an immediate increase in canine jejunal adenylate cyclase activity as measured by enzymatic generation of P32-cyclic AMP from P32-labelled ATP13, also in contrast to the delay in appearance of increased adenylate cyclase activity following exposure to CT12. The possibility that the early effect of ST was mediated by changes in cyclic nucleotide concentrations was investigated; culture filtrates of ST-producing strains of E. coli caused increased cyclic GMP concentrations in rabbit intestinal tissue and the cyclic GMP analogue 8BrcGMP mimicked ST in magnitude and time course of intestinal fluid accumulation in both rabbits and suckling mice.

Gastric Cyclic Nucleotide Concentration in Health and Disease: Response to secretagogues and role of circulating gastrin and intragastric acid secretion

Cyclic AMP and cyclic GMP concentrations were measured in suction biopsy specimens of gastric fundic and antral mucosa and in gastric juice in response to maximum stimulation by histamine (0.015 mg per kg per hr), betazole (1.5 mg per kg), and pentagastrin (6 μg per kg) in 14 normogastrinemic healthy subjects, in 46 patients with dyspepsia or peptic ulcer (PU) disease and normal serum gastrin levels, and in 14 patients with hypergastrinemia, including 8 with pernicious anemia (PA), 3 with Zollinger-Ellison (ZE) disease, and 3 with gastric carcinoma. No regional differences were noted in unstimulated gastric antral or fundic cyclic nucleotide content in normal subjects or patients. During secretagogue stimulation no significant changes in cyclic nucleotide concentrations were observed in antral or fundic mucosa of healthy subjects or patients. During basal hourly secretion, cyclic nucleotide concentration and output in gastric juice was relatively constant, suggesting a steady state of secretion. After secretagogue stimulation, the concentrations of cyclic AMP and cyclic GMP were reduced by at least 50% and correlated with the increased parietal volume output, suggesting a dilutional effect. There was no significant change in gastric juice cyclic nucleotide output except in PU subjects after betazole stimulation, in whom cyclic AMP production increased almost 2-fold. This change in gastric juice cyclic AMP appeared proportional to a greater parietal volume flow and did not reflect intracellular mucosal events. Similarly, a decreased concentration of cyclic AMP in the basal and stimulated gastric juice of ZE patients and a reduced cyclic AMP output in PA patients also appeared proportional to volume flow. The presence of cyclic AMP in unstimulated gastric juice in PA suggested, in part, a nonparietal origin for cyclic AMP, probably derived from interstitial fluid secretion or transmucosal exudation from plasma. It is concluded that intra- or extracellular gastric cyclic AMP or cyclic GMP concentrations are not modulated by secretagogue stimulation, circulating high gastrin levels, alteration in intraluminal pH, or increasing age. These studies fail to implicate cyclic nucleotides as intracellular mediators of stimulated gastric acid secretion in healthy subjects, PU disease PA, ZE disease or gastric carcinoma.