GLP-1 receptor agonists for the treatment of obesity: Role as a promising approach.

Obesity is a complex disease characterized by excessive fat accumulation which is caused by genetic, environmental and other factors. In recent years, there has been an increase in the morbidity, disability rate,and mortality due to obesity, making it great threat to people's health and lives, and increasing public health care expenses. Evidence from previous studies show that weight loss can significantly reduce the risk of obesity-related complications and chronic diseases. Diet control, moderate exercise, behavior modification programs, bariatric surgery and prescription drug treatment are the major interventions used to help people lose weight. Among them, anti-obesity drugs have high compliance rates and cause noticeable short-term effects in reducing obese levels. However, given the safety or effectiveness concerns of anti-obesity drugs, many of the currently used drugs have limited clinical use. Glucagon-like peptide-1 receptor (GLP-1R) agonists are a group of drugs that targets incretin hormone action, and its receptors are widely distributed in nerves, islets, heart, lung, skin, and other organs. Several animal experiments and clinical trials have demonstrated that GLP-1R agonists are more effective in treating or preventing obesity. Therefore, GLP-1R agonists are promising agents for the treatment of obese individuals. This review describes evidence from previous research on the effects of GLP-1R agonists on obesity. We anticipate that this review will generate data that will help biomedical researchers or clinical workers develop obesity treatments based on GLP-1R agonists.

Hydroxyurea ameliorates atherosclerosis in ApoE-/- mice by potentially modulating Niemann-Pick C1-like 1 protein through the gut microbiota.

Rationale: The efficacy and mechanism of hydroxyurea in the treatment of atherosclerosis have rarely been reported. The goal of this study was to investigate the efficacy of hydroxyurea in high-fat diet-fed ApoE-/- mice against atherosclerosis and examine the possible mechanism underlying treatment outcomes. Methods: ApoE-/- mice were fed a high-fat diet for 1 month and then administered hydroxyurea by gavage continuously for 2 months. Aortic root hematoxylin-eosin (H&E) staining and oil red O staining were used to verify the efficacy of hydroxyurea; biochemical methods and ELISA were used to detect changes in relevant metabolites in serum. 16S rRNA was used to detect composition changes in the intestinal bacterial community of animals after treatment with hydroxyurea. Metabolomics methods were used to identify fecal metabolites and their changes. Immunohistochemical staining and ELISA were used for the localization and quantification of intestinal NPC1L1. Results: We showed that aortic root HE staining and oil red O staining determined the therapeutic efficacy of hydroxyurea in the treatment of atherosclerosis in high-fat diet-fed ApoE-/- mice. Serological tests verified the ability of hydroxyurea to lower total serum cholesterol and LDL cholesterol. The gut microbiota was significantly altered after HU treatment and was significantly different from that after antiplatelet and statin therapy. Meanwhile, a metabolomic study revealed that metabolites, including stearic acid, palmitic acid and cholesterol, were significantly enriched in mouse feces. Further histological and ELISAs verified that the protein responsible for intestinal absorption of cholesterol in mice, NPC1L1, was significantly reduced after hydroxyurea treatment. Conclusions: In high-fat diet-fed ApoE-/- mice, hydroxyurea effectively treated atherosclerosis, lowered serum cholesterol, modulated the gut microbiota at multiple levels and affected cholesterol absorption by reducing NPC1L1 in small intestinal epithelial cells.

Rationale and methods of the Antioxidant and NMDA receptor blocker Weans Anoxic brain damage of KorEa OHCA patients (AWAKE) trial.

BACKGROUND: Ischemic brain injury is a major hurdle that limits the survival of resuscitated out-of-hospital cardiac arrest (OHCA). METHODS: The aim of this study is to assess the feasibility and potential for reduction of ischemic brain injury in adult OHCA patients treated with high- or low-dose Neu2000K, a selective blocker of N-methyl-D-aspartate (NMDA) type 2B receptor and also a free radical scavenger, or given placebo. This study is a phase II, multicenter, randomized, double-blinded, prospective, intention-to-treat, placebo-controlled, three-armed, safety and efficacy clinical trial. This trial is a sponsor-initiated trial supported by GNT Pharma. Successfully resuscitated OHCA patients aged 19 to 80 years would be included. The primary outcome is blood neuron-specific enolase (NSE) level on the 3rd day. The secondary outcomes are safety, efficacy defined by study drug administration within 4 h in > 90% of participants, daily NSE up to 5th day, blood S100beta, brain MRI apparent diffusion coefficient imaging, cerebral performance category (CPC), and Modified Rankin Scale (mRS) at 5th, 14th, and 90th days. Assuming NSE of 42 ± 80 and 80 ± 80 µg/L in the treatment (high- and low-dose Neu2000K) and control arms with 80% power, a type 1 error rate of 5%, and a 28% of withdrawal prior to the endpoint, the required sample size is 150 patients. DISCUSSION: The AWAKE trial explores a new multi-target neuroprotectant for the treatment of resuscitated OHCA patients. TRIAL REGISTRATION: ClinicalTrials.gov NCT03651557 . Registered on August 29, 2018.

Isoflurane produces antidepressant effects inducing BDNF-TrkB signaling in CUMS mice.

RATIONALE: The volatile anesthetic isoflurane is suggested to produce a rapid and robust antidepressive effect in preliminary clinical trials. Recently, isoflurane was found to activate the tropomyosin receptor kinase B (TrkB) signaling which is the underlying mechanism of the rapid antidepressant ketamine. OBJECTIVE: Our study investigated the effect of isoflurane anesthesia on chronic unpredictable mild stressed (CUMS) model in mice and verified the role of brain-derived neurotrophic factor (BDNF)/TrkB/ the mammalian target of rapamycin (mTOR) signaling in the antidepressant effect of isoflurane. METHODS: We employed the CUMS model of depression to assess the rapid antidepressant effect of isoflurane by the forced swimming test (FST), the sucrose preference test (SPT), and the novelty suppressed feeding test (NSFT). The protein expression of BDNF and TrkB/protein kinase B (PKB or Akt)/mTOR was determined through Western blot. The dendritic spine density in the hippocampus and medial prefrontal cortex (PFC) was measured by the Golgi staining. RESULTS: A brief burst-suppressing isoflurane anesthesia rapidly reversed the behavioral deficits caused by CUMS procedure, normalized the expression of BDNF and further activated the TrkB signaling pathway in CUMS-induced stressed mice in both prefrontal cortex (PFC) and hippocampus (HC). All of those behavioral and proteomic effects were blocked by K252a, a selective receptor inhibitor of TrkB. Isoflurane significantly promoted the formation of dendritic spines in both medial prefrontal cortex (mPFC), CA1, CA3, and DG of the hippocampus. CONCLUSION: Our study indicates that isoflurane exerts a rapid antidepressant-like effect in CUMS depression animal model, and the activation of BDNF/TrkB signaling pathway plays an indispensable role in the biological and behavioral antidepressant effects of isoflurane. A single exposure to isoflurane could repair synaptic damage caused by chronic stimulation.

Full dose, half dose, or discontinuation of etanercept biosimilar in early axial spondyloarthritis patients: a real-world study in China.

INTRODUCTION: To investigate the effect of dose maintenance, reduction, or discontinuation of the etanercept biosimilar Yisaipu (YSP) on early axial spondyloarthritis (axSpA) patients in remission with YSP 50 mg once weekly (QW). MATERIAL AND METHODS: Patients were enrolled in three groups: full dose (YSP50), half dose (YSP25), and discontinuation (YSP0). Patients were assessed by the same rheumatologist every 8 weeks for 48 weeks. The primary endpoint was the proportion of non-failure patients in each group. If a flare occurred during the study period, the patient resumed YSP 50 mg QW or was switched to another tumor necrosis factor inhibitor. RESULTS: A total of 144 patients were included and each group included 48 patients. The proportion of non-failure patients was significantly greater in the YSP50 group than in the YSP0 group at 48 weeks (91.7% vs. 72.9%, p = 0.032). The difference in the other two comparisons was not statistically significant (YSP50 vs. YSP25 group, p = 0.522; YSP25 vs. YSP0 group, p = 0.132). The median time to flare did not differ significantly between the three groups (p > 0.05). Most patients who flared regained remission rapidly after resuming YSP 50 mg QW or starting adalimumab 40 mg every other week. CONCLUSIONS: For patients with early axSpA in remission on YSP for more than 12 weeks, continuation of YSP at full dose was superior to discontinuation of YSP, but not superior to halving the dose.

Low molecular mass chondroitin sulfate suppresses chronic unpredictable mild stress-induced depression-like behavior in mice.

The present study is aimed at testing the antidepressant--like effects and probable mechanisms of action of low molecular mass chondroitin sulfate (LMMCS) on depression induced by chronic unpredictable mild stress (CUMS) in mice. Four weeks of CUMS exposure resulted in depressive-like behavior, expressed by a significant decrease in the locomotor activity and sucrose consumption and increased immobility time in the forced swim test. Further, there was a significant reduction of 5-HT level in the hippocampus region of depressed mice. Treatment of mice for four weeks with LMMCS ameliorated significantly both the behavioral and biochemical changes induced by CUMS. These novel results suggest that LMMCS produces an antidepressant-like effect in mice subjected to CUMS, which might be related, at least in part, to the increase of 5-HT concentration in the hippocampus.

Effect of up-regulation of Shh-Gli1 signaling pathway on radioresistance and cell cycle in human esophageal cancer cell line Eca109 / 中国病理生理杂志

AIM:To investigate the relationship between Sonic Hedgehog(Shh)signaling pathway and cell cycle and radioresistance of esophageal cancer by up-regulating Gli1,a key factor in Shh signaling pathway.METHODS:The human esophageal cancer cell line Eca 109 was transfected with plasmid to induce Gli 1 over-expression,which served as Eca109-ox-Gli1 group.In addition, Eca109 cells transfected with empty plasmid served as negative control group and the untreated Eca109 cells were used as normal control group.The expression of Gli1 was confirmed by real-time PCR and Western blot.The radiosensitivity of the cells in the 3 groups was determined by colony formation assay.The effect of irra-diation on the cell cycle was analyzed by flow cytometry.RESULTS:The expression of Gli1 in Eca109-ox-Gli1 group was higher than that in the other 2 groups(P<0.05).The survival fraction at dose of 2 Gy in Eca109-ox-Gli1 group was high-er than that in normal control group, indicating that the radioresistance of the Eca 109 cells transfected with Gli1 plasmid was increased.The cells in Eca109-ox-Gli1 group showed higher S phase proportion than that in normal control group and negative control group(P<0.01).After irradiation at dose of 6 Gy,all cells in the 3 groups found that the cell cycle was arrested at G2/M phase,while the cells in normal control group showed higher G 2/M phase proportion than that in Eca109-ox-Gli1 group(P<0.01).CONCLUSION: The up-regulation of Gli1 may enhance the radioresistance of esophageal cancer by regulating the cell cycle.

A convenient method for the enantiomeric separation of α-amino acid esters as benzophenone imine Schiff base derivatives.

A convenient liquid chromatographic method for the separation of α-amino acid esters as benzophenone Schiff base derivatives on coated chiral stationary phases (CSPs) (Chiralcel OD-H, Chiralcel OD, Chiralpak AD-H, Chiralpak AD, and Chiralpak AS) or covalently immobilized CSPs (Chiralpak IA, Chiralpak IB, and Chiralpak IC) derived from polysaccharide derivatives is described. Benzophenone imine derivatives of α-amino acid esters were readily prepared by stirring benzophenone imine and the hydrochloride salts of α-amino acid esters in 2-propanol. The chromatographic separations were conducted at a flow rate 1.0 mL/min and a detection wavelength of 254 nm; 0.5% 2-propanol/hexane (v/v) was used on CSPs. In general, the resolution of Chiralpak IC was superior to those of the other CSPs. In addition, the resolutions of other arylimine derivatives of α-amino acid esters and the effects of different mobile phases on the enantiomeric separation of α-amino acid esters as benzophenone imine derivatives on Chiralpak IC were investigated.

[Epidemiological investigation of back pain and spondyloarthritis in Shougang resident communities].

OBJECTIVE: To investigate the epidemiological features of back pain, spondyloarthritis (SpA) and ankylosing spondylitis (AS) in Beijing Shougang district. METHODS: Set up Chinese version of questionnaire about incidence of spondyloarthropathy. Employees and retired ones were drawn out from sub-factory units by non-randomized sampling.15 357 subjects were investigated, of which 12 125 questionnaires were taken. Suspected cases were then screened with sacroiliac joint X ray and HLA-B(27) testing. 2009 assessment in ankylosing spondylitis (ASAS) criteria were used for diagnosing SpA. RESULTS: Back pain is common with total incidence of 42.7%, and the most common pattern is mechanical pain. The incidence of SpA is 0.58% and that of AS is 0.36%, while only 28.9% AS patients had been diagnosed before and received treatment. CONCLUSION: The AS incidence in Shougang district is similar with the epidemiological data got from other districts of China. And knowledge of SpA and AS is needed in China.

Beta1-adrenergic receptor activation decreases ANP release via cAMP-Ca2+ signaling in perfused beating rabbit atria.

AIMS: Although a beta-adrenoceptor (beta-AR) blockade-induced increase in plasma atrial natriuretic peptide (ANP) levels is implicated in the therapeutic significance of beta-AR antagonists, the role of beta-AR in the regulation of ANP release is not clearly defined. The purpose of the present study was to define the role of beta-AR subtypes and the mechanisms responsible for regulation of atrial ANP release. MAIN METHODS: Experiments were performed in isolated perfused beating rabbit atria, including measurement of atrial contractile response, cAMP efflux, and atrial myocyte ANP release. KEY FINDINGS: beta-AR activation with (-)-isoproterenol decreased ANP release concomitantly with increases in cAMP efflux concentration, atrial dynamics, stroke volume and pulse pressure in a concentration-dependent manner. The ANP response was inversely related to the change in cAMP efflux concentrations. The isoproterenol-induced decrease in ANP release was inhibited by beta(1)-AR blockade with CGP 20712A but not by beta(2)-AR blockade with ICI 118551. The isoproterenol-induced decrease in ANP release was attenuated by the L-type Ca(2+) channel antagonist nifedipine and the cAMP-dependent protein kinase inhibitor KT5720. SIGNIFICANCE: These findings suggest that beta(1)-AR activation decreases ANP release via cAMP- and Ca(2+)-dependent mechanisms.

[The clinical characters of 30 patients with enteropathic arthritis and literature review].

OBJECTIVE: To better understand the clinical characters of enteropathic arthritis patients. METHODS: The clinical, laboratory and X-rays data of 30 enteropathic arthritis in-patients were analyzed. RESULTS: Among the 30 patients, 14 were male, 16 were female. Average age at onset of gastroenteric manifestations was 16 - 48 (32.2 +/- 11.0) years old. The course of disease was 1 month - 20 (5.9 +/- 3.4) years. Average age at onset of arthritis was 15 - 52 (43.4 +/- 6.8) years old. The average interval between onset of diarrhea and arthritis was 0 - 13 (4.2 +/- 4.0) years. Peripheral arthritis was founded in 26 (87%) patients, and only 4 felt low back pain at onset. During the disease course, peripheral arthritis in 14 (54%) patients was similar to rheumatoid arthritis. The history of low back pain or buttock pain was recorded in 22 (73%) patients. Extra-articular features including fever occurred in 24 patients, enthesitis in 6, iritis or conjunctivitis in 4, dactylitis in 1 were observed. HLA-B(27) was positive in 36% (9/25) patients. Sacroiliitis in X-ray or CT was observed in 59% patients. CONCLUSION: The clinical manifestations of enteropathic arthritis are characterized by pauciarticular arthritis or symmetric polyarthritis or(and) sacroiliitis, a wide spectrum of extra-articular features, presence of HLA-B(27) and familial history of spondyloarthropathies. As other spondyloarthropathies, the sacroiliitis in enteropathic arthritis was also associated with HLA-B(27).

Increase of atrial ANP release by 2,3-butanedione monoxime in beating rabbit atria.

2,3-Butanedione monoxime (BDM) is a chemical phosphatase and has been known to dissociate mechanical contraction in the excitation-contraction coupling via inhibition of myofibrillar ATPase. BDM has also been found to decrease sarcolemmal L-type Ca(2+) channel activity and intracellular Ca(2+) in cardiac myocytes. It has been shown that Ca(2+) entry via L-type Ca(2+) channels decreased atrial myocyte atrial natriuretic peptide (ANP) release. The purpose of the present study was to address the effects of BDM in the regulation of ANP release. Experiments were performed in perfused beating rabbit atria. BDM accentuated atrial myocyte ANP release concomitantly with a decrease in atrial stroke volume and pulse pressure in a concentration-dependent manner. The BDM-induced activation of ANP release was attenuated by the treatment with nifedipine, an inhibitor of L-type Ca(2+) channels. BDM further decreased atrial stroke volume and pulse pressure in the presence of nifedipine. Blockade of function of the sarcoplasmic reticulum with thapsigargin plus ryanodine slightly but not significantly attenuated the BDM-induced activation of ANP release. These data show that BDM is a potent stimulator for the ANP release and also suggest that the mechanism by which BDM activates atrial myocyte ANP release is related to inhibition of the L-type Ca(2+) channel activity. The present finding also suggests that the effects of ANP released may be considered in an occasion of uncoupling by BDM of the excitation-contraction coupling of cardiomyocytes.

Cardiac mast cells regulate myocyte ANP release via histamine H2 receptor in beating rabbit atria.

It has been shown that histamine inhibits atrial natriuretic peptide (ANP) release. Because cardiac mast cells are the principal source of histamine in the heart, we hypothesized that cardiac mast cells are involved in the regulation of atrial ANP release. To test the hypothesis, experiments were performed in perfused beating rabbit atria allowing atrial pacing and measurements of changes in atrial stroke volume, intraatrial pulse pressure and myocyte ANP release. Mast cell degranulation with Compound 48/80 decreased atrial myocyte ANP release, and the response was blocked by a selective histamine H(2) receptor blocker, cimetidine, indicating that histamine was responsible for the decrease in ANP release. Mast cell stabilization with cromolyn blocked the Compound 48/80-induced decrease in ANP release. These data suggest that mast cell-derived histamine is involved in the regulation of cardiac ANP release. Thus, the cardiac mast cell-cardiomyocyte communication via the histamine-ANP pathway may implicate in the cardiac disorder associated with mast cell degranulation such as in acute coronary syndrome or cardiac hypertrophy.

Comparative studies between covalently immobilized and coated chiral stationary phases based on polysaccharide derivatives for enantiomer separation of N-protected alpha-amino acids and their ester derivatives.

Liquid chromatographic enantiomer separation of several N-benzyloxycarbonyl (CBZ) and N-tert-butoxycarbonyl (BOC) alpha-amino acids and their corresponding ethyl esters was performed on covalently immobilized chiral stationary phases (CSPs) (Chiralpak IA and Chiralpak IB) and coated-type CSPs (Chiralpak AD and Chiralcel OD) based on polysaccharide derivatives. The solvent versatility of the covalently immobilized CSPs in enantiomer separation of N-CBZ and BOC-alpha-amino acids and their ester derivatives was shown and the chromatographic parameters of their enantioselectivities and resolution factors were greatly influenced by the nature of the mobile phase. In general, standard mobile phases using 2-propanol and hexane on Chiralpak IA showed fairly good enantioselectivities for resolution of N-CBZ and BOC-alpha-amino acids and their esters. However, 50% MTBE/hexane (v/v) for resolution of N-CBZ-alpha-amino acids ethyl esters and 20% THF/hexane (v/v) for resolution of N-BOC-alpha-amino acids ethyl esters afforded the greatest enantioselectivities on Chiralpak IA. Also, liquid chromatographic comparisons of the enantiomer resolution of these analytes were made on amylose tris(3,5-dimethylphenylcarbamate)-derived CSPs (Chiralpak IA and Chiralpak AD) and cellulose tris(3,5-dimethylphenylcarbamate)-derived CSPs (Chiralpak IB and Chiralcel OD). Chiralpak AD and/or Chiralcel OD showed the highest enantioselectivities for resolution of N-CBZ-alpha-amino acids and esters, while Chiralpak AD or Chiralpak IA showed the highest resolution of N-BOC-alpha-amino acids and esters.

Comparison of several polysaccharide-derived chiral stationary phases for the enantiomer separation of N-fluorenylmethoxycarbonyl alpha-amino acids by HPLC.

The liquid chromatographic enantiomer separation of N-fluorenylmethoxycarbonyl (FMOC) protected alpha-amino acids was performed on nine polysaccharide-derived chiral stationary phases (CSPs). The cellulose derived coated CSPs, Chiralcel OD-H (separation factor = 1.09-2.70) and Chiralcel OD (separation factor = 1.08-2.55), had the best performance of all the CSPs for resolution of N-FMOC alpha-amino acids and therefore, all analyte enantiomers were base-line separated on Chiralcel OD-H and/or Chiralcel OD. Enantioseparation on cellulose tris(3,5-dimethylphenylcarbamate) derived CSPs (Chiralcel OD-H, Chiralcel OD and Chiralpak IB) is generally greater than that on amylose tris(3,5-dimethylphenylcarbamate) derived CSPs (Chiralpak AD-RH, Chiralpak AD and Chiralpak IA). Additionally, coated type CSPs (Chiralcel OD-H or Chiralcel OD, and Chiralpak AD) generally provided better enantioseparation for these analytes than the covalently bonded type CSPs (Chiralpak IB and Chiralpak IA) with the same chiral selector of cellulose tris(3,5-dimethylphenylcarbamate) and amylose tris(3,5-dimethylphenylcarbamate), respectively. However, Chiralpak IB and Chiralpak IA had an advantage over the coated type CSPs in that a broader range of solvents could be used due to its covalently bonded nature.

Liquid chromatographic enantiomer resolution of N-hydrazide derivatives of 2-aryloxypropionic acids on a crown ether derived chiral stationary phase.

The liquid chromatographic separation of the enantiomers of several N-hydrazide derivatives of 2-aryloxypropionic acids was performed on a crown ether type chiral stationary phase derived from (18-crown-6)-2,3,11,12-tetracarboxylic acid. The behavior of chromatographic parameters by the change of mobile phases and additives for the resolution of these analytes was investigated. The enantiomers of all analytes were base-line resolved with a mobile phase of 100% methanol containing 20 mM H2SO4. These results are the first reported for enantiomer resolution of chiral acids of 2-aryloxypropionic acids as their N-hydrazide derivatives.

Osmoregulation of atrial myocytic ANP release: osmotransduction via cross-talk between L-type Ca2+ channel and SR Ca2+ release.

Hyperosmolality has been known to increase ANP release. However, its physiological role in the regulation of atrial myocytic ANP release and the mechanism by which hyperosmolality increases ANP release are to be defined. The purpose of the present study was to define these questions. Experiments were performed in perfused beating rabbit atria. Hyperosmolality increased atrial ANP release, cAMP efflux, and atrial dynamics in a concentration-dependent manner. The osmolality threshold for the increase in ANP release was as low as 10 mosmol/kgH2O (approximately 3%) above the basal levels (1.55 +/- 1.71, 17.19 +/- 3.11, 23.15 +/- 5.49, 54.04 +/- 11.98, and 62.00 +/- 13.48% for 10, 20, 30, 60, and 100 mM mannitol, respectively; all P < 0.01). Blockade of sarcolemmal L-type Ca2+ channel activity, which increased ANP release, attenuated hyperosmolality-induced increases in ANP release (-13.58 +/- 4.68% vs. 62.00 +/- 13.48%, P < 0.001) and cAMP efflux but not atrial dynamics. Blockade of the Ca2+ release from the sarcoplasmic reticulum, which increased ANP release, attenuated hyperosmolality-induced increases in ANP release (13.44 +/- 7.47% vs. 62.00 +/- 13.48%, P < 0.01) and dynamics but not cAMP efflux. Blockades of Na+-K+-2Cl- cotransporter, Na+/H+ exchanger, and Na+/Ca2+ exchanger had no effect on hyperosmolality-induced increase in ANP release. The present study suggests that hyperosmolality regulates atrial myocytic ANP release and that the mechanism by which hyperosmolality activates ANP release is closely related to the cross-talk between the sarcolemmal L-type Ca2+ channel activity and sarcoplasmic reticulum Ca2+ release, possibly inactivation of the L-type Ca2+ channels.

High and low gain switches for regulation of cAMP efflux concentration: distinct roles for particulate GC- and soluble GC-cGMP-PDE3 signaling in rabbit atria.

This study tests the hypothesis that particulate (p) guanylyl cyclase (GC) and soluble (s) GC are involved in the distinct roles for the regulation of cGMP-PDE-cAMP signaling and of mechanical and secretory functions in the heart. Experiments were performed in perfused beating rabbit atria. C-type natriuretic peptide (CNP) and SIN-1, an NO donor, or BAY 41-2272 (BAY), a direct activator for sGC, were used to activate pGC and sGC, respectively. CNP and SIN-1 increased cGMP and cAMP efflux in a concentration-dependent manner. Increase in cAMP was a function of cGMP. The changes in cAMP efflux concentration in terms of cGMP were much more prominent in the atria treated with CNP than in the atria treated with SIN-1. Increase in cAMP efflux concentration was blocked by milrinone but not changed by EHNA. BAY increased cGMP but not cAMP in a concentration-dependent manner. CNP and SIN-1 decreased atrial stroke volume and myocytic ANP release. The decreases in terms of cGMP efflux concentration were much more prominent in the atria treated with CNP than in the atria treated with SIN-1 or BAY. Milrinone accentuated GC agonist-induced decreases in atrial stroke volume and ANP release. In the presence of ODQ, SIN-1 or BAY induced effects were not observed. These data suggest that pGC and sGC activations have distinct roles via cGMP-PDE3-cAMP signaling in the cardiac atrium: high and low gain switches, respectively, for the regulation of cAMP levels and contractile and secretory functions.

Histamine inhibits atrial myocytic ANP release via H2 receptor-cAMP-protein kinase signaling.

Changes in cyclic nucleotide production and atrial dynamics have been known to modulate atrial natriuretic peptide (ANP) release. Although cardiac atrium expresses histamine receptors and contains histamine, the role of histamine in the regulation of ANP release has to be defined. The purpose of the present study was to define the effect of histamine on the regulation of ANP release in perfused beating rabbit atria. Histamine decreased ANP release concomitantly with increases in cAMP efflux and atrial dynamics in a concentration-dependent manner. Histamine-induced decrease in ANP release was a function of an increase in cAMP production. Blockade of histamine H2 receptor with cimetidine but not of H1 receptor with triprolidine abolished the responses of histamine. Cell-permeable cAMP analog, 8-Br-cAMP, mimicked the effects of histamine, and the responses were dose-dependent and blocked by a protein kinase A (PKA)-selective inhibitor, KT5720. Nifedipine failed to modulate histamine-induced decrease in ANP release. Protein kinase nonselective inhibitor staurosporine blocked histamine-induced changes in a concentration-dependent manner. KT5720 and RP-adenosine 3',5'-cyclic monophosphorothioate, another PKA-selective inhibitor, attenuated histamine-induced changes. These results suggest that histamine decreases atrial ANP release by H2 receptor-cAMP signaling via PKA-dependent and -independent pathways.

Subtype-specific roles of cAMP phosphodiesterases in regulation of atrial natriuretic peptide release.

cAMP is known to control the release of atrial natriuretic peptide. To define the roles of cyclic nucleotide phosphodiesterase subtypes in the regulation of atrial natriuretic peptide (ANP) release, experiments were done with perfused beating rabbit atria. Phosphodiesterase 3 subtype-specific inhibitors, milrinone and cilostamide, inhibited myocytic ANP release with a concomitant increase in cAMP efflux. Similarly, trequinsin, another phosphodiesterase 3 inhibitor, decreased ANP release. A phosphodiesterase 4 subtype-specific inhibitor, rolipram, did not significantly change ANP release but increased AMP efflux. Also, 4-[(3-butoxy-4-methoxyphenyl)methyl]-2-imidazolidinone (Ro 20-1724), another phosphodiesterase 4 inhibitor, did not significantly change ANP release. The cAMP efflux was higher in the atrium treated with rolipram than in the atrium treated with milrinone or cilostamide. The data show that the cAMP pool, which is metabolized by phosphodiesterase 3, but not phosphodiesterase 4, is closely related to the basal regulation of atrial ANP release. The results suggest that intracellular cAMP is compartmentalized in the regulation of atrial ANP release, and that the release is controlled by a phosphodiesterase subtype-specific mechanism.