Chronotropic Responses to GLP-1 Receptor Agonists and Sitagliptin in Atria From Diabetic Rats.

ABSTRACT: Type 2 diabetes mellitus increases the risk of cardiovascular diseases. Therefore, elucidation of the cardiovascular effects of antidiabetics is crucial. Incretin-based therapies are increasingly used for type 2 diabetes mellitus treatment as monotherapy and in combination. We aimed to study the effects of glucagon-like peptide-1 receptor agonists (GLP-1 RAs) and sitagliptin on beating rates in isolated atria from diabetic rats. The chronotropic responses to GLP-1 RAs and sitagliptin as monotherapy and in combinations with metformin, pioglitazone, and glimepiride in isolated atria from control and diabetic rats were determined. GLP-1 (7-36), GLP-1 (9-36), and exendin-4 (1-39) produced increases in beating rates in both control and diabetic rat atria. However, sitagliptin increased the beating frequency only in the diabetic group. Exendin (9-39), nitro- l -arginine methyl ester hydrochloride, and indomethacin blocked responses to GLP-1 RAs but not the response to sitagliptin. Glibenclamide, 4-aminopyridine, apamin, charybdotoxin, superoxide dismutase, and catalase incubations did not change responses to GLP-1 RAs and sitagliptin. GLP-1 RAs increase beating rates in isolated rat atrium through GLP-1 receptor, nitric oxide, and cyclooxygenase pathways but not potassium channels and reactive oxygen radicals.

Effects of glucagon-like peptide-1 in diabetic rat small resistance arteries.

We investigated the functional effects of glucagon-like peptide-1 [GLP-1(7-36)] and GLP-1(9-36) and the mechanism(s) playing a role in the effects of these agents in isolated small resistance arteries from control and diabetic rats. Cumulative concentrations of GLP-1(7-36) and GLP-1(9-36) produced concentration-dependent relaxations in endothelium-intact but not endothelium-denuded arteries that were significantly decreased in diabetic rats. GLP-1 receptor antagonist exendin(9-39) significantly inhibited responses to GLP-1 analogs. Nitric oxide/cyclic guanosine monophosphate pathway blockers, but not indomethacin, significantly decreased responses to GLP-1(7-36) or GLP-1(9-36) in control and diabetic rats. 4-Aminopyridine or glibenclamide incubation did not alter relaxations to GLP-1 analogs. GLP-1(7-36)- and GLP-1(9-36)-induced relaxations were blunted significantly and to similar extends by charybdotoxin and apamin combination in control and diabetic rats. Catalase did not affect, whereas superoxide dismutase (SOD) caused a significant increase in relaxations to GLP-1 analogs only in diabetic rats. We provided evidence about the relaxant effects of GLP-1(7-36) and GLP-1(9-36) in resistance arteries that were reduced in diabetic rats. Both calcium-activated potassium channels and endothelium played a major role in relaxations. Increment in certain reactive oxygen species and/or reduction in superoxide dismutase function might play a role in reduced relaxant responses of resistance arteries to GLP-1(7-36) and GLP-1(9-36) in diabetic rats.

Can lipid mediators and free fatty acids guide acute coronary syndrome diagnosis and treatment?

OBJECTIVE: The aim of this study was to investigate fatty acids, lipid mediator levels, and the desaturase index rates on different acute coronary syndrome types and their possible relationship with routine lipid parameters. METHODS: The study included 81 patients with myocardial infarction (MI), 20 patients with unstable angina pectoris, and 31 healthy people. Fatty acids, CD59, lipoxin A4, 8-isoprostane, serum lipids, albumin, C-reactive protein (CRP), and high sensitive troponin levels were measured in all participants. RESULTS: When the fatty acid groups were evaluated as a ratio of albumin, MUFA/albumin and SFA/albumin ratios were significantly higher in the MI group compared to the control group. Although CD59 and lipoxin A4 levels were higher in the control group, there was no significant differences between the groups. When lipoxin A4/CRP and CD59/CRP ratios were evaluated, the results were significantly lower than those in the control group. CONCLUSION: Lipid mediators may be useful in treating atherosclerosis by contributing to the resolution of inflammation.

The effect of ascorbic acid supplementation on endosulfan toxicity in rabbits.

We investigated the endosulfan-induced alterations and the effect of vitamin C supplementation on endosulfan-induced alterations in serum biochemical markers of oxidative stress and antioxidant capacity in rabbits. Basal, 4th and 6th week serum levels of total oxidant status (TOS), thiobarbituric acid reactive substances (TBARS), advanced oxidation protein products (AOPP), total antioxidant capacity (TAC), total protein sulfhydryl (T-SH) and glutathione-S-transferase (GST) were measured in rabbits administered endosulfan (1 mg/kg) alone or in combination with vitamin C (20 mg/kg) for 6 weeks. Control rabbits received either vehicles or vitamin C. Serum TOS, TBARS and AOPP levels at 4th and 6th week were significantly higher whereas T-SH levels were significantly lower than basal values in endosulfan-administered rabbits. GST increased significantly at 4th week but decreased below basal value at 6th week. Similarly, TAC decreased significantly at 6th week. Vitamin C supplementation increased TAC at 4th and 6th weeks in controls and increased T-SH and GST and decreased TOS, TBARS and AOPP at 4th week in endosulfan-administered rabbits. TAC increased significantly at 6th week by vitamin C supplementation in endosulfan-administered rabbits. There were significant increments in TBARS and decrements in TAC and GST levels at 6th week compared to 4th week in endosulfan-administered rabbits. Present findings indicated to an increased and progressively uncompensated oxidant stress in endosulfan-administered rabbits that was substantially ameliorated by vitamin C supplementation through an improvement in antioxidant capacity. It was suggested that vitamin C supplementation might be helpful in preventing the detrimental effects of increased oxidative stress caused by endosulfan exposure.

Which proteinase-activated receptor-1 antagonist is better?: Evaluation of vorapaxar and parmodulin-2 effects on human left internal mammary artery endothelial function.

OBJECTIVE: Endothelial dysfunction occurs as an early event in cardiovascular disease. Previously, vorapaxar, a proteinase-activated receptor-1 antagonist, was shown to cause endothelial damage in a cell culture study. Therefore, our study aimed to compare the effects of vorapaxar and parmodulin-2, proteinase-activated receptor-1 biased agonist, on human left internal mammary artery endothelial function in vitro. METHOD: Isolated arteries were hung in the organ baths. Acetylcholine responses (10-11-10-6 M) were obtained in endothelium-intact tissues the following incubation with vorapaxar/parmodulin-2 (10-6 M) to determine the effects of these molecules on the endothelium-dependent relaxation. Subsequently, endothelium-dependent relaxation responses of tissues were investigated in the presence of L-NAME (10-4 M), L-arginine (10-5 M), indomethacin (10-5 M), and charybdotoxin-apamin (10-7 M) in addition to vorapaxar/parmodulin-2 incubation. Besides, the effect of these molecules on endothelium-independent relaxation response was evaluated with sodium nitroprusside (10-11-10-6 M). Finally, the sections of human arteries were imaged using a transmission electron microscope, and the integrity of the endothelial layer was evaluated. RESULTS: We found that vorapaxar caused significant endothelial dysfunction by disrupting nitric oxide and endothelium-derived hyperpolarizing factor-dependent relaxation mechanisms. Parmodulin-2 did not cause endothelial damage. Neither vorapaxar nor parmodulin-2 disrupted endothelium-independent relaxation responses. The effect of vorapaxar on the endothelial layer was supported by the transmission electron microscope images. CONCLUSION: Parmodulin-2 may be a better option than vorapaxar in treating cardiovascular diseases since it can inhibit PAR-1 without caused endothelial dysfunction.

Knowledge level and attitude towards complementary and alternative treatment methods among medical students: a cross-sectional survey study in Turkey.

OBJECTIVE: People often use complementary and alternative medicine (CAM) methods in Turkey, but reliability of the application of these methods is controversial. Considering the role of medical students (i.e. physician candidates) in sustainable health, their perspectives on CAM methods are important. This report explores the level of knowledge, experience, and preferences for the use of CAM methods among medical school students. MATERIAL AND METHODS: A survey about the use of CAM and interest in CAM methods was applied to 101 first-year and 87 fifth-year medical school students. The binary and multinomial logistic regression models were used for statistical analysis. RESULTS: Sixteen percent of the first-year and 9% of the fifth-year students were familiar with "The Regulation on Traditional and Complementary Medical Practices" published by the Ministry of Health of Turkey in 2014. While participants reported the most familiarity with acupuncture treatment, they were the most unfamiliar with prolotherapy among all CAM methods. Seeking advice from a licensed physician before applying CAM methods was the general agreement among the participants. Interest in learning and practicing hypnosis was the highest-rated CAM method among the participants. CONCLUSIONS: Increasing knowledge and awareness of CAM methods by including them into the medical curriculum would be essential for the correct use of CAM methods.

Effects of sulphite supplementation on vascular responsiveness in sulphite oxidase-deficient rats.

1. The aim of the present study was to explore the effect of dietary sulphite supplementation on vascular responsiveness in sulphite oxidase (SO)-deficient rats. 2. Male albino rats were divided into four groups, namely control (n = 8), sulphite-treated (n = 8), SO-deficient (n = 8) and sulphite-treated SO-deficient (n = 8) groups. Sulphite oxidase deficiency was induced by administration of a low-molybdenum diet with concurrent addition of 200 p.p.m. tungsten in the form of sodium tungstate in the drinking water for 9 weeks. Sulphite, in the form of sodium metabisulphite (Na(2)O(5)S(2); 25 mg/kg) was given in the drinking water to sulphite-treated and sulphite-treated SO-deficient groups for the last 6 weeks. The vascular responsiveness of isolated aortic rings to acetylcholine (ACh), sodium nitroprusside (SNP) and histamine was investigated in organ baths. 3. The responsiveness of aortic rings to SNP and histamine did not differ significantly between groups. Conversely, there was a significant decrease in ACh-induced relaxation in aortic rings from the sulphite-treated SO-deficient group compared with the control group (pD(2) 6.2 +/- 0.3 and 7.5 +/- 0.1, respectively; P < 0.05). Incubation of aortic rings in the presence of either l-arginine or superoxide dismutase significantly improved the ACh-induced vasorelaxation in sulphite-treated SO-deficient group (pD(2) 7.2 +/- 0.3 and 7.4 +/- 0.3, respectively). 4. The findings of the present study suggest that the increased production of reactive oxygen species and the resultant increment in l-arginine/nitric oxideconsumption may play a role in the reduced endothelium-dependent vasorelaxation in sulphite-treated SO-deficient rats.

Antinociceptive Effect of Vardenafil on Carrageenan-Induced Hyperalgesia in Rat: involvement of Nitric Oxide/Cyclic Guanosine Monophosphate/Calcium Channels Pathway.

In this study, we aimed to investigate the peripheral antinociception effects of specific phosphodiesterase 5 (PDE-5) inhibitor vardenafil on carrageenan-induced nociception in rats, and the role of calcium besides the L-arginine- nitric oxide (NO)- cyclic guanosine monophophate (cGMP) pathway in these effects. Hyperalgesia was induced by the intraplantar injection of 0.1 mL fresh carrageenan solution to right hind-paw whereas, saline as a vehicle of carrageenan was injected to the left paw. This procedure was used for measuring mechanic nociception pressure via an analgesimeter. Pressure which produced nociception was measured before (0 minute) and after(15, 30, 60 and 120 minutes) carrageenan injection. Local administration of vardenafil produced a dose-dependent antinociceptive effect. Pretreatment with N(W)-nitro-L-arginine methyl ester (L-NAME, nitric oxide synthase inhibitor), oxadiazolo (4, 3, a) quinoxalin -1-one (ODQ, inhibitor of guanylyl cyclase) or A23187 (calcium ionophore) decreased the effect of vardenafil. In contrast, L-arginine (nitric oxide donor) seemed to potentiate the vardenafil-induced antinociception. Our results suggest that phosphodiesterase type-5 inhibitor vardenafil may offer a new therapeutic tool to treat pain. It's effect was probably result from L-arginine/NO-cGMP pathway activation and Ca + 2 channels are also involved.

The inhibitory action of protamine on human internal thoracic artery contractions: the effect of free hemoglobin.

OBJECTIVE: We investigated the mechanism of the protamine action and the effects of free hemoglobin on protamine-induced responses in endothelium-denuded and-intact human internal thoracic artery (ITA) rings precontracted with phenylephrine (PE) or high KCl. METHODS: Samples of redundant ITA obtained from patients undergoing a coronary artery bypass graft surgery were cut into 3 mm wide rings and suspended in 20 ml organ baths. Isometric tension was continuously measured with an isometric force transducer connected to a computer-based data acquisition system. RESULTS: Acetylcholine (Ach, 10(-8)-10(-5) M) caused a concentration-dependent relaxation of PE-precontracted ITA rings. Free hemoglobin (0.1 and 0.5 microM) produced a concentration-dependent and significant decrease in sensitivity (pD(2)) and maximal contractility (E(max)) in response to Ach in PE-precontracted ITA rings (P<0.0001). Protamine (50-800 microg/ml), free hemoglobin (0.1 and 0.5 microM), nitric oxide (NO) blocker N(omega)-nitro-L-arginine methyl ester (L-NAME, 100 microM) or soluble guanylate cyclase inhibitor methylene blue (10 microM) administration did not cause a significant alteration on basal tonus of endothelium-intact or -denuded ITA rings. Protamine (50-800 microg/ml) induced concentration-dependent relaxation responses in ITA rings precontracted by either PE or high KCl. There was no difference in sensitivity or maximal response to protamine between the endothelium-intact and -denuded rings. Incubation of endothelium-intact or -denuded ITA rings with L-NAME or free hemoglobin or methylene blue did not cause a significant inhibition on relaxation responses to protamine. ITA ring contractions induced by stepwise addition of calcium to high KCl solution with no calcium were almost completely inhibited by protamine (P<0.0001). CONCLUSIONS: It was suggested that protamine induced relaxation responses in human ITA rings is not NO- or endothelium-dependent but seems to depend on the interactions of protamine with calcium influxes and/or calcium release from intracellular stores in this tissue.

Chronic treatment with taurine ameliorates diabetes-induced dysfunction of nitric oxide-mediated neurogenic and endothelium-dependent corpus cavernosum relaxation in rats.

This study was aimed to examine the effect of chronic taurine treatment on corpus cavernosum dysfunction in diabetic rats and to investigate possible underlying mechanisms. Thirty male rats were randomized to three groups of 10 each, including control, diabetic, and taurine-treated diabetic. Diabetes was induced in rats by streptozotocin (STZ, single intraperitoneal dose of 50 mg/kg body weight). Taurine was administered orally for 12 weeks (1% w/v in drinking water) from the day on which STZ was injected. At the end of the 12th week, strips of corpus cavernosum were suspended in an organ bath system for functional studies. Nitric oxide (NO)-mediated endothelium-dependent and neurogenic corpus cavernosum relaxation were evaluated by acetylcholine (ACh, 0.1-100 µm) and electrical field stimulation (EFS, 30 V, 5 ms, 2-32 Hz), respectively. The expressions of endothelial nitric oxide synthase (eNOS), phosphorylated eNOS (p-eNOS) (Ser-1177), neuronal nitric oxide synthase (nNOS), NADPH oxidase subunit gp91(phox) , Rho A, and Rho kinase in corpus cavernosum were semi-quantitatively assessed by immunohistochemistry. Induction of diabetes resulted in significant inhibition of NO-mediated endothelium-dependent and neurogenic corpus cavernosum relaxation. Furthermore, eNOS, p-eNOS, and nNOS expressions decreased significantly in diabetic rats compared to controls, while gp91(phox) , RhoA and Rho kinase expressions increased significantly. The diminished relaxation response to ACh and EFS as well as diabetes-related changes in expressions of these proteins in corpus cavernosum of diabetic rats was significantly improved by taurine. Taurine treatment improves NO-mediated relaxations of corpus cavernosum in diabetic rats probably by inhibiting NADPH oxidase/Rho kinase pathways.

The effect of hydrogen peroxide in human internal thoracic arteries: role of potassium channels, nitric oxide and cyclooxygenase products.

INTRODUCTION: We investigated both the effect and the role(s) of potassium channels, nitric oxide (NO) and cyclooxygenase (COX) products in the effect of hydrogen peroxide (H(2)O(2)) in human internal thoracic artery (ITA) rings. MATERIALS AND METHODS: Samples of redundant ITA obtained from patients undergoing a coronary artery bypass graft surgery were cut into 3 mm wide rings and suspended in 20 ml organ baths. Isometric tension was continuously measured with an isometric force transducer connected to a computer-based data acquisition system. RESULTS: H(2)O(2) (10(-7)-10(-4) M) produced concentration-dependent relaxation responses in human ITA precontracted by phenylephrine. The relaxant responses to H(2)O(2) did not differ significantly between endothelium-intact and endothelium-denuded preparations. Incubation of human ITA rings with superoxide dismutase (50 U/ml) did not affect the relaxant responses to H(2)O(2), while 1,000 U/ml catalase caused a significant decrease. Incubation of endothelium-intact or endothelium-denuded human ITA rings with voltage-dependent potassium channel blocker 4-aminopyridine (5 mM) significantly inhibited the relaxant responses to H(2)O(2). COX inhibitor indomethacin (10(-5) M) also caused a significant inhibition. Incubation with ATP-dependent potassium channel blocker glibenclamide (10(-6) M) or Ca(2+)-activated potassium channel blocker iberiotoxin (10(-7) M) or NO synthase (NOS) blocker N(omega)-nitro-L: -arginine methyl ester (10(-4) M) did not alter relaxant responses of ITA rings to H(2)O(2). CONCLUSION: The findings of the present study suggested that H(2)O(2)-induced relaxation responses in human ITA were neither dependant on the endothelium nor blocked by NOS inhibition but they rather seem to depend on the activation of voltage-dependent potassium channels and COX.

Potassium channels in the vasodilating action of levosimendan on the human umbilical artery.

OBJECTIVE: Levosimendan is a calcium-sensitizing agent and inodilator working via potassium channels, which is under current investigation in the treatment of heart failure. We investigated the type of potassium channels that play a role on the dilatating effect of levosimendan on the contractile tones of the isolated human umbilical artery (HUA). METHODS: The response in the HUA was recorded isometrically by a force displacement transducer in isolated organ baths. Levosimendan was added to organ baths after precontraction with serotonin (5-HT, 1 microM). Levosimendan-induced relaxations were tested in the presence of the large conductance Ca2+-activated K+ channel inhibitor tetraethylammonium (TEA, 1 mM), the adenosine triphosphate (ATP)-sensitive K+ channel inhibitor glibenclamide (GLI, 10 microM), and the voltage-sensitive K+ channel inhibitor 4-aminopyridine (4-AP, 1 mM). All experiments were performed in solutions containing the cyclooxygenase inhibitor indomethacin (10 microM) and the nitric oxide synthase inhibitor L-NAME (100 microM). RESULTS: Levosimendan (10 nM to 3 microM) produced potent relaxation in the HUA. Vehicle had no significant relaxant effect. The relaxation to levosimendan was not affected by the K+ channel inhibitor, GLI. However, 4-AP (1 mM) and TEA (1 mM) inhibited levosimendan-induced relaxation significantly (P <.05). CONCLUSION: These results show that levosimendan effectively and directly decreases the tone of the HUA. The mechanism of this levosimendan-induced relaxation in the HUA appears in part to be due to voltage-gated and large conductance Ca2+-activated K+ channel opening action.

Potassium channel-related relaxation by levosimendan in the human internal mammary artery.

BACKGROUND: Levosimendan is a potent inotropic and vasodilator drug used in the treatment of decompensated heart failure. There is no study on in vitro effects of levosimendan in human isolated arteries. METHODS: We investigated the effect of levosimendan on contractile tone of human isolated internal mammary artery (IMA). The responses in IMA were recorded isometrically by a force-displacement transducer in isolated organ baths. Levosimendan was added to organ baths either at rest or after precontraction with phenylephrine (1 micromol/L). Levosimendan-induced relaxations were tested in the presence of cyclooxygenase inhibitor indomethacin (10 micromol/L), nitric oxide synthase inhibitor N122-nitro-L-arginine methyl ester (100 micromol/L), large-conductance calcium-activated potassium-channel inhibitor tetraethylammonium (1 mmol/L), adenosine triphosphate-sensitive potassium-channel inhibitor glibenclamide (10 micromol/L), and voltage-sensitive potassium-channel inhibitor 4-aminopyridine (1 mmol/L). RESULTS: Levosimendan (10 nmol/L to 3 micromol/L) produced potent relaxation in human IMA (maximal effect, 75.3% +/- 4.9% of phenylephrine maximum contraction, 6.8 +/- 0.1, n = 15; -log10 of 50% effective concentration). Vehicle had no significant relaxant effect. The relaxation to levosimendan is not affected by either potassium-channel inhibitors (tetraethylammonium and 4-aminopyridine) or cyclooxygenase and nitric oxide synthase inhibitors. Glibenclamide (10 micromol/L) inhibited levosimendan-induced relaxation significantly (p < 0.01). CONCLUSIONS: Levosimendan effectively and directly decreases the tone of IMA. The mechanism of levosimendan-induced relaxation in IMA appears in part to be adenosine triphosphate-sensitive potassium-channel opening action. Levosimendan may be a cardiovascular protective agent by its relaxing action on the major arterial graft, IMA.