Cahit Nacitarhan

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

Abstract: 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.

Potassium Channels in the Vasodilating Action of Levosimendan on the Human Umbilical Artery

Objective: Levosimendan is a calcium-sensitizing agent and indoilator 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 μM). Levosimendan-induced relaxations were tested in the presence of the large conductive Ca2+-activated K+ channel inhibitor tetraethylammonium (TEA, 1 mM), the adenosine triphosphate (ATP)-sensitive K+ channel inhibitor glibenclamide (GLI, 10 μM), 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 μM) and the nitric oxide synthase inhibitor L-NAME (100 μM). Results: Levosimendan (10 nM to 3 μM) produced potent relaxation in the HUA. Vehicle had no significant relaxant effect. The relaxation of 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-relaxation in the HUA appears in part to be due to voltage-gated and large conductance Ca2+-activated K+ channel opening action.

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.

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 gp91phox, 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 gp91phox, 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 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.

The Effect of Benfotiamine on Mu-opioid Receptor Mediated Antinociception in Experimental Diabetes

Diabetic neuropathy is a prevalent, disabling disorder. Currently, the only treatments available to patients with diabetic neuropathy are glucose control and pain management. B vitamin present neuroprotective effects, which are suggested to be related to their analgesic action in various models of neuropathic pain. According to our literature knowledge there is no report about antinociceptive effects of thiamine as benfotiamine and opioids together in diabetic mice. The purpose of this study was to determine the effects of benfotiamine on the antinociception produced by mu-opioid receptor agonist fentanyl in diabetic mice. The effects of benfotiamine on antinociception produced by fentanyl in diabetic mice were studied in 4 groups. Antinociceptive effect was determined with tail flick, hot plate and formalin test. Our results showed that, mu-opioid agonist fentanyl in benfotiamine applied diabetic group caused more potent antinociceptive effect than in diabetic group without benfotiamine treatment. In brief benfotiamine supplement in diet did not bring out antinociceptive effect itself, but during development of STZ diabetes, benfotiamine replacement increased the antinociceptive effect of fentanyl in mice tail-flick test. This effect is probably due to the replacement of benfotiamine efficiency occurring in diabetes mellitus. Finally, we suppose that oral benfotiamine replacement therapy may be useful to ameliorate analgesic effect of mu-opioid agonists on neuropathic pain in diabetic case.

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 (Na2O5S2; 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 (pD2 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 (pD2 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.