Inci Sahin-Erdemli

Effects of pentoxifylline in Adriamycin-induced renal disease in rats

Tumor necrosis factor-α (TNF-α) is a mediator of inflammation in human and animal renal disease. Pentoxiphylline (PTX) is an inhibitor of TNF-α. In this study we examined the effects of PTX on TNF-α, proteinuria, nitrite production, and apoptosis in an experimental model of Adriamycin (ADR) nephropathy in rats. Rats were divided into four groups: untreated Wistar rats (controls), PTX treatment alone, ADR treatment alone to induce nephropathy, and ADR treatment followed by PTX. ADR treatment followed by PTX treatment prevented the increase in serum TNF-α levels and proteinuria in rats with ADR-nephropathy (P<0.05). Urine nitrite levels were significantly increased in the ADR-induced nephropathy group and the increase was prevented in the ADR-induced nephropathy group when they also received PTX. The urine nitrite levels were not different between the PTX-treated group and the untreated control rats. PTX prevented the rise of serum TNF-α in ADR nephropathy rats and a decrease in proteinuria, urine nitrite, and apoptosis in the renal tissue. These findings suggest a beneficial anti-inflammatory effect of PTX.

Reactive oxygen species-induced impairment of endothelium-dependent relaxation in rat aortic rings: protection by L-arginine.

The protective effect of L-arginine against reactive oxygen species-induced impairment of endothelium-dependent vasorelaxation was investigated in isolated ring preparations of rat aorta. The aortic rings were subjected to reactive oxygen species generated by the electrolysis of the bathing solution or incubation with H2O2. Endothelium-dependent relaxation in response to acetylcholine of precontracted aortic rings was attenuated when the rings were exposed to reactive oxygen species or H2O2. Incubation prior to electrolysis with either L-arginine, the endogenous precursor of nitric oxide (NO), or sodium nitroprusside, an exogenous donor of NO, protected the aortic rings against the impairment of endothelium-dependent relaxation. However, D-arginine and glycine, amino acids which do not produce NO, also afforded protection in this model. Therefore, not only the increased synthesis of NO but also the oxidation of L-arginine, with concomitant disproportionation of reactive oxygen species, may be responsible for the protective effect against reactive oxygen species-induced loss of the endothelial response to acetylcholine in isolated rat aorta.

Synthesis and calcium antagonistic activity of 2,6,6-trimethyl-3-carbomethoxy(ethoxy)-4-aryl-1,4,5,6,7,8-hexahydroquinoline derivatives

Twelve new 2,6,6-trimethyl-3-carbomethoxy(ethoxy)-4-aryl-1,4.5,6.7,8-hexahydroquinoline derivatives have been prepared. Their structures were confirmed by IR, 1H NMR, mass and elemental analysis. The calcium antagonistic activity of these compounds was tested in rat aortic rings precontracted with 30 mM K+. The compounds IVa, IVc, IVe, IVf, IVh-l induced concentration dependent relaxation response in precontracted aortic rings. The concentrations that cause 50% relaxation of K+-contraction were also calculated for the compounds IVe, IVf, IVj. According to pharmacological results, compound IVl exert the most activity and compound IVc has been found to be least active in this series. The methyl ester derivatives carrying mono halogensubstitutent in the phenyl ring, the activity order is F > Br > Cl. Replacement of the substituted phenyl ring with the pyridine ring increases the activity.

The effect of inflammation on rat urinary bladder-dependent relaxation in coaxial bioassay system

The effect of urinary bladder inflammation on the activity of a bladder-derived relaxant factor in the coaxial bioassay system was examined. Bladder inflammation was induced by intraperitoneal (i.p.) cyclophosphamide or intravesical lipopolysaccharide (LPS) injection to male rats. In precontracted rat anococcygeus muscle that was placed within rat bladder (coaxial bioassay system), acetylcholine induced a relaxation response, which was not altered by the denudation of urothelium or incubation with indomethacin and NG-methyl-L-arginine. Acetylcholine-induced relaxation was significantly attenuated, when bladders were removed from cyclophosphamide- and LPS-pretreated group of rats and were used with intact urothelium in the coaxial bioassay system. However, the impairment acetylcholine response in both pretreatment groups was not observed after denudation of the bladder urothelium. These results showed that bladder inflammation did not alter the synthesis and/or release of this bladder-derived relaxant factor, which is neither a cyclooxygenase product nor nitric oxide, but restricted its demonstration by coaxial bioassay assembly probably due to inflammation-induced mucosal oedema.

Competitive antagonism by recognised 5-HT2 receptor antagonists at 5-HT1C receptors in pig choroid plexus

SummaryThe effects of several antagonists, known to interact with 5-HT2 receptors (ritanserin, LY 53857, ICI 169,369, methysergide, mesulergine and ketanserin), were tested against 5-HT-stimulated production of inositol phosphate in pig choroid plexus, a 5-HT1C receptor model. These antagonists produced dextral shifts of the concentration response curve to 5-HT in a parallel manner, without depressing significantly the maximal response. The following pA2 values (in parentheses) were obtained: mesulergine (8.88), methysergide (8.85), LY 53857 (8.69), ritanserin (8.69), ICI 169,369 (7.86), and ketanserin (6.57). These pA2 values were in good agreement with the pKD values determined in radioligand binding studies performed in pig choroid plexus with [3H]mesulergine. The present data demonstrate that several drugs described as 5-HT2 receptor selective antagonists (e.g. ritanserin, LY 53857 and ICI 169,369) are also potent, competitive and surmountable antagonists at 5-HT1C receptors. Thus, the results provide further evidence for the pharmacological similarity of 5-HT1C and 5-HT2 receptors. However, in contrast to the situation described with methysergide, ritanserin and LY 53857 in several 5-HT2 receptor models, none of these antagonists acted in a non-competitive or unsurmountable fashion at 5-HT1C receptors. These results suggest, but do not firmly rule out, that at least in the presence of the drugs tested in the present study, 5-HT1C receptors in the choroid plexus do not undergo an allosteric modulation; these findings are apparently in contrast to a model proposed previously for 5-HT2 receptors (Kaumann and Frenken 1985, Naunyn-Schmiedebergs Arch Pharmacol 328: 295–300)

Further characterization of the 5-hydroxytryptamine 5-HT1-like receptor mediating contraction of guinea-pig iliac artery

We recently described a 5-hydroxytryptamine 5-HT1-like receptor mediating contraction in guinea-pig isolated iliac artery. The present study was aimed at characterizing this receptor with respect to the currently recognized 5-HT1 receptor subtypes (5-HT1A, 5-HT1B, 5-HT1C and 5-HT1D). The potencies of 13 drugs tested as agonists correlated with their affinities for 5-HT1D binding sites only. The concentration-response curve for 5-carboxamidotryptamine (5-CT, a 5-HT1-like receptor agonist) was unaffected by propranolol (10 microM), which is reported to have affinity for 5-HT1A, 5-HT1B and 5-HT1C recognition sites. Yohimbine (3 microM) and metergoline (1 microM) antagonized 5-CT with pKB values of 6.15 and 6.96, respectively. These values are close to those found in a functional correlate of 5-HT1D sites in the same species, namely the presynaptic 5-HT autoreceptor in guinea-pig brain cortex. The overall results support the view that the receptor studied is of the 5-HT1D subtype. The receptor shares close similarities with other vascular 5-HT1-like receptors mediating contraction, for example the receptor present in dog saphenous vein.

Hydrogen sulphide inhibits carbachol-induced contractile responses in β-escin permeabilized guinea-pig taenia caecum

Hydrogen sulphide (H(2)S) is an endogenous mediator producing a potent relaxation response in vascular and non-vascular smooth muscles. While ATP-sensitive potassium channels are mainly involved in this relaxant effect in vascular smooth muscle, the mechanism in other smooth muscles has not been revealed yet. In the present study, we investigated how H(2)S relaxes non-vascular smooth muscle by using intact and β-escin permeabilized guinea-pig taenia caecum. In intact tissues, concentration-dependent relaxation response to H(2)S donor NaHS in carbachol-precontracted preparations did not change in the presence of a K(ATP) channel blocker glibenclamide, adenylate cyclase inhibitor SQ-22536, guanylate cyclase inhibitor ODQ, protein kinase A inhibitor KT-5720, protein kinase C inhibitor H-7, tetrodotoxin, apamin/charybdotoxin, NOS inhibitor L-NAME and cyclooxygenase inhibitor indomethacin. We then studied how H(2)S affected carbachol- or Ca(2+)-induced contractions in permeabilized tissues. When Ca(2+) was clamped to a constant value (pCa6), a further contraction could be elicited by carbachol that was decreased by NaHS. This decrease in contraction was reversed by catalase but not by superoxide dismutase or N-acetyl cysteine. The sarcoplasmic reticulum Ca(2+)-ATPase pump inhibitor, cyclopiazonic acid, also decreased the carbachol-induced contraction that was further inhibited by NaHS. Mitochondrial proton pump inhibitor carbonyl cyanide p-trifluromethoxyphenylhydrazone also decreased the carbachol-induced contraction but this was not additionally changed by NaHS. The carbachol-induced Ca(2+) sensitization, calcium concentration-response curves, IP(3)- and caffeine-induced contractions were not affected by NaHS. In conclusion, we propose that hydrogen peroxide and mitochondria may have a role in H(2)S-induced relaxation response in taenia caecum.

M1 and M3 muscarinic receptors are involved in the release of urinary bladder-derived relaxant factor

We have investigated the muscarinic receptor subtype(s) mediating the release of urinary bladder-derived relaxant factor that is demonstrated by a coaxial bioassay system. Acetylcholine-induced relaxation of a precontracted anococcygeus muscle mounted within the bladder was considered as an evidence for the release of this factor. M(1)-muscarinic agonist McN-A-343 and the cholinesterase inhibitor physostigmine also elicited relaxation responses in the coaxial bioassay besides acetylcholine. Acetylcholine-induced relaxation was antagonized by the subtype-selective muscarinic antagonists (pK(B)): M(3)-antagonist darifenacin (9.36+/-0.11), M(3)/M(1)-antagonist 4-DAMP (9.30+/-0.11), M(1)-antagonist telenzepine (8.56+/-0.21), M(4)-antagonist tropicamide (6.63+/-0.17) and M(2)-antagonist AF-DX 116 (6.01+/-0.21). The pK(B) values of these antagonists have suggested that stimulation of M(1)- and M(3)-muscarinic receptors in the bladder wall mediates the release of urinary bladder-derived relaxant factor. In addition, McN-A-343, by activating the facilitatory M(1) receptors and physostigmine by inhibiting the acetylcholinesterase may induce the release of this factor through endogenous acetylcholine in the coaxial bioassay system.

The investigation into indomethacin‐induced potentiation of the contractile response to antigen in ovalbumin‐sensitized guinea‐pig tracheas

In the present study, we investigated the mediators involved in the potentiation of antigen‐induced contractions by indomethacin in tracheas isolated from ovalbumin (OA)‐sensitized guinea‐pigs. Indomethacin‐induced potentiation of OA contraction was mimicked by prostaglandin DP/EP1/EP2 receptor antagonist, AH‐6809 but not by phospholipase A2 enzyme inhibitor mepacrine. The lipoxygenase inhibitor AA‐861 did not affect the contraction response to OA but prevented its potentiation by indomethacin, while the leukotriene receptor antagonist cinalukast inhibited both the OA response and its potentiation. However, the antagonists of platelet‐activating factor (PAF) (BN‐52021), adenosine (CGS‐15943), endothelin ETA and ETB receptors (BQ‐123, BQ‐788), and the neutral endopeptidase inhibitor phosphoramidon did not alter the OA‐induced contraction and its potentiation by indomethacin. Furthermore, capsaicin and neuropeptide receptor NK1, NK2, and NK3 antagonists (L‐732128, MEN‐10376, and SB‐218795, respectively) also did not affect the OA‐induced contractions and its potentiation. On the other hand, the ‘transient receptor potential vanilloid 1’ (TRPV1) antagonist capsazepine inhibited the potentiation response, while it did not alter the OA contraction itself. In conclusion, the potentiation of OA‐induced contraction by indomethacin is more likely due to the increase in lipoxygenase products by the shift of arachidonic acid towards lipoxygenase pathway. Because some of the lipoxygenase products are potent vanilloid agonists, the stimulation of TRPV1 receptors besides leukotriene receptors seems to participate in the potentiation of contraction response in sensitized guinea‐pig tracheas. PAF, adenosine, endothelins, and the neuropeptides present in the afferent neurons do not contribute to the potentiation of OA‐induced contraction by indomethacin.

Effects of Aminoguanidine and N ω -nitro-L-arginine Methyl Ester on Vascular Hyporeactivity Induced by Endotoxaemia

OBJECTIVE To investigate the effects of endotoxaemia on the reactivity of the aortic bed in rats, and to compare the effects of the nitric oxide (NO) synthase inhibitors aminoguanidine and N(omega)-nitro-L-arginine methyl ester (L-NAME), on endotoxaemia-induced changes in vascular reactivity. DESIGN Randomised experiment. SETTING University laboratory, Turkey. SUBJECTS 54 Wistar rats. INTERVENTIONS Rats were divided into control (n = 24) and endotoxaemia (n = 30) groups and were treated with an intraperitoneal injection of saline (control) and lipopolysaccharide (20 mg/kg), respectively. Subgroups of control and endotoxaemic rats were given either aminoguanidine or L-NAME by the same route. MAIN OUTCOME MEASURES Contractile responses to phenylephrine and relaxation responses to acetylcholine 4 hours after treatment. RESULTS Incubation with aminoguanidine and L-NAME potentiated the phenylephrine-induced contractile response and inhibited acetylcholine-induced relaxation in aortic rings in the control group. The vascular responses to phenylephrine and acetylcholine were less pronounced in the endotoxaemia group, and in vitro incubation with aminoguanidine and L-NAME partially restored the contraction induced by phenylephrine but did not affect the impaired response to acetylcholine. Aminoguanidine given in vivo prevented the impairment of vascular responses to both phenylephrine and acetylcholine whereas L-NAME gave no such protection. CONCLUSION Aminoguanidine acted similarly to L-NAME when incubated with the tissues in vitro, and did not show selectivity to inducible compared with constitutive isoforms of NO synthase. The finding that aminoguanidine but not L-NAME, prevented the endotoxin-induced impairment of vascular reactivity when administrated in vivo, therefore, suggested a role other than inhibition of NO synthase.