MESNA (2-Mercaptoethanesulfonate) Attenuates Brain, Heart, and Lung Injury Induced by Carotid Ischemia-Reperfusion in Rats.

Background: Ischemia-reperfusion (I/R) causes organ dysfunction as a result of the increased formation of various reactive oxygen metabolites, infiltration of inflammatory cells, interstitial edema, cellular dysfunction, and tissue death. Aim: The study aimed to investigate the cytoprotective effect of 2-mercaptoethanesulfonate (MESNA) against tissue damage in rats exposed to carotid ischemia-reperfusion. Materials and Methods: Twenty-four male Wistar albino rats were divided into four groups (n = 6): sham, carotid I/R, I/R + MESNA (75 mg/kg), and I/R + MESNA (150 mg/kg) groups. To induce ischemia in rats, the carotid arteries were ligated with silk sutures for 10 min; the silk suture was then opened, and 1 h reperfusion was done. MESNA (75 and 150 mg/kg) was administered intraperitoneally 30 min before ischemia-reperfusion. Tissue samples from the animals were taken for histological examination, while the serum levels of some biochemical parameters were utilized to evaluate the systemic alterations. ANOVA and Tukey's post hoc tests were applied with a significance level of 5%. Results: The ischemia-reperfusion-induced tissue damage as evidenced by increase in serum levels of alanine transaminase, aspartate aminotransferase, alkaline phosphatase, malondialdehyde, lactate dehydrogenase, and matrix metalloproteinases (MMP-1, -2, -8) was significantly (P < 0.05-0.0001) reversed after treatment with MESNA in a dose-dependent manner. Treatment with MESNA (75 and 150 mg/kg), significantly (P < 0.05-0.0001) decreased the I/R-induced increase in serum tumor necrosis factor-alpha (TNF-α) and Interleukin-1-beta (IL-1 ß). Conclusion: The results of this study suggest that MESNA has a protective effect on tissues by suppressing cellular responses to oxidants and inflammatory mediators associated with carotid ischemia-reperfusion.

The role of L-arginine/nitric oxide pathway in the antinociceptive activity of pyridoxine in mouse.

In the present study the role of L-arginine/nitric oxide (NO)/cGMP pathway in the antinociceptive activity of pyridoxine in p-benzoquinone-induced abdominal constriction test in mouse was investigated. Pyridoxine (CAS 58-56-0) displayed dose-dependent antinociceptive activity at 0.0625-1 mg/kg (s.c.) doses. L-arginine (CAS 1119-34-2), a NO precursor, displayed a triphasic pattern as antinociception-nociception-antinociception (61.8 +/- 7.8, -36.5 +/- 12.7 and 17.0 +/- 4.3%, 5, 40 and 50 mg/kg, s.c., respectively). The antinociceptive effect of pyridoxine at ED50 dose (0.43 mg/kg, s.c.) (47.7 +/- 3.9%) was significantly decreased by L-arginine at 40 and 50 mg/kg doses (4.1 +/- 9.3 and 37.8 +/- 1.6%, respectively) while 5 mg/kg dose of L-arginine significantly potentiated the pyridoxine analgesia. On the other hand, pyridoxine reversed the L-arginine-induced nociception to antinociception (4.1 +/- 9.3%) and augmented the antinociceptive effect of L-arginine (37.8 +/- 1.6%). L-NG-nitroarginine methyl ester (CAS 51298-62-5), a NO synthase inhibitor, at 75 mg/kg, s.c. produced antinociception and significantly increased the antinociceptive effect of pyridoxine (63.7 +/- 1.2%). Methylene blue (CAS 61-73-4, MB), a guanylyl cyclase and/or NO synthase inhibitor, was antinociceptive and nociceptive at 5 and 40 mg/kg doses, respectively, 5 mg/kg dose of MB significantly increased the antinociceptive effect of pyridoxine, but did not change it at 40 mg/kg dose. On the other hand, pyridoxine significantly decreased the antinociceptive effect of MB and reversed the MB-induced nociception to antinociception. Combination of pyridoxine and morphine (CAS 57-27-2) (ED50: 0.13 mg/kg, s.c.) at 49.8 +/- 1.9% revealed a significant antinociceptive potentiation (69.1 +/- 1.8%). The findings of the present study emphasise the contribution of central and/or peripheral L-arginine/NO/cGMP nociceptive processes in pyridoxine-induced antinociception.

Role of L-arginine/nitric oxide pathway in the antinociceptive activities of morphine and mepyramine in mice.

The p-benzoquinone (PBQ)-induced abdominal constriction test was used to assess the involvement of L-arginine/nitric oxide (NO) pathway in the antinociceptive activity of the subcutaneously administered H1-receptor antagonist, mepyramine (CAS 59-33-6), and an opioid receptor agonist, morphine (CAS 57-27-2), in mice. Mepyramine (ED50: 5.6 mg/kg) and morphine (ED50: 0.13 mg/kg) produced antinociceptive effects. The NO precursor L-arginine (CAS 1119-34-2) (50 mg/kg) also produced antinociception similar to mepyramine, but significantly less than morphine. The NO synthase (NOS) inhibitor L-NG-monomethylarginine (L-NMMA) (CAS 53308-83-1) (50 mg/kg) did not significantly change p-benzoquinone-induced abdominal constrictions. L-arginine significantly increased the antinociceptive effects of morphine and mepyramine. The antinociceptive activity of morphine, but not that of mepyramine, was completely abolished when combined with L-NMMA. L-NMMA also significantly decreased the antinociception induced by morphine or mepyramine in combination with L-arginine. The present results suggest that morphine and mepyramine could produce peripheral antinociception by the involvement of L-arginine/NO cascade or other related pathways of nociceptive processes induced by NO.

Effects of econazole on receptor-operated and depolarization-induced contractions in rat isolated aorta.

In our previous study, econazole caused a decrease in serum nitrite levels in septic mice in vivo, but it enhanced the mortality rate. The aim of the study was to investigate the in vitro effects of econazole on receptor-operated and depolarization-induced contractions on endothelium-intact and -denuded rat isolated aorta. Econazole (0.1, 1 and 10 microM) significantly inhibited receptor-operated (phenylephrine, Phe) and depolarization (KCl)-induced contractions of endothelium-intact or -denuded rings in a noncompetitive and concentration-dependent manner. Removal of endothelium changed the pD'2 values only for KCl-induced responses. The pD'2 values of L-type calcium channel blocker nifedipine were significantly higher than the econazole on Phe concentration-response curves in endothelium-intact and -denuded rings. Econazole caused a biphasic response in precontracted by Phe or KCl in endothelium-intact and -denuded rings, first a transient contraction following sustained relaxation. Removal of endothelium did not affect the contractile responses induced by Phe. The contractile responses induced by 10 microM econazole in the KCl-precontracted rings were antagonized by the treatment of alpha-adrenergic receptor antagonist, phentolamine (10 microM). Deendothelization was significantly increased the IC50 values of econazole obtained from Phe- and KCl-precontractions. The relaxations induced by 10 microM econazole in endothelium-intact rings precontracted with Phe or KCl were not changed by NO synthase inhibitor, L-N(G)-nitroarginine (100 microM). The IC50 values of econazole were significantly higher than nifedipine in endothelium-intact and -denuded rings. These results suggest that econazole is a noncompetitive antagonist on alpha1-adrenoceptor-mediated and depolarization-induced contractions in rat isolated aorta by inhibiting Ca2+ entry through L-type calcium channels, and the endothelium seems to modulate vascular responses induced by this agent. The vascular effects of econazole may limit the usage of this agent in septic shock.

Role of guanylyl cyclase activation via thiamine in suppressing chemically-induced writhing in mouse.

The possible role of L-arginine/nitric oxide (L-arginine/NO) pathway in the antinociceptive activity of thiamine (vitamin B1) in p-benzoquinone-induced mouse writhing model was investigated. Thiamine (ED50, 0.11 mg/kg), L-arginine (50 mg/kg), NG-nitro L-arginine methyl ester (L-NAME, 75 mg/kg) and morphine (ED50: 0.13 mg/kg) displayed antinociceptions following s.c. administrations (52.4 +/- 5.5%, 36.8 +/- 7.7%, 27.8 +/- 11.1%, 66.1 +/- 3.5%, respectively). However, methylene blue (MB, 40 mg/kg, s.c.) produced a nociception (-32.1 +/- 9.9%). Coadministration of B1 with L-arginine did not significantly change L-arginine-induced antinociception (48.9 +/- 3.7%). Cotreatment of thiamine with L-NAME and MB significantly increased the L-NAME-induced antinociception (53.9 +/- 3.9%) and reversed the MB-induced nociception to antinociception (46.0 +/- 4.2%). L-Arginine and L-NAME-induced antinociceptions were significantly increased (55.9 +/- 3.9% and 61.1 +/- 5.0%, respectively) by morphine. MB-induced nociception significantly reversed to antinociception by the concomitant administration of morphine (41.6 +/- 8.9%). Thiamine and morphine coadministration displayed antinociception (46.0 +/- 4.2%). The present results suggest that thiamine could produce antinociception by the activation of guanylyl cyclase mediated by cyclic guanosine monophosphate (cGMP) that may trigger the possible involvement of central and/or peripheral L-arginine/NO/cGMP pathway.

Participation of the components of L-arginine/nitric oxide/cGMP cascade by chemically-induced abdominal constriction in the mouse.

The purpose of this study was to investigate the role of the L-arginine/nitric oxide (NO)/cGMP pathway in p-benzoquinone-induced writhing model in mouse. L-arginine, a NO precursor, displayed antinociceptive effects at the doses of 0.125-1.0 mg/kg. When the doses of L-arginine were increased gradually to 10-100 mg/kg, a dose-dependent triphasic pattern of nociception-antinociception-nociception was obtained. The NO synthase (NOS) inhibitor, NG-nitro-L-arginine methyl ester (L-NAME) (18.7515 mg/kg), possessed antinociceptive activity. Methylene blue (MB), a guanylyl cyclase and/or NOS inhibitor, (5-160 mg/kg) also produced a dose-dependent triphasic response. When L-arginine (50 mg/ kg) was combined with L-NAME (75 mg/kg). L-arginine-induced antinociception did not change significantly. Cotreatment of L-arginine with 5 mg/kg MB significantly decreased MB-induced antinociception and reversed the nociception induced by 40 mg/kg MB to antinociception. It is concluded that the components of L-arginine/nitric oxide/cGMP cascade may participate in nociceptive processes both peripherally and centrally by a direct effect on nociceptors or by the involvement of other related pathways of nociceptive processes induced by NO.

Biological-time-dependent differences in effect of verapamil on rat aorta and influence of endothelium.

The biological-time-dependent variation in the vasodilator effect of verapamil on rat thoracic aorta was assessed in both endothelium-intact and denuded preparations. Groups of adult male rats were housed in light from 08:00 to 20:00 and in darkness from 20:00 to 08:00 and sacrificed at six different times of the day (1, 5, 9, 13, 17, and 21 hours after lights on; HALO). Verapamil caused concentration-dependent relaxations in both endothelium-intact and denuded aortic rings precontracted with phenylephrine (Phe). In endothelium-intact rings, neither the AUC nor the EC50 values for verapamil exhibited significant biological-time-dependent effects, as determined by one-way analysis of variance (ANOVA). In endothelium-denuded rings, AUC values did vary in a statistically significant manner according to the biological time of study, while the EC50 values did not. Endothelium denudation led to an increase in EC50 values at almost every time point. Statistically significant interactions between the biological time of study and treatment (intact vs. denuded endothelium) in both AUC and EC50 values were documented by two-way ANOVA; this indicated differences in the clock-time staging of verapamil-induced relaxation in endothelium-denuded versus intact aortic rings.

Temporal variation in serum nitrite levels in rats and mice.

Although considerable evidence implicates involvement of nitric oxide (NO) in circadian regulation, little is known about possible 24 h variations in basal NO metabolism. In this study, daily variations in serum nitrite levels were studied in locally bred mice and rats during the months of September and October. The serum was separated from blood samples obtained at six different times of the day and night (1 h, 5 h, 9 h, 13 h, 17 h, and 21 h after lights off [HALO] from male albino mice and rats). As an index of in vivo NO generation, serum nitrite levels (determined by the diazotization method) in rats exhibited significant temporal fluctuation (unpaired Student t test), with the concentration highest at 5 HALO and 21 HALO and lowest at 9 HALO. No such temporal variation was detected in mice in these studies conducted on locally bred animals in the autumn.

The role of nitric oxide in digoxin-induced arrhythmias in guinea-pigs.

We have investigated the effects of nitric oxide synthase inhibitor (L-NAME), nitric oxide precursor (L-arginine) and nitric oxide donor (sodium nitroprusside) on digoxin-induced arrhythmias both in guinea-pig isolated hearts and in anaesthetised animals. Sodium nitroprusside (0.1 mumol kg-1 min.-1 for 70 min.) caused a marked inhibition in mortality and arrhythmia score but L-NAME (10 mg kg-1) and L-arginine (30 mg kg-1 intravenous bolus followed by 10 mg kg-1 min.-1 for 60 min.) treatments were ineffective in anaesthetised guinea-pigs. None of the drugs markedly affected the time of onset of first arrhythmias or ventricular fibrillation incidence. In isolated heart experiments, nitric oxide generated by either L-arginine (1 mM) or sodium nitroprusside (1 mM) significantly reduced the arrhythmia score whereas L-NAME (1 mM) had no effect. Ventricular fibrillation incidence was totally abolished by sodium nitroprusside and none of the hearts treated with L-arginine had an irreversible ventricular fibrillation. L-NAME decreased ventricular tachycardia duration but increased ventricular fibrillation duration. There were no marked changes in the time of onset of first arrhythmias with these drugs in in vitro experiments. These results suggest that nitric oxide may play a modulatory role in the digoxin-induced arrhythmias in guinea-pigs.

Effects of nitric oxide synthase inhibition in lipopolysaccharide-induced sepsis in mice.

In the present study, we have investigated the effects of nitric oxide (NO) synthase inhibition on mortality in lipopolysaccharide (LPS)-induced sepsis in mice. Serum nitrite levels peaked at 15 h after an injection of LPS (10 mg kg-1, i.p.). Aminoguanidine, a selective inducible NO synthase (iNOS) inhibitor, at a dose of 100 mg kg-1 significantly reduced the LPS-induced increase in nitrite levels and improved mortality. Econazole, iNOS inhibitor, calmodulin antagonist, 5-lipoxygenase and a specific thromboxane synthase inhibitor, at a 1 mg kg-1 dose significantly decreased the LPS-induced increase in nitrite levels, but increased mortality 4. 9-fold when compared to the LPS group (control). Indomethacin, a putative iNOS and non-selective cyclo-oxygenase (COX) inhibitor, of 1, 10 and 100 mg kg-1, dose dependently decreased the LPS-induced increase in nitrite levels. This decrease was significantly different from the control at 10 and 100 mg kg-1 dose levels. When indomethacin (100 mg kg-1) was combined with aminoguanidine (100 mg kg-1), LPS-induced nitrite levels were significantly attenuated. NO precursor, L-arginine, was added to this combination in order to test the inhibition of iNOS activity which resulted in no change in nitrite levels. An indomethacin and aminoguanidine combination increased mortality twofold when compared to the control. The addition of L-arginine to the combination enhanced the mortality rate to 1.5-fold. These results suggest that NO appears to play a role in the LPS-induced septic shock model in mice. The improvement in sepsis-induced mortality enhanced by aminoguanidine by the inhibition of iNOS but not with the other agents or combinations should be re-evaluated in order to make an appropriate choice of the therapeutic target. In addition, it may also suggest that other mediators, such as arachidonic acid products and cytokines play a role in septic shock pathogenesis as well. (c) 1998 The Italian Pharmacological Society.

Circadian-rhythm-dependent effects of L-NG-nitroarginine methyl ester (L-NAME) on morphine-induced analgesia.

Circadian changes in the interactions between L-NG-nitroarginine methyl ester (L-NAME), a nitric oxide synthase (NOS) inhibitor, and morphine-induced antinociception were investigated by the mouse hot-plate test. Both the basal pain sensitivity and morphine-induced analgesia undergo significant 24 h variations. L-NAME (40 mg/kg, i.p.) alone did not show any antinociceptive activity, but potentiated morphine-induced analgesia when combined with morphine at all injection times. In terms of percentage absolute potentiation (%AP), L-NAME dramatically augmented the analgesic effect of morphine in the late dark period at 19 hours after lights on (HALO). It is concluded that nitric oxide (NO) is involved in the modulation of the analgesic effect of morphine; thus, the L-NAME and morphine combination might be beneficial in alleviating pain.

Comparison of nitric oxide production by monocyte/macrophages in healthy subjects and patients with active pulmonary tuberculosis.

The aim of the present study was to determine the NO production by human cultured macrophages (m phi) and to compare the NO production between healthy subjects and patients with active pulmonary tuberculosis. The bioassay method was used for assessment of validation. Lipopolysaccharide (125 ng ml-1)-activated m phi from healthy and diseased subjects released a substantial amount of NO. NO synthase inhibitor, NG-nitro-L-arginine methyl ester, (0.1 mmol l-1) suppressed NO synthesis significantly in m phi of healthy subjects. Nitrite formation measured by the diazotization method in the supernatants taken from cultured m phi of tuberculous patients were significantly lower than the healthy subjects. The supernatants obtained in both subjects caused relaxation of guinea-pig aorta reversed by methylene blue (10 mumol l-1). There was a significant difference between relaxations of healthy and diseased supernatants. Nitrite formation measured by the bioassay method in the supernatants taken from cultured m phi of tuberculous patients was significantly higher than the healthy subjects. It was concluded that NO production appeared to be decreased in tuberculosis. The reason for decreased production of NO in tuberculosis may be related to the interaction of several cytokines and/or eicosanoids by means of the disease related induction of immune reactions.

In vitro susceptibility rhythms. II. Biological-time-dependent differences in effect of beta 1- and beta 2-adrenergic agonists of rat aorta and influence of endothelium.

Time-dependent variations in the vasodilator effects of beta-adrenergic agonists terbutaline (Ter) and dobutamine (Dob) were studied in isolated rings of rat thoracic aorta in both endothelium-intact and endothelium-denuded preparations. Rats were housed in light from 08:00 to 20:00 and in darkness from 20:00 to 08:00 and sacrificed at six different times of the day. In endothelium-intact and endothelium-denuded aortic rings precontracted submaximally with phenylephrine (Phe), addition of Ter and Dob produced concentration-dependent relaxations. Removal of endothelium reduced the relaxant responses and area under curve (AUC) values and augmented the EC50 values to Ter and Dob at most, but not all, time points. Two-way analysis of variance (ANOVA) revealed that AUCs, maximum responses, and EC50 values significantly depended on both treatment (endothelium intact/endothelium denuded) and time of sacrifice. Results of the present study clearly show that in vitro sensitivity of rat thoracic aorta to beta-adrenergic agonists displays temporal variations depending on the time of animal sacrifice, and the presence of endothelium modifies the rhythmicity in beta-adrenergic activity. These variations may be due to the circadian rhythmicity in the adenylyl cyclase-cAMP-phosphodiesterase system that mediates the responses to beta-adrenergic agonists.

Bradykinin-induced responses in a coaxial bioassay system composed of rat anococcygeus muscle and guinea pig trachea.

1. Epithelium-dependent effects of bradykinin (BK) were investigated in a coaxial bioassay system which consisted of guinea pig trachea as donor organ and rat anococcygeus muscle as test tissue. 2. BK (10(-9) to 10(-5) M) produced concentration-dependent relaxations on the phenylephrine (3 x 10(-6) M)-precontracted rat anococcygeus muscle mounted alone. Relaxations decreased significantly when muscle was mounted in epithelium-intact trachea. There was also a significant difference between the relaxations obtained in the muscle within epithelium-intact and epithelium-denuded trachea (at 10(-7) to 10(-5) M concentrations). 3. Capsaicin (10(-5) M) pretreatment did not change BK (10(-9) to 10(-5) M)-induced relaxations in each preparation compared with vehicle pretreatment. Indomethacin (10(-6) M) in combination with thiorphan (10(-5) M) and atropine (10(-6) M) did not affect the BK-induced relaxations of the muscle within capsaicin-pretreated epithelium-intact or denuded trachea. 4. CGS 8515 (a specific 5-lipoxygenase inhibitor, 10(-6) M) did not change BK (10(-5) M)-induced relaxation on the muscle alone, and caused an increase of BK-induced relaxation on the muscle within epithelium-intact trachea compared with that obtained without CGS 8515. 5. Results showed that epithelial or nonepithelial factors were capable of modulating the responsiveness of rat anococcygeus muscle to BK. The decreased relaxation by BK in anococcygeus muscle did not occur by the release of cyclooxygenase products or tachykinins from tracheal epithelium, but it may have occurred by the contractile action of lipoxygenase product secreted by nonepithelial sources. In addition, BK might stimulate the secretion of an epithelium-derived inhibitory factor from the trachea.

In vitro evidence of tissue susceptibility rhythms. I. Temporal variation in effect of potassium chloride and phenylephrine on rat aorta.

In this study, time-dependent variations in the in vitro sensitivity of rat thoracic aorta rings to potassium chloride (KCl) and phenylephrine (Phe) were investigated. Animals were synchronized with a 12h light and 12h darkness (lights on 08:00-20:00) schedule, and thoracic aortas were obtained at six different times of the day (1, 5, 9, 13, 17, and 21 hours after lights on). In order to avoid endothelial influence, all experiments were performed in endothelium-denuded preparations. Responses to KCI showed time-dependent variations in all the concentrations used. Phe-induced contractions also exhibited time-dependent differences. The rhythmic pattern of Phe responses did not change with the presence of the alpha1-adrenergic antagonist prazosin. In addition, both the EC50 values of KCl and Phe, and also the K(B) values of prazosin, displayed rhythmicity. In conclusion, time of obtaining tissues is an important factor for experimental standardization in, at least, vascular smooth muscle preparations.

Twenty-four-hour variations in the effect of nitrodilators in rat aorta: lack of influence of the endothelium.

Time-dependent variations of the vasodilator effects of sodium nitroprusside and glyceryl trinitrate on isolated smooth muscle have been studied on rings of rat thoracic aorta, both endothelium-intact and endothelium-denuded. For most of the concentrations of sodium nitroprusside used the induced relaxations were significantly dependent on the time the tissues were obtained. However, significant temporal differences were obtained for glyceryl trinitrate-induced relaxations at lower concentrations only for both endothelium-intact and endothelium-denuded preparations. EC50 values of sodium nitroprusside and glyceryl trinitrate (i.e. the concentrations inducing half the maximum response) were also significantly different and they had quite similar rhythmic features both in endothelium-intact and in endothelium-denuded preparations. These results clearly show that the in-vitro sensitivity of rat thoracic aorta to nitrodilator agents varies over a 24-h period and thus depends on when the animals were killed; the presence of endothelium does not change the rhythm of nitrodilator activity. These variations might be a result of circadian rhythm in the guanylate cyclase-cGMP system which mediates responses to nitrodilator agents.

Antinociceptive effect of some amaryllidaceae plants in mice.

The antinociceptive effects of ethanolic extracts of Pancratium maritimum L., Narcissus tazetta subspecies tazetta and Leucojum aestivum L. bulbs have been investigated in mice using the p-benzoquinone-induced abdominal constriction and hot-plate tests. In the p-benzoquinone-induced abdominal constriction test the ethanolic extracts of P. maritimum (300, 600 or 1200 mg kg-1, s.c.) and N. tazetta subsp. tazetta (5, 50, 100 or 200 mg kg-1, s.c.) caused dose-dependent inhibition of abdominal constrictions whereas a fluctuating response was obtained from ethanolic extracts of L aestivum (2.5-500 mg kg-1, s.c.). In the hot-plate test P. maritimum and L. aestivum caused a significant increase of latency only at the highest concentrations used (1200 mg kg-1 and 500 mg kg-1, i.p., respectively). However, at these concentrations they also caused significant toxic effects. In contrast with P. maritimum and L. aestivum, N. tazetta subsp. tazetta (5-500 mg kg-1, i.p.) extracts had no antinociceptive effect in this test. These findings indicate that the antinociceptive effect of Amaryllidaceae plants differs depending on the model of nociception investigated.

Effects of platelet-activating factor antagonists WEB 2086 and BN 50730 on digoxin-induced arrhythmias.

Effects of platelet-activating receptor antagonists WEB 2086 (1.0-30.0 mg.kg-1 intravenously) and BN 50730 (10.0 mg.kg-1 intravenously) alone or in combination with CGS 8515 (a specific 5-lipoxygenase inhibitor, 0.3 mg.kg-1 intravenously) and Dazmegrel (a thromboxane synthase inhibitor, 1.0 mg.kg-1.hr-1 intravenous infusion) on digoxin-induced arrhythmias were investigated in anaesthetised guinea-pigs. ECG, mean arterial blood pressure, heart rate and arrhythmias were recorded, starting 30 min. before digoxin administration and continuing for 60 min. afterwards. WEB 2086 (10.0 mg.kg-1 intravenously) reduced the mortality rate and arrhythmia score significantly compared to the control values. However, in combination with CGS 8515, it did not affect the mortality rate. BN 50730 (10.0 mg.kg-1) reduced the incidence of ventricular fibrillation and also arrhythmia score. BN 50730 in combination with Dazmegrel was reduced the arrhythmia score, incidence of ventricular fibrillation and mortality rate significantly, compared to control values. Digoxin-induced acute rise in mean arterial blood pressure was not affected by any of drug treatment except WEB 2086 (10.0 mg.kg-1) in combination with CGS 8515. Heart rate values did not differ between groups. However, pressure-rate index was reduced by WEB 2086 alone or in combination with CGS 8615. Results showed that although two different platelet-activating factor antagonists have different effects on the incidence of ventricular fibrillation and mortality, they improved the digoxin-induced arrhythmias when they were used either separately or in combination with CGS 8515 or Dazmegrel by implicating that platelet-activating factor has a role on digoxin-induced arrhythmias.

Effect of ovalbumin challenge on endothelial reactivity of pulmonary arteries from sensitized guinea-pigs.

It has been generally demonstrated that sensitization process and/or specific antigen challenge causes an increase in the responsiveness of airway smooth muscle preparations to contractile agonists. However, there is no report elucidating such modifications in vascular preparations. In this study, we examined the influence of ovalbumin sensitization and challenge on the reactivity of guinea-pig pulmonary arteries to various vasoactive agents. Guinea-pigs were actively sensitized to ovalbumin (10 mg/kg) by i p injections on days 1, 3 and 5. Beginning 21 days after the last injection, animals were challenged with ovalbumin either in vitro or in vivo. The effects of sensitization process and challenge were studied on endothelium-dependent and -independent responses of guinea-pig pulmonary arteries. Ovalbumin challenge but not sensitization process significantly reduced the endothelium-dependent relaxant responses to acetylcholine and histamine. Similar reductions were also observed in the responses of calcium ionophore, A 23187. However, no alteration was observed in the responses to glyceryl trinitrate and potassium chloride which excludes an abnormality in the relaxant and contractile capacities of pulmonary artery smooth muscle following sensitization and challenge. In addition, an enhancement was observed in the contractile effect of phenylephrine after ovalbumin sensitization and challenge different from U 46619, a thromboxane analogue, and potassium chloride induced contractions. Incubation of the sensitized arteries with the mast cell stabilizer, disodium cromoglycate but not with the free radical scavenger superoxide dismutase protected the reduced responsiveness to endothelium-dependent vasodilators following challenge. We conclude that ovalbumin challenge causes an abnormality in endothelial cell reactivity of pulmonary vasculature possibly due to destructive enzymes released from mast cells.

Nitric oxide production by human umbilical vessels in severe pre-eclampsia.

OBJECTIVE: Pre-eclampsia is characterized by an increased vascular tone which might be related to an abnormal endothelial cell function. As representatives of the fetal circulation, we compared the nitric oxide (NO)-releasing capacity of human umbilical vessels from normal and pre-eclamptic pregnancies. METHODS: Normal and pre-eclamptic umbilical vessels were mounted in parallel in an organ chamber with three perfusion lines superfusing the same detector tissue (rubbed rat aortic ring). In this cascade system the capacity of the umbilical vessels to release NO was measured under basal conditions and after stimulation with histamine, bradykinin or calcium ionophore A23187. RESULTS: Relaxations dependent on basal NO release were found to be significantly higher in pre-eclamptic vessels (especially in veins) than in normal vessels. Conversely, stimulated NO release in response to histamine or bradykinin was significantly decreased in pre-eclamptic umbilical arteries, but not in veins, compared with normal vessels. However, there was no significant difference in the release of NO in response to A23187 between normal and pre-eclamptic vessels. CONCLUSIONS: The NO-releasing and NO-producing capacity in the vessels from fetal circulation is not diminished in pre-eclampsia. However, in pre-eclamptic umbilical arteries the NO release in response to certain stimuli (histamine or bradykinin) is diminished, probably as a result of alterations in the receptor function.