A narrative review on the association of high intraocular pressure and glaucoma in patients with retinal vein occlusion.

Background and Objective: Retinal vein occlusion (RVO) is a major cause of vision loss and elevated intraocular pressure (IOP), high ocular perfusion pressure, and glaucoma are known ophthalmic risk factors for RVO. The aim of this paper is to provide the update on the association and management of high IOP/glaucoma and RVO. Methods: A literature review was performed in PubMed and Medline until May 2022 utilizing specific keywords and cross-matched reference lists. Key Content and Findings: The association of RVO with high IOP/glaucoma may be attributed to retinal ganglion cell loss due to retinal ischemia in high IOP and glaucoma. As new modalities showed, decreased optic disc perfusion, reduced density of blood vessels in the optic nerve head of glaucoma patients, changes in the peripapillary microvascular parameters, and decreased retinal nerve fiber layer (RNFL) thickness of the optic nerve head of eyes with RVO suggest a common pathway between RVO and glaucoma. Literature suggests the close follow up for glaucoma development among patients with non-arteriovenous (AV) crossing (optic cup or optic nerve sited) RVO in fellow eye and management of elevated IOP among RVO cases treated with anti-vascular endothelial growth factor (VEGF) antibodies/corticosteroids and those with preexisting primary open angle glaucoma (POAG). Conclusions: Determining potential patient responses to treatment and considering therapeutic options are challenging among patients with RVO and glaucoma. However, IOP lowering managements in preventing IOP spikes in patients with preexisting glaucoma and early treatment of macular edema in eyes with RVO is recommended.

Model for Gold Nanoparticle Synthesis: Effect of pH and Reaction Time.

The synthesis of gold nanoparticles is dependent on both the concentration of trisodium citrate dihydrate and the time that it interacts with tetrachloroauric acid. A wide range of gold nanoparticles with various sizes and dispersity can be produced based on control variables, such as time of reaction and acid concentration, using a similar approach to that of the Turkevich model. In this model, the pH of the solution decreases slightly throughout the reaction (0.005 unit/min) due to the chemical interactions between trisodium citrate dihydrate and tetrachloroauric acid. Dicarboxy acetone is formed during citrate oxidization, resulting in gold nuclei formation over time. In addition, gold nanoparticle nucleation causes pH fluctuation over time based on gold nanoparticle sizes. An inverse correlation (coefficient of smaller than -0.97) was calculated between the pH and reaction time at different ratios of trisodium citrate dihydrate to tetrachloroauric acid. Regression analysis was used to develop a model for the prediction of the size of gold nanoparticles ranging from 18 to 38 nm based on the concentration of trisodium citrate dihydrate and the reaction time.

Corneal Epithelial Immune Dendritic Cell Alterations in Subtypes of Dry Eye Disease: A Pilot In Vivo Confocal Microscopic Study.

PURPOSE: To evaluate density and morphology of corneal epithelial immune dendritic cells (DCs) in different subtypes of dry eye disease (DED) using in vivo confocal microscopy (IVCM). METHODS: This retrospective study included 59 eyes of 37 patients with DED and 40 eyes of 20 age-matched healthy controls. Based on clinical tests, eyes with DED were categorized into two subtypes: aqueous-deficient (n = 35) and evaporative (n = 24). For all subjects, images of laser scanning in vivo confocal microscopy (IVCM) of the central cornea were analyzed for DC density and DC morphology (DC size, number of dendrites, and DC field). These DC parameters were compared among all dry eye and control groups. RESULTS: Compared with the controls, patients with DED had significantly higher DC density, larger DC size, higher number of dendrites, and larger DC field (all P < 0.001). Comparison between aqueous-deficient and evaporative subtypes demonstrated that DC density was significantly higher in aqueous-deficient subtype (189.8 ± 36.9 vs. 58.9 ± 9.4 cells/mm2, P = 0.001). However, there were no significant differences in morphologic parameters between DED subtypes. When aqueous-deficient DED with underlying systemic immune disease (Sjögren's syndrome and graft versus host disease) were compared with nonimmune conditions, the immunologic subgroup showed significantly higher DC density, DC size, and number of dendrites (all P < 0.05). CONCLUSIONS: Corneal IVCM demonstrated differential changes in DC density and morphologic DC parameters between subtypes of DED. These changes, which reflect the degree of immune activation and inflammation in DED, can be used for clinical practice and endpoints in clinical trials.

HMGB1 release triggered by the interaction of live retinal cells and uveitogenic T cells is Fas/FasL activation-dependent.

BACKGROUND: It is not clear how invading autoreactive T cells initiate the pathogenic process inside the diseased organ in T cell-mediated organ-specific autoimmune disease. In experimental autoimmune uveitis (EAU) induced by adoptive transfer of interphotoreceptor retinoid-binding protein (IRBP)-specific T cells in mice, we have previously reported that intraocular inflammation was initiated by infiltrating IRBP-specific T cells that directly interacted with retinal cells and resulted in the active release of high mobility group box 1 (HMGB1), an important member of damage associate molecular patterns (DAMPs). Furthermore, blockade of HMGB1 in our murine model reduced intraocular inflammation via suppression of IRBP-specific T cell functions. These results have demonstrated that HMGB1 is an early and critical mediator of induction of intraocular inflammation. The present study identified the cell surface molecule that triggers HMGB1 secretion. METHODS: Retinal explants from Fas-deficient (Fas(lpr)) and wild-type (Wt) C57BL/6 (B6) mice were cultured with activated IRBP 1-20 peptide-specific T cells or with a Fas-activating antibody (Jo2), and then the level of HMGB1 in culture supernatants were detected by ELISA. In addition, released HMGB1 was examined in the eye of Fas(lpr) and Wt mice after IRBP-specific T cell transfer. Uveitis was evaluated in the IRBP-specific T cell transferred Fas(lpr) mice after recombinant HMGB1 was restored within the eye and in the IRBP-specific T cell transferred Wt mice after they were treated with a Fas antagonist (Met12). RESULTS: In contrast to retinal explants from Wt mice, those from Fas(lpr) mice did not release HMGB1 after exposure to IRBP-specific T cells or to Jo2. The release of HMGB1 by Wt retinal explants was suppressed by Met 12. Moreover, after IRBP-specific T cell injection, Fas(lpr) mice did not release HMGB1 in the eye or develop EAU, but intravitreous injection of HMGB1 resulted in intraocular inflammation. Finally, tEAU in Wt mice was attenuated by local treatment with Met 12. Unlike HMGB1, Fas-induced IL-1 and IL-18 were not essential for tEAU induction. CONCLUSION: Our results show that interaction of retinal cells with infiltrating uveitogenic T cells leads to rapid release of HMGB1 via the Fas/FasL inflammatory signaling pathway.

Exosomes from retinal astrocytes contain antiangiogenic components that inhibit laser-induced choroidal neovascularization.

Exosomes released from different types of host cells have different biological effects. We report that exosomes released from retinal astroglial cells (RACs) suppress retinal vessel leakage and inhibit choroidal neovascularization (CNV) in a laser-induced CNV model, whereas exosomes released from retinal pigmental epithelium do not. RAC exosomes inhibit the migration of macrophages and the tubule forming of mouse retinal microvascular endothelial cells. Further, we analyzed antiangiogenic components in RAC exosomes using an angiogenesis array kit and detected several endogenous inhibitors of angiogenesis exclusively present in RAC exosomes, such as endostatin. Moreover, blockade of matrix metalloproteinases in the cleavage of collagen XVIII to form endostatin using FN-439 reverses RAC exosome-mediated retinal vessel leakage. This study demonstrates that exosomes released from retinal tissue cells have different angiogenic effects, with exosomes from RACs containing antiangiogenic components that might protect the eye from angiogenesis and maintain its functional integrity. In addition, by identifying additional components and their functions of RAC exosomes, we might improve the antiangiogenic therapy for CNV in age-related macular degeneration and diabetic retinopathy.

Light and ocular immunity.

PURPOSE OF REVIEW: Current scientific evidence suggests that the systemic immune response is affected by exposure to light. During the past century man has been exposed for the first time in evolution to light at night, as well as increasing ultraviolet radiation through depletion of the ozone layer in our atmosphere. These ecological changes have enhanced the impact of light on our systemic immune response. We will review the effect of light on the systemic immune response with particular emphasis on ocular immunity. RECENT FINDINGS: Visible light is now recognized to be important in the maintenance of immune privilege within the eye; however, little is known about the mechanism through which this effect occurs. Recent studies suggest that the generation of regulatory T cells involved in immune privilege within the eye is dependent on retinoic acid formation by retinal pigment epithelial cells. Light is also important in modulation of multiple pathways including adjustment of circadian rhythm and production of vitamin D. SUMMARY: Light regulates our biologic systems in many different ways. Its effect on the systemic immune response suggests that it is important in maintaining health, as well as in the induction of disease. A better understanding of the interaction of light with our biologic systems may allow new preventive measures to avoid disease and novel forms of treatment.

Effect of topical azithromycin on corneal innate immune responses.

PURPOSE: To determine the effect of azithromycin (AZM) in a murine model of corneal inflammation. METHODS: The effect of topical AZM was studied in murine corneal inflammation. Corneal inflammation was induced by thermal cautery in BALB/c mice. Leukocyte infiltration at different time points was analyzed by flow cytometry. At set time points, real-time polymerase chain reaction was performed to quantify the expression of different inflammatory cytokine transcript in the cornea. Corneal samples were analyzed immunohistochemically for the expression of intercellular adhesion molecule-1 (ICAM-1). Corneal neovascularization (CNV) was induced by micropellet (VEGF-A) placement. Mice were then treated topically with either AZM or vehicle. CNV was evaluated morphometrically. RESULTS: Eyes receiving AZM showed a significant decrease in corneal infiltration compared with the vehicle-treated group. AZM also significantly decreased messenger RNA expression levels of interleukin-1ß (IL-1ß), tumor necrosis factor-α (TNF-α) and ICAM-1 in the cornea. There was no significant difference in CNV between the AZM- and vehicle-treated groups. CONCLUSIONS: After an inflammatory insult, topical AZM significantly reduced leukocyte infiltration into the cornea. This was further supported by an associated decrease in expression of IL-1ß, TNF-α, and ICAM-1 in the cornea, indicating AZM may have a potential anti-inflammatory effect on corneal inflammation.

The nonadrenergic noncholinergic-mediated relaxation of corpus cavernosum was impaired in chronic lithium-treated rats: improvement with l-arginine.

One-third of lithium-treated men complain from sexual dysfunction, although the exact mechanisms of which are not yet known. In this study we investigated the effect of chronic lithium (LiCl, 600 mg/l for 30 days) administration on the neurogenic relaxation of isolated rat corpus cavernosum. The corporal strips were precontracted with phenylephrine and electrical field stimulation (EFS) was applied to obtain relaxation. Relaxation to EFS was significantly (P<0.001) impaired in LiCl-treated rats. The nitric oxide (NO) synthase inhibitor Nomega-nitro-l-arginine methyl ester (l-NAME; 100 microM) inhibited the relaxation to EFS in both LiCl-treated and control rats. The NO precursor l-arginine, at per se noneffective concentration (0.1 mM), significantly (P<0.001) enhanced the EFS-induced relaxation of LiCl-treated corporal strips. The relaxation responses to the NO donor sodium nitroprusside were similar between two groups. These data demonstrate that chronic lithium treatment could impair the NO-mediated neurogenic relaxation of rat corpus cavernosum which could be prevented by l-arginine.

Endogenous cannabinoids contribute to remote ischemic preconditioning via cannabinoid CB2 receptors in the rat heart.

In addition to well-known neurobehavioral effects, endogenous cannabinoids exert diverse cardiovascular actions. Recently, they have been suggested to protect the myocardium against ischemia/reperfusion injury. The aim of this study is to examine the contribution of endogenous cannabinoids to cardioprotection afforded by remote ischemic preconditioning. Three groups of remote preconditioned (15 min of mesenteric artery occlusion followed by 15 min of reperfusion) and three groups of sham-operated rats were included in the study. Animals were pretreated intravenously by vehicle, cannabinoid CB(1) (AM251, 1 mg/kg) or CB(2) (AM630, 1 mg/kg) receptor antagonist 15 min prior to remote preconditioning or sham operation. Myocardial injury was induced by 30 min of coronary artery occlusion followed by 2 h of reperfusion. The resultant arterial hypotension, ventricular arrhythmias, and infarct size were compared among the groups. Remote preconditioning exerted potent cardioprotection manifested as significant reductions in infarct size (P<0.001) as well as number and duration of arrhythmias (P<0.01, 0.01 and 0.05 for premature ventricular contractions, ventricular tachycardias and fibrillations; respectively). The cannabinoid CB(1) receptor antagonist pretreatment had no significant effect on ischemia-induced hypotension, arrhythmias or infarct size. On the other hand, the cannabinoid CB(2) receptor antagonist pretreatment abolished the protective effects of remote preconditioning on infarct size (P<0.01) and arrhythmias (P<0.01), without any significant effect on ischemia-induced hypotension. The results of this study suggest that endogenous cannabinoids, through acting on cannabinoid CB(2) receptors, are involved in the cardioprotective phenomenon of remote ischemic preconditioning, induced by mesenteric artery occlusion and reperfusion.

Role of ATP-sensitive potassium channels in the biphasic effects of morphine on pentylenetetrazole-induced seizure threshold in mice.

Although several studies have indicated that the opioid receptor agonist morphine exerts biphasic effects on clonic seizure threshold, as yet little is known of the underlying mechanisms in this effect. In the present study, using the specific ATP-sensitive K(+) (K(ATP)) channel blocker glibenclamide and the specific K(ATP) channel opener cromakalim, the possible involvement of K(ATP) channels in the effects of morphine on pentylenetetrazole (PTZ)-induced seizure threshold in mice was investigated. Acute administration of lower doses of morphine (1, 3 and 7.5 mg/kg, i.p.) increased and higher doses of morphine (30 and 60 mg/kg, i.p.) decreased the PTZ-induced seizure threshold. Glibenclamide (2.5-5 mg/kg) increased the PTZ-induced seizure threshold. Non-effective dose of cromakalim (0.1 microg/kg) inhibited anticonvulsant effect of glibenclamide (5 mg/kg). Acute administration of non-effective dose of glibenclamide (1 mg/kg) interestingly inhibited both anticonvulsant and pro-convulsant effects of morphine and this effect was significantly reversed by cromakalim (0.1 microg/kg). These results support the involvement of K(ATP) channels in the modulation of seizure threshold by morphine.

Reduced susceptibility to epinephrine-induced arrhythmias in cirrhotic rats: the roles of nitric oxide and endogenous opioid peptides.

BACKGROUND/AIMS: The clinical relevance of QT prolongation, the most widely recognized cardiac electrophysiological abnormality of cirrhosis, is still undefined. The aim of this study is to examine the susceptibility of chronic (4-week) bile duct-ligated rats to epinephrine-induced arrhythmias. The roles of nitric oxide and endogenous opioids were also evaluated. METHODS: Sham-operated and cirrhotic rats were treated with daily subcutaneous administrations of normal saline (1 ml/kg/day), L-NAME (a non-selective nitric oxide synthase inhibitor, 3mg/kg/day), and naltrexone (20mg/kg/day) during the fourth week after operation. In order to evaluate the effects of acute nitric oxide synthesis inhibition, additional groups of animals were treated by acute intraperitoneal L-NAME injections (3mg/kg). Arrhythmias were induced by intravenous injections of 10 microg/kg epinephrine. RESULTS: Despite QT prolongation (P<0.001), epinephrine induced fewer arrhythmias in cirrhotic rats compared to sham-operated animals (P<0.05). Chronic, but not acute, L-NAME administration corrected the QT prolongation in cirrhotic rats (P<0.001), and restored the susceptibility of cirrhotic rats to arrhythmias (P<0.05). Naltrexone injection without a significant effect on epinephrine-induced arrhythmias corrected QT interval in cirrhotic rats (P<0.001). CONCLUSIONS: This study shows that despite QT prolongation, cirrhotic animals are resistant against epinephrine-induced arrhythmias. This resistance is mediated by chronic nitric oxide overproduction.

Involvement of endogenous opioid peptides and nitric oxide in the blunted chronotropic and inotropic responses to beta-adrenergic stimulation in cirrhotic rats.

It is well known that chronotropic and inotropic responses to beta-adrenergic stimulation are impaired in cirrhosis, but the exact reason is not clear. Considering the inhibitory effect of endogenous opioid peptides and nitric oxide (NO) on beta-adrenergic pathway, we examined their roles in hyporesponsiveness of isolated atria and papillary muscles to isoproterenol stimulation in cirrhotic rats. Cirrhosis was induced by chronic bile duct ligation. Four weeks after ligation or sham operation, the responses of the isolated atria and papillary muscles to isoproterenol stimulation were evaluated in the absence and presence of naltrexone HCl (10(-6) m), N(omega)-nitro-L-arginine methyl ester (L-NAME, 10(-4) m), and naltrexone plus L-NAME in the organ bath. Considering the role of inducible NOS (iNOS) in hemodynamic abnormalities of cirrhotic rats, the chronotropic and inotropic responses of cirrhotic rats to isoproterenol stimulation were also assessed in the presence of aminoguanidine (a selective inhibitor of iNOS, 3 x 10(-4) m). Sham operation had no significant effect on basal atrial beating rate, contractile force, and maximal time derivatives for the development and the dissipation of papillary muscle tension. The basal atrial beating rate of cirrhotic rats did not show any significant difference compared with the sham-operated ones; however, the basal contractile parameters were significantly decreased in cirrhosis. Although the maximum effects of isoproterenol on chronotropic and inotropic responses were significantly reduced in cirrhotic rats, there was no difference in half-maximal effective concentrations of isoproterenol in these concentration-response curves. The basal abnormalities and the attenuated chronotropic and inotropic responses to isoproterenol were completely corrected by the administration of naltrexone, L-NAME and aminoguanidine. Concurrent administration of naltrexone and L-NAME also restored to normal the basal abnormalities and the blunted responses to isoproterenol in cirrhotic rats, and did not show any antagonistic effect. Based on these findings, both the endogenous opioid peptides and NO may be involved in the attenuated chronotropic and inotropic responses to beta-adrenergic stimulation in cirrhosis. It seems that the iNOS activity results in NO-induced hyporesponsiveness to beta-adrenergic stimulation in cirrhosis.

Modulated hemodynamic response to clonidine in bile duct-ligated rats: the role of nitric oxide.

Despite the well-known involvement of the peripheral sympathetic abnormalities in the development of cardiovascular complications of cholestasis, the role of the central sympathetic system is still elusive. The goal of this study was to evaluate the effects of central sympathetic tone reduction, through clonidine administration, on hemodynamic parameters of 7-day bile duct-ligated rats. The contributions of nitric oxide and endogenous opioids were also examined by acute intravenous (10 min before clonidine) or chronic daily subcutaneous administrations of N(omega)-nitro-L-arginine methyl ester (L-NAME, 3 mg/kg) or naltrexone (20 mg/kg). Seven days after bile duct ligation or sham operation, animals were anesthetized with sodium pentobarbital. After hemodynamic stabilization, clonidine (10 microg/kg) was injected intravenously, which elicited an initial hypertension (the peripheral effect) followed by persistent hypotension and bradycardia (the central effects). Cholestatic rats demonstrated significant basal bradycardia (P<0.001) and hypotension (P<0.05), which were corrected by chronic naltrexone but not L-NAME treatment. While the peripheral effect of clonidine was blunted, the central effects were exaggerated in cholestatic rats (P<0.01). Acute L-NAME treatment accentuated the hypertensive phase in sham-operated and cholestatic rats (P<0.05). However, the difference between the two groups was preserved (P<0.01). This treatment attenuated the central effects in both sham-operated and cholestatic rats to the same level (P<0.001). Chronic L-NAME treatment resulted in exaggeration of the peripheral response in cholestatic and central responses in sham-operated rats (P<0.05), and abolished the difference between the groups. Naltrexone treatment had no significant effect on either the central or the peripheral responses to clonidine. This study shows that both central and peripheral hemodynamic responses to clonidine are altered in cholestasis. It also provides evidence that nitric oxide contributes to the development of these abnormalities.

Effect of anandamide on nonadrenergic noncholinergic-mediated relaxation of rat corpus cavernosum.

The purpose of this study was to investigate the effect of the endogenous cannabinoid anandamide on the nonadrenergic noncholinergic (NANC) relaxant responses to electrical field stimulation in isolated rat corpus cavernosum. The corporal strips were mounted under tension in a standard oxygenated organ bath with guanethidine sulfate (5 microM) and atropine (1 microM) (to produce adrenergic and cholinergic blockade). The strips were precontracted with phenylephrine hydrochloride (7.5 microM) and electrical field stimulation was applied at different frequencies to obtain NANC-mediated relaxation. The expression of CB1, CB2 and vanilloid receptor proteins within the rat corpus cavernosum was evaluated using western blot analysis. The results showed that the relaxant responses to electrical stimulation were significantly enhanced in the presence of anandamide at 1 and 3 microM. The potentiating effect of anandamide (1 microM) on relaxation responses was significantly attenuated by either the selective cannabinoid CB1 receptor antagonist N-(piperidin-1-yl)-5-(4-iodophenyl)-1-(2, 4-dichlorophenyl)-4-methyl-1H-pyrazole-3-carboxamide (AM251; 1 microM) or the vanilloid receptor antagonist capsazepine (3 microM), but not by the selective cannabinoid CB2 receptor antagonist 6-iodo-2-methyl-1-[2-(4-morpholinyl) ethyl]-1H-indol-3-yl (4-methoxyphenyl)methanone (AM630; 1 microM). Neither of these antagonists had influence on relaxation responses. Indomethacin (20 microM) had no effect on NANC-mediated relaxation in the presence or absence of anandamide (1 microM). Preincubation with Nw-Nitro-L-Arginine Methyl Ester (L-NAME; 1 microM) significantly inhibited the relaxation responses in the presence or absence of 1 microM anandamide. Although at 30 nM, L-NAME did not cause a significant inhibition of relaxant responses individually, it significantly inhibited the potentiating effect of anandamide (1 microM) on relaxation responses. Anandamide (1 microM) had no influence on concentration-dependent relaxant responses to sodium nitroprusside (10 nM-1 mM), a nitric oxide (NO) donor. The western blotting of corporal tissues demonstrated the existence of both vanilloid and CB1 receptors in corporal strips. In conclusion, our results showed that anandamide has a potentiating effect on NANC-mediated relaxation of rat corpus cavernosum through both CB1 and vanilloid receptors and the NO-mediated component of the NANC relaxant responses to electrical stimulation is involved in this enhancement.

Pentoxifylline improves reoxygenation-induced contractile recovery through a nitric oxide-dependent mechanism in rat papillary muscles.

In this study, the protective effect of pentoxifylline against hypoxia-reoxygenation injury and the possible involvement of nitric oxide (NO)-mediated pathways in this protection were investigated in isolated rat papillary muscles. Papillary muscles were excised and isolated in Krebs-Henseleit solution aerated with 95% O2 and 5% CO2. Hypoxia was simulated by substituting O2 with argon. Three sets of experiments, testing 30, 60, and 90 min of hypoxia, were performed. The effects of different pentoxifylline concentrations on papillary muscle contractile parameters and responsiveness to isoproterenol were assessed. To investigate the role of NO, N(omega)-nitro-L-arginine methyl ester was added before pentoxifylline treatment. Pentoxifylline did not show any inotropic effect on papillary muscles. Hypoxia caused a profound depression of contractile parameters, which was not affected by pentoxifylline treatment. Reoxygenation resulted in significant partial recovery of contractile parameters after 30 and 60 but not 90 min of hypoxia. In experiments with 30 and 60 min of hypoxia, reoxygenation-induced contractile recovery and responsiveness to isoproterenol were improved by pentoxifylline in a concentration-dependent fashion. These functional improvements were completely blocked by N(omega)-nitro-L-arginine methyl ester pretreatment. No improvement was observed in 90-min hypoxia experiment. In conclusion, pentoxifylline improved contractile recovery during reoxygenation and postreoxygenation responsiveness to beta-adrenergic stimulation through the NO-dependent mechanism.

Contribution of endogenous opioids and nitric oxide to papillary muscle contractile impairment in cholestatic rats.

Attenuated responsiveness to adrenoceptor stimulation has been proposed as an important factor underlying cardiovascular complications of cholestasis. We examined isolated papillary muscle responsiveness to alpha (phenylephrine) and beta-adrenoceptor (isoproterenol) agonists in 7-day bile duct-ligated rats. We investigated the role of nitric oxide (NO) and endogenous opioids in papillary muscle hyporesponsiveness to isoproterenol stimulation. In order to evaluate the effect of NO and endogenous opioids, animals were treated with chronic subcutaneous injections of N(omega)-nitro-L-arginine methyl ester (L-NAME, 10 mg/kg/day) or naltrexone (20 mg/kg/day), or isolated papillary muscles were exposed acutely to the same drugs (10(-4) and 10(-6) M, respectively) in an organ bath. The basal contractile force of papillary muscle, +dT/dtmax and -dT/dtmax, was significantly decreased in bile duct-ligated rats compared to sham-operated ones (P<0.05, for each value). The concentration-response curve for phenylephrine and isoproterenol demonstrated a reduced maximum effect in bile duct-ligated rats compared to the sham-operated group (P<0.01 and 0.05, respectively). Basal contractile abnormalities of bile duct-ligated rats were corrected by L-NAME or naltrexone treatment, either acute or chronic. While chronic L-NAME treatment resulted in a left-ward shift (P<0.05), it had no effect on the maximum effect in bile duct-ligated rats. Acute L-NAME treatment did not influence isoproterenol responsiveness. Acute and chronic naltrexone treatment resulted in partial and complete correction of the hyporesponsiveness of bile duct-ligated rats, respectively (P<0.05). This investigation demonstrates that the papillary muscles of 7-day bile duct ligated-rats have an impaired basal contractility and hyporesponsiveness to both alpha and beta-adrenoceptor stimulation. It also provides evidence for the involvement of increased opioidergic tone and NO overproduction in cholestasis-induced cardiac impairment.

Cholestatic liver disease modulates susceptibility to ischemia/reperfusion-induced arrhythmia, but not necrosis and hemodynamic instability: the role of endogenous opioid peptides.

BACKGROUND/AIMS: Acute cholestasis is associated with cardiovascular complications, which mainly manifest during stressful conditions. The goal of this study is to evaluate susceptibility of 7-day bile duct-ligated rats to ischemia/reperfusion-induced injury. METHODS: Sham-operated and cholestatic rats, treated with daily normal saline, L-NAME (a non-selective NO synthase inhibitor) naltrexone, or both L-NAME and naltrexone were subjected to 30 min of ischemia followed by 2 h of reperfusion. RESULTS: Cholestatic rats demonstrated significant bradycardia, hypotension (P < 0.01), and QT prolongation (P < 0.001). The incidence of premature ventricular contractions (P < 0.01), incidence and duration of ventricular tachycardia (P < 0.05), but not ventricular fibrillation, were significantly lower in cholestatic rats. There was no significant difference in hemodynamic instability and infarct size between the groups. L-NAME corrected QT prolongation in cholestatic rats (P < 0.05), with no effect on heart rate, blood pressure and arrhythmia. Naltrexone restored normal heart rate (P < 0.05), blood pressure (P < 0.05) and susceptibility to arrhythmia (P < 0.05) in cholestatic animals, with no significant effect on QT interval. L-NAME and naltrexone co-administration corrected bradycardia (P < 0.05), hypotension (P < 0.05), QT prolongation (P < 0.05) and abolished resistance of cholestatic rats against arrhythmia (P < 0.05). CONCLUSIONS: This study suggests that short-term cholestasis is associated with resistance against ischemia/reperfusion-induced arrhythmia, which depends on availability of endogenous opioids.

alpha2-Adrenoceptor subsensitivity in mesenteric vascular bed of cholestatic rats: the role of nitric oxide and endogenous opioids.

Cholestasis is associated with vascular changes and in previous studies decreased response of visceral vessels of cholestatic animals to phenylephrine and acetylcholine has been shown. In the present study, the response of mesenteric vascular bed of cholestatic rats to clonidine (an alpha2-adrenoceptor agonist) was investigated and we also examined the role of endogenous opioids and nitric oxide (NO). Seven-day ligation of bile duct was used as the model to study cholestasis. Six groups of rats, each of which divided into two subgroups (bile duct-ligated and sham-operated), were examined. Three groups of animals were chronically treated with either normal saline, naltrexone (an opioid receptor antagonist, 20 mg/kg/day, s.c.) or aminoguanidine (a selective inducible nitric oxide synthase inhibitor, 150 mg/kg/day, s.c.) for 7 days. After 7 days the response of the mesenteric vascular bed to subsequent doses of clonidine was studied. In other two groups, 7 days after the operation, the response of the mesenteric vascular bed to clonidine in the presence of either yuhimbine, an alpha2-adrenoceptor antagonist, or N(omega)-nitro-L-arginine methyl ester (L-NAME), a non-selective nitric oxide synthase inhibitor, was studied. In the last group, vasodilation response to sodium nitroprusside (an endothelium-independent vasorelaxant) was evaluated. Clonidine caused vasodilation in a dose-dependent manner by acting on endothelial alpha2-adrenoceptors since its effect was antagonized by yohimbine, and this vasodilation was through the L-arginine pathway since there was no response in the presence of L-NAME in the perfusate. Compared to sham-operated rats, there was a significant right shift in the clonidine concentration curves of cholestatic animals. Maximum response in cholestatic rats was significantly lower comparing to the sham group (P<0.01) and the dose of clonidine that causes 50% of maximum response (ED50) was significantly higher in cholestatic rats (P<0.05). Vasodilation response to sodium nitroprusside was the same in cholestatic and sham-operated rats. Seven-day treatment with aminoguanidine recovered the effect of cholestasis. Seven-day treatment with naltrexone caused an increase in maximum response (P<0.01) and a decrease in ED50 (P<0.05) in cholestatic rats, while this treatment in sham-operated rats caused a decrease in the maximum response (P<0.01) and an increase in ED50 (P<0.05). This study showed that cholestasis is associated with decreased responsiveness of mesenteric vascular bed to clonidine and the cholestasis-associated NO overproduction and increased level of endogenous opioids may contribute to this process.

Resistance of cholestatic rats against epinephrine-induced arrhythmia: the role of nitric oxide and endogenous opioids.

Short-term ligation of bile duct has been used as a model to study acute cholestasis and is associated with various cardiovascular abnormalities. We examined the role of nitric oxide (NO) and endogenous opioids on epinephrine-induced arrhythmia in 7-day bile duct-ligated (BDL) rats. Six groups of rats, each of which was subdivided into two subgroups (sham-operated and BDL), were examined. First group of animals were chronically treated with normal saline. In the second and third groups, single intraperitoneal administration of N(omega)-nitro-L-arginine methyl ester (L-NAME, 10 mg/kg) or naltrexone (20 mg/kg) was performed 30 min before evaluation of epinephrine-induced arrhythmia. Two groups received chronic administration of low dose (3 mg/kg/day) or high dose (10 mg/kg/day) L-NAME; and the last group was treated chronically with naltrexone (20 mg/kg/day). Chronic drug administration was performed subcutaneously for 6 consecutive days following BDL or sham operation. After induction of arrhythmia by intravenous injection of 10 microg/kg epinephrine, mean arterial pressure and electrocardiogram were recorded for 1 min. Heart rate and mean arterial pressure were significantly lower in BDL rats (P<0.01). Chronic injection of naltrexone increased heart rate and mean arterial pressure in BDL (P<0.05). Chronic low dose L-NAME administration had no effect on baseline hemodynamic parameters. High dose L-NAME injection corrected hypotension in BDL rats, but not bradycardia (P<0.05). Epinephrine induced less arrhythmia in BDL rats (P<0.05). Acute and chronic injection of naltrexone had no effect on the resistance of BDL rats against epinephrine-induced arrhythmia. Although acute L-NAME administration enhanced arrhythmias in sham-operated rats (P<0.001), it had no effect on BDL animals. Chronic injection of low dose or high dose L-NAME, without having any effect on sham-operated animals, increased arrhythmias in BDL rats (P<0.01). This study showed that BDL animals are resistant against epinephrine-induced arrhythmia and this resistance depends on long-term NO overproduction.

Time-dependent reduction of acetylcholine-induced relaxation in corpus cavernosum of cholestatic rats: role of nitric oxide and cyclooxygenase pathway.

The endothelium-dependent relaxation of corpus cavernosum smooth muscle and the roles of nitric oxide (NO) and arachidonic acid products of cyclooxygenase were investigated in non-operated, SHAM-operated, and bile duct-ligated rats. We further investigated the time-dependent alterations of corpus cavernosum relaxation in 2-, 7-, and 14-day bile duct-ligated animals. Acetylcholine produced concentration-dependent relaxation in phenylephrine-precontracted strips of corpus cavernosum. A significant reduction in the acetylcholine-induced relaxation was observed 2 days after bile duct ligation, and a greater reduction was observed on subsequent days. Incubation with 20 microM indomethacin reduced the acetylcholine-induced relaxation of the corpus cavernosum of unoperated rats while it had no effect in the corpus cavernosum of bile duct-ligated rats. Chronic treatment with Nomega-Nitro-L-Arginine Methyl Ester (L-NAME, 3 mg/kg/day, intraperitoneally) reduced the relaxation responses in the unoperated group while it had no effect in the bile duct-ligated group. These results show that acetylcholine-induced corporal relaxation is impaired in cholestatic rats, and this may be related to deficient nitric oxide production by the endothelium. The involvement of prostaglandins in this impairment seems unlikely.