Effects of inhibition of nitric oxide synthase on basal anterior segment ocular blood flows and on potential autoregulatory mechanisms.

Experiments were undertaken to determine the role played by nitric oxide (NO) in basal ocular blood flow in the anterior aspect of the eye. Subsequent studies focused on existence of autoregulatory mechanisms and on the potential involvement of NO. Cats were anesthetized with pentobarbital (36 mg/kg, i.p.). A femoral artery and vein were cannulated for measuring blood pressure and for drug administration, respectively. Anterior segment blood flow was measured in a continuous fashion from the long posterior ciliary artery (LPCA) using ultrasonic flowmetry and from the anterior choroid using laser-Doppler flowmetry. A needle was placed into the anterior chamber, and autoregulatory mechanisms were studied by decreasing ocular perfusion pressure via stepwise elevations of IOP. Non-selective inhibition of NO synthase with L-NAME (20 mg/kg, i.v.) significantly decreased basal blood flow from both sites. L-NAME (5 mg/kg, i.v.) was without effect as was D-NAME (25 mg/kg, i.v.). Increasing IOP produced a linear decrease on LPCA blood flow indicating absence of autoregulation. In contrast, stepwise elevation of IOP produced a delayed, non-linear response in the anterior choroid suggestive of a strong autoregulatory response. Neither response to elevated ocular perfusion pressure was further altered by inhibition of NO synthase with L-NAME (20 mg/kg, i.v.). The results confirm previous reports that nitric oxide plays a pivotal role in maintenance of basal ocular blood flow. Autoregulation was not seen in the LPCA. In contrast, there was a clear autoregulatory response in the anterior choroid, although neither response was altered by inhibition of NO synthase.     

Effect of chronic inhibition of nitric oxide synthase on ocular blood flow and glucose metabolism in the rat

AIMS—To investigate the effects of chronic administration of nitric oxide synthase inhibition on ocular blood flow and metabolic demand in the rat and to compare these effects with changes in the cerebral and peripheral circulation.
METHODS—Male Sprague-Dawley rats were injected with the nitric oxide synthase inhibitor L-NAME (75 mg/kg ip), either on a single occasion only or once daily for 10 consecutive days. Controls were injected with saline. Regional blood flow and glucose metabolism were measured from tissue samples, using [¹⁴C]-iodoantipyrine and [¹⁴C]-2-deoxyglucose respectively, 1 hour after either acute L-NAME injection or 1 hour after the last injection of the chronic treatment protocol.
RESULTS—Mean arterial pressure was significantly increased (+31%) following the acute injection (indicating peripheral vasoconstriction) and this effect was enhanced (+50%) following chronic treatment. In both the ocular and cerebral circulation, blood flow was decreased following acute treatment (−48% and −43% respectively). However, while this response was totally attenuated in the cerebral circulation following chronic L-NAME treatment (−4%), the ocular circulation remained responsive (−57%). Metabolic demand in brain and eye tissue, as reflected in the accumulation of 2-deoxyglucose, was unaffected by either acute or chronic treatment with L-NAME.
CONCLUSION—Homeostatic mechanisms appear to be activated in the cerebral circulation which re-establish flow metabolism homeostasis, and the effect of L-NAME on cerebral blood flow is attenuated following repeated exposure. This process does not seem to happen in the ocular circulation and, thus, the ocular vasculature appears to behave more like those blood vessels which determine total peripheral resistance than the cerebral circulation. It remains to be seen whether the sustained decrease in blood flow in the eye is sufficient to compromise ocular function and render the eye susceptible to damage from chronic L-NAME induced oligaemia.

     

Possible role for nitric oxide releasing nerves in the regulation of ocular blood flow in the rat

AIM—To investigate the role of nitrergic nerves in the regulation of ocular blood flow.
METHODS—Conscious, lightly restrained rats were treated with either the neuronal nitric oxide synthase inhibitor 7-nitroindazole (7-NI), or the non-selective inhibitor, NG-nitro-L-arginine methyl ester (L-NAME), and ocular blood flow was measured ex vivo from tissue samples, using the fully quantitative [14C]-iodoantipyrine technique.
RESULTS—In the peripheral circulation, L-NAME produced an increase in arterial blood pressure (+22%) while 7-NI had no effect. In contrast, both 7-NI and L-NAME produced significant decreases in ocular blood flow (−31% and −59% respectively). The ocular vascular resistance calculated from ocular blood flow and mean arterial blood pressure increased by 29% following 7-NI, but by 130% following L-NAME.
CONCLUSIONS—Nitric oxide releasing neurons may play an important contributory role in regulating ocular blood flow.

Keywords: nitric oxide; neuronal nitric oxide synthase; 7-nitroindazole; NG-nitro-L-arginine methyl ester; ocular blood flow     

Effects of adrenomedullin on ocular hemodynamic parameters in the choroid and the ophthalmic artery

PURPOSE: Adrenomedullin acts as a vasodilator and may play a role in inflammatory processes in the eye. This study was designed to determine whether nitric oxide formation is involved in the response to adrenomedullin in the ocular vasculature in vivo. METHODS: The effects of systemic intravenous adrenomedullin (3.2-16.0 pmol/[kg. min])) on choroidal blood flow were assessed by measurement of fundus pulsation amplitude and laser Doppler flow in the macula, and on blood flow in the ophthalmic artery by ultrasound Doppler flow in pilot studies (n = 7). Subsequently, in a double-blind randomized placebo-controlled crossover study in eight healthy male subjects the effects of 12.8 pmol/(kg. min) adrenomedullin on ocular and systemic hemodynamics were investigated. Adrenomedullin was co-infused with the nitric oxide synthase inhibitor N(G)-monomethyl-L-arginine (3 mg/kg bolus and 30 micro g/[kg. min] continuous intravenous infusion) or vehicle control on separate study days. RESULTS: Adrenomedullin dose dependently increased choroidal blood flow and flow velocity in the ophthalmic artery. N(G)-monomethyl-L-arginine reduced the effect of adrenomedullin on fundus pulsation amplitude, but did not alter the flow response in the ophthalmic artery. Systemic hemodynamics were unaffected by adrenomedullin infusion. CONCLUSIONS: Ocular blood flow is sensitive to changes in adrenomedullin concentrations. The acute vasodilator effects of adrenomedullin are nitric oxide-dependent in the choroid, but not in the ophthalmic artery.     

Topical application of a nitric oxide synthase inhibitor reduces intraocular pressure in rabbits with experimental glaucoma.

The role of nitric oxide (NO) in neuronal degeneration of glaucoma is well established, and drugs to inhibit NO production have been introduced in preclinical studies. The present experiments were made to investigate the pharmacological efficacy of a topical formulation of the nonselective nitric oxide synthase (NOS) inhibitor, nitro-L-arginine methyl ester (L-NAME), in an experimental model of glaucoma in rabbits. L-NAME was dissolved in an isotonic, mucoadhesive, viscosized, buffered solution in concentrations of 0.1%, 0.5%, or 1% (w/v). Ocular hypertension (of at least 15 mmHg compared to basal values) was induced by intra-ocular injection of alpha-chymotrypsin. The instillation of L-NAME topical formulations lowered the IOP of hypertensive rabbits in a dose-related manner, with a maximum drop of 12.0 mmHg 60 minutes after administration of the highest concentration. The area under the curve (AUC) of the DeltaIOP (mmHg) versus time (minutes) was 1050.3 +/- 141.7 and 15.1 +/- 2.5 for the 1% L-NAME-treated group and vehicle-treated group, respectively. No change was found in IOP or pupil diameter after instillation of L-NAME eye drops in normotensive rabbits. This study provides the first evidence that topical L-NAME significantly reduces the IOP in a model of ocular hypertension.     

急性高眼压状态大鼠视网膜一氧化氮 及其合酶变化的研究

目的通过对急性高眼压下大鼠视网膜一氧化氮(nitric oxid e,NO)及其合酶(nitric oxide synthase,NOS)变化的分析,探讨一氧化氮在高眼压视网膜损伤中的作用。方法Wistar大鼠60只,随机分成为高眼压30 min组;高眼压60 min组;高眼压90 min组;高眼压后12 h组和高眼压后24 h 组。前房加压灌注成高眼压模型。利用镀铜镉还原法测定视网膜中NO₂^－/NO₃^－ 的 含量从而间接反映视网膜组织中NO的含量。利用免疫组织化学法研究视网膜内神经结构型一氧化氮合酶(neuronal constitutive nitric oxide synthase,ncNOS)的分布及其变化。结果正常及缺血大鼠视网膜神经结构型一氧化氮合酶(ncNOS)主要位于大鼠视网膜内核层内侧,节细胞层,内丛状层。急性高眼压30min,60min ,90min大鼠视网膜NO的含量逐渐下降(P<0.01),ncNOS阳性 细胞数也逐渐减少(P<0.05),阳性物质表达减弱;急性高眼压 90min后再灌注过程中,NO的含量比90min时明显升高(P<0.05),但与正常比较仍显著下降(P<0.01)。ncNOS阳性细胞数继续减少(P <0.01)。结论一氧化氮参与了急性高 眼压下视网膜损伤过程;通过ncNOS催化的途径合成的NO对缺血以及缺血再灌注的视网膜可能具有重要的作用。(中华眼底病杂志,2001,17:230-233)     

Effects of nitric oxide synthase inhibition on ciliary blood flow, aqueous production and intraocular pressure

A prior study found that inhibition of nitric oxide synthase with L-NAME causes a large, rapid decrease in IOP in anesthetized rabbits. In this follow-up study we sought to determine if this hypotensive effect was due to decreased aqueous production, possibly caused by ciliary vasoconstriction. Two protocols were performed in anesthetized rabbits. In the first protocol, mean arterial pressure (MAP) and IOP were measured by direct cannulation, and aqueous flow was measured by fluorophotometry, before and after L-NAME (5 mg kg(-1), i.v., n = 7). In the second protocol, ciliary blood flow was measured transclerally by laser Doppler flowmetry while MAP was varied mechanically over a wide range before and after L-NAME (5 mg kg(-1), i.v., n = 8). L-NAME caused a significant increase in MAP and decreases in IOP, ciliary blood flow and aqueous flow. L-NAME also caused a significant downward shift in the ciliary pressure-flow relation over the entire pressure range examined. The results indicate that L-NAME causes ciliary vasoconstriction and decreases aqueous production, suggesting that the L-NAME ocular hypotensive effect may be due in part to a blood flow-dependent decrease in aqueous production. However, assuming no uveoscleral outflow and constant episcleral venous pressure and outflow facility, the decrease in aqueous flow accounts for 66% of the drop in IOP, suggesting an additional effect of L-NAME on aqueous outflow.     

Effect of nitric oxide synthase inhibitor on optic nerve head circulation in conscious rabbits

PURPOSE: To study the effect of a nitric oxide synthase inhibitor on tissue circulation in the optic nerve head (ONH) of conscious rabbits. METHODS: N(G)-nitro-L-arginine methyl ester (L-NAME) (1, 10, or 100 mg/kg), D-NAME (10 mg/kg), or physiological saline was administered intravenously to albino rabbits. A quantitative index of blood velocity, the normalized blur (NB), was measured in the ONH by laser speckle tissue circulation analyzer. The intraocular pressure (IOP) and blood pressure (BP) were also measured. L-arginine (10 mg/kg) was intravenously administered 20 minutes after L-NAME (10 mg/kg) injection. Acetylcholine (ACh; 10 microg/kg per minute) was infused for 15 minutes, with or without pretreatment of L-NAME (1 mg/kg). RESULTS: L-NAME induced a continuous decrease of the NB in a dose-dependent manner, but D-NAME caused no significant change. At 100 mg/kg, L-NAME significantly increased the IOP, mean BP, and ocular perfusion pressure, but the other doses caused no significant changes. When L-arginine was administered after L-NAME injection, the NB returned to its initial level and remained there. Pretreatment with L-NAME inhibited the increase of NB induced by ACh. CONCLUSIONS: These results indicate that nitric oxide regulates basal tissue circulation in the ONH of conscious rabbits and suggest that ACh increases the circulation by promoting nitric oxide synthesis.     

ZX-5及其光学异构体对兔眼血流和大鼠视网膜功能恢复的影响

目的:研究ZX-5对缺血后视网膜功能的恢复作用,并比较其光学异构体(R,R)-ZX-5和(S,S)-ZX-5对脉络膜血流及缺血后视网膜功能恢复的影响。方法:用彩色微球技术研究兔高眼压下(40mmHg)脉络膜血流的变化。用视网膜电生理仪测量b波,评价大鼠缺血后视网膜功能的恢复情况。结果:10g/L(R,R)-ZX-5滴眼液50μL能在不同时间点提高脉络膜血流(P<0.05),而(S,S)-ZX-5在相同条件下对提高脉络膜血流没有影响。ZX-5和(R,R)-ZX-5在不同时间点对视网膜缺血后功能恢复作用明显(P<0.05),(R,R)-ZX-5的作用优于ZX-5;而(S,S)-ZX-5对缺血后视网膜功能的恢复作用不明显。结论:ZX-5和(R,R)-ZX-5对增加脉络膜血流量和促进视网膜功能的恢复有显著功效,(R,R)-ZX-5恢复视网膜功能的作用更强,有可能进一步开发成有效防治眼血流障碍相关性眼病的药物。     

Role for nitric oxide in the hyperpermeability and hemodynamic changes induced by intravenous VEGF

PURPOSE: To explore the effects of brief intravenous (IV) infusion of vascular endothelial growth factor (VEGF) on vascular albumin permeability, blood flow, and vascular conductance (blood flow normalized to arterial blood pressure) in ocular tissues and brain and to assess the role of nitric oxide in mediating these changes. METHODS: A quantitative, double-tracer, radiolabeled albumin permeation method was combined with radiolabeled microspheres for assessment of changes in vascular permeability and blood flow, respectively, induced in ocular tissues by IV infusion of recombinant human VEGF165 for 20 minutes (80-450 picomoles/kg body weight). An inhibitor of nitric oxide synthase (NOS), NG-monomethyl-L-arginine (L-NMMA; 50 micromoles/kg body weight infused simultaneously with VEGF), was used to explore the role of nitric oxide in mediating the vascular changes induced by VEGF. RESULTS: Infusion of VEGF165 in thiopental-anesthetized rats dose-dependently increased 125I albumin permeation in the retina, anterior uvea, and choroid/sclera and in brain, aorta, lung, kidney, small intestine, and peripheral nerve. Mean arterial blood pressure, cardiac output, and stroke volume were decreased only at the highest dose of VEGF, whereas heart rate remained unchanged. Blood flow was increased in the anterior uvea, and vascular conductance was increased in retina, anterior uvea, choroid/sclera, and brain at the highest dose of VEGF. The NOS inhibitor, L-NMMA, blocked VEGF-induced vascular hyperpermeability in all ocular and nonocular tissues, prevented the increase in vascular conductance in all ocular tissues, and blocked the decrease in mean arterial blood pressure, cardiac output, and stroke volume. Infusion of L-NMMA alone decreased vascular conductance in choroid/sclera and kidney, slightly increased mean arterial blood pressure, and in general, did not affect 125I-albumin permeation. (L-NMMA slightly decreased albumin permeation in the retina and increased it in the brain.) CONCLUSIONS: Intravenous infusion of VEGF can acutely impair endothelial cell barrier functional integrity and relax resistance arterioles in ocular tissues and brain through a mechanism involving activation of NOS.     

Evidence that nitric oxide is involved in autoregulation in optic nerve head of rabbits

PURPOSE: To determine the role played by nitric oxide (NO) in the autoregulation of circulation in the optic nerve head (ONH). METHODS: The intraocular pressure (IOP) was increased and maintained at 50 mm Hg by the infusion of balanced saline solution (BSS) into the anterior chamber of albino rabbits. Experiments were performed with or without an intravenous injection of 10, 20, or 50 mg/kg N(G)-nitro-L-arginine methyl ester (L-NAME), a nitric oxide synthase (NOS) inhibitor. The blood flow in the ONH was evaluated by the hydrogen clearance method, and NO metabolites (nitrite and nitrate) were measured in the ONH under the same experimental conditions in other rabbits. Visual evoked potentials (VEPs) were recorded before the IOP elevation and every 15 minutes during the 60 minutes of elevation. The effect of elevated IOP on the VEPs and the hemodynamics and NO levels in the ONH were determined. The effect of pretreatment with a NOS inhibitor on the IOP-induced changes was also investigated. RESULTS: The implicit time of the VEP was prolonged after L-NAME in a dose-dependent manner, whereas the implicit time in the control group (saline) was less affected. Blood flow in the ONH was not reduced by an elevation of the IOP (50 mm Hg) but was significantly reduced by L-NAME (20 mg/kg). The NO metabolites, which were elevated in the ONH during IOP elevation in the control, were also depressed by L-NAME pretreatment. CONCLUSIONS: These results indicate that NO may play a role in the autoregulation of circulation in the ONH during elevated IOP. This would mean that NO provides some neuroprotection during an acute phase of ischemia in the ONH.     

Role of nitric oxide in choroidal blood flow regulation during light/dark transitions

PURPOSE: Several studies have recently shown that a transition from light to dark is associated with a reduction in choroidal blood flow. The mechanism underlying this effect is unclear but may be related to changes in neural input. In the present study, the authors hypothesized that either the alpha-receptor agonist phenylephrine or the nitric oxide synthase (NOS) inhibitor L-NMMA may alter the choroidal blood flow response during a transition from light to dark. METHODS: In 15 healthy male nonsmoking subjects, the response of choroidal perfusion was studied in a randomized placebo-controlled three-way crossover study. Phenylephrine, L-NMMA or placebo was administered on different study days, and the effect of a light/dark transition on choroidal perfusion parameters was studied. Subfoveal choroidal blood flow and fundus pulsation amplitude were assessed with laser Doppler flowmetry and laser interferometry, respectively. RESULTS: Before drug administration, a transition from light to dark reduced both choroidal hemodynamic parameters by 11% to 20%. Neither phenylephrine nor placebo altered basal choroidal blood flow or choroidal blood flow responses to the light/dark transitions. By contrast, the NOS inhibitor L-NMMA significantly reduced basal choroidal blood flow by 20.5% +/- 5.9% (P < 0.001) and basal fundus pulsation amplitude by 21.5% +/- 4.8% (P < 0.001). In addition, the response of subfoveal choroidal blood flow (-6.2% +/- 3.2%; P = 0.008) and fundus pulsation amplitude (-4.2% +/- 2.4%; P < 0.001) to the light/dark transition was significantly diminished. CONCLUSIONS: The present study indicates that NO plays a role in the choroidal blood flow decrease during a transition from light to dark. Given that L-NMMA is a nonspecific inhibitor of NOS, the present study does not clarify whether this NO is from endothelial or neural sources.     

The effect of the nonspecific nitric oxide synthase inhibitor NG-nitro-L-arginine methyl ester on the choroidal compensatory response to myopic defocus in chickens.

PURPOSE: Chick eyes show rapid compensation to retinal defocus. One component of this mechanism involves changes in the thickness of the choroid: when the retina is exposed to myopic defocus, the choroid thickens, pushing the retina forward; conversely, when the eye is exposed to hyperopic defocus, the choroid thins. The underlying mechanism(s) for these changes are unknown. We tested the hypothesis that nitric oxide might play a role. METHODS: We examined the effect of the nonspecific nitric oxide synthase inhibitor NG-nitro-L-arginine methyl ester (L-NAME) on the compensatory choroidal thickening in response to myopic defocus using two visual paradigms: first, in previously form-deprived "recovering" eyes and, second, in eyes wearing +15 D spectacle lenses. L-NAME was injected intravitreally after removal of the diffuser or immediately before putting on the lenses. In addition, we looked at the effect of L-NAME on experimentally thickened choroids (induced by 1 week of recovery from deprivation myopia or 1 week of +15 D lens wear) and on choroids of normal eyes. Eyes were measured using A-scan ultrasonography before the injections and at subsequent intervals for several days. As a control for the injection procedure, eyes with the same visual conditions were injected with saline. Fellow eyes were untreated and uninjected. RESULTS: L-NAME inhibited choroidal thickening in both previously form-deprived eyes (2 vs. 117 microm; p < 0.001) and eyes wearing +15 D lenses (3 vs. 137 microm; p < 0.02). The effect was rapid, transient, and dose dependent (ED50, 0.26 micromoles). L-NAME produced thinning in experimentally thickened choroids (recovering: -116 microm; lenses: -219 microm) and in normal choroids (-47 microm) within 7 hours. CONCLUSIONS: Nitric oxide may play a role in modulating choroidal thickness. The mechanism is as yet unknown.     

Role of nitric oxide in the control of ocular blood flow

In the recent years it has been recognized that nitric oxide is an important regulator of ocular blood flow. Nitric oxide is involved in the control of basal blood flow in the choroid, optic nerve and the retina. In addition, nitric oxide mediates a number of vasodilator responses in ocular vessels to agonists such as acetylcholine, bradykinin, histamine, substance P and insulin. Nitric oxide also plays a role in hypercapnia-induced vasodilation in the choroid and is a modulator of pressure autoregulation in this vascular bed. Abnormalities of the L-arginine/nitric oxide system have been observed in a variety of ocular diseases including glaucoma, diabetic retinopathy and retinopathy of prematurity. This makes the L-arginine/nitric oxide pathway an attractive target for therapeutic interventions. Additional research is required, particularly in characterizing the role of the three nitric oxide synthase isoforms in the control of ocular perfusion, to implement this concept into the clinical management of ocular diseases.     

The effect of sildenafil on ocular blood flow

Sildenafil is a potent phosphodiesterase (PDE) 5 inhibitor that is used for patients with erectile dysfunction. Sildenafil induces vasodilation in selected smooth muscle via increased levels of guanosine 3', 5' cyclic monophosphate and increase in nitric oxide. The vasodilatory effects of the PDE 5 inhibitors led us to review its effect on the ocular vasculature. Sildenafil appears to increase blood flow velocity significantly in the retrobulbar and choroidal circulation. Most studies suggest an increase in choroidal blood flow, with a lesser effect on the retinal vasculature.     

高眼压缺血-再灌注中视网膜NOS的表达及L-NAME对其表达的影响

目的探讨高眼压缺血－再灌注损伤时视网膜一氧化氮合酶（ＮＯＳ）的表达、Ｌ－ＮＡＭＥ对ＮＯＳ表达的影响及视网膜ＮＯＳ的作用。方法用免疫组织化学ＳＡＢＣ法检测ｎＮＯＳ，ｅＮＯＳ和ｉＮＯＳ在高眼压缺血－再灌注模型视网膜中的表达及ＮＯＳ抑制剂Ｌ－ＮＡＭＥ对其表达的影响。结果在高眼压缺血－再灌注下，视网膜神经节细胞、神经胶质细胞ｎＮＯＳ，ｅＮＯＳ，ｉＮＯＳ均呈阳性，对照组ｎＮＯＳ呈弱阳性；注射Ｌ－ＮＡＭＥ后，在高眼压缺血－再灌注中，视网膜神经节细胞、神经胶质细胞均呈ｉＮＯＳ强阳性，ｎＮＯＳ，ｅＮＯＳ呈阴性。结论在高眼压缺血－再灌注中ｎＮＯＳ，ｅＮＯＳ，ｉＮＯＳ合成的一氧化氮（ＮＯ）可能对视网膜细胞等有细胞毒性作用；Ｌ－ＮＡＭＥ通过抑制ｎＮＯＳ，ｅＮＯＳ的活性，对高眼压缺血－再灌注视网膜损伤产生保护作用。     

The significance of nitric oxide for parasympathetic vasodilation in the eye and other orbital tissues in the cat

The role of nitric oxide formation in the vasodilation in the eye and other orbital tissues caused by pre-ganglionic stimulation of the facial nerve was studied in cats under alpha-chloralose anaesthesia. Regional blood flows were determined with radioactive microspheres during unilateral stimulation of the facial nerve before and after inhibition of nitric oxide synthase (NOS), alone or in combination with muscarinic blockade.N(omega)-nitro-L-arginine (L-NA), a non-selective NOS-inhibitor, caused a significant increase in mean arterial blood pressure (MABP) and a decrease in cardiac output (CO). Concomitantly, local blood flows on the non-stimulated control side were reduced in most of the investigated tissues, indicating marked vasoconstriction. An inhibitor selective for neuronal NOS, 7-nitro-indazole (7-NI), had no significant effect on MABP, CO or local blood flows. During facial nerve stimulation at 5 Hz (n =6), choroidal blood flow on the stimulated side was 108+/-41% (P相似文献   

Nitric oxide/guanylate cyclase pathways and flow in anterior segment perfusion

BACKGROUND: The nitric oxide/guanylate cyclase pathway has been suggested to participate in the regulation of intraocular pressure. In the present study, the involvement of nitric oxide pathways on the outflow through the trabecular meshwork was assessed using pharmacological manipulation of the nitric oxide pathway. METHODS: Anterior segments of human donor eyes were maintained in an organ culture perfusion system, and the effects of L-NAME, an inhibitor of nitric oxide synthase, on the flow rate was determined. In a second series, the effects of consecutive application of L-arginine as substrate for nitric oxide synthase, L-NAME, and sodium nitroprusside, a nitric oxide-donor, were studied. The cyclic GMP levels in the perfusate were assessed with an ELISA immunoassay kit. RESULTS: In the first series of experiments, L-NAME caused a statistically significant decrease in flow rate of 10%, accompanied by a decrease in cGMP levels. In the second series, L-arginine did not alter flow, and the effect of L-NAME seen in the first series was prevented by the high preload of L-arginine. Nitroprusside caused a significant 10% increase of flow rate. In the perfusate, cGMP levels were not altered by L-arginine and L-NAME, but were increased after nitroprusside. CONCLUSION: Under organ culture perfusion conditions, modulation of the nitric oxide/guanylate cyclase system alters the flow rate through the trabecular meshwork within a total range of 20%; i.e. the difference between inhibition of NO synthesis and the presence of a NO-donor. These results indicate that the nitric oxide/guanylate cyclase system plays a role in aqueous humour dynamics and, therefore, in the regulation of intraocular pressure.     

Effects of systemic NO synthase inhibition on choroidal and optic nerve head blood flow in healthy subjects

PURPOSE: There is evidence from animal studies that nitric oxide (NO) is a major determinant of ocular blood flow. In humans NO synthase inhibition reduces pulsatile choroidal blood flow, but no data on optic nerve head (ONH) vasculature are available yet. The goal of this study was to investigate the effects of NO synthase inhibition on human choroidal and ONH blood flow using laser Doppler flowmetry. METHODS: The study design was a randomized, placebo-controlled, double-masked, balanced three-way crossover. On separate study days 12 healthy male subjects received infusions of N:(G)-nitro-L-arginine (L-NMMA; either 3 mg/kg over 5 minutes followed by 30 microg/kg per minute over 55 minutes or 6 mg/kg over 5 minutes followed by 60 microg/kg per minute over 55 minutes) or placebo. The effects of L-NMMA or placebo on choroidal and ONH blood flow were measured with laser Doppler flowmetry. In addition, laser interferometric measurement of fundus pulsation was performed in the macula to assess pulsatile choroidal blood flow. RESULTS: L-NMMA reduced all outcome parameters in the choroid and the ONH. The higher dose of L-NMMA caused a significant decrease in blood flow in the choroid (-26% +/- 9%; P: < 0.001) and the ONH (-20% +/- 16%; P: < 0.001) as evidenced from laser Doppler flowmetry and a significant decrease in fundus pulsation amplitude (-26% +/- 5%; P: < 0.001). CONCLUSIONS: These results indicate that NO is continuously released in human choroidal and ONH vessels.     

胼酞嗪对眼血流和激光诱导的脉络膜新生血管及体外培养的内皮细胞的影响

目的：研究胼酞嗪对兔脉络膜血流和激光诱导的鼠脉络膜新生血管及人脐静脉内皮细胞管状结构形成的影响。方法：雌性新西兰白兔左眼眼内压升高至40mmHg后，滴入10g／L胼酞嗪滴眼液，采用彩色微球技术测量眼血流变化。用Nd：YAG激光诱导雄性BrownNorway大鼠至Bruch膜破裂，而后分别予生理盐水或5，10和20g/L胼酞嗪滴眼液点眼，3次／d，连续4wk。采用眼底荧光血管造影和脉络膜平片测量新生血管的面积。此外亦用不同浓度的胼酞嗪作用于培养之人脐静脉内皮细胞并探讨对其管状结构形成的影响。结果：10g／L胼酞嗪滴眼液滴入眼内压为40mmHg的兔眼30，60min后，脉络膜血流明显增加。眼底荧光血管造影和脉络膜平片测量均显示，经过4wk药物治疗，5，10，20g／L胼酞嗪滴眼液均明显抑制了鼠眼CNV的形成。3—30mg／L胼酞嗪对在基质凝胶中培养了48h的人脐静脉内皮细胞的管状结构的形成有抑制作用。结论：胼酞嗪可以抑制体内脉络膜新生血管及体外培养的人脐静脉内皮细胞管状结构的形成，并增强缺血后的兔脉络膜血流。胼酞嗪有望成为治疗年龄相关性黄斑变性的药物。