ISSN:0271-3683    

DOI:10.3109/02713689309001837

出版商:Taylor&Francis    

年代:1993

数据来源: Taylor

摘要:

Ocular tissues appear to require high levels of ascorbic acid and the elucidation of the mechanisms by which those tissues maintain the vitamin in its reduced state remains an important objective. The regeneration of ascorbate from its oxidative by-product, dehydroascorbic acid (DHAA), was studied in bovine iris-ciliary body. Iris-ciliary body was removed by scalpel, weighed, minced, and homogenized in 20 mM MOPS, 62 mM sucrose, and 0.1 mM EDTA at pH 7.0. The homogenate was centrifuged and precipitated with ammonium sulfate such that maximal DHAA reducing activity was enhanced in a 50–75% ammonium sulfate fraction. This fraction was employed for subsequent characterization of DHAA reduction by iris-ciliary body. Results indicate that the iris-ciliary body enzymatically reduces DHAA to ascorbate at a rate significantly greater than can be accounted for by a nonenzymatic glutathione-dependent mechanism. In addition, saturation kinetics are observed, and the enzymatic activity is dependent on protein concentration, DHAA concentration, and reduced glutathione (GSH) concentration. The activity is sensitive to pH, to high temperature, and to digestion by trypsin and is greatest in the presence of both GSH and NADPH. The reducing activity is therefore attributed to one or more proteins that are distinct from the known ascorbate regenerating enzyme, GSH-dependent DHAA reductase (EC 1.8.5.1).

ISSN:0271-3683    

DOI:10.3109/02713689309001838

出版商:Taylor&Francis    

年代:1993

数据来源: Taylor

摘要:

We assessed in vitro the antimicrobial activity of four agents (vancomycin, teicoplanin, mupirocin, and imipenem) which are effective against Gram-positive cocci causally associated with bacterial keratitis, as well as their corneal epithelial cytotoxicity. Minimal inhibitory concentrations inhibiting 90% of strains (MIC90s) against 10 strains each of methicillin-sus-ceptible and -resistant Staphylococcus aureus and Staphylococcus epidermidis, penicillin-susceptible and -resistant Streptococcus pneumoniae, and viri-dans group streptococci were as follows: vancomycin (MIC90s 0.25–2μg/ml), teicoplanin (MIC90s 0.25–4μg/ml, mupirocin (MIC90s 0.12–4μg/mJ), and imi-penem (MIC90s 0.008–0.25μg/ml, except for methicillin-resistant staphylococci with MIC90of 16μg/ml). Cytotoxicity was assayed by uptake of3H-thymidine by rabbit corneal epithelial cell cultures at drug concentrations of 12.5–100 mg/ml for vancomycin and teicoplanin, 1–8 mg/ml for mupirocin and 0.125–8 mg/ml for imipenem, with exposure times of 5, 30 and 60 min. Cytotoxicity was as follows: imipenem

ISSN:0271-3683    

DOI:10.3109/02713689309001839

出版商:Taylor&Francis    

年代:1993

数据来源: Taylor

摘要:

A method is reported in which the isolated bovine eye is perfused through a long posterior ciliary artery with buffered physiological saline, to provide simultaneous monitoring of drug effects on intraocular pressure (IOP), vascular resistance and the condition of the blood-aqueous barrier.With perfusion under constant pressure of 45 mm Hg, perfusate flows at 1.64±0.12 tnl.min−1(mean±SEM) and IOP is 7.26±0.16 mm Hg. Applying a constant flow rate of 2.25 ml.min−1, IOP averages 10.19±0.32 mm Hg and in both cases this can be maintained for around 2h. Increasing the perfusion flow rate from 1.5 to 3.5 ml.min−1produces a 76% rise in perfusion pressure but IOP increases only insignificantly (<10%). The inclusion in the perfusion fluid of dextran and albumin to maintain oncotic pressure similar to that of plasma makes no difference to the IOP achieved and does not affect the leakiness of the barrier. The preparation shows a net consumption of oxygen, supporting the hypothesis that the aqueous humour formed is secreted by active transport processes.Timolol (in bolus doses of 1–300 nmol) injected into the perfusing fluid is shown to induce a dose-dependent fall in IOP within 5 min, reaching a steady state within 40 min. Timolol, however, causes no significant change in vascular resistance, whether this is measured as perfusion flow rate under constant pressure or as perfusion pressure at constant flow rate, nor does it alter the permeability of the barrier. Other beta-blockers such as oxprenolol and betaxolol also induce dose-dependent decreases in IOP.By applying a fluorescein dilution technique, it is found that the aqueous formation rate (Kout= 0.0046 min−1, or 12.9μ1.min−1) is also reduced by timolol and, in a dose-dependent manner, by the new carbonic anhydrase inhibitor, MK-927.The bovine perfused eye offers a useful method for studying the mechanisms of action of drugs on IOP and aqueous humour formation, in isolation from the complicating influences of the CNS and the cardiovascular system and without the necessity to kill animals for experimental purposes.

ISSN:0271-3683    

DOI:10.3109/02713689309001840

出版商:Taylor&Francis    

年代:1993

数据来源: Taylor

摘要:

The technique of Anjou and Krakau for measuring flare and Krakau's method for estimating aqueous humor flow in humans was compared to the fluorophotometric procedure of Jones and Maurice.The precision of flare was measured in 20 normal human volunteers, and the precision of flow was measured with fluorophotometry in 24 volunteers. In addition, the circadian rhythms of both flow and flare were measured simultaneously in a separate group of 20 subjects. This simultaneous measurement allowed us to calculate the entry rate of scattering substances into the aqueous humor as a function of time of day. This entry rate is critical for measuring flow by the method of Krakau.The mean coefficient of variation (±SD) of repeated measurements of flare at the same time of day was 23.2%±10.3%. The mean coefficient of variation of the measurement of aqueous flow by fluorophotometry was 15.9%±8.2%, significantly better than the measurement of flare (p=0.01).The daytime entry rate of scattering substances into the aqueous humor varied from 1.39±0.86μg/min (calculated as albumin) to 1.05±0.58μg/min. The rates in daytime hours were not significantly different from each other. At night during sleep, the entry rate was 0.67±0.48μg/min, significantly slower (p between 0.002 and<0.001). These data indicate that the flare technique cannot be used alone to calculate the circadian rhythm of flow and that direct measurement of flow by fluorescein clearance is likely to be the most repeatable and accurate of the two.

ISSN:0271-3683    

DOI:10.3109/02713689309001841

出版商:Taylor&Francis    

年代:1993

数据来源: Taylor

摘要:

To facilitate identification of transplanted retinal pigment epithelial (RPE) cells, we sought to double-label the cells with 5-bromodeoxyuridine (BrdU) and with natural pigment. The BrdU is not lost during cell division but does require immunohistochemical methods for visualization; the pigment, on the other hand, allows immediate, obvious identification, but is gradually lost with cell division. Together they provide a convenient, long-term double label. Herein we report the successful allotransplantation of double-labelled RPE cells onto Bruch's membrane of albino rabbits. The labelled cells were localized by anti-BrdU antibody and the avidin biotin-alkaline phosphatase complex (ABC-AP) method, and by visible inclusions of pigment. Using this double-label method, allotransplanted RPE cells could be readily and reliably identified on the recipient Bruch's membrane eight months after transplantation. The cells had distinct basal and apical morphology, and were in close contact with the photoreceptor outer segments of the host. This successful allotransplantation raises the possibility that the subretinal space of the rabbit might enjoy some degree of immunologic privilege.

ISSN:0271-3683    

DOI:10.3109/02713689309001842

出版商:Taylor&Francis    

年代:1993

数据来源: Taylor

摘要:

Cyclodextrins have been used to improve drug solubility, stability and absorption for oral and parenteral administration. However, their potential for improving ocular drug delivery has received little attention. To evaluate the ability of hydroxypropyl-β-cyclodextrins to improve ophthalmic drug bioavailability following topical administration, the miotic effect of topical solutions of pilocarpine was studied in New Zealand White rabbits. Pilocarpine varying in dose from 5 to 500μg in the presence or absence of 5% cyclodextrin was administered (50μ1) topically and the change in pupil diameter determined. These results demonstrated that pilocarpine alone or in the presence of cyclodextrin produces a dose-related reduction in pupil diameter. The addition of cyclodextrins produced a significant left-shift in the dose response curve, with an ED50 of 64μg and 19μg for pilocarpine and pilocarpine/5% cyclodextrin solutions, respectively. Studies in which the concentration of cyclodextrin was varied revealed that a one-to-one molar ratio of pilocarpine to cyclodextrin was sufficient to provide maximum increase in pilocarpine bioavailability. Electrophysiology and scanning electron microscopic studies demonstrated that cyclodextrin does not disrupt the normal ion transport currents, barrier properties or surface features of the corneal epithelium. Viscosity measurements indicated that difference in the viscosity of pilocarpine and pilocarpine/cyclodextrin solutions cannot account for increased bioavailability of pilocarpine. These data support the idea that the addition of cyclodextrin significantly improves the ocular bioavailability of pilocarpine. This enhanced bioavailability of pilocarpine does not appear to be due to a mechanism destructive to the epithelium or to an increase in vehicle viscosity.

ISSN:0271-3683    

DOI:10.3109/02713689309001843

出版商:Taylor&Francis    

年代:1993

数据来源: Taylor

摘要:

The primary, known physiologic effect of interleukin-2 (IL-2) is to act as a T lymphocyte growth factor. We investigated the potential contribution of IL-2 to intraocular inflammation by studying the inflammation resulting from the intravitreal injection of recombinant, human IL-2 in New Zealand white rabbits. Serial slit lamp observations indicated that 40 ug of intravitreally injected IL-2 induced an anterior uveitis which was maximal 5 days after the injection. Inflammation was less marked but still significant with amounts of IL-2 as low as 400 ng. Direct examination of aqueous humor confirmed elevations of protein, prostaglandin E2, and mononuclear cells which correlated with the clinical observations. The kinetics of the response to intravitreal IL-2 distinguished it from the responses to other intravitreally injected cytokines such as interleukins 1, 6, or 8 as well as tumor necrosis factor.Intramuscular injection of cyclosporine A significantly reduced the protein extravasation associated with IL-2 injection, but cyclosporine had no effect on inflammation secondary to an intravitreal injection of interleukin-1. These observations implicate IL-2 as a potential contributor to uveitis. In addition, the studies with cyclosporine indicate the heterogeneity of inflammation such that pharmacologic agents which affect one cause of uveitis are not necessarily efficacious in another model.

ISSN:0271-3683    

DOI:10.3109/02713689309001844

出版商:Taylor&Francis    

年代:1993

数据来源: Taylor

摘要:

The purpose of this study was to isolate the platelet-activating factor (PAF) precursor and other choline phosphoglycerides (GPC) i.e. the alkenylacyl and diacyl lipids from the rabbit cornea, to analyze their fatty acid content and to determine which pool was the most susceptible to arachidonate depletion when activated corneal tissue released arachidonic acid (AA) and metabolites. Rabbit iridal GPC was also analyzed for comparative purposes. The fatty acid methyl esters of the GPC components extracted from the rabbit cornea and iris-ciliary body, isolated by high performance liquid chromatography (HPLC), were determined by capillary gas liquid chromatography. Rabbit corneas were labelled in vivo by intracameral injection of3H-AA (1μCi, specific activity = 218 Ci / mmol) and cryogenically injured 18 h later. Corneas were incubated in vitro and the AA and eicosanoids released into the medium were extracted and separated by HPLC. The GPC was extracted from the tissues and the labeling of the three GPC constituents was quantified by liquid scintillation counting. The corneal and iridal PAF precursor represented 4.1±0.2% and 2.9±0.2% respectively of total GPC in those tissues. On a mole basis, the alkyl arachidonoyl species constituted 12.7±0.7% of the corneal and 38±0.6% of the iridal PAF precursors respectively. The release of AA and prostaglandins by the cornea was linear until 15 min; whereas 12-HETE levels continuously increased until 60 min. All GPC components lost label but 1-0-alkyl-2-arachidonoyl was the most affected, with its labeled content 50% less than the non-injured control. These results suggest that the PAF precursor could be an important source of bioactive lipids in the cornea after phospholipase A2activation induced by injury.

ISSN:0271-3683    

DOI:10.3109/02713689309001845

出版商:Taylor&Francis    

年代:1993

数据来源: Taylor

摘要:

The rabbit isolated iris sphincter muscle maintained in an isotonic state is unaffected by applied serotonin (5-hydroxytryptamine or 5-HT) whereas carbachol causes the muscle to contract. Serotonin does, however, produce a relaxation of the contracted muscle in a dose-dependent manner. This effect is also induced by the 5-HT receptor agonists 8-OH-DPAT (8-hydroxy-2-[di-n-propyl-amino] tetralin, RU 24969 (5-methoxy-3-[l, 2, 3, 6, tetrahydro-4-pyridinyl]-1-indole) and ipsapirone, suggesting the involvement of 5-HT1Areceptors. This view is supported by the finding that metergoline, methysergide and propranolol all counteracted the effect produced by serotonin. While 5-HT3receptors are not involved in the described process, a minor involvement of 5-HT2receptors cannot be excluded as methysergide partially counteracted the serotonin response. These data provide evidence that serotonin receptors, in particular the 5-HT1Asubtype, may be associated with the iris sphincter muscle and suggest their involvement in the regulation of pupil size.

ISSN:0271-3683    

DOI:10.3109/02713689309001846

出版商:Taylor&Francis    

年代:1993

数据来源: Taylor