摘要:

The central cornea obtains its glucose by diffusion through the cornea from the aqueous humor to the epithelium. The diffusion of glucose in the cornea is analogous to the flow of current in an electrical resistance network. The cellular consumption of glucose can be compared to shunting a portion of the charge to electrical ground. An electrical analog model of the cornea was developed to predict the availability of glucose to the epithelium and the distribution of glucose in the stroma. The glucose constant concentration lines in the normal stroma are parallel to the corneal surface and have decreasing values from 880 to 580μg/ml. The effects on epithelial glucose concentration by implanting an intracorneal lens (ICL) of varying diameter, depth, permeability and thickness can be modeled. Glucose permeability through the intracorneal lens has the most significant effect on glucose availability. The ICL profile i.e. power, can also be an important fact in determining glucose availability. A minus power design requires a thin central lens zone with a thick peripheral zone. The design results in relatively more glucose flux through the optical zone of the lens and thus improves central epithelial glucose availability.

ISSN:0271-3683    

DOI:10.3109/02713689008997577

出版商:Taylor&Francis    

年代:1990

数据来源: Taylor

摘要:

DNA synthesis was evaluated in vitro by measuring incorporation of3H-thymidine in rat lens following systemic delivery of a cataractogenic dose of selenite. Among early metabolic changes observed in the lenses of rats receiving a single dose of 30 nmol Na2SeO3/g body weight was a 30% decrease in DNA replication in lens epithelium occurring between 6 and 12 h after administration of the selenite. This change was followed by an 80% increase in replication by 24 h. Thymidine incorporation in DNA remained elevated compared to controls through 96 h. Unscheduled DNA synthesis was found to be approximately 10% of the total DNA formed, but there was a 30% and 70% increase of this putative DNA repair in the lenses from selenite-treated animals at 6 and 24 h after the injection. Using the alkaline unwinding assay, the proportion of single-strand DNA in lenses from selenite-treated animals increased after 24 h. This estimate of DNA damage was greater in lenses after 96 h. Each component of DNA metabolism: damage, repair, and replication, was affected by the occurrence of selenite stress in lens. These changes both preceded and accompanied nuclear cataract formation.

ISSN:0271-3683    

DOI:10.3109/02713689008997578

出版商:Taylor&Francis    

年代:1990

数据来源: Taylor

摘要:

The ocular penetration pathways of threeα2-adrenergic agents (p-aminoclonidine, AGN 190342, and clonidine) were Investlgated in rabbits bothin vitroandin vivo. The corneal permeabilities of the compounds correlated positively with their octanol/water distribution coefficients. The ocular drug absorptlon via corneal and conjunctival/scleral penetration routes was evaluated separately after drug perfusionin vivo. In most cases, the corneal route was the major pathway for the intraocular drug absorption. However, the conjunctival/ scleral penetration pathway was the predominant pathway for the delivery of p-aminoclonidine, the least lipophilic compound among the three drugs, to the ciliary body. The drug concentration in the iris was contributed mainly by the corneal route and correlated well with drug lipophilicity.

ISSN:0271-3683    

DOI:10.3109/02713689008997579

出版商:Taylor&Francis    

年代:1990

数据来源: Taylor

摘要:

Photoreceptor cell degeneration in rodents from a variety of causes results in neovascularization of the retinal pigment epithelium as a late stage phenomenon. Even though the vessels within the pigment epithelium arise from the retinal circulation, they can manifest the choroidal endothelial cell phenotype of fenestrated endothelial cells. In order to study the detailed cellular events which result in incorporation of retinal vessels within the retinal pigment epithelium, a morphological and morphometric analysis of the RPE and vasculature was performed in rats. Urethane, given subcutaneously to newborn rats, results in a photoreceptor degeneration but does not affect the RPE, choroid or inner retinal layers. Retinas were studied from rats of 8 to 24 weeks of age, the time period when vascularization of the RPE occurs.Loss of retinal vessels is first seen at 12 weeks, primarily in substantial dropout of vessel profiles in the outer plexiform layer (OPL) vessel bed. There is a gradient of loss from the OPL bed to the nerve fiber layer (NFL) bed and from the central to peripheral region. Total vessel density of the experimental retinas is greater than controls at 8 and 12 weeks. This occurs because there is marked loss of retinal thickness, due to photoreceptor degeneration, without a comparable loss of vessel profiles. The total retinal vessel density decreases from 8 to 20 weeks, and appears to stabilize at 20 and 24 weeks. Analysis of the separate vessel beds shows that this apparent stabilization is due to continued loss of vessels within the sensory retina, and increased presence of vascular profiles within the RPE. Total absence of the photoreceptor cell is necessary for incorporation of vessels within the RPE. Since new vessel profiles develop in the RPE but not the adjacent sensory retina, we speculate that the RPE may stimulate neovascularization of the RPE. A model of the cellular events leading to RPE neovascularization is proposed.

ISSN:0271-3683    

DOI:10.3109/02713689008997580

出版商:Taylor&Francis    

年代:1990

数据来源: Taylor

摘要:

We studied the modifications of the standing potential (SP) of the eye and of the light peak (LP) after exposure to dopamine, a neurotransmitter released at light by the inner retina and known to affect electrical properties of the retinal pigment epithelium. Intravenous or intravitreal injections of dopamine (DA) were performed on intact chickens.“Choroidal”application (through an intravenous injection) induced a transient increase of the SP and the LP was preserved. On the other hand,“apical”applications of DA (through an intraocular injection) also increased the SP but considerably depressed the LP. These results are in agreement with the hypothesis that the light-induced release of dopamine from the neuroretina may be responsible for the LP generation in the intact chicken eye.

ISSN:0271-3683    

DOI:10.3109/02713689008997581

出版商:Taylor&Francis    

年代:1990

数据来源: Taylor

摘要:

Two alternative methods for the study of the lens cytoskeleton are described which serve to overcome some of the difficulties imparted by the unique biology of the lens. The first technique involves rapid freezing, thick sectioning, and selective extraction and/or fixation of the lens section. This approach offers several advantages: 1) enhanced visualization of the cytoskeleton, 2) avoidance of fixation gradients, 3) free access for immunocytochemical probes, 4) retention of tissue-wide spatial relationships, with a sharp increase in the resolution of regional analysis, and 5) the capacity for correlative morphological and biochemical comparisons. The second method involves the covalent immobilization of the plasma membrane-cytoskeleton complex (PMCC) to acrylamide beads. This approach permits: 1) avoidance of fixation in the immunocytochemical analysis of lens cytoskeleton and plasma membranes 2) rapid processing of multiple, small-quantity samples for immunocytochemistry/ biochemical analysis 3) cleaner and more rapid analysis of cytoskeletal extraction conditions.Both approaches, while particularly suited to the study of the lens PMCC, may also be of value to the study of the PMCC of other tissues, particularly where preservation/analysis of regional relationships is essential.

ISSN:0271-3683    

DOI:10.3109/02713689008997582

出版商:Taylor&Francis    

年代:1990

数据来源: Taylor

摘要:

Exposure of cultured rabbit lens epithelial cells to repetitive doses of UV-B radiation delays their growth and alters the synthesis of specific proteins. Irradiated cells on the shoulder of the survival curve exhibited a dose-dependent decrease in growth when subcultured in serum-supplemented medium. UV-B irradiation did not affect the subsequent attachment efficiency of the cells. Control and UV-B irradiated cells were incubated with [35S]methionine and the pattern of protein synthesis in the cells was analyzed by SDS-PAGE and autoradiography. Analysis of the labeled proteins from cells exposed to UV-B radiation showed the induction of a 32 kD polypeptide and the loss of a 26 kD polypeptide compared with controls. Analysis of the proteins released by the UV-B irradiated cells into the culture medium revealed the 50% loss of a 37 kD radiolabeled protein compared with controls. The alteration of protein synthesis in lens epithelial cells by UV-B radiation may contribute to cataract formation.

ISSN:0271-3683    

DOI:10.3109/02713689008997583

出版商:Taylor&Francis    

年代:1990

数据来源: Taylor

摘要:

Pneumolysin, a cytolytic protein produced byStreptococcus pneumoniae, has many properties which suggest it may be an important virulence factor in pneumococcal ocular infections. To directly test this possibility, we have constructed pneumolysin-negative strains of U.,pneumoniaeand compared their virulence with that of the wild type in a rabbit model of intracorneal infection. A pneumolysin-negative strain produced by chemical mutagenesis (probably a point mutant) was found to be no less virulent than the parent strain. However, a strain bearing a deletion in the pneumolysin gene showed greatly reduced virulence. This strain produced less pathology while showing significantly higher bacterial counts. These results suggest that a property of the pneumolysin molecule other than its cytolytic (hemolytic) activity may be involved in its pathogenic mechanism of action. This property may be the ability to activate complement, known to be a function of pneumolysin, which results in influx of PMNs, reducing the bacterial counts but also producing tissue damage.

ISSN:0271-3683    

DOI:10.3109/02713689008997584

出版商:Taylor&Francis    

年代:1990

数据来源: Taylor

摘要:

Taurine immunoreactivity in one micron sections of the adult rat optic nerve was observed using light microscopy. Prominent staining was seen in glial cell somata in the perinuclear region and in their processes throughout the nerve, particularly in endfeet on capillaries and in the peripheral basal lamina (glia limitans). Axons and blood vessels showed relatively little or no staining in the mature nerve. The pattern of glial fibrillary acidic protein immunoreactivity on subsequent sections was similar in many respects to that of taurine, suggesting that a sub-population of taurine immunoreactive glial cells are optic nerve astrocytes.

ISSN:0271-3683    

DOI:10.3109/02713689008997585

出版商:Taylor&Francis    

年代:1990

数据来源: Taylor

摘要:

The effect of retinoic acid on DNA synthesis and cell morphology was studied using corneal stromal fibroblasts in culture. All-trans retinoic acid induces an increase in DNA synthesis after 24 hours of exposure. Autoradiographic studies of3H-thymidine incorporation into corneal stromal cells exposed to 10−6M retinoic acid for 24 hours showed an increase in labeling which ranged from 19.2% to 67.6% over control cultures. Scintillation analysis of labeled cultures also showed an increase in incorporation of3H-thymidine into cells treated with 10−6M retinoic acid, with increases ranging from 21.8% to 114.7% above control cultures. Exposure of cultured corneal stromal cells to 10−6M retinoic acid resulted in a dramatic change in cell morphology such that they changed from spindle-shaped to round, flattened cells which were epithelioid in appearance. These data demonstrate the biological activity of retinoic acid in stromal fibroblasts and imply a role for vitamin A in maintenance of stroma structure and function.

ISSN:0271-3683    

DOI:10.3109/02713689008997586

出版商:Taylor&Francis    

年代:1990

数据来源: Taylor