A comparative study of elasmobranch corneal and scleral collagens.
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Animals↗
Biomedical subjects
H F Edelhauser
Publications and source records attributed to H F Edelhauser.
Effects of nucleoside antivirals and their metabolites on the corneal endothelium.
The endothelial surface of rabbit corneas were perfused in vitro with bicarbonate Ringer's containing 5 mM glucose, 0.3 mM reduced glutathione, and various concentrations of nucleoside antivirals or their metabolites. During three hour perfusions, the swelling rates of corneas perfused with buffer containing either antivirals or metabolites were not significantly different from controls. Scanning electron microscopy of the endothelial cell layer revealed no structural abnormalities in any treatment group. One metabolite, fluoride ion, reduced endothelial glucose oxidation by about 60 percent when incubated with corneal tissue in vitro. The inhibition of glucose metabolism by fluoride ions was observed only at concentrations at least sixty times greater than would be anticipated in the anterior chamber of patients receiving topical F3TdR therapy. These studies indicate that 5-trifluoromethyl-2'-deoxyuridine, 5-iodo-2'-deoxyuridine, 9-(2-hydroxyethoxymethyl)-guanine, and their metabolites do not alter endothelial function when studied at physiological concentrations over a short term of exposure.
Acyclovir↗
Effects of ionophores X537a and A23187 and calcium-free medium on corneal endothelial morphology.
Past studies have shown that apical junctional complexes (AJCs) of corneal endothelial cells break down in the presence of a Ca++-free medium. The purpose of this study was to examine the ability of Ca++ ionophores to maintain the AJCs in the Ca++-free media in both isolated perfused corneas and cultured endothelial cells. In addition, the ability of disintegrated AJCs to re-form when the endothelium is returned to a medium containing calcium ws also examined. Rabbit corneas were mounted in an in vitro specular microscope and perfused with a Ca++-free medium, or a Ca++-free medium containing 10(-5)M X537A or A23187 calcium ionophore. Also, confluent monolayer cultures of bovine corneal endothelial cells were placed in a Ca++-free medium or a Ca++-free medium containing 10(-5)M X537A or A23187 Ca++ ionophore and incubated for selected time periods. When junctional breakdown occurred, one cornea or culture plate was fixed for scanning and transmission electron microscopy (SEM and TEM), and the other was returned to a medium containing Ca++ and subsequently fixed for SEM and TEM. Both isolated perfused and cultured corneal endothelial cell AJCs exhibited marked disintegration in the presence of Ca++-free medium. The presence of an ionophore in the medium cultured cells. When returned to a medium containing Ca++, the corneas that had been perfused with Ca++-free medium containing an ionophore re-formed the junctions sooner than did those that had been perfused with a Ca++-free medium alone. These results suggests that the ionophores may be capable of mobilizing intracellular calcium to protect the AJCs.
Animals↗
Cytotoxicity of pivalylphenylephrine and pivalic acid to corneal endothelium.
We examined the effects of topically applied pivalylphenylephrine (PPE) and pivalic acid (PA) on the corneal endothelium of rabbits and the direct effects of PPE and PA on monolayer cultures of bovine corneal endothelium. The PPE-treated corneas without epithelium significantly increased in thickness, whereas no change in thickness was observed in corneas with epithelium intact. The PA did not alter the thickness of corneas with or without epithelium. Although 0.001% PE had no noticeable effect in two hours, 0.01% PPE caused breakdown of intercellular junctions in cultured cells in five minutes. Higher concentrations of PPE caused the cells to detach from the culture dishes within 30 minutes of treatment. Only 1% PA caused cell elongation and loss of intercellular contact after 60 to 90 minutes of exposure; lower concentrations did not effect cultured cells.
Administration, Topical↗
Intraocular fluid dynamics. Measurements following vitrectomy and intraocular sulfur hexafluoride administration.
Partial vitrectomies were performed in rabbits, replacing 40% of initial vitreous volume with 100% sulfur hexafluoride, and concentrations of sodium, potassium, calcium, magnesium, ascorbate, and protein were determined in aqueous and vitreous at 10, 14, 21, 28, 56, and 110 days. There were significant increases of potassium, calcium, magnesium, and protein above control values at varying times throughout the study. Vitreous potassium concentration was decreased at 14 and 21 days. All other measurements were similar to control values. Results of studies indicate that, following vitrectomy in rabbits, the blood-retinal barrier can re-form in 14 days and blood-aqueous barrier in ten days. However, a greater than normal exchange diffusion of these measured substances occurs between aqueous and vitreous through 21 days. Four eyes with cataracts, vitreous membranes, and/or detached retinas demonstrated elevated aqueous and vitreous protein concentrations through 110 days, although other measurements returned to normal levels.
Animals↗
Glucose metabolism in the cornea and lens in elasmobranchs, teleosts and mammals: response to thiol-oxidation.
Various structural and metabolic adaptations that have occurred in elasmobranchs, in salt and fresh water teleosts, and in mammals have enabled these species to adapt to varied environments. In all cases the corneas of these species remain transparent and expend metabolic energy to maintain this transparency. The studies reported in this paper describe the structural and the metabolic adaptations that have occurred in these corneas. Included are measurements of corneal oxygen consumption, Q10 and corneal hydration. Thiol-oxidation of the intracellular glutathione with diamide has been shown to produce marked stimulation of the hexose-monophosphate shunt in the component layers of the cornea and the lens of rabbit, dogfish, and sculpin. Activities of glycolytic, citric acid cycle, and pentose phosphate shunt enzymes in the corneal and muscle tissue were also studied. Species variations were found between elasmobranchs, marine teleosts, and rabbits. In each of these species, the corneal endothelium was distinguished from the epithelium by much lower enzyme activities. It can be concluded that the enzyme activities and metabolic differences represent functional adaptations that have occurred to insure transparency under these extremely varied osmotic conditions.
Adaptation, Physiological↗
The effect of phenylephrine on the cornea.
Rabbit corneas were treated with three drops of phenylephrine hydrochloride with the epithelium intact or denuded. Corneal thickness was measured before and after drug treatment, and at various times after treatment the corneas were fixed for scanning and transmission electron microscopic observation. The results of this study show that phenylephrine caused a dramatic increase in corneal thickness (drug-induced edema) and cellular vacuolation within the keratocytes and endothelial cells in the corneas without the epithelium. Corneal thickness did not change and the ultrastructural changes were minimal following drug application in those corneas with the epithelium intact. Results of this study also suggest that phenylephrine has a cytotoxic effect on the corneal endothelium and keratocytes when used in corneas where the epithelium has been removed. In coreas with intact epithelium, the damage was less severe and limited to the epithelium.
Animals↗
The pH tolerance of rabbit and human corneal endothelium.
The endotheliums of rabbit corneas were perfused in an in vitro perfusion specular microscope up to 3 hr with solutions varying in pH from 3.5 to 10.0. Corneal thickness was monitored throughout the experiment, and at appropriate times the corneas were prepared for SEM and TEM. Analysis of the corneal thickness data and interpretation of the electron micrographs reveals that outside of the pH range of 6.5 to 8.5, structural and functional alterations occur. Direct cellular damage, as well as disruption of junctional complexes, lead to a breakdown in the barrier function of the corneal endothelium. The extent of this breakdown is dependent upon both the magnitude of the pH change and the exposure time. Further experiments on banked human eyes support this finding.
Aged↗
Effect of phenylephrine on normal and regenerated endothelial cells in cat cornea.
Topical commercial phenylephrine HCl (Neo-Synephrine 10%) has been shown to cause an increase in corneal thickness and reversible vacuolization of corneal endothelial cells in rabbits. Using an in vivo model of regenerated corneal endothelial cells in the cat, we compared the cytotoxicity of phenylephrine-HCl 10% to regenerated and to normal, nonregenerated cells. Following removal of the epithelium, topical application of the drug causes the appearance of anterior and posterior bands of stromal edema and reversible vacuolization in both normal and regenerated endothelial cells. Phenylephrine was not more damaging to the regenerated cells. Polymorphonuclear leukocytes infiltrated between the regenerating cells 24 hr after treatment but did not appear to destroy them. Phenylephrine may therefore be implicated as a causative factor of corneal edema and postoperative inflammation.
Animals↗
The pentose phosphate pathway in developing chick cornea.
Embryonic chick corneas at different stages of development were evaluated for activity of the pentose phosphate pathway. The appearance of activity was concurrent with the onset of corneal transperancy (stage 40). Highest values were found after complete transparency is achieved (stage 45 and after hatching). Phenazine methosulfate, an artificial electron acceptor, increased activity at all stages studied even before endogenous activity was measurable; however, no increase in glucose uptake was observed. Thus, the enzymes for the pathway are present at early stages (i.e., stage 38 and 40) although in latent form. The pathway probably functions in the developing cornea to generate NADPH rather than sugar moieties for macromolecular incorporation.
Age Factors↗
Intraocular sulfur hexafluoride and octofluorocyclobutane. Effects on intraocular pressure and vitreous volume.
Partial vitrectomies were performed on rabbits and the amount of vitreous removed was replaced with either 100% sulfur hexafluoride (SF6), 100% octofluorocyclobutane (freon-C318), 40% SF6, or air. Intraocular pressure and vitreous volume were determined. Replacing 40% of the initial vitreous volume with either 100% SF6 or 100% octofluorocyclobutane caused an increase over 20 mm Hg in the IOP with an associated loss of the remaining vitreous, whereas replacement with 40% SF6 or air caused no significant increase in IOP. Replacement with 40% SF6 caused a significant loss of the remaining vitreous, whereas the air replacement did not result in a vitreous loss. The experiments were repeated substituting only 20% of initial vitreous volume with 100% SF6 and 100% octofluorocyclobutane. Using this amount of SF6 and octofluorocyclobutane, the IOP did not increase but an associated vitreous loss occurred equal to twice the amount of SF6 injected and three times the amount of octofluorocyclobutane injected.
Air↗
Intraocular irrigating solutions. A comparative study of BSS Plus and lactated Ringer's solution.
Isolated human corneas maintained normal corneal thickness and endothelial ultrastructural integrity throughout a three-to four-hour period of perfusion of BSS plus to the endothelial surface. By comparison, only one of six human corneas perfused with lactated Ringer's solution was able to maintain normal thickness and ultrastructural integrity. The other five corneas perfused with lactated Ringer's solution showed various degrees of endothelial cell breakdown and corneal swelling during three hours of perfusion. The results of these studies suggest that BSS plus is a better solution for maintenance of human corneal endothelium during long-term (one- to three-hour) surgical procedures.
Cornea↗
Endothelial degeneration and posterior collagenous proliferation in aphakic bullous keratopathy.
In series of 39 corneal grafts, aphakic bullous keratopathy comprised 13 (33%) of the cases. By scanning and transmission electron microscopy, endothelial degeneration and posterior collagenous proliferation were consistent features. In all 13 cases, the patchy loss of endothelial cells occurred diffusely over the entire posterior corneal surface. The remaining endothelial cells had become extremely attenuated to increase their surface area. In nine cases, acellular proliferations of collagenous tissue were interposed between the endothelial cells and Descemet's membrane. These posterior collagenous layers were composed of collagen fibrils and basement membrane material, randomly arrayed in a feltwork of uniform thickness; they appeared ultrastructurally identical to those encountered in a variety of conditions involving endothelial distress.
Aphakia, Postcataract↗
Glutathione in rabbit corneal endothelia: the effects of selected perfusion fluids.
Although the ameliorating effect of glutathione on corneal deturgescence is known, its chemical mechanism is not understood. An endeavor toward the latter was made by perfusing freshly excised rabbit corneas with selected perfusion fluids, measuring corneal thickness, and assaying the endothelial cells for reduced and oxidized glutathione after 2 and 5 hr of perfusion. Ringer's solution, containing either lactate or bicarbonate, caused significant decreases in both forms of glutathione after perfusion. The corneas increased in thickness considerably during these periods. When 5 mM glucose was added to bicarbonate-Ringer's solution, the corneas swelled about half as much as before. However, glutathione levels were as depressed as with simple Ringer's fluid. Adenosine (0.5 mM) in the presence of glucose (bicarbonate-Ringer's) caused a further swelling decrease so that the corneas were maintained at near normal thickness. The levels of glutathione were 84% of control values compared to 35% to 45% for Ringer's solutions (+/- glucose). The addition of glutathione to glucose (bicarbonate-Ringer's) caused intracellular glutathione levels to be higher than control values while allowing minimal tissue swelling. Glutathione in combination with adenosine, glucose, and bicarbonate produced the highest intracellular glutathione levels and a slight corneal deswelling. After oxidation of intracellular glutathione with t-butyl hydroperoxide in glucose (bicarbonate-Ringer's), endothelial cells were destroyed within 1 hr. The oxidant, however, may have had a direct effect upon the endothelial cell membranes.
Adenosine↗
Ultrastructural alterations associated with loss of transparency in the cornea of buphthalmic rabbits.
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Animals↗
The corneal penetration of trifluorothymidine, adenine arabinoside, and idoxuridine: a comparative study.
Trifluorothymidine (F3TdR) and idoxuridine (IDU) were observed to penetrate through the cornea from the epithelial side at a greater rate than adenine arabinoside (ARA-A) during in vitro corneal perfusions. Removal of the epithelium increased the rate of penetration of F3TdR and IDU by about twofold and the rate of ARA-A penetration by fivefold. The kinetics of antiviral penetration did not display saturation points at high antiviral concentrations, thus indicating that these three antiviral drugs penetrate the cornea by nonfacilitated diffusion. The sole breakdown product detected following F3TdR penetration in vitro, in situ, and in controls was 5 carboxy-2'-deoxyuridine (5-COOH-2'-dUd). The sole breakdown product isolated during ARA-A penetration experiments was hypoxanthine arabinoside (ARA-HX), and control experiments indicated that ARA-A was stable at pH 7.6. IDU was degraded to 2'-deoxyuridine (dUd) in control experiments, but during corneal penetration experiments IDU was degraded to a mixture of dUd and iodouracil (IU).
Animals↗
Oxygen consumption in the developing chick cornea.
Embryonic chick corneas at different stages of development were evaluated for O2 consumption. Some embryos were treated with thyroxine or thiouracil. In untreated animals, corneal QO2 (oxygen consumption/hr./mg. dry weight) decreased from 3.60 at stage 38 to 1.58 after hatching. The temperature coefficient Q10 increased from 1.55 at stage 40 to 2.03 after hatching. If O2 consumption is calculated as microliters of O2 consumed per hour per corneal pair, it increases between stage 38 (3.20) and hatched chicks (6.20) with a plateau between stages 40 and 45. Thiouracil treatment reduced O2 consumption by the cornea at stages 42 and 45, and thyroxine treatment elevated it at stage 40.
Age Factors↗
The role of thyroid hormone in the development of the chick corneal endothelium and epithelium.
Previous studies have established that thyroxine or thiouracil treatments affect the development of corneal transparency in the chick. The effects of these drugs on chick corneal epithelial and endothelial development were investigated because in the adult the integrity of these cell layers is necessary for the maintenance of corneal transparency. Chick embryos were treated with thiouracil or thyroxine at stage 36 or 38; the corneas were excised 2 to 12 days after treatment (between stages 38 and 45), and prepared for electron microscopy. The colloidal tracer ruthenium red was added during fixation to study epithelial and endothelial permeability and to stain the intercellular endothelial spaces. At all stages studied, the epithelium was impermeable to ruthenium red and this property was not affected by drug treatment. The epithelial barrier to this tracer is located in the outermost cell layer. The ease of penetration of ruthenium red through the endothelial intercellular spaces indicated the lack of zonular tight functions and the presence of gap functions in this cell layer. Thiouracil treatment delayed the development of the corneal epithelium so that at stage 45 it resembled epithelium from a normal embryo 3 stages younger. In normal animals, chick corneal endothelial development is characterized by an increasing degree of interdigitation of the lateral plasma membranes of adjacent endothelial cells with advancing embryonic age. Thiouracil treatment delayed this progressive development of adjacent cell membrane interdigitation. In contrast, thyroxine treatment accelerated the development of the lateral borders of the endothelial cells. It also appears that thyroid hormone can affect the development of the cell membranes of apposed cells in epithelium as well as the endothelium of the embryonic chick cornea.
Animals↗