PubMed Health⌕ Search

Biomedical subjects

K Bowman

Publications and source records attributed to K Bowman.

At least 37 records · Page 2Linked to original sources
PubMed1983

Topical epinephrine and regional ocular blood flow in aphakic eyes of rabbits.

The effects of 4% topical epinephrine bitartrate on regional ocular blood flow were studied in normal, "sham-operated," and aphakic eyes of rabbits. Anterior uveal blood flow decreased in all cases, but reductions in the ciliary processes were less pronounced in aphakic eyes than in sham-operated eyes. Doubling the dose (from 2 to 4 drops) abolished this difference in the ciliary processes, but the increased dose was accompanied by the emergence of a similar (although lesser) effect in the iris. The latter dose additionally decreased retinal blood flow in aphakic eyes compared with the sham-operated eyes. Lens extraction, thus, seems to remove a notable diffusion barrier to topical epinephrine, resulting in both attenuation of its anterior segment effects and in potentiation of a vasoconstrictive response in the posterior pole.

Animals↗
PubMed1983

Penetration of topical indomethacin into phakic and aphakic rabbit eyes.

The penetration of indomethacin labeled with radioactive carbon (14C) into all ocular tissues and fluids was determined at various intervals in both phakic and aphakic rabbit eyes after either single or multiple (every 12 hours for three days) topical application (50 microL) regimens. More indomethacin was found in the vitreous of aphakic eyes compared with phakic eyes after single- or multiple-drop administration. Retinal and choroidal indomethacin concentrations were equal in both phakic and aphakic eyes after either drug regimen and are much greater than those of the vitreous. A pathway other than diffusion through the vitreous exists for the drug to reach these tissues. The concentration of indomethacin reaching the retina and choroid is not sufficient to inhibit prostaglandin formation locally. The concentrations of indomethacin are high enough to inhibit the biotransformation of prostaglandin precursor only in the anterior segment.

Administration, Topical↗
PubMed1983

Radial keratotomy. Effect on cornea and aqueous humor physiology in the rabbit.

Radial keratotomy may cause anatomical damage to the rabbit corneal endothelium. To determine if physiological and functional alterations occur, radial keratotomy was performed on rabbit corneas using eight incisions with sparing of a 3.5-mm central pupillary area. Cornea endothelial membrane permeabilities were determined at various times up to ten weeks following the procedure using simultaneous flux determinations of tritiated inulin and dextran labeled with radioactive carbon on isolated corneas. At all times after radial keratotomy, there was no probable physiologically important change in corneal endothelial permeability to either of the labeled compounds. Fluorophotometry performed in a second group of animals at varying intervals following radial keratotomy showed no probable physiologically important change in endothelial fluorescein permeability. Aqueous humor turnover rate was reduced 16% and 29% at one week and nine to ten weeks, respectively, following radial keratotomy.

Animals↗
PubMed1983

Radial keratotomy and corneal permeability in Owl Monkey.

Radial keratotomy was performed on Owl Monkey corneas using 8 incisions with sparing of a 3.5mm central pupillary area. Cornea endothelial membrane permeabilities were determined at 2 days, and 4 weeks, following the procedure using simultaneous flux determinations of 3H-labeled inulin and 14C-labelled dextran. Inulin permeability was increased 27% two days following the procedure, and had returned to levels comparable to the unoperated eye 4 weeks following the procedure. Dextran permeability was unaltered at both 2 days, and 4 weeks, following the procedure. This study has shown that radial keratotomy causes a transient reduction in endothelial barrier function with the production of physiologically significant 'holes' in the membrane in the immediate post-operative period. The relationship of this physiological alteration to ultimate endothelial cell function is, at the present time, unknown.

Animals↗
PubMed1983

Intracellular pH and glutathione levels in rabbit corneal endothelium following storage in moist chamber and MK medium.

Rabbit corneas were stored for up to 14 days at 4 C either as the whole eye in a moist chamber or as the isolated cornea in MK medium with HEPES buffer. The intracellular pH, the glutathione content, and its oxidation state were determined in the endothelial cells of fresh and stored tissue. The endothelial pH was found to be unchanged following storage of up to 7 days by either method, but after 14 days the pH rose slightly but statistically significantly in corneas stored by both techniques. The intracellular pH was similar in endothelia of those corneas stored in MK medium and of those stored as the whole eye in a moist chamber, for all time periods studied. The intracellular total and percent oxidized glutathione of the endothelium were increased by 50 and 180%, respectively, following 7 days of moist chamber storage. Over this time period there was a 50-fold increase in total glutathione content of the aqueous humor in the stored eyes. In contrast, corneas stored in MK medium for 7 days maintained intracellular total glutathione at levels similar to those of fresh corneas. A gradual but constant decrease in percent oxidized glutathione was observed with increasing length of storage. In terms of pH and glutathione content, the MK medium provided a much more stable environment for the stored cornea than did the aqueous humor in the stored eye.

Animals↗
PubMed1982

Interlaboratory comparison of serum thyroxine analyses.

Approximately 300 clinical chemistry laboratories participated in a survey of measurements of the thyroxine (T4) concentration in 13 lyophilized serum specimens prepared by spiking a base serum pool with several different levels of T4. Of 35 commercially available kit methods, 4 kits were used by 30 or more laboratories, and 9 by 10 or more laboratories. Values obtained with the Abbott or Nuclear Medical laboratories, kits, which were used by one-third of all laboratories that named a specific kit, averaged 1 to 2 micrograms/dL greater than those obtained with the other methods. Within-run coefficients of variation were 10 to 20% for specimens containing less than 3 micrograms/dL of T4 and 3 to 6% for specimens with more elevated T4 levels.

Clinical Laboratory Techniques↗
PubMed1980

Chlorhexidine effects on corneal epithelium and endothelium.

Chlorhexidine digluconate, a soft contact lens disinfectant, was perfused over rabbit corneal peithelial and endothelial surfaces under a variety of concentrations and conditions. Without protein in the bathing solutions, the cornea swelled when chlorhexidine concentrations of 20 microgram/mL or greater were perfused over the endothelium. Scanning electron microscopy demonstrated rounded, swollen cells with loss of microvilli. Perfusion of the epithelium with chlorhexidine in protein-free Ringer's solution resulted in a dose-dependent sloughing of cells and loss of microvilli, which resulted in little or no swelling when the endothelium was concomitantly bathed with oil. Corneal swelling followed at concentrations of 500 and 1,000 microgram/mL when both corneal surfaces were bathed with protein-free Ringer's solution and the epithelium was perfused with chlorhexidine. With protein included in the bathing solution, no swelling occurred when separate chlorhexidine (500 microgram/mL) and albumin (1%) solutions were applied simultaneously to the epithelial surface of corneas, with the endothelial surface bathed in Ringer's solution.

Animals↗
PubMed1978

Iontophoresis of vidarabine monophosphate into rabbit eyes.

In order to investigate the efficacy of iontophoresis for increasing the penetration of vidarabine monophosphate into the eye, tritium-labeled vidarabine monophosphate was applied to rabbit eyes by topical and iontophoretic application, and the penetration of the compound into the eye, and its subsequent metabolism, were studied. At 20 min after treatment, the ratios of radioactivity for cathodal iontophoresis compared to topical application alone were cornea 8.6, aqueous humor 4.8, and iris 2.4; for 60 min the ratios were cornea 12.2 aqueous humor 17.5 and iris 2.5. In addition, the acid-soluble components were extracted from the cornea and aqueous humor. Vidarabine monophosphate, vidarabine, hypoxanthine arabinoside, adenosine, hypoxanthine, and adenine from the acid-soluble fraction were separated by thin-layer chromatography. The amount of vidarabine monophosphate and vidarabine in the cornea and aqueous humor from the iontophoretically treated group was six to 15 times higher than from the group that received topical application of the drug. It was concluded that cathodal iontophoresis resulted in significantly increased penetration of the antiviral drug vidarabine monophosphate into the anterior chamber of the eye. The effects of iontophoresis of vidarabine monophosphate on corneal epithelium, as observed by scanning electron micrographs, were equal to or less than those seen with the topical application of widely used preservatives in ophthalmic preparations.

Adenine↗
PubMed1977

Rabbit endothelial response to ophthalmic preservatives.

The endothelial surface of isolated rabbit corneas were perfused for three hours with varying concentrations of benzalkonium chloride and cetylpyridinium chloride. The threshold for physiological and ultrastructural alteration of corneal endothelium is approximately 0.0001% for benzalkonium chloride and 0.01 mM for cetylpyridinium chloride. The effects of the surfactants can be induced with as little as a 15-minute exposure without subsequent recovery. Use of ophthalmic medications or irrigating solutions containing these agents inside the eye is potentially hazardous to the corneal endothelium. Topical administration of 0.133% benzalkonium chloride to the anterior surface of deepithelialized in vivo corneas (five doses, seven minutes apart) caused no alterations of corneal endothelial cell function or ultrastructure.

Animals↗
PubMed1977

Modification of the antibiotic system in M-K medium.

Corneal endothelial cell function and ultrastructure were studied in rabbit corneas stored in M-K medium with different antibiotics. At concentrations about ten times greater than their minimum inhibitory concentrations, tobramycin, gentamicin, polymixin B, penicillin and streptomycin mixture, cephaloridine, and cephalothin did not damage corneal endothelia. Corneas stored in M-K medium with bacitracin did not have temperature reversals as did other corneas after storage. This is probably not significant since they maintained almost constant thickness and the endothelial layer remained intact.

Animals↗
PubMed1977

Effect of vidarabine and related compounds on corneal endothelium.

The endothelial surface of rabbit corneas was perfused with vidarabine monophosphate (with and without adenosine deaminase inhibitor), vidarabine (with and without adenosine deaminase inhibitor), and ara-Hx. In concentrations 10 times to 1,500 times higher than those that have been obtained in the aqueous humor following topical, subconjunctival, or systemic administration, none of the compounds had any effect on corneal endothelial cell function or ultrastructure for the duration of the experimental model.

Animals↗