Rabbit Ocular Tissues Research Articles

Autoradiographic localization of intravitreally- or intracamerally-injected [ 3H]prostaglandins

The distribution of [ 3H]prostaglandins in the ocular tissues of rabbits was studied using autoradiography. Also the effect of intravitreally-injected prostaglandin E 1 on the intraocular pressure and blood-aqueous barrier was investigated. To a greater extent [ 3H]prostaglandins were distributed in the iris-ciliary processes following administration either into the anterior chamber or into the vitreous body. In the ciliary processes, [ 3H]prostaglandins were found predominantly in the stroma. Intravitreally-injected [ 3H]prostaglandins were transported out of the vitreous body very rapidly and did not appear in the aqueous humour. The intraocular pressure and protein content of the aqueous but not of the vitreous humour were found to increase within 15–30 min of the intravitreal injection of prostaglandin E 1. The leakage of India ink in the ciliary stroma of prostaglandin-treated eyes was observed. It is suggested that the site of action of prostaglandins on the blood-aqueous barrier is the ciliary processes.

Inhibition of the prostaglandin synthetase systems in ocular tissues by indomethacin.

1 We have compared the sensitivity of the prostaglandin synthetase systems derived from microsomal fractions of rabbit ocular tissues (anterior uvea, conjunctiva and retina) with other rabbit tissues such as the kidney medulla and spleen, to inhibition by indomethacin.2 Generation of prostaglandin-like activity by the microsomal fractions from added arachidonic acid varied with the tissue used. Highest activity was found in the kidney medulla, then in descending order, the conjunctiva, anterior uvea, spleen, retina and cornea.3 Indomethacin was most potent in the spleen (ID(50) 0.045 mug/ml) then in decreasing order in the kidney medulla, conjunctiva, anterior uvea and weakest in the retina, where the ID(50) for indomethacin was 50 mug/ml.4 The differential sensitivity to inhibition of the prostaglandin synthetase systems from different tissues is an important consideration in the development of new ocular anti-inflammatory agents.

Uptake of [ 3H]noradrenaline by the ocular tissues of rabbit

The uptake and storage of exogenous noradrenaline by adrenergic nerve terminals in the ocular tissues of rabbits were studied by autoradiography and fluorescence microscopy. Within 2 hr of intracameral injection of [3H]noradrenaline, uptake by iris, ciliary epithelium, episcleral and intrascleral vessels was complete. The exogenous noradrenaline stored up in the nerve terminals was slowly released over a period of 4–24 hr. The uptake by any tissue was dependent on the extent of adrenergic innervation. The uptake and storage of topically administered noradrenaline followed a similar pattern. Seventy-two hours after superior cervical ganglionectomy it was found that adrenergic nerve terminals had completely lost their uptake and storage capacity. It is suggested that the release of stored noradrenaline over a long period is responsible for the prolonged action on the outflow channels in rabbit eyes.

Antibiotic concentration in ocular tissues. Penicillin G and dihydrostreptomycin.

The total antibiotic concentration of penicillin G potassium (benzylpenicillin) and dihydrostreptomycin sulfate were determined in the ocular tissues of rabbits by radioactive tracer methods following systemic and subconjunctival administration. Free, unbound active antibiotic concentrations were determined by a modified disk diffusion assay. Both methods correlated well at concentrations greater than 200μg/gm wet tissue, but below this level the free antibiotic concentrations averaged 30% of the total for penicillin G and 75% for dihydrostreptomycin. After both systemic and subconjunctival administration, the free antibiotic levels in all tissues except lens and vitreous exceeded that in aqueous humor. Thus, the use of aqueous humor assays to determine the intraocular penetration of penicillin G and dihydrostreptomycin is not a valid indication of ocular tissue concentration.

Cholinesterase isoenzymes in rabbit ocular tissue homogenates.

Proteins of rabbit ocular tissue homogenates were separated by discelectrophoresis and analyzed for cholinesterase. By the use of specific substrates and selective inhibitors it is shown that true cholinesterase is largely present in ocular tissue with a small amount of nsChE also present. The number of isoenzymes (bands) varies with a given tissue.

Penetration of pyrimethamine (daraprim) into ocular tissues of rabbits.

Chemically, pyrimethamine (Daraprim) is 2,4-diamino-5-p-chlorophenyl-6-ethylpyrimidine, with the empirical formula C₁₂H₁₃N₄Cl. This chemical was synthesized by the Wellcome Research Laboratories, Tuckahoe, N. Y., as an antimalarial drug which arrests plasmodial development at those stages involving nuclear division. Besides this antimalarial activity, pyrimethamine has been shown to have an extraordinarily potent antimetabolite activity. To my limited knowledge, the mode of action of the preparation against toxoplasmosis has not been entirely elucidated. However, Eyles and his associate,¹in 1952, reported antitoxoplasminic action of the drug in mice and, in 1953, showed that pyrimethamine and sulfadiazine were synergistic to each other against experimental toxoplasmosis in the mouse.²Since these reports, the drug has been widely used in the treatment of presumptive toxoplasmic infections of man as well as of experimental toxoplasmosis of animals. In the past years, numerous papers on the subject have been published, creating