Prostaglandin E2 binding sites in bovine iris-ciliary body.

In the eye, prostaglandins (PGs), in particular PGE2 and PGF2 alpha, may induce vasodilation, disruption of the blood-aqueous barrier, and biphasic effects on intraocular pressure, depending on the species. The initial event leading to many of these physiologic responses is the interaction between the PG and a receptor. We have explored the specificity and selectivity of PGE2 receptors in bovine iris-ciliary body (ICB) membrane preparations. Pigment-free bovine ICB membranes were prepared by high-speed sucrose density-gradient centrifugation. Membranes were incubated with 1 nM 3H-PGE2 in the presence or absence of varying concentrations of unlabeled PGE2 or F2 alpha. Binding of 3H-PGE2 to membranes at 37 degrees C increased linearly with protein concentration, and binding reached equilibrium in 30 min. Specific PGE2 binding represented 80% of total 3H-PGE2 binding. Studies with unlabeled PGE2 or F2 alpha, as competing ligands, showed a dose-dependent inhibition of 3H-PGE2 specific binding. The IC50 for unlabeled PGE2 and F2 alpha was 3 and 379 nM, respectively, which suggests a 100-fold greater selectivity of the binding sites for PGE2 over F2 alpha. Scatchard analysis of saturation data revealed a mean Kd value of 13.3 nM with a Bmax of 156 fmoles bound/mg protein. The general linearity of our Scatchard plots tends to suggests a single class of binding sites for PGE2, although more than a single binding site could be present. These results indicate that binding sites selective for PGE2 exist in the bovine ICB.

The origin of the intrinsic glycoproteins of the rabbit vitreous body: an immunohistochemical and autoradiographic study.

A cartilage matrix glycoprotein (CMGP), previously identified in human and bovine vitreous, now has been found in the vitreous body of rabbits aged 1-22 months by immunohistochemical techniques. Epithelial cells of the inner layer of the ciliary epithelium contain material that has immunologic cross-reactivity with a specific antibody to CMGP. These cells also secrete glycoproteins, as determined by autoradiography after intravitreal injection of [3H]fucose. Approximately 14 bands, representing intrinsic glycoproteins containing fucose residues, can be identified in fluorograms of SDS-polyacrylamide gels of vitreous bodies from 6- and 22-month-old rabbits. Fluorograms of gels of samples of vitreous and ciliary bodies from several time points after intravitreal injection of [3H]fucose reveal at least seven comigrating protein bands and also demonstrate turnover of the labeled ciliary body glycoproteins. These results suggest that the inner layer of the ciliary epithelium is the source of the glycoproteins of the vitreous body and that these glycoproteins undergo turnover, probably throughout the entire life of the animals.

G protein complement of SV40-transformed ciliary epithelial cells.

Guanine nucleotide-binding proteins (G proteins) are a family of receptor-coupled signal-transducing proteins that regulate a variety of second-messenger systems and ion channels. The complement of G proteins in SV40-transformed pigmented and nonpigmented ciliary epithelial cells was determined by Western blot analysis utilizing peptide and holoprotein derived antisera to known G protein alpha and beta subunits and cholera toxin catalyzed ADP-ribosylation. The complement of alpha subunits found in both SV40-transformed NPE and PE cells includes Gs alpha and all three members of the Gi alpha family. Neither cell type contains Go alpha or Gz alpha. Both cell lines contain beta 35 and beta 36. Future studies will examine the functional involvement of these G proteins in the regulation of aqueous humor stimulus-secretion coupling.

M3-muscarinic receptor subtype predominates in the bovine iris sphincter smooth muscle and ciliary processes.

The distribution of mRNAs encoding muscarinic acetylcholine receptor (mAChR) subtypes (M1, M2, M3, and M4) was investigated in the bovine iris-ciliary body by Northern blot hybridization with subtype-specific oligonucleotide probes that were complementary to unique regions of the M1, M2, M3, and M4 mAChRs. Whole rat brain RNA, which contains all four subtypes, was employed as a positive control. Both the iris sphincter and the ciliary processes were found to contain predominantly the M3 mAChR subtype and minor amounts of the M2 subtype. Traces of the M4 subtype were detected also in the ciliary processes.

Localization of smooth muscle myosin-containing cells in the aqueous outflow pathway.

Cells containing smooth muscle myosin were localized in the human aqueous outflow pathway by immunohistochemical techniques. In the majority of eyes, immunoreactive cells were observed adjacent to the collector channels and slightly distal to the outer wall of Schlemm's canal. In a few eyes, smooth muscle myosin was localized to cells in the juxtacanalicular tissue and the trabecular meshwork. The immunoreactive cells from these regions may be true smooth muscle cells or pericytes, which can contain smooth muscle myosin. No obvious differences were observed in the pattern of distribution of smooth muscle myosin-containing cells in a comparison of age groups. In the majority of eyes, we observed an apparent direct insertion of the longitudinal portion of the ciliary muscle in the corneoscleral meshwork far internal to the scleral spur.

Beta adrenergic binding sites in the human eye: an autoradiographic study.

Beta adrenergic binding sites were localized and characterized in the human eye by means of "in vitro" autoradiography, using [125I] (-) iodocyanopindolol (125ICYP) as radioligand. Binding sites were visualized by apposition of isotope sensitive film to slide mounted eye sections. Receptor sites were present in the extraocular muscles, in the conjunctiva, in the epithelium and endothelium of the cornea, in the trabeculum and in the ciliary muscle. They were also present in the lens epithelium and in the retina. The pigmented ocular structures were heavily labelled but the binding was nonspecific. Characterization of these binding sites was achieved by testing the ability of selective adrenergic compounds to displace 125ICYP binding. These studies suggested that the majority of adrenergic binding sites in nonpigmented structures of human eye were of a beta2 type.

[Age-related changes in fibronectin of the eye outflow drainage system]. / Vozrastnaia dinamika fibronektina drenazhnogo apparata glaza.

The content of the fibronectin, an extracellular glycoprotein in the drainage outflow system of human eyes was determined by the indirect immunoperoxidase staining technique. The degree of fibronectin accumulation in ocular tissues was evaluated by quantitative morphometric analysis. It was shown that the fibronectin level was elevated in ageing. Increased deposit of fibronectin in trabecular tissues, mainly, in the inner wall of Schlemm's canal and juxta-canalicular zone was demonstrated along with ageing. Comparison of fibronectin accumulation in glaucoma and ageing support the idea that ageing is a risk factor of glaucoma.

Presence and actions of vasopressin-like peptides in the rabbit anterior uvea.

The presence of vasopressin-like immunoreactivity (VP-IR) in the rabbit eye was demonstrated by radioimmunoassay. Trigeminal nerve denervation resulted in a significant and selective decrease in the levels of VP-IR in the iris sphincter muscle and the cornea. The isolated iris sphincter muscle contracted in response to low concentrations of [Arg8]vasopressin (AVP) and related peptides. The V1 vasopressin receptor antagonist, d(CH2)5Tyr(Me)AVP, potently inhibited the contractile responses to AVP. AVP was found to induce an increase in the accumulation of inositol phosphates in the iris sphincter muscle but not in the dilator/ciliary body preparation in vitro. The present investigation demonstrates the presence of VP-IR in the rabbit eye and that this substance may be another sensory nerve-derived mediator acting on specific target sites in the anterior uvea.

Characterization of specific binding sites for PAF in the iris and ciliary body of rabbit.

The protective effect exerted by BN 52021 a specific PAF-receptor antagonist in experimentally induced ocular inflammatory disorders led us to investigate the possible presence of specific receptors for PAF in rabbit iris and ciliary body. Two classes of PAF binding sites were found in isolated iris and ciliary process of pigmented rabbit eyes: a high affinity site Kd1 congruent to 4.9 +/- 0.47 nM, Bmax1 congruent to 3.17 +/- 0.50 pmoles/mg protein, a low affinity sites Kd2 congruent to 11.6 +/- 0.33 nM, Bmax2 congruent to 12.46 +/- 2.3 pmoles/mg protein for iris. The specific binding was not affected by lyso-PAF the biologically inactive precursor and metabolite of PAF, up to 10(-6) M; inhibition by unlabelled PAF demonstrated a biphasic curve partially antagonized by BN 52021. The present results demonstrate the presence of specific binding sites for PAF in rabbit eyes which could mediate the action of this mediator in eye inflammatory processes and explain the protective effect observed with BN 52021.

Estimation of DNA content in uveal melanomas by flow cytometry.

Flow cytometry was used to evaluate ploidy and tumour cycle kinetics in fresh tissue samples obtained from 19 uveal melanomas. The results were compared with other parameters including, histological cell type, tumour size and anatomical location. Three tumours (15.8%) were aneuploid (two mixed cell, one epithelioid cell). Cell turnover was estimated in the 16 diploid tumours by summating the total percentage of cells in S and G2/M phases. We found the mean percentage of cells in G2/M/S to be 5.96% (range 2.2-9.8%). Spindle cell neoplasms appeared to have lower cell turnover rates (4.5 +/- 1.2%) than epithelioid cell turnover (8.4 +/- 1.2%). There was no correlation between cell turnover and either tumour size or anatomical location.

Patterns of cytokeratin/vimentin coexpression in the guinea pig.

The distribution of cytokeratin and vimentin in guinea pig tissues as seen by immunohistochemistry using monoclonal antibodies is described and a similar distribution pattern of coexpression of cytokeratin and vimentin in various cell types as compared to human tissues were found. The possible explanations for the unusual coexpression of both types of intermediate filaments in normal cells are discussed.

Ocular biodistribution of clonidine after topical application with ophthalmic rods or solution.

We compared the ocular tissue and systemic blood distribution patterns of clonidine, an alpha 2-adrenergic agonist with ocular hypotensive activity, after topical application with ophthalmic rods or ophthalmic solution (eyedrops) in rabbits. We measured tissue concentrations at 0-240 minutes after administration with rods containing 5 micrograms, 10 micrograms, or 20 micrograms clonidine, or a 0.125% (62.5 micrograms) solution. The delivery efficiency of the rods was 65 - 71%. The rods and eyedrops had similar absorption and distribution patterns intraocularly and in systemic blood. Tissue concentrations of clonidine achieved were proportional to the dose delivered; peak ocular tissue concentrations were reached within 20 minutes (except for the lens). Clonidine concentrations were: tears greater than cornea greater than iris/ciliary body greater than or equal to aqueous humor greater than lens. We concluded that the ophthalmic rod offers a viable alternative to ophthalmic solution for the topical delivery of clonidine.

Ocular hypotensive activity and disposition of the topical carbonic anhydrase inhibitor 6-hydroxy-benzo[b]thiophene-2-sulfonamide, L-650,719, in the rabbit.

The carbonic anhydrase (C.A.) inhibitor, L-650,719 (6-hydroxy-benzo[b]thiophene-2-sulfonamide) is an advance over the corresponding 6-OH benzothiazole-2-sulfonamide in increased water solubility (4 mM) and CHCl3/buffer partition (0.05). KI vs CA is 10(-8) M. Topical treatment with 1 drop of 0.15-8% suspensions (in hydroxyethylcellulose-HEC) lowered intraocular pressure (IOP) up to 2.6 mmHg, with a plateau at 2%. Two hours after 2% treatment ocular drug distribution showed (microM or mumole/kg): cornea, 115, anterior aqueous 27, posterior aqueous 4, ciliary processes 15. Calculated inhibition of C.A. is 99.7%. IOP lowering effect disappeared at 6 hrs. L-650,719 was also given in solution (17 mM, pH 9.3). One drop every 5 min x 5 or 10 min residence on cornea of this solution produced an IOP lowering and drug distribution similar to that of the 2% suspension. Increasing HEC concentration in the single drop solution from 0 to 1%, led to a 3-fold increase in anterior aqueous drug levels and an improved delta IOP. The pressure lowering is somewhat less than achieved with parenteral sulfonamides in the rabbit. Clinical trials showed modest activity, so L-650,719 is not being developed further. It is evident, however, that sulfonamides with a variety of chemical and pharmacological properties are conducive to development for topical treatment of glaucoma.

Retinol-binding protein is synthesized in the mammalian eye.

As the chromophoric component of the visual pigment, retinol plays an essential role in vision. In the plasma, retinol is transported by retinol-binding protein (RBP) in complex with transthyretin (TTR, prealbumin). In previous work we demonstrated intraocular synthesis of TTR. To determine whether RBP is also synthesized in the eye, we performed Northern and Western blot analysis of rat eye, and detected both RBP mRNA and immunoreactive RBP. Regional Northern analysis of bovine eye localized RBP mRNA to ciliary body/iris and retina/RPE. Preliminary immunohistochemical studies revealed a widespread but heterogeneous distribution of RBP in rat eye. We postulate that ocular RBP and TTR are involved in the intraocular translocation of retinol.

Association of elastin with pseudoexfoliative material: an immunoelectron microscopic study.

Using immunoelectron microscopy, the presence of elastin and tropoelastin was demonstrated in pseudoexfoliative (PSX) material in all its classical sites on the lens capsule, ciliary non-pigment epithelium, iris epithelium and stroma, and conjunctiva. Some variability in binding affinity was seen in different sites, and labelling was more often on the periphery than the center of the PSX fibers. The elastin epitope on PSX material was more sensitive to processing than the remarkably stable epitope on mature elastic fibers. Since neither elastin nor a related component of PSX fibers, elastic microfibrillar protein, is a circulating protein, both are likely to be secreted by local ocular cells. Most of these local cells are not involved in elastogenesis normally, suggesting that an abnormal stimulus or defective regulation of matrix synthesis exists in this disease.

Ocular renin-angiotensin: immunohistochemical evidence for the presence of prorenin in eye tissue.

Angiotensin II (A2) is a vasoconstrictor generated by the renin-angiotensin system. A2 appears to act also as an angiogenic factor. Recent evidence suggests that renin is synthesized at many tissue sites and may generate A2 locally. Local A2 may have important functions in the normal and diseased eye. We examined eight human eyes by immunostaining with an antibody to prorenin, the biosynthetic precursor of renin. In all eyes, prorenin staining was extensive in the pars plicata of the ciliary body suggesting that the ciliary body synthesizes renin and this renin may be part of an ocular A2 generating system.

[Cyclic nucleotides in experimental glaucoma]. / Tsiklicheskie nukleotidy pri éksperimental'noi glaukome.

cAMP and cGMP contents were studied in various eye tissues of rabbits with experimental glaucoma induced by chronic intravenous adrenaline administration. Cyclic nucleotide level was measured in the retina, choroid, iris and ciliary body. An increase in the tissue cAMP level was found especially in the iris and ciliary body. An increase in tissue cAMP content is explained by an enhanced beta-adrenergic regulation in the eyes of rabbits with experimental glaucoma. No consistent changes were found in cGMP content in eye tissues.

Pharmacological characterization of human ciliary muscle adrenoceptors in vitro.

The in vitro pharmacological characteristics of adrenoceptors of the human ciliary muscle were investigated. Tissue was obtained from 30 eyes used previously for corneal transplantations which had been enucleated 6-24 hr after death. Experiments were performed within 2 days of enucleation. Strips of the meridional and circular portion of the ciliary muscle were attached to a tension gauge in an organ bath and the effect of drugs added to the perfusion medium was monitored isometrically. The muscle was precontracted with physostigmine (10(-5) M) and acetylcholine (10(-5) M). The non-selective beta adrenoceptor agonist isoproterenol (10(-6)-10(-3) M) caused a dose-related relaxation of the ciliary muscle, an effect which was completely inhibited by the non-selective beta adrenoceptor antagonist timolol (10(-5) M), while the beta 1 adrenoceptor antagonist betaxolol (10(-5) M) had no effect. The beta 2 adrenoceptor agonist salbutamol (10(-6)-10(-3) M) produced a dose-related relaxation of the ciliary muscle, an effect which was completely blocked by the beta 2 adrenoceptor antagonist L1 32-468 (10(-5) M). The non-selective alpha adrenoceptor agonist noradrenaline (10(-6)-10(-3) M) also caused a dose-related relaxation of the ciliary muscle. The non-selective alpha adrenoceptor antagonists phentolamine (10(-5) M) and thymoxamine (10(-5) M) and the alpha 1 adrenoceptor antagonist prazosin (10(-5) M) partially blocked the response to noradrenaline, while the alpha 2 adrenoceptor antagonist idazoxan (10(-5) M) and timolol (10(-5) M) had no effect. The alpha 1 adrenoceptor agonist phenylephrine (5 X 10(-6)-5 X 10(-3) M) caused a dose-dependent relaxation in five out of 12 isoproterenol-sensitive muscle strips. Further, it was not possible to block the phenylephrine-induced relaxation with thymoxamine (10(-5) M). The alpha 2 adrenoceptor agonist clonidine (10(-6)-10(-3) M) had no effect. No qualitative difference between drug effects on the meridional and circular ciliary muscles was observed. We conclude from these data that beta 2, and most probably alpha 1, adrenoceptors are present on both the meridional and circular portions of the ciliary muscle of the human eye.

Identification of extractable proteins from the bovine ocular zonule: major zonular antigens of 32kD and 250kD.

Using Western immunoblotting, the extractable proteins of the bovine zonular fibers were examined for reactivity with two zonular antisera known to have strong affinity for zonular fibers in tissues, in order to identify the antigenic components. The extracts were also tested with antisera to several matrix proteins that have been reported to be associated with zonular fibers. Proteins reactive with antisera to bovine serum albumin, serum immunoglobulins and fibronectin were present. No bands reactive with antisera to a-elastin, prealbumin, amyloid P component, collagen VI, lysyl oxidase or monoclonal antibody to fibrillin were demonstrated. The major nonserum protein band identified by both antisera was a 32kD polypeptide. An equally strong 250kD polypeptide was shown by the antiserum to guanidine-dithiothreitol extracted zonular fibers. Both of these proteins were PAS-positive and were demonstrated also by the antisera in extracts of bovine elastic neck ligament. Whether the two glycoproteins are related to each other, with the higher molecular weight protein either a precursor or aggregate form, is not yet clear. They appear to bear a close relationship to the elusive core microfibrillar protein.