Intraocular pressure and aqueous humor dynamics in rabbit and primate with d- and 1-adrenergic compounds.

The effects of the d- and 1-isomers of epinephrine and norepinephrine have been determined on intraocular pressure (IOP) in conscious rabbits and rhesus monkeys, and on aqueous humor turnover rate (AHTR) in rabbits. Relatively specific beta-adrenergic antagonists (butoxamine and metoprolol) were used to attempt to modify the responses. The effects on IOP in both species are similar to those of racemic mixtures. The d- and 1-isomers of norepinephrine and epinephrine reduced IOP, and reduced AHTR in rabbits. The d- and 1-isomers of norepinephrine had little effect on IOP in monkeys while d- and 1-epinephrine increased IOP. Metoprolol, a beta 1-antagonist was more effective than butoxamine (beta 2-antagonist) at modifying the effect of the norepinephrine isomers in rabbits.

Effect of oxygen free radical products on rabbit iris vascular permeability.

Oxygen free radicals and their products are known to be elaborated by inflammatory cells during the 'respiratory burst'. Xanthine oxidase combined with hypoxanthine was injected into the anterior chamber of rabbit eyes. This combination is known to result in the production of oxygen free radicals. Iris fluorescein angiography performed 2 h and 24 h following injection of xanthine oxidase and hypoxanthine into the anterior chamber resulted in increased iris vascular permeability. The increased permeability was not modified by either of the prostaglandin inhibitors naproxen or aspirin nor by the free radical scavenger D-penicillamine. This study demonstrates that iris vascular permeability, and possibly blood-aqueous barrier permeability is increased following exposure to chemically generated oxygen free radicals. It is possible that the increased iris vascular permeability that occurs during ocular inflammatory processes may in part be mediated by oxygen free radical products. This model may be useful in developing therapeutic modalities directed at preventing the damaging effect of oxygen free radical products, and this may be of benefit in reducing the untoward effects of ocular inflammatory disorders.

Ocular fluid dynamics response to topical RU486, a steroid blocker.

A steroid antagonist applied to one eye of 18 young pigmented rabbits during a 10-week period caused a statistically significant fall in IOP, but no statistically significant nor clinically relevant change in the rate of aqueous humor turnover. The pressure change is therefore ascribed to an alteration in outflow channels. No changes occurred in a parallel group of 5 animals in which one eye was treated with vehicle and the contralateral eye was untreated. The drug effects became evident after two weeks of application, suggesting that a slow turnover pathway is involved.

Decreased intraocular pressure and aqueous humor turnover rate during longitudinal ocular studies in the rabbit.

One group of 5 pigmented rabbits, during a period of 10 weeks, and two groups of 8 albino rabbits, during 16 weeks, showed a fall in aqueous turnover rate and outflow facility of about 30%. A fall in intraocular pressure also occurred of about 10 mm Hg. The biochemical correlative mechanism, systemic and/or local, is conjectural (reduction of "stress"; homeostasis). Empirically a parallel completely untreated control group should accompany any longitudinal study group in order to differentiate these temporal trends from experimental effects.

Pharmacological modification of corneal endothelial intracellular pH, intracellular electrical potential difference, and corneal swelling and deswelling rates.

Rabbit corneal endothelial intracellular pH and electrical potential difference were measured using radioactive tracer techniques. A variety of drugs and chemicals were used to modify specific aspects of cell membranes in order to determine, in this steady state system, whether a close relationship existed between intracellular pH and potential. Corneal swelling and deswelling rates were also determined in the presence and absence of the drugs. Longer times of immersion of tissue with drugs (3 hours) tended to provide more support for a link between intracellular pH and the inability of the cornea to maintain a constant thickness. Drugs that altered corneal thickness without altering either intracellular pH or potential difference presumably acted on extracellular pathways. No conclusive evidence was obtained for a direct link between intracellular pH and the intracellular electrical potential difference of the endothelial cell.

Intracellular potential and pH of rabbit corneal endothelial cells.

Rabbit corneal endothelial pH and electrical potential have both been determined using tracer distribution techniques. Intercellular pH was measured using the dimethyloxazolidine-dione method and intracellular potential was measured using tetraphenylphosphonium bromide. Intracellular pH was determined as 7.10 in an ambient solution of pH 7.5. The only solution variations which altered intracellular pH were variations in the external solution pH, bathing in sodium-free or bicarbonate-free solution, incubation for 3 hours with 10(-6) or 10(-4) M ouabain or for 1 hour with 10(-4) M ouabain or in a high (60 mM) bicarbonate solution. The data indicate a close correlation between sodium and bicarbonate needs for the endothelium which corresponds with known effects of these ions on transendothelial ion fluxes. Intracellular potentials were measured of -34 mV, which were stable in the face of all environmental perturbations except 1 mM acetazolamide and 10(-6) M ouabain exposure for 3 hours. These newer techniques may be employed to provide some clues into the mechanism of endothelial transport systems.

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.

Intraocular pressure following systemic administration of cannabinoids.

Various cannabinoids have been tested for activity compared to delta 9-THC in reducing intraocular pressure after intravenous administration in rabbits at 0.1 mg or 1 mg/animal. Comparison of l-delta 9-, delta 8-, 11-OH-delta 9- and 11-OH- delta 8-THC indicates that minor configurational changes have only a small influence on activity with regard to induction of a fall in intraocular pressure, although 11-OH-delta 8-THC has increased activity. 8 alpha-OH-, 8 alpha-diOH- and 8 beta-diOH-delta 9-THC have little or no activity but 8 beta-OH-delta 9-THC is as active as delta 9-THC indicating that the hydroxyl group in the beta-position does not influence activity. Modification of the C5H11 alkyl side chain (3'-OH-delta 9-THC) reduced activity to 20% relative to delta 9-THC. Cannabidiol (CBD), cannabichromene, cannabigerol and olivetol had no activity, but 10-OH-CBD had some activity at 2 mg/animal. Cannabinol (CBN) had about half the activity of delta 9-THC and activity was reduced further with 1'-OH-CBN, indicating that side chain modification reduced activity. Neither delta 9-THC, nor cannabigerol, had any effect on intraocular pressure or total outflow facility in the rhesus monkey, suggesting species differences in ocular responses to cannabinoids. Further studies on modification of these compounds is warranted in order to further delineate the structure-activity relationships.

Water soluble marihuana-derived material: pharmacological actions in rabbit and primate.

Further studies have been made with water soluble marihuana-derived material (MDM). Neither adrenergic, cholinergic, aldosterone, dopamine or serotonin antagonism affected the fall in intraocular pressure induced by MDM. Partial blockade was obtained with galactose, glucose, or mannose, but not arabinose, when the latter were given at intravenous concentrations of 1 gm/animal and MDM was given at 25 micrograms animal, suggesting that these sugars may be involved at the active site of the MDM glycoproteins. Dexamethasone was without effect on either intravenous or intravitreal MDM indicating that the MDM effect is not a non-specific response to a protein. A similar plant glycoprotein, larch arabinogalactan, at 200 micrograms/animal was without effect on intraocular pressure. Aqueous humor flow rate was increased 3 hours after MDM administration, a period corresponding to the intraocular pressure increase caused by MDM, and fell to 20% of control values when the fall in intraocular pressure occurred. Blood flow through the iris was increased at both one and six hours after intravenous MDM injection indicating a vasodilation which could contribute to the initial increase in intraocular pressure. Intravitreal injection of MDM in rabbit and rhesus monkey caused a fall in intraocular pressure only after a 24 hour delay: the unilateral response indicated that systemic metabolism was not required for activity and the delay was likely caused by the diffusion time to the ciliary processes from the mid-vitreal injection site. The changes in beta-receptors, adenylate cyclase and carbonic anhydrase in the ciliary processes are minimal indicating a possible vascular mechanism of action of MDM.

Ocular and systemic responses to water soluble material derived from Cannabis sativa (marihuana).

A water soluble material, isolated from Cannabis sativa, has been tested in albino and pigmented rabbits and rhesus monkeys for both ocular and systemic effects. Intravenous administration produced a dose-related fall in intraocular pressure in both albino and pigmented rabbits with concentrations as low as 0.005 mg/animal being effective, but no response was found in monkeys. High concentrations (0.2 to 1 mg/animal) induced a hypertensive phase in intraocular pressure prior to the ocular hypotension; higher concentrations (2 or 5 mg/animal) also induced antidiuresis and general relaxation. Tachyphylaxis was found to repeated daily injections. Alpha and beta-adrenergic antagonists caused some reduction of the hypertensive phase but had no effect on the hypotensive phase. Superior cervical ganglionectomy did not influence the time course of the intraocular pressure response. Indomethacin inhibited the hypertensive intraocular pressure phase but was ineffective against the hypotensive phase. Systemic blood pressure was unchanged following intravenous administration of 0.2 mg material/animal. Aqueous tumor protein concentration was increased at both 1 and 6 hours after intravenous administration, becoming greater at the later time. Aqueous humor turnover rate was substantially reduced reaching a minimum 8.75 hours after administration. Topical administration was ineffective in eyes when the epithelium was removed in rabbits with and without pretreatment with aspirin. Neither gastric nor suppository administration of large quantities (10 mg or greater) of material had any influence on intraocular pressure.