Investigation of Rabbit Eye Anterior Segment Reducing Capacity: Interplay Between Hydrogen peroxide, Ascorbic Acid and Reductive Enzyme Systems

Abstract

Investigation of -'Rabbit Ey.e. Anterior Segment_ Reducing Capacity: Interplay Between Hydro·gen Peroxide, Ascorbic Acid. and Reduc~ive Enzyme Systems (Under the Direction of KEITH- GREEN, Ph.D., D.Sc.) The experiments perfo~ed in this' body of work lay the. foundation. •. . for· describing the- sequelae .of an in vivo modification in. the reducing · ca.pacity. of the normal rabbit ocular ntilieu following the intro.ductiO? of an oxidative insult into the anterio·r- chamber .. of th~ rabbit eye. The· concentration of intracame:rally ·injected hydrogeri: peroxi-de (HP),. strong en~ugh to c·ause oxidative d~mage, ·and y~t not elicit a white cell response was first determined. The morp~ological and physiological responses to this. ·dose of HP were studied_ ·and described.~ · . - . Age related differences in response· to HP inj e_ction were manifested

' - . between young and adult rabl:?its •.. Catala-se levels· were measured i~- i:r:i.s ~ ·. ciliary body, cor~eal endothel-fum, liver ·and- lung. tfssues. Catalase · levels· ·were· demonstrated· to decrease with maturation. Values for ascorbate and HP in· aqueous-humor, an4 ascorbate ·in pla~ma were determined. ·.Ascorbate and HP levels. correlated in young and :adult anitnals •. -Corneal endothelia_l glutathione ·-redox state· ~as .. shifted . toward ·the heavily oxid:i.ze_d $tate ·.a.ftfiar intracameral hydrogen· peroxide . . . injectio? confirming 'that the· capacity for HP reduction of the_ . glutathione redox system wit~in the endothelium was being overwhelmed by-· the bolus. HP injection. ·Catalase levels were chemically inhibited by intravenous injection ·of· 3-aminotriazole (3AT) into adult ·animals to mimic the ·condition of a X diminished .ocular-· r~ducing power. The dose response relationship was determined between the dose· ;of 3AT ·and the resultant catalase activ:i,tie~. : ... . . in ocular tissues. · The t~ Jo.r loss of HP from the aqueous humor was determined under control and.catalase inhibited-conditions,· and . ' demonstrated. a trend of fnGreasing length concurrent to increased catalase inhibition. The relationship between 'total ocular· reducing· power and.the t~ of,HP dissipation was determined by combining data ·from . . . . - the two experiments. Ocular. tissues exposed· to intracamerally injected I HPwhile· under 3AT inhibition of catalase activity demonstrated an exacerbated response compared with non-3AT treated· t:j_ssues •. These ' 'results suggest. 'an underlyin'g· r:elationship _between ~otal ocular reducing ' power and exte~t.of damag~ arising from contact with oxidants. 3AT was given orally ~o adult rabbits to determine the .effects of long term-inhibition of catalase levels. These.animals were not . ' challenged. with in.tracamerally intro<iuced HP but rather were studied· to . ' ·determin~ the effects of 3AT on .endogenous.HP levels. Decreases were noted in levels· of qcular· ascorbate.· and HP but not in levels of plasma ascorbate. Concurrent morphological changes were also rioted in the- .posterior portion of the rabbit lens. These inclqded bleb bing and · · macuolization of· lens fibers~. The findings of thes·e studies witk rabbits suggest that: 1) . ' . catalase-activity decreases with maturation: in rabbits; 2) decreases in catalase activity can beachieved using 3AT; 3) challenging oculaJ; tissues with exogenous HP can expose the underlying relationship .. between .ocular reducing power _and· levels of oxidants under normal· conditions and during inflammatory .condi:tions; 4) und·er conditions of greater than· 50% inhibition of catalase levels, other reductive .systems such. as the glutathione redox cycle play. an increasingly important role; and 5) when catalase levels are inhibited for long periods of time without concurrent exogenous HP challenge, major morphological and chemical changes occur in the aqueous humor.