Enhanced Ocular Hypotensive Response to Epinephrine in Rabbits with Prior Dexamethasone Treatment

Abstract

The purpose of this study was to determine glucocorticoid modulation of ocular pressure to epinephrine applied topically to rabbit eyes that were pretreated with dexamethasone. Rabbit eyes were pretreated with five applications of topical 0.07% dexamethasone (0.1% dexamethasone phosphate) or saline drops, administered at ten minute intervals. The eyes were then treated with epinephrine bitartrate drops at concentrations of free base epinephrine of 1.1%, 0.27%, 0.05%, 0.027%, 0.005% or 0.0005%. An additional group of rabbits received dexamethasone pretreatment only. Intraocular pressure (IOP) was measured for the next four hours. Enhanced lowering of intraocular pressure was observed with dexamethasone pretreatment. Rabbits receiving the smaller dose of epinephrine with dexamethasone had the largest decrease in IOP at 135 minutes after instillation of the epinephrine drops (0.005% epinephrine, mean difference +/- standard error of mean = 5.4 +/- 1.1 mmHg). Similarly, the duration of significant decrease of the IOP was prolonged in the groups receiving the lower concentrations of epinephrine (0.005% epinephrine, 255 minutes after administration of epinephrine). The synergism between glucocorticoids and adrenergic agonists in lowering IOP may be potentially useful in the therapy of ocular hypertension and glaucoma.

Dose Response of Dexamethasone for the Enhanced Ocular Hypotensive Response to Epinephrine in Rabbits With Prior Dexamethasone Treatment

“…We have also reported that in vivo, the administration of epinephrine to the rabbit eye with dexamethasone pretreatment resulted in a significant decrease in IOP compared to the use of epinephrine alone (2). Furthermore, we have shown that this decrease in IOP is dose-dependent on epinephrine with the smaller doses producing the largest decrease in IOP.…”

“…We have previously shown that rabbits treated with epinephrine demonstrated an enhanced ocular hypotensive response when pretreated with dexamethasone (2). We have also shown that this effect was dose-dependent on epinephrine.…”

“…The three groups were: a control group which received saline (0.9% sodium chloride) drops in both eyes; an epinephrine group that was treated with saline drops, followed by epinephrine bitartrate drops; and a dexamethasone/epinephrine group that received pretreatment with dexamethasone phosphate drops followed by epinephrine drops. Previous studies using a fourth control group of dexamethasone drops alone showed no tendency for an effect on IOP compared to the saline control group (2).…”

“…The protocol for this study was similar to the one used for the study of the ocular hypotensive response to different doses of epinephrine with prior dexamethasone treatment (2).…”