Some effects of topically applied (−)-adrenaline bitartrate on the rabbit eye

Abstract

A 2·5% solution of thymoxamine hydrochloride applied topically to the eyes of conscious rabbits did not affect ocular tension. When 2·5% thymoxamine was administered prior to 0·5% adrenaline, a decline in ocular tension commenced 1–2 hr after adrenaline, in contrast to the observation with 0·5% adrenaline alone in which tension remained unchanged for 2 hr after administration. Topical adrenaline solutions of several concentrations were shown to reduce penetration of tritiated water from the blood into the aqueous humour of conscious rabbits and also to reduce the clearance of [ 14C]inulin injected into the anterior chambers of conscious and anaesthetized rabbits. However, these effects were short-lived, being negligible after approximately 2 hr and absent after 4 hr. Another early effect of adrenaline observed in conscious rabbits was a concentration-related decrease in the anterior chamber depth. Experiments performed on anaesthetized rabbits showed a correlation to exist between the magnitudes of facility increases and ocular tension reductions observed after the topical administration of 0·5% adrenaline. The discussion suggests that the reduction of ocular tension present 4–5 hr after topical administration of adrenaline in the rabbit is mainly due to increased outflow facility. It is further suggested that the delay in onset of the hypotension is due to a hypertensive mechanism which temporarily negates the potentially hypotensive effects of increased facility and decreased aqueous inflow.