Ocular esterase composition in albino and pigmented rabbits: possible implications in ocular prodrug design and evaluation.

A methodology was developed to determine the proportion of acetyl- (AChE) and butyrylcholinesterase (BuChE) in the albino and pigmented rabbit eye. It was found that BuChE contributed over 75% of the cholinesterase activity in all the ocular tissues but the corneal epithelium of the albino rabbit. This esterase was principally responsible for the parabolic chain length dependence of ocular hydrolysis of model naphthyl ester prodrugs reported previously. In contrast, when incubated with AChE, the rate of hydrolysis of these esters decreased monotonically with increasing ester chain length. Together these findings suggest that esters whose chain length exceeds 4 carbons will be hydrolyzed primarily by BuChE. It is suggested that the dominance of BuChE in ocular tissues is another factor which merits consideration in the design and evaluation of ocular ester prodrugs.