Enzymatic and nonenzymatic hydrolysis of D,L-dipivefrin

D,L-dipivefrin hydrochloride was administered bilaterally to rabbit eyes five or 150 minutes after unilateral application of a cholinesterase inhibitor. Aqueous humor levels of D,L-epinephrine, measured 30 minutes later by high-performance liquid chromatography, were not significantly different in the two eyes. Nonenzymatic conversion of D,L-dipivefrin to D,L-epinephrine was measured in tissue-free (pH 7.4) solutions; after three hours less than 1% of D,L-dipivefrin became D,L-epinephrine. Homogenates of corneal epithelium were 16 times more effective in converting D,L-dipivefrin to D,L-epinephrine than after heat-inactivation. The ocular hypotension produced by 0.25% D,L-dipivefrin eyedrops was unaffected by prior administration of 0.25% echothiophate iodide eyedrops provided the D,L-dipivefrin was administered after the echothiophate-induced ocular hypertensive phase. It was concluded that D,L-dipivefrin was converted to D,L-epinephrine in vivo primarily by enzymatic hydrolysis and that cholinesterase inhibitors did not affect this conversion.