title: Nerve terminal degeneration in the rat iris observed following chronic topical 2% epinephrine and 0.1% dipivalyl epinephrine: a quantitative comparison of electron microscopic observations and tissue norepinephrine levels.
abstract: This is the first report of nerve terminal degeneration within the iris following topical dipivalyl epinephrine 0.1% treatment. A quantitative comparison of the effects of topically applied epinephrine 2%, dipivalyl epinephrine 0.1%, and placebo vehicle on the nerve terminals within the iris of a rat was made using electron microscopy and a catecholamine radioenzyme assay. Thirty-nine rats were divided into these 3 treatment groups and treated for 10 weeks, after which they were killed and studied. Both the epinephrine 2%- and dipivalyl epinephrine 0.1%-treated groups showed greater nerve terminal degeneration compared with the placebo-treated group (P < 0.05). The epinephrine-treated group showed greater nerve terminal degeneration than the dipivalyl epinephrine-treated group. The clinical significance of these observations is unknown. It is impossible to decide whether these degenerative changes are related unavoidably to a desired therapeutic effect or to an undesirable, potentially avoidable, toxic side effect.
authors.affiliation: University of California, San Francisco Medical Center.
authors.forename: A J
authors.initials: AJ
authors.lastname: Flach
authors.forename: M E
authors.initials: ME
authors.lastname: Donahue
authors.forename: I S
authors.initials: IS
authors.lastname: Wood
mesh_terms: D000818:Animals; D004837:Epinephrine / Q000008:administration & dosage / Q000031:analogs & derivatives* / Q000633:toxicity*; D007498:Iris / Q000294:innervation* / Q000378:metabolism / Q000648:ultrastructure; D008297:Male; D009410:Nerve Degeneration / Q000187:drug effects*; D009411:Nerve Endings / Q000187:drug effects* / Q000378:metabolism / Q000648:ultrastructure; D009638:Norepinephrine / Q000378:metabolism*; D051381:Rats; D017207:Rats, Sprague-Dawley
chemical_list: C015173:dipivefrin; D009638:Norepinephrine; D004837:Epinephrine