Insulin and tropicamide accumulate in the contralateral, untreated eye of rats following ipsilateral topical administration by a mechanism that does not involve systemic uptake.
BACKGROUND
This study was designed to determine: (1) whether the accumulation of insulin in the contralateral retina and aqueous humor following ipsilateral topical insulin administration was due to systemic uptake and (2) whether tropicamide, applied to one eye, could induce dilation in the contralateral eye by a mechanism that did not involve systemic uptake.


METHODS
Insulin eye drops were applied to the left eye of intact and decapitated rats, and their retinas and aqueous humors were then removed and their insulin levels quantified. In a separate experiment live animals received 0.1% tropicamide in their left eye and had their pupillary dilation response in both eyes measured at different time points.


RESULTS
Administration of insulin to the left eye of decapitated rats resulted in its significant accumulation not only in the left retina and aqueous humor, but also in the retina and aqueous humor of the right eye. Similar aqueous humor results were obtained when live animals were used. Tropicamide drops induced marked pupillary dilation in treated eyes; the pupils of the contralateral, untreated eyes also dilated significantly, but less than did the treated pupils. The pupils of rats injected with tropicamide intravenously showed negligible dilation.


CONCLUSIONS
These results showed that insulin accumulated in the retina and aqueous humor of contralateral, untreated eyes following topical application, by a mechanism that did not appear to involve systemic uptake. Similarly, tropicamide provoked a dilation response in the unheated eye by a mechanism that similarly did not appear to involve uptake from the blood.
Patsiopoulos
Georgia
G
Department of Biomedical Sciences and Disease, New England College of Optometry, Boston, Massachusetts 02115, USA.
Lam
Vincent
V
Lake
Stephen
S
Koevary
Steven B
SB
D000042:Absorption; D000287:Administration, Topical; D000818:Animals; D001082:Aqueous Humor / Q000378:metabolism*; D005260:Female; D007004:Hypoglycemic Agents / Q000493:pharmacokinetics*; D007328:Insulin / Q000493:pharmacokinetics*; D009184:Mydriatics / Q000493:pharmacokinetics*; D009883:Ophthalmic Solutions; D011680:Pupil / Q000187:drug effects; D051381:Rats; D012160:Retina / Q000378:metabolism*; D014331:Tropicamide / Q000493:pharmacokinetics*
D007004:Hypoglycemic Agents; D007328:Insulin; D009184:Mydriatics; D009883:Ophthalmic Solutions; D014331:Tropicamide