Neurologic evaluation of acute lacrimomimetic effect of cyclosporine in an experimental rabbit dry eye model

Abstract

Purpose: To evaluate neurologically acute lacrimation caused by cyclosporine (CsA) eyedrops in rabbit.

Methods: Normal adult male New Zealand White rabbits and those that underwent parasympathectomy each received a single instillation of 0.1% CsA or vehicle eyedrops. Schirmer tear test (STT) results, flow rate of lacrimal gland (LG) fluid from the excretory lacrimal duct of the main LG, and blink rate (over a 3-minute period) were measured before and after instillation of CsA or vehicle. Light microscopy was performed to examine the main LG in vitro. Protein release from LG fragments was assessed after incubation with CsA for 30 minutes.

Results: In normal rabbits, the STT value and the flow rate of LG fluid were significantly increased after treatment with CsA compared with vehicle (P < 0.05). In contrast, no changes were found in denervated eyes. The blink rate of CsA-treated eyes was significantly higher than that of vehicle-treated eyes in normal rabbits (P < 0.005), whereas that of denervated eyes decreased significantly after CsA instillation compared with before administration (P < 0.005). Light microscopy showed that the cytoplasm of acinar cells was packed with secretory granules in denervated LG tissue 7 days after parasympathectomy. The same finding was observed 3 hours after CsA instillation. CsA had no stimulatory effect on protein release by acinar cells in LG fragments at all concentrations tested.

Conclusions: These results suggest that CsA has no direct effect on tear fluid secretion from the LG in an acute model. Instead, CsA increases reflex tear flow.

Figures

FIGURE 1

Tear flow measured by the STT in both eyes before and after topical administration of CsA or vehicle in (A) normal rabbits (n = 7) and (B) denervated rabbits (n = 7). (A) Tear flow reached a maximum 3 hours after CsA treatment and then gradually returned to baseline. There were significant differences at 3 and 5 hours after CsA treatment compared with the control side (*P < 0.05). Tear flow also increased between 1 hour and 5 hours compared with flow before instillation in CsA-treated eyes (†P < 0.005). No difference was found in the contralateral vehicle-treated eyes. (B) Similar changes seen in the CsA-treated eyes of normal rabbits were exhibited by the CsA-treated contralateral intact eyes of denervated rabbits compared with before instillation (†P < 0.005), whereas no significant increase of tear flow occurred in denervated eyes.

FIGURE 2

Blink rate at 3 hours after topical administration of CsA or vehicle in (A) normal rabbits (n = 7) and (B) denervated rabbits (n = 7). (A) The blink rate was significantly increased in CsA-treated eyes after vehicle administration and was significantly greater than in the contralateral eyes before and after vehicle administration (***P < 0.005). (B) Intact contralateral eyes showed an increase at 3 hours after CsA administration compared with before CsA treatment (***P < 0.005). In the denervated eyes, the blink rate before CsA administration was significantly higher than in contralateral vehicle-treated eyes (†P < 0.005). The blink rate of denervated eyes showed a significant decrease at 3 hours after CsA treatment compared with the rate before CsA administration (‡P < 0.005).

FIGURE 3

Flow rate of LG fluid from the main lacrimal duct before and 3 hours after topical administration of CsA or vehicle to one eye each in (A) normal rabbits (n = 4) and (B) denervated rabbits that received CsA in both eyes (n = 4). (A) Flow rate was significantly increased in CsA-treated eyes compared with before administration and before and after vehicle administration in the contralateral eyes of normal rabbits (*P < 0.05). (B) Similar changes were seen in the contralateral intact eyes 3 hours after CsA administration compared with before CsA treatment (***P < 0.005). In the denervated eyes, tear flow was very low before and after administration of CsA.

FIGURE 4

Light micrographs showing acini of the main LG from the contralateral control intact side (A) and the denervated side (B) before CsA administration and from the contralateral side after CsA treatment (C) and the denervated side after CsA treatment.(D). Scale bars, 50 µm.

FIGURE 5

Dose-response curve for protein secretion by main LG fragments in response to carbachol (CCh) (□) and CsA (○).