Tear Production After Bilateral Main Lacrimal Gland Resection in Rabbits

This study reports tear compensation observed in rabbits with bilateral resection of main lacrimal gland (LG) and explored the potential mechanisms.

Dry eye conditions were created by resection of nictitating membrane (NM), Harderian gland (HG), and main LG in eight (16 eyes) male New Zealand White rabbits. In addition to Schirmer test, Periodic acid-Schiff (PAS) staining, and ocular surface staining with fluorescein and rose Bengal, conjunctival impression cytology was employed before and up to 4 months after excision (AE). Using reverse transcription-quantitative polymerase chain reaction (RT-qPCR), expression of inflammatory biomarkers (IL-1β, TNF-α, and matrix metalloproteinase-9) were monitored. Further, involvement of ionic and water transporters were investigated in conjunctival epithelium.

Significant dry eye phenotypes in rabbits were observed 1 month AE, which corroborated with elevated biomarker mRNA expression. However, Schirmer test score and goblet cell numbers never decreased AE in conjunctival epithelium. Moreover, ocular surface staining, and biomarker expression declined to baseline in over 4 months AE. No upregulation was observed of the following conjunctival ionic transporters: cystic fibrosis transmembrane conductance regulator, sodium potassium chloride cotransporters, sodium potassium ATPase, and epithelial sodium channels. Instead, aquaporin (AQP) 4 and AQP5 were upregulated. Immunolocalization and immune blotting of AQP4 was demonstrated in rabbit conjunctival epithelium.

In the absence of NM, HG, and main LG in rabbits, tear secretion was not decreased and significant improvement of dry eye phenotypes observed with time AE. Conjunctival AQPs are possibly involved in a compensatory tear fluid production.