Abstract

Background/aims: Prostaglandins are important in blood flow regulation. Carbon dioxide (CO₂) breathing and carbonic anhydrase inhibition increase the oxygen tension in the retina and optic nerve. To study the mechanism of this effect and the role of cyclo-oxygenase in the regulation of optic nerve oxygen tension (ONPO₂), the authors investigated how indomethacin affects ONPO₂ and the ONPO₂ increases caused by CO₂ breathing and carbonic anhydrase inhibition in the pig.

Methods: Optic nerve oxygen tension was measured in 11 pigs with a polarographic oxygen electrode. The tip of the electrode was placed 0.5 mm above the optic disc. The effects of indomethacin, CO₂ breathing (3%) before and after indomethacin treatment, and carbonic anhydrase inhibition with or without indomethacin treatment were investigated.

Results: Administration of 300 mg indomethacin decreased optic nerve oxygen tension significantly. Carbonic anhydrase inhibition and CO₂ breathing increased ONPO₂ significantly. After indomethacin had been given, the rise in ONPO₂ caused by CO₂ breathing and carbonic anhydrase inhibition was significantly reduced.

Conclusion: Systemic administration of indomethacin decreases the optic nerve oxygen tension; this is probably the result of decreased blood flow through vasoconstriction of vessels in the optic nerve. Additionally, indomethacin diminishes the ONPO₂ increasing effect of CO₂ breathing and carbonic anhydrase inhibition, thus affecting the reactivity of vessels in the optic nerve.