Intraocular dynamics of lactic acid in the rabbit.

Lactic acid is found in the aqueous humor at a concentration higher than that in the blood. The processes which determine this distribution have been investigated in the rabbit. After parenteral injection of isotopically labeled lactate, samples of intraocular fluids and plasma were taken and analyzed for radioactivity. It was found that lactate entered the posterior aqueous fairly rapidly from the blood, but that it did not accumulate above the plaima concentration. Entry into the anterior aqueous was somewhat slower and into the vitreous much slower. When glucose was the injected tracer compound, it was found that labeled lactate, derived by glycolysis from the glucose, accumulated rapidly in the vitreous and aqueous humors, reaching levels five times higher than the corresponding level in the plasma. It was concluded that metabolism of glucose by the ciliary epithelium and retina, in addition to that in the lens and cornea, contributes significantly to the lactate content of the aqueous. Quantitative analysis of the data according to Kinsey and Reddy's theory of aqueous humor dynamics showed that in the resting animal net lactate diffusion is from the aqueous to the blood. The lactate turnover in the rabbit aqueous can be accounted for by the known glycolytic activity of the intraocular tissues.