Effect of hypoxemia and hyperglycemia on pH in the intact cat retina.

OBJECTIVE: To examine the effects of acute hypoxemia and hyperglycemia on retinal pH to understand hyperglycemia-induced changes in the normal intact cat retina.
METHODS: Spatial profiles of extracellular hydrogen ion (H+) concentration were obtained from the cat retina, in vivo, using pH-sensitive microelectrodes during normoxia (arterial partial pressure of oxygen [PaO2] = 114.5 +/- 7.9 mm Hg), normoglycemia (plasma glucose concentration, 117 +/- 19 mg/dL), acute hypoxemia (PaO2 = 29.5 +/- 2.2 mm Hg), and acute hyperglycemia (plasma glucose concentration, 303 +/- 67 mg/dL). An H+ diffusion model was fitted to the outer retinal data to quantify photoreceptor H+ production. The inner retinal pH was also examined.
RESULTS: Hypoxemia induced a mean acute panretinal acidification of 0.16 pH units that originated from a 2.55-fold increase in net photoreceptor H+ production. Hyperglycemia induced an acute panretinal acidification of 0.12 pH units; however, photoreceptor H+ production levels remained unchanged. Retinal pH changes followed the course of arterial PaO2 and blood glucose changes.
CONCLUSIONS: The increase in photoreceptor H+ production during hypoxemia confirms the importance of glycolysis in the retina. Hyperglycemia-induced pH changes resulted from either increased inner retinal H+ production or decreased H+ clearance/neutralization. Clinical Relevance The hyperglycemia-induced acidification that originates in the inner retina suggests that retinal acidosis may contribute to the development of diabetic retinal disease.