Abstract
Abstract: :
Purpose: To measure the buffering capacity of bovine vitreous to hydrochloric acid (HCl) and sodium hydroxide (NaOH). Methods: Ten bovine globes were obtained fresh, transported on ice, and the vitreous dissected. Homogenized vitreous was divided into 5–mL aliquots. Control 0.9% NaCl was aliqoted into 5–mL portions. The pH of the control saline (SAL) solution was recorded during stirring using a pH meter over 20 min. Then 0.05 mL of 1N HCl (pH 1.020) was periodically added. This experiment was repeated while a 5% CO2/95% air gas mixture (GAS–AIR) was blown over the surface of the solution at 1.0 psi. The pH was recorded over 20 min while 0.05 mL of 1N HCl (pH 1.020) was periodically added. For the first 5.0–mL aliquot of bovine vitreous, pH was recorded during stirring over 60 min. This experiment was repeated using a second 5.0–mL aliquot of bovine vitreous while GAS–AIR was blown over the surface of the solution at 1.0 psi. The pH of aliquots 3 and 4 was measured using the same technique as aliquots 1 and 2, respectively, except that 0.05 mL of 1N HCl was periodically added to the solution during stirring. The pH of the fifth aliquot was measured during stirring with 0.05 mL of 0.1 N NaOH (pH12.883) added periodically to assess the buffering capacity to base. This was repeated for the sixth aliquot with the GAS–AIR mixture blown over the surface of the solution at 1.0 psi. Results: SAL had a buffering capacity in room air of 4.3 x 10–3 moles of 0.1N HCl per 5.0 mL of SAL, which increased to 4.8 x 10–3 moles of 0.1N HCl per 5.0 mL of SAL if the GAS–AIR was blown over the surface of the solution. Bovine vitreous in room air had a buffering capacity of 1.8 x 10–2 moles of 0.1N HCl which was increased to 4.7 x 10–2 moles of 0.1N HCl per 5.0 mL when GAS–AIR was blown over the surface of the solution at 1.0 psi. Bovine vitreous in room air had a buffering capacity of 1.9 x 10–3 moles of 0.1N NaOH per 5.0 mL which was increased to 2.0 x 10–2 moles of 0.1N NaOH per 5.0 mL with GAS–AIR mixture blown over the surface of the solution at 1.0 psi. Conclusions: The true buffering capacity of the vitreous or SAL can only be accurately measured if the physiologic conditions of the GAS–AIR mixture are replicated. Vitreous has a 10–fold greater buffering capacity than SAL, indicating a greater capacity to remain stable when acidic pharmaceuticals are injected in microliter amounts. Bovine vitreous also has the capacity to buffer bases.
Keywords: vitreous • drug toxicity/drug effects