Distribution and Metabolism of Dietary Nitrate in Porcine Ocular Tissues

Extensive recent studies have provided evidence of the important role of dietary nitrates in improving cardiovascular health and enhancing exercise performance. This is generally attributed to the conversion of these nitrate ions (NO3−) obtained from dietary sources into nitrite (NO2−) and subsequently into nitric oxide (NO) within the body. In a prior study, we demonstrated that porcine ocular tissues contain significant amounts of nitrate and nitrite, comparable to those found in the blood. Notably, cornea and sclera exhibited the capability to reduce nitrate to nitrite. In our current study, we sought to gain a deeper understanding of ocular nitrate metabolism. To achieve this, we administered two groups of pigs either NaCl or Na15NO3 orally and evaluated the levels of both total and 15N-labeled nitrate and nitrite in various ocular tissues three hours after Na15NO3 ingestion. We observed a substantial increase in both 15NO3− and 15NO2− in all parts of the eye measured by LC-MS/MS. Particularly, the aqueous and vitreous humor displayed a remarkably high 15NO3− enrichment similar to that of plasma and even higher 15NO2− enrichment than that of plasma. Cornea, sclera, retina and lens also showed notable increases in 15NO3−. The 15NO2− analysis revealed that most eye parts, except aqueous and vitreous humor, had levels similar to those observed in plasma. Furthermore, the total amounts of NO3− and NO2− measured by chemiluminescence in these tissues exhibited patterns consistent with those observed in the 15N analysis. These findings provide valuable insights into the distribution and metabolism of dietary nitrates within ocular tissues, shedding light on their potential roles in ocular health and function. This work was supported by intramural NIDDK/NIH grant ZIA DK 025104-15 to Alan N. Schechter. This is the full abstract presented at the American Physiology Summit 2024 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.