Effect of NO synthase inhibition on retinal vessel reaction to isometric exercise in healthy humans
Article first published online: 15 JUL 2010
© 2010 The Authors. Journal compilation © 2010 Acta Ophthalmol
Volume 90, Issue 4, pages 362–368, June 2012
How to Cite
Lasta, M., Polak, K., Luksch, A., Garhofer, G. and Schmetterer, L. (2012), Effect of NO synthase inhibition on retinal vessel reaction to isometric exercise in healthy humans. Acta Ophthalmologica, 90: 362–368. doi: 10.1111/j.1755-3768.2010.01970.x
- Issue published online: 28 MAY 2012
- Article first published online: 15 JUL 2010
- Received on November 3rd, 2009. Accepted on May 28th, 2010.
- isometric exercise;
- nitric oxide;
- retinal blood flow
Purpose: It has been shown that retinal blood flow is autoregulated, meaning that flow is independent of perfusion pressure within a certain range. We tested the hypothesis that nitric oxide (NO) synthase inhibition alters the response of retinal arterial and venous vessels during isometric exercise.
Methods: In this study, nine healthy subjects were included. Each subject received the NO synthase inhibitor Ng-monomethyl-l-Arginine (l-NMMA, the α-receptor agonist phenylephrine or placebo intravenously on three study days. Retinal vessel diameter was assessed with the retinal vessel analyser (RVA), at baseline and during a squatting period of 6–7 min in absence or presence of l-NMMA, phenylephrine or placebo.
Results: Mean arterial pressure (MAP) and pulse rate (PR) increased significantly during all pretreatment squatting periods (p < 0.001) Retinal venous and arterial diameters showed a continuous decrease during squatting (p < 0.001). Phenylephrine increased MAP and PR but did not alter the retinal vessel diameter response to squatting. Administration of l-NMMA lead to a significant decrease in venous diameter before isometric exercise (p = 0.004). In addition, the retinal venous diameter response during administration of the NO synthase inhibitor was less pronounced than during phenylephrine or placebo (p < 0.001).
Conclusion: Our study confirms that NO plays an important role in the control of retinal vascular tone at rest. In addition, the present data indicate a role of NO in retinal autoregulation, because the response of retinal venous diameters was altered after NO synthase inhibition. The nature of involvement, however, appears to be complex and requires further studies.