NEW CONCEPTS OF REGULATION OF RETINAL VESSEL TONE

Objective: To review the mechanisms of local regulation of the vascula r tone of the retinal and choroidal circulations. Design: Literature r eview. Results: The vascular endothelial cell may produce nitric oxide , endothelins, prostaglandins, and reninangiotension products in respo nse to chemical stimuli such as acetylcholine and bradykinin, to chang es in blood pressure and vessel wall stress, to changes in local oxyge n levels, and to other local stimuli. These substances are among the m ost potent vasoconstrictors and vasodilators known. Preliminary invest igations suggest a potential role for these substances in endothelial autoregulation of the retinal and choroidal vasculatures. Conclusion: Hormonal products of the vascular endothelium may provide the final co mmon pathway for vessel autoregulation in response to varying physiolo gic stress in many vascular beds, including the retina and choroid. Ph armacologic modulation of this process may provide treatment modalitie s for diseases such as hypertensive and diabetic retinopathies.