Ascorbate elevates perfusion pressure in the bovine extraocular long posterior ciliary artery: role of endothelium-derived hyperpolarizing factor (EDHF).

Ascorbate blocks agonist-induced, endothelium-derived hyperpolarizing factor (EDHF)-mediated vasodilatation in the bovine perfused ciliary artery and this is associated with a rise in perfusion pressure. We now report the origins of this ascorbate-induced rise in perfusion pressure. In segments of ciliary artery perfused at 2.5 ml/min, the addition of ascorbate (10-150 microM) enhanced U46619-induced perfusion pressure. Ascorbate produced no enhancement in the absence of U46619, suggesting that its effects resulted not from a constrictor action but through removal of a tonic vasodilator influence. Experiments revealed the endothelial source of this vasodilator influence, and EDHF, but not nitric oxide or prostanoids, appeared to be involved. The ascorbate-induced enhancement of vasoconstrictor tone was not seen in a static myograph or in segments perfused at low rates of flow, but was seen at flow rates of 2.5 ml(-1) and above. We conclude that ascorbate augments vasoconstrictor tone through inhibition of flow-induced EDHF activity.