No clear pattern in efficacy and affinity for CA isoenzymes could be discerned from the results, although Compound 5, with a low affinity for all isoenzymes except the human (h) CA isoform IV, had the greatest potency, with the lowest EC 50 and inducing the most rapid and profound dilation of the vessels. The dilation induced by benzolamide (BZA) and DZA was additive, suggesting that they may act on separate mechanisms. All compounds had a lower mean EC 50 compared to DZA. We found that all compounds tested cause a vasodilation of pre-contracted retinal arteries, but with varying efficacy, as indicated by the calculated mean EC 50 of each compound, ranging from 4.12 µM to 0.86 mM. Vessels were pre-contracted by the prostaglandin analog U-46619, and CAIs with varying affinity for five different carbonic anhydrase (CA) isoenzymes found in human tissue tested. Here we have addressed the issue by using small vessel myography to examine the effect of CAIs of the sulfonamide and coumarin type on the wall tension in isolated segments of porcine retinal arteries. The exact mechanism behind the vasodilatory effect is not yet clear. Carbonic anhydrase inhibitors (CAIs), such as dorzolamide (DZA), are used as anti-glaucoma drugs to lower intraocular pressure, but it has been found that some of these drugs act as vasodilators of retinal arteries.
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