The results of nitric oxide (NO) infusions in normal volunteers and NO infusions and inhalation in experimental animals confirms that NO can be transported as a hormone and thus has the potential to be a pharmacological agent (i.e., a drug). We believe that the lack of vascular effects in our sickle cell patients is due to the presence of circulating hemoglobin and that this contributes to the pathophysiology of this and other chronic and acute hemolytic syndromes, especially the pulmonary hypertension complications which we have found to be severe and of high frequency in older patients. In order to study possible therapies for this condition, we analyzed the effects of methemoglobin formation on blood pressure and other cardiovascular parameters in dogs to see if the ferric species of hemoglobin-which could be pharmacologically effected- is safe as has been assumed. To our suprise we find that infusions of methemoglobin lead to prolonged increases in blood pressure and systemic resitance and believe that the mechanisms relates to reduction of methemoglobin to ferrous hemoglobin by plasma ascorbate and the destruction of plasma or cellular NO and nitrite by this species. These results, already published, have important implications for attempts at therapy of diseases related to hemolysis and circulating cell free hemoglobin. An alternative approach to this problem is the infusion of haptoglobin or other agents which may bind hemoglobin or some of its degradation products. Studies of these pathways, in animals and possibly patients, are now being planned. Lastly, as part of this work we have prepared and published two reviews of the state of nitrate and nitrite in the diet as having potential nutritional benefits in protecting against cardiac and other diseases. Although it is too early to know the long effects of such supplements, there is reason to be optimistic that they may be of benefit and the concerns that limited their use in the past were not significant. In recent work we have demonstrated that nitrate ions can be converted to nitrite (and then NO) or to ammonia by various commensal bacteria, depending on oxygen concentration and pH. The half dozen species of microorganisms that we have been studying, especially related to the Lactobacilli, are prevalent in the human oral cavity and gut. We believe that these reactions are important in determining overall nitrogen metabolism in humans and especially the roles of nitrite and NO in regualting the cardiovascular system. They may also be relevant for the production of ammonia in humans normally and in disease, such as with liver failure. Our second major new project has been to measure nitrate and nitrite levels in various rodent organs. The most surprising result was our finding of very high nitrate levels in muscle tissue. These levels are much higher than in blood and suggest either active transport into muscle or some production of NO and oxidation to nitrate in the tissue itself. Our preliminary results suggest that it is the latter process, with production via NOS1 and oxidation via myoglobin, that explains most of our observations. We are now studying the potential physiological and pathological implications of these results.
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