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 recent studies we have infused nitrite into the brachial arteries of normal human volunteers and have shown that this increases blood flow, suggesting that nitrite could function physiologically as a source of NO and could be used pharmacologically. However, we find that the effects of nitrite infusion, both on vascular properties and on methemoglobin formation, are relatively long lasting and suggest partition of the nitrite into various tissues. We find that in vitro deoxyerythrocytes and nitrite cause aortic ring preparations to dilate, suggesting a mechanism of nitrite activation by deoxyheme proteins. We also find that nitrite inhalation in hypoxic newborn sheep lead to decreased pulmonary artery pressures and exhalation of NO;nitrite infusions in these animals leads to decreases in mean arterial blood pressure. We are currently studying the formation and compartmentalization of nitrite in the blood, in erythrocytes in particular, and whether nitrite levels may be a marker of cardiovascular risk in humans. These studies are designed to allow us to initiate nitrite infusions in normal human subjects and those with a variety of ischemic (including sickle cell anemia) diseases. We have shown that the maximum production of NO from nitrite occurs near the p50 of hemoglobin and is dependent on the allosteric conformation of hemoglobin. We have also developed methods to measure nitrite levels precisely in human blood and have found that most of blood nitrite is contained in the red cells. This reaction may be the major mechanism for the formation of red cell nitrite, which we believe is one of the major storage sites for bioactive NO in the body, and has led us to develop a model of the interaction of the ascorbic acid/dehyroascorbic acid and the NO/nitrite cycles inside the erythrocyte. We believe that the above studies should contribute to our understanding of the role of the human erythrocyte in modulating NO bioactivity, especially via a nitrite intermediate, and also facilitate the development of nitrite as a useful drug for cardiovascular pathology. In recent work we have been investigating changes in NO-related species during red blood cell storage to ascertain whether these contribute to the complications of blood, especially red cell, transfusion know as the """"""""storage lesion."""""""" We find, as expected from our previous work that nitrite levels fall rapidly after venisection but then, surprisingly level off at about 1/4 of the initial value for up to 42 days. We find no evidence of other relevant NO changes and are now investigating whether the nitrite changes contribute to red cell-induced pathology and, equally importantly, the mechanism of control and stabilization of red cell nitrite levels. We have been studying the effects of methemoglobin formation on blood pressure and other cardiovascular parameters in dogs to see if the ferric species of hemoglobin is as 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 mechanims 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 have important implications for attempts at therapy of diseases related to hemolysis and circulating cell free hemoglobin. In recent work we have demonstrated that nitrite in the gut can be converted to nitrite (and then NO) or to ammonia by various commensal bacteria, depending on oxygen concentration and pH. 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. 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.
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