Abstract: . . .  The aforementioned studies have clearly indicated, however, that in humans, as well as in other mammals, it is the tissue-bound ACE - mostly pulmonary - which is responsible for the conversion of angiotensin I to angiotensin II, and thus it is the tissue ACE which is the primary locus of action of ACE inhibitors in the treatment of hypertension. 5. Conclusions In vivo measurements of pulmonary endothelial ectoenzyme function provide new means for the evaluation of pulmonary microvascular function in vivo . During the last 10 years, methodological advances have made possible the routine monitoring of ectoenzyme functions in vivo . Studies from this and other laboratories suggest that endothelial ectoenzyme functions can serve as markers for microvascular surface area as well as early indicators of endothelial cell injury and repair. The association between alterations in enzyme function and endothelial . . .
. . .  Med 328: 399-404, 1993. 21. Zapol WM and Snider MT: Pulmonary hypertension in severe acute respiratory failure. N Engl J Med 296: 476-480, 1977. 22. Puybasset L, Rouby JJ, Mourgeon E, Stewart TE, Cluzel P, Arthaud M, Poete P, Bodin L, Korinek AM and Viars P: Inhaled nitric oxide in acute respiratory failure: dose-response curves. Intensive Care Med 20: 319-327, 1994. 23. Tomashefski JF Jr, Davies P, Boggis C, Greene R, Zapol WM and Reid LM: The pulmonary vascular lesions of the adult respiratory distress syndrome. Am J Pathol 112: 112-126, 1983. 24. Montgomery AB, Stager MA, Carrico J and Hudson LD: Cause of mortality in patients with the adult respiratory distress syndrome. Am Rev Respir Dis 132: 485-489, 1985. 25. Villar J, Manzano JJ and Blasquez MA: Multiple system organ failure in acute respiratory failure. J Crit Care 6: 75-80, 1991. 26. Faist E, Baue AE, Dittmer H and Craigh D: Multiple organ failure . . .
. . .  inhibitors, iii) quantify the efficacy and duration of action of different ACE inhibitors. During the last two decades significant advances have been achieved in the performance of in vivo assays of endothelial ectoenzyme function and interpretation of experimental results. The challenge for the next years will be 2-fold: i) to test this knowledge further in clinical practice in order to find out whether it can be useful routinely in the early diagnosis of lung disease , and ii) to exploit these experiences in gaining new insights into the physiology of the pulmonary circulation. Acknowledgments We would like to express our gratitude to John D. Catravas the director and regent professor of the Vascular Biology Center of Medical College of Georgia, USA, for giving the opportunity to conduct the experimental sections of this work in his laboratory. References 1. Ryan JW, Ryan US, Schultz DR, et al:  . . .
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