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J Thorac Cardiovasc Surg 2004;127:1285-1292
© 2004 The American Association for Thoracic Surgery
Cardiopulmonary support and physiology |
a Department of Cardiothoracic Surgery, University of California, San Francisco, San Francisco, Calif, USA
b Department of Pediatrics, University of California, San Francisco, San Francisco, Calif, USA
c Department of Pediatrics, Northwestern University Medical School, Chicago, Ill, USA
d Cardiovascular Research Institute, University of California, San Francisco, San Francisco, Calif, USA
Received for publication June 21, 2003; revisions received July 17, 2003; revisions received July 22, 2003; accepted for publication July 31, 2003.
* Address for reprints: Jeffrey R. Fineman, MD, Medical Center at UC San Francisco, 505 Parnassus Ave, Box 0106, San Francisco, CA 94143-0106, USA
jfineman{at}pedcard.ucsf.edu
BACKGROUND: Inhaled nitric oxide produces potent pulmonary vasodilation by activating soluble guanylate cyclase and increasing smooth muscle cell concentrations of cyclic guanosine monophosphate. However, responses are often nonsustained, and clinically significant increases in pulmonary vascular resistance have been noted on its acute withdrawal. In vitro and in vivo data suggest that inhaled nitric oxide decreases endogenous nitric oxide synthase activity. The effects of inhaled nitric oxide on the downstream mediators of the nitric oxide/cyclic guanosine monophosphate cascade, soluble guanylate cyclase and phosphodiesterase 5, have not been investigated. We sought to determine the effects of inhaled nitric oxide on endogenous cyclic guanosine monophosphate levels, soluble guanylate cyclase, and phosphodiesterase 5 protein levels in the intact lamb.
METHODS: Eleven 1-month-old lambs were mechanically ventilated. In 7 lambs, inhaled nitric oxide (40 ppm) was administered for 24 hours and then acutely withdrawn. Intermittent lung biopsy samples were obtained for cyclic guanosine monophosphate concentrations and soluble guanylate cyclase and phosphodiesterase 5 protein levels (Western blot analysis).
RESULTS: Initiation of nitric oxide decreased left pulmonary vascular resistance by 26.2%, and withdrawal rapidly increased pulmonary vascular resistance by 77.8% (P < .05). Tissue cyclic guanosine monophosphate concentrations initially increased during nitric oxide therapy but were not maintained during the 24-hour exposure. In addition, cyclic guanosine monophosphate concentrations rapidly decreased after nitric oxide withdrawal (P < .05). The
soluble guanylate cyclase (45.7%) and ß soluble guanylate cyclase (48.4%) protein levels decreased during nitric oxide therapy (P < .05), whereas phosphodiesterase 5 proteins levels were unchanged.
CONCLUSIONS: These data suggest a role for decreased soluble guanylate cyclase and its resulting decrease in cyclic guanosine monophosphate concentrations in the nonsustained response to nitric oxide and the rebound pulmonary hypertension noted on its acute withdrawal. Phosphodiesterase 5 inhibitors may be a useful adjunct therapy during inhaled nitric oxide to preserve cyclic guanosine monophosphate levels and thereby preserve nitric oxide responsiveness and prevent rebound pulmonary hypertension.
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