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This Article Full Text Full Text (PDF) All Versions of this Article: 294/2/L205    most recent 00234.2007v1 Alert me when this article is cited Alert me if a correction is posted Citation Map Services Email this article to a friend Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via HighWire Citing Articles via ISI Web of Science (1) Citing Articles via Google Scholar Google Scholar Articles by McNamara, P. J. Articles by Jankov, R. P. Search for Related Content PubMed PubMed Citation Articles by McNamara, P. J. Articles by Jankov, R. P.

Acute vasodilator effects of Rho-kinase inhibitors in neonatal rats with pulmonary hypertension unresponsive to nitric oxide

¹Newborn and Developmental Paediatrics, Sunnybrook Health Sciences Centre; ²Clinical Integrative Biology, Sunnybrook Research Institute; ³Physiology & Experimental Medicine Program, Hospital for Sick Children Research Institute; and the Departments of ⁴Anaesthesia, ⁵Paediatrics, and ⁶Physiology, University of Toronto, Toronto, Ontario, Canada

Submitted 13 June 2007 ; accepted in final form 20 November 2007

Pulmonary hypertension (PHT) in neonates is often refractory to the current best therapy, inhaled nitric oxide (NO). The utility of a new class of pulmonary vasodilators, Rho-kinase (ROCK) inhibitors, has not been examined in neonatal animals. Our objective was to examine the activity and expression of RhoA/ROCK in normal and injured pulmonary arteries and to determine the short-term pulmonary hemodynamic (assessed by pulse wave Doppler) effects of ROCK inhibitors (15 mg/kg ip Y-27632 or 30 mg/kg ip fasudil) in two neonatal rat models of chronic PHT with pulmonary vascular remodeling (chronic hypoxia, 0.13 FI_O2, or 1 mg·kg^–1·day^–1 ip chronic bleomycin for 14 days from birth). Activity of the RhoA/ROCK pathway and ROCK expression were increased in hypoxia- and bleomycin-induced PHT. In both models, severe PHT [characterized by raised pulmonary vascular resistance (PVR) and impaired right ventricular (RV) performance] did not respond acutely to inhaled NO (20 ppm for 15 min) or to a single bolus of a NO donor, 3-morpholinosydnonimine hydrochloride (SIN-1; 2 µg/kg ip). In contrast, a single intraperitoneal bolus of either ROCK inhibitor (Y-27632 or fasudil) completely normalized PVR but had no acute effect on RV performance. ROCK-mediated vasoconstriction appears to play a key role in chronic PHT in our two neonatal rat models. Inhibitors of ROCK have potential as a testable therapy in neonates with PHT that is refractory to NO.

Y-27632; fasudil; two-dimensional echocardiography; pulse wave Doppler; SIN-1

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