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

Abstract

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(O(2)), 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 mug/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.

Effects of Rho-Kinase Inhibition on Pulmonary Hypertension, Lung Growth, and Structure in Neonatal Rats Chronically Exposed to Hypoxia

“…We have further shown that a single bolus of either Y-27632 (15 and 30 mg/kg) or fasudil (30 mg/kg) completely normalized pulmonary vascular resistance (PVR) in both models of chronic neonatal PHT (10). These findings suggest that ROCK is central to sustained vasoconstriction in chronic neonatal PHT, but the question about its role in the structural changes of chronic PHT remains unexplored.…”

“…We have recently reported evidence of RhoA/ROCK pathway activation in the pulmonary arteries of neonatal rats with NO-unresponsive chronic PHT, secondary to either chronic hypoxia (CH) or bleomycin exposure (10). We have further shown that a single bolus of either Y-27632 (15 and 30 mg/kg) or fasudil (30 mg/kg) completely normalized pulmonary vascular resistance (PVR) in both models of chronic neonatal PHT (10).…”

“…Recent studies have implicated the RhoA/Rho-kinase (ROCK) pathway as central to the initiation and perpetuation of chronic PHT (5), based largely on the effects of two ROCK-specific kinase inhibitors: Y-27632 and fasudil (6). ROCK inhibitors have been reported to inhibit pulmonary artery myogenic responses in hypoxiaexposed adult rats (7) and fetal sheep (8) and to reverse sustained pulmonary vasoconstriction in response to hypoxia (9,10), bleomycin (10), or the infusion of vasoconstrictors, such as endothelin-1 (11). Systemic administration of ROCK inhibitors, commenced at the onset of injury, has been reported to prevent PHT induced either by hypoxia (9) or monocrotaline (12) in adult rodents.…”

“…Because growth factors, particularly PDGFs (15,16), are known to mediate smooth muscle proliferation in immature pulmonary vessels (16) and have been implicated in the persistence and progression of chronic PHT in humans (17), we also hypothesized that attenuation of hypoxia-induced SMC proliferation by inhibition of ROCK would be associated with changes in expression of PDGFs and their receptors. Finally, given that ROCK is highly expressed throughout the hypoxiaexposed neonatal rat lung (10) and has been shown to play a major role in proliferation of epithelial cells and other cell types (18,19), we examined whether sustained ROCK inhibition would impact lung growth and alveologenesis. 20 ; sc-15370), and goat anti-mouse and -rabbit IgG-biotin secondary antibodies were from Santa Cruz Biotechnology (Santa Cruz, CA).…”

Advances in the Management of Pediatric Pulmonary Hypertension

“…For example, in animal models of severe PH, Rho kinase inhibition resulted in vascular relaxation in animals unresponsive to nitric oxide or PGI 2 analogs. 224,225 Clinical data, although limited, have been less impressive. Fujita and colleagues administered fasudil, a Rho kinase inhibitor, and INO to 15 adult patients with PAH.…”