# Inhibition of Rho‐kinase restores impaired relaxation of airway smooth muscle in rat pups exposed to neonatal hyperoxia

## TL;DR

Inhibiting Rho-kinase helps restore airway muscle relaxation in rat pups exposed to high oxygen levels, which could aid in treating lung conditions like BPD.

## Contribution

This study shows that Rho-kinase inhibition can reverse hyperoxia-induced airway dysfunction in neonatal rats.

## Key findings

- Rho-kinase inhibitors restored impaired tracheal smooth muscle relaxation in hyperoxia-exposed rat pups.
- The NO-cGMP pathway is involved in the mechanism of Rho-kinase inhibition's effects.
- Pharmacological inhibition of Rho-kinase shows therapeutic potential for airway dysfunction in BPD.

## Abstract

Neonatal hyperoxia is a key contributor to bronchopulmonary dysplasia (BPD) which is characterized by airway hyperreactivity due to increased contraction and impaired relaxation of airway smooth muscle (ASM). This study investigated whether inhibition of the Rho/Rho‐kinase signaling pathway restored tracheal smooth muscle (TSM) relaxation and reactivated the nitric oxide–guanosine 3′,5′‐cyclic monophosphate (NO‐cGMP) pathway in neonatal rats exposed to hyperoxia. Newborn rats (P4) were exposed to either ambient air (AA; n = 61) or hyperoxia (FiO2 >95%; n = 58) for 7 days. The effects of Rho‐kinase inhibitors (Y‐27632 or fasudil) in vitro (10 μM) or in vivo (10 mg kg−1 day−1) on electric field stimulation‐induced TSM relaxation were assessed. In subsets of the experiment, tissues were pre‐incubated in a nitric oxide synthase (NOS) inhibitor—N
ω‐nitro‐L‐arginine methyl ester (L‐NAME; 100 μM) or a Rho activator—lysophosphatidic acid (LPA; 30 μM). Rho‐kinase inhibitors, both in vitro and in vivo, restored hyperoxia‐impaired TSM relaxation to levels comparable to those of ambient air TSM. The relaxant responses in tissues supplemented with Y‐27632 or fasudil were significantly increased compared to hyperoxia control (p < 0.01 and p < 0.001), and the maximal values at 20 V were 77.90 ± 3.80%; 81.20 ± 6.10% and 40.20 ± 3.60%, respectively. These Rho‐kinase inhibitor effects in TSM were attenuated by L‐NAME, indicating mechanistic action through the NO‐cGMP pathway. Activation of Rho reduced relaxation in the AA group, an effect that was reversed by Rho‐kinase inhibition. Hyperoxia impairs ASM in neonatal rats via upregulation of Rho‐kinase activity and suppression of NO‐cGMP signaling. Pharmacological inhibition of Rho‐kinase restores relaxation, highlighting its therapeutic potential for airway dysfunction in BPD.