Abstract

Background: Fasudil hydrochloride, a Rho kinase inhibitor, was reported to dilate the constricted ductus arteriosus in vitro, and was suggested as a neonatal bridge to heart surgery. Objectives: To clarify the in vivo effectiveness of fasudil to dilate the neonatal ductus arteriosus, and its usefulness as a bridge to heart surgery. Methods: We studied the dose and timing of administration of fasudil in the neonatal rat. Postnatal ductal closure was studied on the 21st gestational day following cesarean section and incubation for 30–480 min in room air at 33°C, with a rapid whole-body freezing method. In control rats, the ductus closed rapidly after birth, and the ductal diameter was 0.80 and 0.12 mm at 0 and 30 min after birth. Fasudil was injected peritoneally into the neonate, and the ductus was studied 30 min after injection and 60 min after birth. Results: Fasudil, 10 mg/kg, injected within 5 min after birth, dilated the ductus completely to 0.8 mm, and the dose used clinically, 1 mg/kg, dilated the ductus to 0.4 mm. The ductus-dilating effect of fasudil decreased rapidly as the neonatal ductus constricted. Fasudil, 100 mg/kg, dilated the ductus completely, but induced severe respiratory depression and frequent death in 1-hour-old rats. Conclusions: Fasudil dilates the neonatal ductus arteriosus dose-dependently in the rat. Fasudil in large doses dilates the neonatal ductus completely, but is associated with fatal side effects, including respiratory depression.

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