Smooth muscle cell proliferation in the ductus arteriosus and the descending aorta, and effects of enalapril on SMC proliferation in perinatal rats

B-type natriuretic peptide prevents postnatal closure of ductus arteriosus by both vasodilation and anti-remodeling in neonatal rats

The physiologic process of postnatal ductus arteriosus (DA) closure consists of vasoconstriction followed by vascular remodeling. We have recently reported that B-type natriuretic peptide (BNP), a potent vasodilator, also has anti-remodeling effects in pulmonary vasculature. However, its effects on DA have not been elucidated. We investigated whether BNP can prevent DA closure, and if so, the underlying mechanisms. Using in vivo studies, we examined effects of BNP (10 mg/kg, ip at birth) on DA closure in neonatal rats within 4 h after birth. We found that in control rats, the DA spontaneously closed at 4 h with a decreased DA diameter, enhanced intimal thickening, and luminal occlusion. BNP prevented DA closure at 4 h with a preserved DA diameter, attenuated intimal thickening, and preserved luminal patency. Ex vivo, BNP attenuated oxygen-induced vasoconstriction of isolated DA rings of newborn rats. These vasodilating effects were blunted by Rp-8-Br-PET-cGMPS, a cGMP inhibitor. In vitro, BNP inhibited angiotensin II (Ang II)-induced proliferation and migration of DA smooth muscle cells (DASMCs). BNP inhibited Ang II-induced mitochondrial reactive oxygen species (ROS) production and calcium overload in DASMCs. Finally, BNP inhibited Ang II-induced ERK1/2 activation. These in vitro effects were antagonized by Rp-8-Br-PET-cGMPS. In conclusion, BNP prevents postnatal DA closure by both vasodilation and anti-remodeling through the cGMP pathway. The mechanisms underlying anti-remodeling effects include anti-poliferation and anti-migration, with attenuation of mitochondrial ROS production and intracellular calcium and ERK1/2 signaling. Therefore, the BNP/cGMP pathway can be a promising therapeutic target for clinical management of DA patency.

Gamma-secretase Inhibitor Prevents Proliferation and Migration of Ductus Arteriosus Smooth Muscle Cells through the Notch3-HES1/2/5 Pathway

Patent ductus arteriosus (PDA) can cause morbidity and mortality in neonates. Vascular remodeling, characterized by proliferation and migration of smooth muscle cells (SMCs), is an essential process for postnatal DA closure. Notch signaling is an important mediator of vascular remodelling but its role in DA is unkonwn. We investigated the effects and underlying mechanisms of γ-secretase inhibitor DAPT, a Notch signaling inhibitor on angiotensin II (Ang II)-induced proliferation and migration of DASMCs. Proliferation and migration of DASMCs cultured from neonatal Wistar rats were induced by Ang II, with or without DAPT pre-treatment. In addition, potential underlying mechanisms including cell cycle progression, Ca(2+) influx, reactive oxygen species (ROS) production, signal transduction of MAPK and Akt, and Notch receptor with its target gene pathway were examined. We found that DAPT inhibited Ang II-induced DASMCs proliferation and migration dose dependently. DAPT also arrested the cell cycle progression in the G0/G1-phase, and attenuated calcium overload and ROS production caused by Ang II. Moreover, DAPT inhibited nuclear translocation of Notch3 receptor intracellular domain, with decreased expression of its down-stream genes including HES1, HES2 and HES5. Finally, Ang II-activated ERK1/2, JNK and Akt were also counteracted by DAPT. In conclusion, DAPT inhibits Ang II-induced DASMCs proliferation and migration. These effects are potentially mediated by decreased calcium influx, reduced ROS production, and down-regulation of ERK1/2, JNK and Akt, through the Notch3-HES1/2/5 pathway. Therefore, Notch signaling has a role in DA remodeling and may provide a target pathway for therapeutic intervention of PDA.

Role of nitric oxide in regulating the ductus arteriosus caliber in fetal rats

The role of nitric oxide (NO) on the ductus arteriosus (DA) patency was examined in fetal rats at various stages of gestation. N(G)-nitro-L-arginine methyl ester (L-NAME, 50 mg/kg, i.p.), an NO synthase (NOS) inhibitor, or indomethacin (3 mg/kg, p.o.), a cyclooxygenase inhibitor, was administered at 3 hr before cesarean section to pregnant rats ranging from day 17 to day 21 of gestation. Dams were decapitated and the fetuses were obtained by cesarean section. The fetuses were rapidly frozen in an acetone-dry ice mixture. Using rapid-freezing and shaving methods, the calibers of the DA and pulmonary artery were measured. The constrictive effect of L-NAME on the fetal DA caliber was stronger than that of indomethacin in 19-day-old and immature fetuses. In near-term fetuses, the constrictive effects of L-NAME were reduced, while indomethacin caused marked DA constriction. We conclude that endogenous NO may play a major role in regulating the patency of the DA in earlier fetal stages, while dilator prostaglandins may play a greater role in regulating the ductal patency in the near-term fetus.