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Persistent pulmonary hypertension of the newborn (PPHN) is defined as the failure of normal pulmonary vascular relaxation at birth. Hypoxia is known to impede postnatal disassembly of the actin cytoskeleton in pulmonary arterial myocytes, resulting in elevation of smooth muscle α-actin and γ-actin content in elastic and resistance pulmonary arteries in PPHN compared with age-matched controls. This review examines the original histological characterization of PPHN with attention to cytoskeletal structural remodeling and actin isoform abundance, reviews the existing evidence for understanding the biophysical and biochemical forces at play during neonatal circulatory transition, and specifically addresses the role of the cortical actin architecture, primarily identified as γ-actin, in the transduction of mechanical force in the hypoxic PPHN pulmonary circuit. [ABSTRACT FROM AUTHOR]

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Chloride (Cl–) efflux induces depolarization and contraction of vascular smooth muscle cells. In the basilar arteries from the New Zealand white rabbits, the role of Cl– flux in serotonin-induced contraction was demonstrated by (i) inhibition of Na+-K+-2Cl– co-transporter (NKCC1) to decreased Cl– influx with bumetanide; (ii) a disabled Cl–/HCO3– exchanger with bicarbonate free HEPES solution; (iii) blockade of Cl– channels using 5-nitro-2-(3-phenylpropylamino) benzoic acid (NPPB) and indanyloxyacetic acid 94, R-(+)-methylindazone (R-(+)-IAA-94); and (iv) substitution of extracellular Cl– with methanesulfonate acid (113 mmol/L; Cl–, 10 mmol/L). In addition, the expression of NKCC1 in brain tissues after neonatal hypoxia-ischemia was examined at mRNA and protein levels using RT-PCR and Western blotting techniques. NKCC1 mRNA and protein expressions were increased at 24 and 48 h and returned to normal levels at 72 h after hypoxia insult when compared with the control littermates. In conclusion, Cl– efflux regulates cerebral circulation and the up-regulation of NKCC1 after neonatal hypoxia-ischemia may contribute to brain injury. [ABSTRACT FROM AUTHOR]