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Aims We determined whether decreased reactive oxygen species (ROS) production in the aorta of pregnant spontaneously hypertensive rats (SHR) resulted in increased nitric oxide (NO) bioavailability and hyporeactivity to phenylephrine (PE). Main methods Systemic and aortic oxidative stress were measured in pregnant and non-pregnant Wistar rats and SHR. Furthermore, the hypotensive effects of apocynin (30 mg/kg) and Tempol (30 mg/kg) were analyzed. Intact aortic rings of pregnant and non-pregnant rats were stimulated with PE in the absence of or after incubation (30 min) with apocynin (100 μmol/L). The effect of apocynin on the concentrations of NO and ROS were measured in aortic endothelial cells (AEC) using DAF-2DA (10 mmol/L) and DHE (2.5 mmol/L), respectively. Western blotting was performed to analyze eNOS, NOX1, NOX2, NOX4 and SOD expression. ROS production was analyzed by the lucigenin chemiluminescence method. Key findings Aortic oxidative stress and ROS concentration in AEC were reduced in pregnant Wistar rats and SHR, when compared to non-pregnant rats. ROS production and NOX1, NOX2 and NOX4 expression in the aortas were decreased in pregnant SHR, but not in pregnant Wistar rats. Increased eNOS expression in aortas and NO concentration in AEC were observed in pregnant Wistar rats and SHR. Apocynin reduced PE-induced vasoconstriction in the aortas of non-pregnant Wistar rats and SHR, and pregnant Wistar rats, but not in the aortas of pregnant SHR. Significance Taken together, these results suggest that ROS production was decreased in the aortas of pregnant SHR and could contribute to higher NO bioavailability and hyporeactivity to PE in the aortas of pregnant SHR. [ABSTRACT FROM AUTHOR]

Peroxynitrite (ONOO−) has been recently known to act as a potent cytotoxin during pathogenesis of various diseases. This study aimed to investigate the possible effect of ONOO− on the cremaster muscle arteriolar reactivity in response to noradrenaline and subsequently determined whether membrane hyperpolarization and potassium channel activation were involved in ONOO−-induced alteration of arteriolar reactivity. The results demonstrated that 1) ONOO− could decrease arteriolar reactivity in a time- and concentration-dependent manner with no significant alteration of arteriolar diameter; 2) Superfusion with 20 μM ONOO− over 40 minutes showed slight but not significant influence on the resting potential (Em) of arteriolar smooth muscle cells (ASMCs). However, ASMCs subjected to 50 or 100 μM ONOO− administration were significantly hyperpolarized. As control, treatment with 50 μM decomposed ONOO− or Kreb''s solution had little effect on the Em of ASMCs; 3) ONOO−-induced arteriolar hyporeactivity could be greatly reversed by co-administration of KCl and partially by TEA. The above results indicated that membrane hyperpolarization and potassium channel activation were preferentially responsible for the reduction of cremaster muscle arteriolar reactivity after exposure to ONOO−. [Copyright &y& Elsevier]