Effect of exogenous hydrogen sulfide on iNOS/NO in neonatal rats with hyperoxia lung injury

Abstract

Objective To study the effect of hydrogen sulfide (H2S) on iNOS/NO in neonatal rats with hyperoxia-induced lung injury. Method Eighty full-term neonatal SD rats were randomly assigned into 4 groups (each group 20 rats including control group, hyperoxia group, NaHS+ hyperoxia group, PPG+ hyperoxia group. Rats in NaHS+ hyperoxia group had 90 μmol/kg NaHS injected intraperitoneally, those in PPG+ hyperoxia group had PPG 50 mg/kg injected, and those in the other 2 groups had the same amount of 0.9% normal saline injected. Except for the control group that exposed to air, the other three groups were exposed to 95% O2 for 7 days. Then pulmonary histopathology was studied by HE staining, the ratios of lung wet/dry weight (W/D) were determined as measurement of the severity of pulmonary edema, maleic dialdehyde (MDA), iNOS activity and NO levels in lung tissue were measured using commercial kits, iNOS mRNA expression was detected by Real-time PCR. Analysis of variance and LSD-t test were used for statistical analysis. Result (1) Compared with control group, the hyperoxia group showed erythrocyte extravasation and leukocyte infiltration in the alveoli with inflammatary cell infiltrations, alveolar septum edema, whereas pathological injury changes induced by hyperoxia were alleviated by NaHS and the damage was exacerbated by PPG. (2) In hyperoxia group, H2S was decreased compared with control group (117.6±20.4 μmol/L vs. 184.3±13.7 μmol/L). In NaHS+ hyperoxia group, H2S was apparently increased compared with the hyperoxia group (247.3±32.4 μmol/L vs. 117.6±20.4 μmol/L), while in PPG+ hyperoxia group H2S was decreased compared with the hyperoxia group (89.2±8.3 μmol/L vs. 117.6±20.4 μmol/L) (P<0.01). (3) In the hyperoxia group, the ratios of lung W/D (5.81±0.22), the contents of MDA (1.69±0.14 ) nmol/ml, iNOS activity (2.24±0.19 ) U/mg prot, NO levels (22.37±3.04 )×10-3 μmol/g prot, iNOS mRNA expression (1.43±0.09) showed significant increase respectively (P<0.01) compared with the control group (5.06±0.15), (0.78±0.08)nmol/ml, (1.18±0.18) U/mg prot, (7.49±1.91)×10-3 μmol/g prot, (0.90±0.08). NaHS administration showed a significant decrease in lung W/D, lung tissue MDA content, iNOS activity, NO level, iNO SmRNA expression (5.59±0.19), (1.44±0.11) nmol/ml, (1.84±0.27) U/mg prot, ( 14.23±2.00)×10-3 μmol/g prot, (1.28±0.10) compared with the hyperoxia group (P<0.01). The above markers were significantly increased after PPG administration (6.18±0.26), (1.99±0.19) nmol/ml, (2.66±0.23) U/mg prot, (30.94±3.31)×10-3 μmol/g prot, (1.73±0.06) (P<0.01). Conclusion Exogenous H2S can relieve hyperoxia-induced lung injury by down-regulating the expression of iNOS mRNA, decreasing iNOS activity and decreasing NO production. Key words: Hydrogen sulfide; Hyperoxic lung injury; Nitric oxide; Inducible nitric oxide synthase; Rats