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INTRODUCTION Hydrogen (H2) has been reported to be effective in the treatment of oxidative injury, which plays an important role in the process of decompression sickness (DCS). This study was designed to test whether H2-rich saline (saline saturated with molecular hydrogen) protected rats against DCS. METHODS Models of DCS were induced in male Sprague-Dawley rats weighing 300-310 g. H2-rich (0.86 mmol x L(-1)) saline was administered intraperitoneally (10 ml x kg(-1)) at 24 h, 12 h, immediately before compression, and right after fast decompression. RESULTS H2-rich saline significantly decreased the incidence of DCS from 67.57 to 35.14% and partially counteracted the increases in the total concentration of protein in the bronchoalveolar lavage from 0.33 +/- 0.05 to 0.14 +/- 0.01 mg x ml(-1) (mean +/- SD; P < 0.05), myeloperoxidase activity from 0.86 +/- 0.16 to 0.44 +/- 0.13 U/g, levels of malondialdehyde (MDA) from 0.80 +/- 0.10 to 0.48 +/- 0.05 nmol x mg(-1), 8-hydroxydeoxyguanosine from 253.7 +/- 9.3 to 191.2 +/- 4.8 pg x mg(-1) in the lungs, and MDA level from 1.77 +/- 0.20 to 0.87 +/- 0.23 nmol x mg(-1) in the spinal cord in rat DCS models. The histopathology results also showed that H2-rich saline ameliorated DCS injuries. DISCUSSION It is concluded that H2-rich saline may have a protective effect against DCS, possibly due to its antioxidant action.

Decompression sickness (DCS) is a major concern in diving and space walk. Hyperbaric oxygen (HBO) preconditioning has been proved to enhance tolerance to DCS via nitric oxide. Heat-shock protein (HSP) 70 was also found to have protective effects against DCS. We hypothesized that the beneficial effects of HBO preconditioning on DCS was related to levels of elevated HSP70. HSPs (70, 27 and 90) expressed in tissues of spinal cord and lung in rats was detected at different time points following HBO exposure by Western blot. HSP27 and HSP90 showed a slight but not significant increase after HBO. HSP70 increased and reached highest at 18 h following exposure before decreasing. Then rats were exposed to HBO and subjected to simulated air dive and rapid decompression to induce DCS 18 h after HBO. The severity of DCS, along with levels of HSP70 expression, as well as the extent of oxidative and apoptotic parameters in the lung and spinal cord were compared among different groups of rats pretreated with HBO, HBO plus NG-nitro-L-arginine-methyl ester (l-NAME), HBO plus quercetin or normobaric air. HBO preconditioning significantly reduced the morbidity of DCS (from 66.7% to 36.7%), reduced levels of oxidation (malondialdehyde, 8-hydroxyguanine and hydrogen peroxide) and apoptosis (caspase-3 and 9 activities and the number of apoptotic cells). l-NAME or quercetin eliminated most of the beneficial effects of HBO on DCS, and counteracted the stimulation of HSP70 by HBO. Bubbles in pulmonary artery were detected using ultrasound imaging to observe the possible effect of HBO preconditioning on DCS bubble formation. The amounts of bubbles in rats pretreated with HBO or air showed no difference. These results suggest that HSP70 was involved in the beneficial effects of HBO on DCS in rats, suspected be by the antioxidation and antiapoptosis effects.

The spinal cord is one of the most commonly affected sites in decompression sickness (DCS). Alternative methods have long been sought to protect against DCS spinal cord dysfunction, especially when hyperbaric treatment is unavailable. Use of perfluorocarbon (PFC) emulsion with or without oxygen breathing has shown survival benefits in DCS animal models. The effectiveness of intravenous PFC emulsion with oxygen breathing on spinal cord function was studied. Somatosensory-evoked potentials (SSEPs) and histologic examination were chosen to serve as measures. After fast decompression (203 kPa/minute) from 709 kPa (for 60 minutes), male Sprague-Dawley rats randomly received: 1) air and saline; 2) oxygen (O2) and saline; 3) O2 and PFC emulsion. The incidence and average number of abnormal SSEP waves in survival animals that received O2 and PFC emulsion were significantly reduced (P0.05). Foci of demyelination, necrosis and round non-staining defects in white matter regions of the spinal cord could be found in severe DCS rats. We concluded that administration of PFC emulsion combined with oxygen breathing was beneficial for DCS spinal conductive dysfunction in rats.