Effect of exposure to hyperbaric oxygen on nitric oxide production in the rat

Acute exposure to hyperbaric oxygen (HBO) is associated with a significant decrease in pulmonary vascular reactivity.1 In the present study we evaluated the hypothesis that this decrease might be due to an increase in nitric oxide (NO) production. Male Sprague-Dawley rats were studied after different durations of exposure to HBO at 2.8 atm: 1.5h (n-4), 3h (n-5), and 6h (n-6). Another group (n-4) was allowed to recover in room air for 24h after 6h of exposure to HBO. All groups were compared to a control group (n-4) not exposed to HBO. After anesthesia blood samples were collected via carotid artery catheterization. The plasma was then separated and kept frozen at -70°C until analyzed for cGMP, the second messenger of NO, by using enzymeimmunoassay. Exposure to HBO resulted in a gradual increase in cGMP level from 16.1±1.7 fmol/HL in controls to 17.0±.3 and 20.3±2.3 after 1.5h and 3h; respectively. After 6h of exposure to HBO the increase in cGMP became significantly different compared to the previous three groups (33.8±7.4; P<0.05) [ANOVA-Fisher's PLSD]. Although cGMP level remained elevated in the recovery group (30.1±5.6), it was not significant from the control level. In conclusion, the reported attenuation in pulmonary vascular reactivity after acute exposure to HBO could be attributed to an increase in the production of NO. 1] Amin et al.: Can J Physiol Pharmacol 1993;71:592-596.