Hypoxia increases nitric oxide concentrations that are not completely inhibited by L-NMMA

Recent investigations have demonstrated a wealth of knowledge about the biology of nitric oxide (NO) and the synthases (NOS) that generate it, under both physiologic and pathophysiologic conditions. In this study, we investigated the generation of NO under conditions of hypoxia in the absence of confounding functions such as blood loss or hypovolemia.

Rats were subjected to either 30 or 60 min of hypoxia and sacrificed immediately or after 1 or 24 h of recuperation. Splenocyte proliferative ability and NO concentrations were determined in whole splenocytes and purified T-cell populations, with and without the use of 20 mg/kg L-NMMA, a potent NOS inhibitor. RT-PCR was performed to determine the presence or absence of inducible NOS transcription after hypoxia and hypoxia followed by reoxygenation with and without L-NMMA.

Hypoxia followed by reoxygenation stimulated NO production in whole splenocytes, which correlated with a decrease in splenocyte proliferation. T-cell stimulation and NO production were not upregulated under these conditions. Additionally, NO generation occurred following hypoxia, even in the presence of L-NMMA.

These results demonstrate that NO production after hypoxia may be due to an alternate, O2-independent pathway. Further investigations into the generation of NO through alternate pathways may identify treatments for hypoxia-related injury.