In the sentence extracted from biomedical literature, identify all the chemical entities. The required answer format is the same sentence with HTML <span> tags to mark up specific entities. 
### Entity Markup Guides:
Use <span class="chemical"> to denote a chemical.

### Input Text: These data suggest that while NO deficiency increases oxidative stress and sympathetic activity in both arterial and venous vessels , the impact on veins does not make a major contribution to this form of hypertension .
### Output Text:
These data suggest that while <span class="chemical">NO</span> deficiency increases oxidative stress and sympathetic activity in both arterial and venous vessels , the impact on veins does not make a major contribution to this form of hypertension . 