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 results indicate that FK 506 may increase blood pressure not only by increasing ET - 1 production but also by decreasing NO synthesis in the vasculature .
### Output Text:
These results indicate that <span class="chemical">FK 506</span> may increase blood pressure not only by increasing ET - 1 production but also by decreasing <span class="chemical">NO</span> synthesis in the vasculature . 