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: Mechanisms of FK 506 - induced hypertension in the rat .
### Output Text:
Mechanisms of <span class="chemical">FK 506</span> - induced hypertension in the rat . 