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: Role of xanthine oxidase in dexamethasone - induced hypertension in rats .
### Output Text:
Role of <span class="chemical">xanthine</span> oxidase in <span class="chemical">dexamethasone</span> - induced hypertension in rats . 