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 activation of bradykinin B2 receptors in disruption of the blood - brain barrier during acute hypertension .
### Output Text:
Role of activation of <span class="chemical">bradykinin</span> B2 receptors in disruption of the blood - brain barrier during acute hypertension . 