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: The goal of this study was to determine the role of synthesis / release of bradykinin to activate B2 receptors in disruption of the blood - brain barrier during acute hypertension .
### Output Text:
The goal of this study was to determine the role of synthesis / release of <span class="chemical">bradykinin</span> to activate B2 receptors in disruption of the blood - brain barrier during acute hypertension . 