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: Prostaglandin E2 - induced bladder hyperactivity in normal , conscious rats : involvement of tachykinins ?
### Output Text:
<span class="chemical">Prostaglandin E2</span> - induced bladder hyperactivity in normal , conscious rats : involvement of <span class="chemical">tachykinins</span> ? 