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: Combined effects of prolonged prostaglandin E1 - induced hypotension and haemodilution on human hepatic function .
### Output Text:
Combined effects of prolonged <span class="chemical">prostaglandin E1</span> - induced hypotension and haemodilution on human hepatic function . 