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: Endothelial function was assessed by acetylcholine - induced vasorelaxation and phenylephrine - induced vasoconstriction in aortic segments .
### Output Text:
Endothelial function was assessed by <span class="chemical">acetylcholine</span> - induced vasorelaxation and <span class="chemical">phenylephrine</span> - induced vasoconstriction in aortic segments . 