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: In the media of the saphenous artery and its distal branch , vasoconstriction induced by L - norepinephrine produced many cell - to - cell hernias within 15 minutes .
### Output Text:
In the media of the saphenous artery and its distal branch , vasoconstriction induced by <span class="chemical">L - norepinephrine</span> produced many cell - to - cell hernias within 15 minutes . 