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: However , L - dopa restored the bradycardia caused by norepinephrine in addition to decreasing blood pressure and heart rate .
### Output Text:
However , <span class="chemical">L - dopa</span> restored the bradycardia caused by <span class="chemical">norepinephrine</span> in addition to decreasing blood pressure and heart rate . 