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: 5 - HTP ( 5 mg / kg i . v . ) decreased blood pressure and heart rate and decreased the reflex bradycardia to norepinephrine .
### Output Text:
<span class="chemical">5 - HTP</span> ( 5 mg / kg i . v . ) decreased blood pressure and heart rate and decreased the reflex bradycardia to <span class="chemical">norepinephrine</span> . 