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 , the head - up tilt induced orthostatic hypotension in the SHR treated with prazosin ( - 16 % MAP , n = 6 ) , but not in the SHR treated with rauwolscine ( less than + 2 % MAP , n = 6 ) .
### Output Text:
However , the head - up tilt induced orthostatic hypotension in the SHR treated with <span class="chemical">prazosin</span> ( - 16 % MAP , n = 6 ) , but not in the SHR treated with <span class="chemical">rauwolscine</span> ( less than + 2 % MAP , n = 6 ) . 